Fluid Mechanics and Fluid Power, Volume 1

In case of Safety Control Rod-Accelerated Movement (SCRAM) in Indian Prototype Fast Breeder Reactor (PFBR), the electromagnet gets de-energized and releases the Diverse Safety Rod (DSR) to fall under gravity and finally deposited on the dashpot of DSR Sub-assembly (DSRSA) to shut down the reactor. DSR contains Boron Carbide, which is a neutron absorber material and absorbs neutrons to bring down the neutron flux which is controlling the chain reaction. The maximum amount of heat that can be generated in DSR while absorbing the neutrons is estimated as 1 MWt. To remove this heat, a minimum sodium coolant flow rate of 3 kg/s is required to pass through the mobile DSR. This required flow rate through mobile DSR is 95% of the total flow rate of 3.18 kg/s, which is passing through the DSRSA when DSR is deposited on the dashpot. Therefore, only 5% of the total flow is allowed to leak through the DSR–dashpot interface. In this study, leakage through DSR–dashpot interface has been measured experimentally using water as simulant fluid in a simplified, full-scale model of DSR–dashpot interface region. This paper primarily focuses on the modelling techniques for such kind of experiments using geometrically similar models of particular zone of interest. The predictions for prototype from the experimental results are also discussed.

Loop heat pipe (LHP) is a thermal management device used in different applications like mobile, laptop, air conditioning, space, defense, etc. Water-based LHP was analyzed in present work for the thermal management in terrestrial applications. Modeling of LHP with water as a working fluid was done in MATLAB with two-phase analysis and the effects of different ambient conditions (i.e., 10 °C, 22 °C, and 40 °C) were analyzed on the parameters on steady-state operating temperature (SSOT), condenser outlet temperature (Tco), liquid line outlet temperature (Tlo), two-phase pressure drop across the condenser (i.e., ΔP2ɸ), heat exchanged from the compensation chamber (C.C.), and liquid line to ambient (i.e., Qc.c.-amb, QL.L.-amb) and resistance of LHP. When Tamb was increased from 10 °C to 40 °C, SSOT, Tco, and Tlo increased by 24.4 °C, 11.9 °C, and 13.92 °C, respectively, at 160 W. It was found that the condenser ΔP2ɸ has significant effect on ΔPtotal at higher heat loads. Qc.c.-amb and QL.L.-amb have reduced by 0.36 W and 0.28 W, respectively, when Tamb was increased from 10 °C to 40 °C at 600 W.

An investigation of inlet blockage in the central subassembly (SA) of a medium-sized sodium-cooled fast reactor (SFR) is carried out. To analyze the accident scenario, a sodium boiling model is developed based on two-fluid approach. The model is added to the thermal model based on the single-pin assumption developed in the previous study. The developed model is validated with CABRI BI1 loss of flow experimental data. Having established the validity of the model, a detailed analysis of inlet blockage in the central SA of a medium-sized SFR is carried out. The model is able to predict the accident detection time by temperature monitoring thermocouple located at the SA outlet. Boiling front evolution, temperature evolution of the core components, dryout time, and clad melting time are predicted. A parametric study on the effect of growth of blockage at the SA inlet on time of detection and boiling is carried out.

Lithium-ion batteries (especially, 18,650 cells) are extensively used in electric vehicles because of their superior performance and low cost. The dissipation of excessive heat generated in these batteries during charging and discharging cycles is a challenge when designing a battery thermal management system (BTMS). The pulsating heat pipe (PHP) can be used for cooling these batteries. In this work, an experimental investigation of a three-dimensional pulsating heat pipe (PHP) specially designed for cooling of 18,650 lithium-ion battery module is conducted. This work aims to study the effect of working fluid (CuO + Fe3O4–water nanofluid and water) and PHP inclination (90°, 45°, and 0°) on the thermal performance of PHP. It is observed that at all the PHP inclinations, hybrid nanofluids have better thermal performance compared to that of water, and the thermal resistance of PHP is decreased by an average of 7.8% with nanofluids. It is also observed that the use of hybrid nanofluid considerably reduced the start-up temperature of the PHP. The lowest start-up temperature observed with hybrid nanofluid is 49 °C at a 45° inclined position.

In the present study, numerical analysis of slot jet impingement using SiO2–water nanofluid on flat surface is carried out. The slot jet width is 5 mm and the Reynolds number is fixed as 10,000. The flat surface is treated with thermal boundary condition of uniform temperature. The SiO2 solid particle volume fraction in nanofluid is spanning from 0 to 5%. The thermophysical properties of nanofluid is evaluated from mathematical expression which involves water properties and solid particle volume fraction. The dynamic viscosity of nanofluid is evaluated from three different models. The single phase property model is used for numerical simulation. The effect of particle volume fraction and separation distance on friction factor and Nusselt number is investigated. To consider combined effect of flow and heat transfer performance of jet impingement, the Performance Index is evaluated. With increasing particle volume fraction in nanofluid, Performance Index increases which indicates overall improvement of system efficiency.

The present study reviews the heat transfer intensification techniques utilized by the researchers in recent decades. By discussing the methods of augmentation of heat transfer, the study confined to passive techniques which are being used in tube-type heat exchangers. The passive techniques of heat transfer intensification in tubular heat exchangers include surface modification, extended surfaces, artificial roughness, and the insertion of turbulence enhancement devices like winglets, baffles, twisted tape inserts, etc. The prime objective of the enhancement devices is to break the thermal boundary layer and to change the pattern of the flow inside the tube. Nanofluids additionally play a sizable position due to their better thermal conductivity. In the present review, the vital investigations associated with nanofluid usage in tubular heat exchangers have additionally included.

Totally enclosed fan cooled (TEFC) motors primarily dissipate the electromagnetic losses (heat) generated by various motor components through the housing. Thus, the thermal performance of this class of motors depends on the efficient housing design. This paper presents a numerical investigation of three different housings, each occupying the same volume. The designs are Finned housing (Design 1), Finned housing with fillet profiles of various angles (Design 2), and Finned housing with fillet profiles and a thin central strip (Design 3). We evaluate the thermal performance factor for all the designs to quantify the combined effect of heat transfer and fluid flow. Numerical results illustrate that the proposed designs exhibit superior thermohydraulic performance compared to design 1. The heat transfer coefficient improves by 16% for design 2, and the base temperature reduces by 12% for design 3.

A synthetic jet is a flow technique and mostly useful for cooling applications. In a synthetic jet, actuator fluid is moved in and outside a cavity, from a small orifice, by the continuous oscillation of a diaphragm. A numerical study of an electronic cooling module employing a periodic jet flow at an orifice is represented in this paper. Numerical simulations are carried out using ANSYS Fluent software and for modelling of a diaphragm, a moving wall boundary condition is applied using a user-defined function. Based on standard k-ε turbulent, dynamic mesh model, and PISO algorithm, numerical simulation of the 2D, viscous, unsteady synthetic jet model is proposed. Here, an average heat transfer coefficient is determined for varying axial distance amongst the orifice exit and heated surface and validated with existing experimental results. Also, the average ejection and suction velocities are validated for a given actuation frequency. Additionally, the heat transfer performance of synthetic jet for divergent-shaped orifice and the convergent-shaped orifice is investigated. It is observed that a diversion-shaped orifice has the highest heat transfer enhancement. A heat transfer enhancement of approximately 14% over that of round orifices was observed.

The packed bed latent heat storage system has drawn much interest because of its favorable application potential and inexpensive investment costs. The development of mathematical models and the structural optimization of the thermal energy storage (TES) tank were the main focuses of earlier research on this technology. There was not much experimental research on this kind of system's thermal performances at medium temperature ranges. This study uses a detailed thermal performance analysis of phase change material (PCM)-based energy calculations. Experiments were conducted on stainless steel encapsulations without fins and stainless steel encapsulations with solid internal fins for the mass flow rates of 2, 4, and 6 L/min with a heating source of constant temperature bath. Water and paraffin wax was used as the heat transfer fluid and phase change material. The charging duration of PCM revealed a desire to increase the heat exchange surface to increase the heat exchange power. The stratification performance of the storage tank was also analyzed for this study. Increasing the encapsulation material's heat transfer surface reduces the charge duration and improves the system's thermal performance.

The present experimental study focuses on analyzing the heat transfer characteristics and understanding the axis switching phenomenon for impinging elliptic jets with high aspect ratios. The hot-wire anemometry is used to study the flow characteristics of synthetic jet, while heat transfer characteristics are studied by using a thermal imaging technique. The heat transfer characteristics of elliptical orifices with aspect ratios 10 & 14 are being studied and compared to an equivalent circular orifice. Results show that in the near-field region ( $$z/d\le 3$$ z / d ≤ 3 ), the average Nusselt number of elliptical orifices (AR = 10 &14) is obtained to be higher than the circular counterpart. However, with the rise of AR from 10 to 14, thermal performance of elliptical orifices decreases in the near-field region. In the intermediate and far-field region, the thermal performance of such elliptical orifices depreciates, since most of the momentum of the elliptic jet is lost before arriving at the impingement plate due to significant entrainment and substantial mixing with the ambient fluid. It is also observed that with orifice to surface spacing, circular orifice jet produces a single peak in the average heat transfer rate, while elliptical orifice produces double peaks in the average heat transfer rate lying in near-field (z/D = 1 to 3) and mid-field regions (z/D = 6 to 10).

In this study, the second law analysis of ethylene glycol-based TiO2-SiO2 non-Newtonian hybrid nanofluid under turbulent flow conditions has been investigated. A helically corrugated tube is used to examine the effect of corrugation-height ratio (e/dh) and volume fraction (φ) on entropy generation rate and the second law efficiency. These tubes are widely preferred in many engineering applications, such as pharmaceuticals, naval, paint production, food industry, heat exchangers, chemical process and gas industries. ANSYS FLUENT 19.0 is used to simulate the model with the corrugated wall maintained at a constant heat flux of 25 kW/m2 with a range of volume flow rate of hybrid nanofluid from 15 to 25 lpm. The use of corrugation with hybrid nanofluid shows a promising result from the point of view of the second law of thermodynamics. The entropy generation rate and the exergy destruction rate of the HCT decrease as the corrugation height and the particle volume fraction increase. Furthermore, second law efficiency increases with both e/dh and φ.

The present paper is based on the experimental and numerical investigation of a cooling device. The device is focused to concentrate cooling effect on a specific zone in a given three-dimensional volume. A wall jet configuration is investigated on a curved surface initially with a straight portion. The mean flow parameters are measured like, mean velocity profiles, maximum velocity decay and jet growth rate and temperature. The same result shave has been calculated using commercial CFD code. The mean velocity profiles show good agreement with the experimental and with the existing literature. Maximum velocity decay, growth of half width and temperature profiles show good correlation with the experimental results. The existing system parameter of the device is found to be appropriate to achieve the solution of the localized cooling concept.

This study investigates the 2-dimensional bio-convective MHD stagnation point flow through a porous medium. The fluid is considered as a Casson fluid in steady flow. Heat generation, chemical reaction and the consequences of non-linear thermal radiation are all considered. The governing equations are converted into a set of PDEs with different physical boundary constraints. The similarity transformations are used to alter into the set of ODEs. To resolve the set of ODEs, the HAM is used to find the expression of momentum, energy and concentration profiles. Based on data from a Mathematica program, the effects of several prominent parameters on velocity field, temperature curve and concentration field are depicted graphically. We examined the rate of heat transfer.

Heat exchangers are popularly used in industrial and engineering applications. The design procedure of heat exchangers is quite complicated, as it needs exact analysis of heat transfer rate, efficiency and pressure drop apart from issues such as long-term performance and the economic aspect of the equipment. One of the most important techniques used is passive heat transfer enhancement technique. These techniques when adopted in heat exchanger proved that the overall thermal performance improved significantly. The current work presents computational analysis on a plain tube with and without twisted tape insert at constant wall heat flux. In this work, the validated model predicts heat transfer coefficient for twisted tape of different materials viz. Polyetheretherketone and polytetrafluoroethylene (PEEK and PTFE), respectively. The twisted tape used has a constant twist pitch of 82.5 mm with two different widths (26 and 10 mm) and thickness of 0.487 mm. Pipe with an inner diameter of 27.5 mm is used. Reynolds number varies from 9000 to 14,500. It is observed that there is an enhancement of heat transfer in the range of 75 to 110% for different Reynolds numbers.

Energy storage in batteries is an emerging subject in the sustainable energy revolution. Battery utilization in Electric Vehicles (EVs) is increasing. Lithium-Ion Batteries (LIBs) will help meet emission objectives by promoting the use of renewable energy and electric vehicles. Extended cycle life and high energy density make LIBs popular for EVs. LIBs used in electric vehicles create excessive heat during discharge and charging. A thermal management system is required to improve the effectiveness of LIBs in EVs. Air cooling, Water cooling, Thermoelectric cooling, Heat Pipe cooling, Phase Change Materials (PCM) cooling, and hybrid cooling are methods of a thermal management system. A heat pipe-assisted Battery Thermal Management System (HP-BTMS) is a passive method to enhance the thermal performance of EVs by ensuring temperature uniformity for the battery. Integrated HPs with PCM (hybrid system) are better than HP-BTMS in terms of temperature distribution. This study takes an opportunity to present a critical review of the thermal performance of HP-BTMS. The effects of wick structure, construction material, working fluid, and heat input variations have been discussed briefly on the thermal characteristics of heat pipe-based battery thermal management applications. The circular heat pipe, L-shape heat pipe, flat heat pipe, loop heat pipe, and oscillating/pulsating heat pipes are the various types of HP-BTMS. Sintered powder, groove structure, screen mesh, etc. are types of wick structures applied in HP-BTMS. Water, methanol, acetone, ammonium, etc. are working fluids utilized in HP-BTMS. Oscillating heat pipes have a wickless structure and are lighter than other heat pipes. The Maximum Temperature (Tmax) and Temperature difference (ΔTmax) are a battery’s two most significant factors. This paper also discusses the effect of varying power input and charge–discharge rates on Tmax and ΔTmax. Tmax and ΔTmax should be controlled below 50 °C and 5 °C, respectively.

In this paper, we obtained the design parameters, namely the length of the heat pipe and the PPI of the copper foam for a given maximum heat flux required for the flat heat pipe to work. The PPI of the copper foam was obtained for the different values of the maximum heat flux for the various values of the length of the heat pipe. We also determined the optimum PPI of copper foam based on the balance between the capillary pressure and the viscous losses in the flow of liquid in porous media and the vapour section. The behaviour of maximum heat flux with various PPIs for different gravity factors is also discussed. By linear interpolation, we found the behaviour of the maximum heat flux, which will be zero for a given length and a gravity factor for the flat heat pipe.

This work reports data-driven fault diagnosis and performance prediction framework for a boiler. In-house experimental setup of a boiler and heat exchanger is used to generate the data for various parameters. Various combinations of two, three and four state variables are used to develop eight different regression models using PYTHON in-house code. Performance of all these models is analyzed by comparing different statistical parameters like sum squared residual, mean squared residual and standard error. It is noticed that models with two state variables namely, steam temperature and volume of water or steam temperature and volume of steam predict the steam pressure with optimum error. These models are further tested to diagnose the fault which is added numerically in terms of upward and downward temperature drifts. The models are statistically robust and can diagnose the fault and predict the pressure which is within the target as evidenced through EWMA charts.

Nowadays, designing and development of more efficient Electric Vehicles (EVs) have attracted worldwide attention. The major challenges of Electric Vehicles (EVs) are limited battery life, long charging time problems and limitation on driving range per charge. However, higher power density and higher power electric systems using power modules (SiC MOSFET/IGBT) can compensate for these challenges. But these power modules in the inverter of EV are sensitive to high temperature which may cause damage to the devices. In order to avoid this problem, an efficient cooling system has to be incorporated. The main objective of this work is to study the performance of liquid cooled Pin–Fin heat sink for an inverter by changing number and size of Pins and Mass Flow Rate of the liquid. The power loss for continuous load is estimated based on design calculations subsequently initial heat sink model is designed. The different heat sink models are developed and CFD analysis is conducted on each design. Final geometry is checked with a mass flow rate of 14.82 L/min. All the designs are done using Spaceclaim, and CFD analysis is conducted using ANSYS Fluent which is included in ANSYS products.

The safety of a nuclear reactor should be ensured at all reactor operating conditions. During an unexpected transient in the secondary circuit, the inlet temperature of primary sodium into the grid plate (inlet plenum) through different inlet windows differentiates. In such cases, the mixing behavior of the flow inside the grid plate needs to be established in order to estimate the rise in central sub-assembly outlet temperature, which acts as an important alarming parameter. Toward this, a 3D thermal hydraulic analysis is carried out for the grid plate of FBRs 1 & 2 to establish and quantify the thermal mixing of primary sodium inside the grid plate. The differential inlet temperature of primary sodium, of 10 °C, during transient conditions is considered between two and four inlets, respectively in the present study. Based on the conservative analysis, thermal influence is observed in 120° in the vicinity of these pipes. Good mixing is observed at the outlet of central SA.

In this article, we investigated the rarefied gaseous flow through a micro-tube channel filled with homogeneous and heterogeneous porous media. An analytical study is carried out to model the flow and heat transfer using the Brinkman momentum equation and the thermal energy equation. The influence of rarefied gaseous flow at the micro-tube wall is accounted for using the velocity slip and temperature jump conditions. The micro-tube wall is subjected to a uniform heat flux boundary condition. An exact solution for velocity, temperature, and average Nusselt number is obtained for both homogeneous and heterogeneous cases. The results show that flow through heterogeneous porous medium shows better heat transfer characteristics than homogeneous porous media. The results also show that raising the velocity slip coefficient increases the Nusselt number, whereas increasing the temperature jump coefficient decreases the Nusselt number.

The majority of the thermo-physical processes are developed into a mathematical model, which is then linearized to give some insight into the operational characteristics. A model without linearization, however, can better capture the nature of the observed occurrences. Research has long focused on how to choose between a nonlinear model, which has a larger computing cost, and a linear model, which might not give true and accurate dynamics. For a pulsating heat pipe (PHP), the limitations of the linear model over the nonlinear model are discussed. The difference between the two models largely highlight the nonlinear model's ability to accurately represent real dynamics. Based on the finding of an additional Zero-Hopf point in the nonlinear model from (Kumar and Singh in IJTS 2023), an analysis of the possible presence of a hidden attractor is done.

This paper addresses the heat transfer evaluation problem in RC members at standard fire loads. Accidental fire events in building structures are common, in which structural RC members come often into contact with severe fire conditions that directly affect their stability and integrity against collapse. The code and standard practices do not provide any provisions for fire resistance rating evaluation and specify the fire resistance rating of RC members by acknowledging their applicability in terms of concrete cover provision. RC member failure appraisal in performance-based design and analysis is one of the significant concerns in the recent era which depends on appropriate heat transfer analysis. In transient heating boundary conditions with associated influencing material properties, i.e., thermal conductivity, specific heat carry capacity, and diffusivity for normal strength concrete (NSC) and high strength concrete (HSC) are completely different, which directly influence heat transfer behavior using heating mechanisms. Therefore, a finite difference method (FDM) based heat transfer evaluation method has been proposed for both NSC and HSC with consideration of thermally induced material properties and appropriate heating mechanisms. The proposed method prediction has been verified with the experimentally performed database and it is observed suitable to evaluate heat transfer in RC members made by NSC and HSC at exposure to the standard fire load.

This work attempts to investigate the enhanced heat transfer performance of phase change materials (PCMs) utilizing a rectangular fin placed vertically in a rectangular cavity filled with paraffin wax (RT-45). The top wall is considered an isothermally heated wall and all other walls are insulated. A rectangular thin conducting fin is vertically attached to the top heated surface. The total cross-sectional area of the fin is kept constant so that the volume of the PCM remains the same for every case. The evolved transport equations are solved numerically using the finite volume-based solver. For analyzing the enhanced performance of the PCM, the fin is divided into multiple fins keeping the same surface area. Thus, the number of fins on the total melting time is keenly observed with the help of stream trace lines. The analysis revealed that the melting time of PCM decreases by 48.36% when the heated surface increases from 78 to 120 mm adopting fin. With a further increase in the heated surface from 120 to 160 mm, the melting time decreases by 17.73%. The formation of the circulation loops affects the average melting time. The results also show that as the amount of heated surfaces increases, the rate of reduction in the total melting time reduces. Consequently, an optimum length of the heated surface could be obtained.

Heat transfer enhancement techniques are extensively used in circular pipe heat exchangers to reduce their size and improve heat transfer. Heat transfer enhancement techniques usually include passive, active, and compound heat transfer enhancement. Unlike active techniques, passive techniques don’t require external power to improve heat transfer. Passive techniques include twisted tapes, conical inserts, coils, nozzles, baffles, etc. Twisted tapes are studied extensively among all passive techniques for their lower manufacturing, operating, and maintenance cost and better thermal performance than others. Research is done mainly on finding new techniques and improving present passive techniques, no effort has been made to find the best passive techniques. The present study should determine the best passive heat transfer enhancement techniques for circular pipe heat exchangers using the MCDM technique, applied with technical and economic criteria for twisted tapes. MCDM (Multi-Criteria Decision Making) techniques are used to find the best passive heat transfer enhancement technique. Nusselt number, friction factor, Reynolds number, the surface to volume ratio, and cost to thermal performance are criteria to rank among each other. Our study has shown that twisted tape with the peripheral rectangular cut is the best possible twisted tape among the chosen ones for passive heat transfer analysis.

The paper investigates unsteady MHD flow of nanofluid in a perforated vertical medium. The effect of thermos-diffusion, thermal radiation, heat generation, and chemical reaction are considered $$. {Fe}_{3}{O}_{4}$$ . Fe 3 O 4 nanoparticles are taken in convectional base fluid like water. The formulated problems are converted into a system of PDE’s with initial and boundary conditions. The governing equations transfer into a non-dimensional form using similarity transformation. The Laplace transformation is applied and obtained analytical solutions. The exact expression of velocity gradient, temperature gradient, and concentration gradient are defined. The different physical parameters effects are discussed through graphs. From the graph, it is seen that motion of the fluid is raised with pressure gradient and porous medium parameter. The magnetic field tends to reduce the velocity, whereas heat transfer process improved with radiation. It is also concluded that, the mass transfer process was decrease with the increasing the values of chemical reaction parameter.

Lithium-ion (Li-ion) batteries have great potential to power EVs and hybrid EVs (HEVs). These batteries are lightweight, high-specific energy, low-self-discharge, long-lasting, and have no memory effect. These batteries create a lot of heat during operation, affecting their performance and increasing the danger of capacity deterioration, thermal runaway, and fire. The current research examines the critical thickness of PCM required to control the cell temperature undergoing rapid discharging. A commercial 18,650 Li-ion of 2.6 Ah capacity has been used for experiments and numerical modelling. It is found that the PCM is able to significantly control the cell temperature. A PCM thickness of 2.5 mm keeps the cell temperature in the optimum temperature range.

The present study investigates the effect of orientation on phase change material (PCM)-based finned heat sink (HS). The heat sinks are made of aluminum with an outer diameter of 58 mm, an inner diameter of 48 mm, and a height of 55 mm with different configurations like (i) bare heat sink, (ii) heat sink with central stem, (iii) heat sink with three fins having a central gap, and (iv) heat sink with four fins. The PCM considered for the experimental work is n-eicosane. The fins of a thickness of 2 mm and stem having a diameter of 5 mm are placed for the purpose of thermal conductivity enhancement. Experiments are conducted on all heat sinks with a constant fill ratio of 99%, and charging and discharging times are recorded. Of them, the heat sink with four partitions gives better results, and further, the experimental investigations are carried out on four fin heat sink at different orientations (0°, 45°, 90°, 135°, 180°) and at different power levels ranging from 6 to 12 W. The charging is done to a set point temperature of 50 °C. The discharging is done under natural convection conditions at controlled room temperature. Based on the experimental results, the heat sink performance depends on orientation as the gravitational and buoyancy force directions vary.

Presented experimental study investigates on employing cross-finned heat sinks embedded with nano-enhanced phase change material (NePCM) for thermal management applications. Paraffin as the phase change material (PCM), aluminium oxide (Al2O3) and copper oxide (CuO) as nanoparticles and aluminium metallic fins have been employed. Six different configurations of heat sinks, namely single cavity (1 × 1), 4 cavity (2 × 2), 9 cavity (3 × 3), 16 cavity (4 × 4), 25 cavity (5 × 5) and 36 cavity (6 × 6) with two different nanoparticles weight concentration of 0.5% and 1% have been tested for a constant heat flux of 2.5 kW/m2. The analysis of temperature–time distribution and the operation time enhancement for different combinations of NePCM and heat sink is carried out. Results from the investigation show that due to the increased fin number, the temperature of the base of the heat sink was kept to a comparatively low value for a more extended period, than heat sinks with no fins. Further, it has been reported that the use of nanoparticle may not be advisable for a higher fin number heat sink.

This study is a numerical investigation of the performance of electronic cooling heat sinks in natural convection. A heat sink is a heat dissipation device that consists of a base and fins that extend outward. Different iterations are performed to find the most optimal fin arrangement of the heat sinks. Extruded and cross-cut type heat sinks are taken as a reference for geometry formation. A CFD analysis is carried out on the geometries with boundary conditions as the base temperature of 80 °C and ambient temperature as 32 °C and results are obtained. The parameters, such as temperature drop, heat flux, and heat transfer coefficients are obtained and a comparative study is carried out to find the optimal geometry with maximum efficiency.

In recent years, the automobile industry has witnessed a revamp of its fossil fuel-driven conventional vehicles by electric vehicles (EVs) and hybrid electric vehicles (HEVs). The recent EV fires are the predominant hindrances to the market rise of EVs. This study addresses this problem with the easily retrofitted phase change material (PCM) embedded battery thermal management system. A multi-scale multi-dimensional (MSMD) framework’s equivalent circuit model (ECM) is employed to model the battery. The solidification and melting model is used to analyse the n-octadecane PCM. The results concluded that the optimal thickness of the PCM enclosure is 3 mm as the highest reduction of 2.8 K in the maximum temperature of the battery pack (Tmax) is witnessed. The PCM embedded design has lowered the Tmax by 2.82 K, 2.82 K, and 2.63 K when the 4S2P battery pack is discharged at constant C-rates of 10C, 8C, and 6C, respectively. The batteries in immediate contact with PCM (side-BATT) have shown significantly lower Tmax values than central batteries (centre-BATT). A reduction of 43.38 K, 1.24 K in Tmax is observed in side-BATT, whereas 2.48 K, 0.6 K in centre-BATT when the battery pack is discharged at constant 10 C-rate and dynamic loading, respectively.

The demand for high heat flux removal techniques is increasing rapidly. Different techniques have been proposed to enhance the heat transfer in microchannel heat exchanger (MCHX) devices. The current work numerically investigates the enhancement of heat transfer and fluid flow through miniature channels with microfins. The effect of microfins with variable fin height along the flow axis is analyzed. Three designs of cylindrical finned rectangular miniature channels are proposed and they are as follows: uniform fin height (Case-1), fin height increasing (Case-2), and decreasing (Case-3) along flow direction. The pitch of the microfins in all three cases is kept constant. A constant heat flux is applied at the bottom wall of the channel. The thermal performance of all three cases of the finned miniature channels is analyzed and compared with the unmodified channel. The channel with designed microfins shows better thermal performance than the plain miniature channel, and heat transfer is enhanced significantly but with the expense of a considerable pressure drop. Case-1 with uniform fins shows better thermal performance than the other two cases and has a comparatively higher pressure drop. These findings will be helpful in design optimization of miniature channels used in heat transfer applications.

The present research aims to determine the single-phase heat transfer and pressure drop across the heating tube (bluff body) of different configurations using the ANSYS-2020R2 fluent module in the 2D computational domain. The water flows across the tube with a velocity ranging from 0.01 to 0.05 m/s. The heat transfer coefficient (HTC) is found to decrement from horizontal ellipse to semicircle to hexagon to vertical ellipse to inverted triangle to circular, to triangle. The maximum enhancement in HTC, about 19%, is found for horizontal ellipse than that of circular. The horizontal ellipse has the largest pressure drop among all the bluff bodies, followed by the triangle, inverted triangle, rotated hexagon, horizontal semicircle, vertical semicircle, hexagon, circle, and vertical ellipse. The vertical ellipse provides a 21% lesser pressure drop among all bluff bodies than circular. The vertical ellipse exhibits a higher heat transfer coefficient to lower pressure drop ratio, followed by vertical semicircle, hexagon, circle, inverted triangle, rotated hexagon, horizontal semicircle, horizontal ellipse, and triangle. The vertical semicircle has the maximum enhancement ratio, and minimal is found in the triangle case. The highest PDR is found in the case of the horizontal ellipse, whereas the lowest value is obtained for the horizontal semicircle.

Indian nuclear power program is currently based on indigenous pressurized heavy water reactors (PHWR). PHWR uses natural uranium as fuel eliminating the need for enrichment. PHWR is a pressure tube type reactor which means calandria is pierced by a large number of pressure tubes. These pressure tubes contain coolant at high pressure, while the moderator takes the rest of the space in calandria. Moderator and coolant (both heavy water, D2O) are having their separate circuits. The number of pressure tubes varies depending upon the power rating of the reactor. For the case of 540 MWe and 700 MWe number of pressure tubes are 392.

A 3-D computational analysis has been reported in the following study to determine a better design of internally finned tube for the enhancement of convective heat transfer coefficient in, combined, developing and developed region. In this type of tube, heat transfer depends upon Reynolds number, helix angle and fin height. This kind of tubes also have a shortcoming, i.e. exorbitantly high pressure drop. For this analysis, solution is obtained for different helix angle at fixed Reynolds number and it is compared with a tube having straight triangular serrations and for different fin height, comparison is drawn against plain tube. Performance enhancement criteria is used to decide the best variants of tube. According to the results, as the helix angle and fin height keeps on increasing, convective heat transfer coefficient gets enhanced and contrary to this, the pressure drop increases. Similarly, the convective heat transfer coefficient is also directly proportional to Reynolds number.

The study of heat transfer characteristics in a microchannel is very important in the context of enhancing heat transfer in electronic cooling applications. In the present study, the heated surface of the microchannel is provided with semi-circular grooves or dimples to enhance the cooling capacity in heat sinks. Numerical simulations were performed to quantify the heat transfer enhancement and the corresponding increase in pressure drop in a microchannel with and without the circular grooves. The influence of the Reynolds number (Re), i.e. the inlet coolant velocity on the heat transfer characteristics in the microchannel is investigated. It was noticed that for lower Re, the presence of dimples is deteriorating the heat transfer rates further, whereas, for higher Re, the heat transfer enhancement is noticed for the microchannel with dimples by 2.273%.

A three-dimensional numerical study is performed to analyze the combined effect of phase change material cooling and natural air cooling on a prismatic lithium-ion battery. The Newman, Tiedemann, Gu, and Kim method under the Multi-Scale Multi-Domain battery model is chosen to predict the actual behavior of a battery during charging. To study the thermal behavior of a 20 Ah cell with a proposed cooling system, a prismatic pouch cell of 192 × 145 × 7 mm3 combined with a 2-mm-thick PCM chamber having the same surface area is built. The performance of a cooling system is tested for different charging rates. In addition, a comparison of the thermal performance of battery with the proposed phase change material cooling system and air cooling is also performed. The result shows that with phase change material cooled system, the cell temperature is maintained below 335 K at high charging rate.

Porous media are known to improve heat transfer and fluid flow properties at the expense of pressure drop. Numerical modelling techniques open up a broad scope of research avoiding colossal cost and time. The flow of fluid in an upright symmetrical passage is dealt through this numerical research. The numerical model consists of a heater plate assembly next to a partially filled porous metallic foam. Metal foams with 4 distinct PPIs of 10, 20, 30, and 45 and porosity spanning from 0.90 to 0.95 are the subject of numerical calculations. Various structural arrangements of the aforementioned porous media (combinations of various porosity and pore density) are considered. Heat is dispersed through forced convection with air as working fluid. This study's comparison focuses solely on the differences between laminar and turbulent flows when there is a porous media in terms of fluid flow characteristics and heat transfer qualities. The Darcy–Forchheimer equation, coupled with the local non-thermal equilibrium model, is incorporated in the partially filled metal foam region. Numerical outcomes of the laminar scenario are validated against the findings of earlier research. Reaffirming the solution process, the turbulent case's outcomes are compared.

This numerical research uses the two equation SST $$k - \omega$$ k - ω model to investigate supercritical carbon dioxide (sCO2) in a vertical divergent tapered annular channel at an axis-symmetric condition. Under the same operating conditions, this tapered annular channel enhances heat transfer over a simple cylindrical annular channel due to its geometrical configuration. This geometrical structure provides tapering to the heat generation rod because wall heat flux continuously changes along flow direction, and this effect appears in heat transfer. The computational domain is 3 m long, with 0.5 m at the beginning being regarded as an adiabatic section for fully developed turbulent flow and 2.5 m at the end for investigating the thermalhydraulic characteristics of sCO2. According to the report, the divergent tapered cylindrical annular channel’s wall temperature seemed lower with a more excellent heat transfer coefficient value at the same boundary conditions, including mass flux, power, pressure, and inlet temperature. Besides, the heat transfer has been observed to be impaired and enhanced relatively at low (400 to 500 kg/m2s) and high mass fluxes (600 to 700 kg/m2s) conditions. Heat transfer impairment at low mass conditions arises due to a substantial temperature disparity amid the core and wall fluids area, which induces strong buoyancy forces, unlike at high mass flux conditions.

The discrepancy between the supply and demand of the power due to such a steeply rising population and its electronic requirements results in a substantial fluctuation in the load management and the operational cost. A latent heat-based storage system is always beneficial over a sensible storage system due to its superior charge holding capacity over a nearly constant isothermal behaviour. The impact of mixing phase change material (PCM) RT82 with alumina nanoparticles on the solidification process is investigated in the present study. To further enhance the process, an extended Y-shaped fin with the nanoparticle-enhanced phase change material (NEPCM) is numerically simulated for reduced total solidification time and improved heat transfer rate. Fins are always beneficial for obtaining a better heat transfer rate, and as solidification is mainly a conduction-dominated process, employing fins will enhance and fasten the process. The process is evaluated in terms of total solidification time under different nanoparticle concentrations, which are 0, 3, and 7%. The combination of a Y-shaped fin with a higher volumetric concentration of nanoparticles is more fruitful in saving the solidification time.

A three-dimensional computational study of a novel heat sink design under natural convection heat transfer is performed. All fins are mounted on a vertical base plate of dimension 80 × 50 × 5 mm. In this study, a novel interrupted secondary branched fin heat sink is compared with continuous rectangular plate fin heat sink, interrupted continuous rectangular plate heat sink and secondary branched heat sink. The effect of symmetric number interruptions on secondary branched fin on the overall performance of the heat sink (i.e., heat transfer, Nusselt Number, effectiveness) has been investigated. The temperature difference between the ambient air and base plate varied between 10 and 60 °C. The Rayleigh number considered for this simulation is 1.1 × 105 ≤ Ra ≤ 6.1 × 105. Simulation results show that overall heat transfer rate increases with increase in number of interruption on the secondary branched fin. The maximum heat dissipation occurs on two interruptions is higher than the conventional heat sink (i.e., continuous rectangular plate heat sink), which is 7.62% more compared to the conventional design.

This paper describes the combined effect nanoparticles volume fraction and magnetic field on melting of Fe3O4–beeswax as nano-enhanced phase change material (NePCM). A differentially heated square annulus cavity is selected in this present computation. There are four sets of thermal boundary conditions which are considered based on temperature difference above the melting point of phase change material (PCM). Enthalpy porosity technique is adopted to study the melting process of PCM. The governing equations with suitable boundary conditions are solved by the finite volume method (FVM)-based commercial software package ANSYS Fluent. A user-defined function (UDF) is written separately for adding Lorentz force source term. The simulations are performed for different controlling parameters like temperature difference (10 ≤ ∆T ≤ 40), volume fraction of nanoparticles (0 ≤ ϕ ≤ 0.02), Hartmann number (0 ≤ Ha ≤ 40). The results are quantified in the form of melt fraction of the NePCM. Finally, it is evaluated that presence of nanoparticles augments melting process at lower temperature difference, but at higher temperature difference, a contradictory observation has been found. Additionally, it is also found that the presence of external magnetic field declines the melt fraction.

The efficiency of an integrated circuit, which are building blocks of every modern-day computer, decreases with increase in temperature. This decreases the overall computational efficiency, and therefore, thermal management of these electronic circuit has become a highly researched area in recent years. It is quite evident that the forced convection air-cooling method has lower effectiveness and may not be suitable for industrial applications. In order to overcome this limitation, several alternative cooling methods have been proposed out of which liquid-based systems have been used preferentially primarily due to higher effectiveness and simplicity of construction. In this paper, the performance characteristics of a compact rectangular liquid cold plate-based thermal management system has been studied using numerical simulations and validated with experimental results. This study focuses on the correlation between the flow rate and the surface temperature of the cooling surface of a channel type rectangular cold plate-based liquid cooling system. It was observed that increasing flow rates produced larger deviations due to effects of turbulences and recirculation. Furthermore, numerical simulations revealed that non-uniform flow distribution in channels significantly contributed to various temperature hot spots on the cold plate’s surface.

Lithium-ion battery (LIB) performance highly depends upon the operating temperature. Thermal management of batteries using phase-changing material (PCM) has drawn attention recently because of zero or negligible power requirement to perform cooling compared to air/liquid-based cooling. In the present study, a numerical model has been developed to simulate the phase change behavior of phase-changing material encapsulated over a 18,650 LIB (capacity 2.4 Ah and nominal voltage of 3.6 V). Investigations were performed to see the response of temperature under different charging/discharging rates (C-rates). To visualize the effect of PCM module thickness on battery temperature under 3 C-rate, three different thicknesses of insulation were taken and the temperature of the cell was tracked. A comparison between the magnitude of solidification and melting time is also performed for cell operating under 3 C-rate. The complete solidification and melting cycle took 370 min. PCM takes 170 min to melt entirely from the initial state. The current in the battery is switched off at this moment to regenerate the PCM in solid state. PCM takes 97 min to solidify, and cell regains its initial configuration at about 200 min (i.e., 370–170 min).

The present study aims at identifying the critical Reynolds number for transition from laminar to turbulent in irregular shaped mini-channels. Numerical study including conjugate heat transfer and axial conduction is carried out using commercially available software ANSYS Fluent®. The channel of length 105 mm, width 4.5 mm, and height 2 mm is fabricated in an aluminium substrate of length 114 mm (L), width 15 mm (W), and height 6.3 mm (H). Water is used as working fluid. Average hydraulic diameter (Dh) of mini-channel is 2.86 mm, and cross-section area varies non-uniformly from 10 mm2 to 18 mm2 along the length. Problem is set up with mass flow rate and outflow boundary condition at inlet and outlet, respectively. Bottom wall is given with uniform heat flux (q) of 200 watts thus incorporating conduction in solid wall of channel. Temperature difference between the inlet and outlet is compared with experimental measurement and found to be in good agreement. It is observed that the heat transfer coefficient as well as pressure drop both increases with increase in mass flow rate; however, increase in pressure drop is found larger compared to increase in heat transfer coefficient. Further, we also found the axial conduction in the solid wall. It is interesting to note that the transition from laminar to turbulent is observed at lower Reynolds number. Present work provides platform to study thermal and fluid flow behaviour of the irregular shaped mini-channels.

Passive heat transfer enhancement may be accomplished effectively by having longitudinal fins. They provide relatively more surface area for heat transmission to take place and make it possible to achieve bulk mixing in otherwise streamlined flows. This study takes into account three different geometries for the internal fins, curved, triangular, and annular-sector in the plain tube. The enhancement in heat transmission depends on the fins’ shape, density, and height, as well as their relative position on the internal surface of the tube. A comparative numerical study of the turbulent heat transfer characteristics of a tube with internal fins has been conducted via a numerical study for enhancement of the convective heat transfer coefficient in developing, transition, and developed region. All the three geometries with same surface area and Reynolds number are compared with the tube without fins. Curved fins, which stands out the best, then studied with different radial pitches, different fin heights, and at different Reynolds numbers and compared with the Dittus–Boelter equation. Performance enhancement criteria are taken into consideration to compare different variants of tube. The findings of this study demonstrate that the convective heat transfer coefficient and pressure drop improve with decrease in radial pitch of fins, increase in fin height, and rise in Reynolds number.

High flux research reactor (HFRR) is a 40 MW pool type research reactor being developed at BARC for providing various facilities for basic and applied research in nuclear science and technology, neutron radiography, neutron transmutation doping and material irradiation studies. In this reactor, an irradiation test loop (ITL) is provided to support fuel and material testing under simulated conditions present in light water power reactors (PWR/BWR). It is a high pressure and high temperature loop with operating pressures reaching up to 17.5 MPa whereas the temperatures as high as 330 °C. Specific provisions are also made to simulate water chemistry environment as present in various PWR/BWR reactor types. To evaluate process system design of the ITL, thermal hydraulic transient analysis was carried out to assess thermal parameters and safety margins of the test fuel during loss of electric power supply using RELAP5/MOD 3.2. It was found that the ITL process system provides sufficient cooling flow to the test fuel cluster to maintain all the thermal hydraulic parameters and safety margins under the acceptable limits during loss of electric power supply.

During a hypothetical severe accident in a sodium-cooled fast reactor, core melt-down is expected to occur. As a result, molten corium would fall through sodium as a jet. The dispersion of the fissile material within the molten jet is important to avoid re-criticality. This occurs in several stages with different sequence of complex controlling physical phenomena. The present work is in the direction of understanding the initial jet behavior influenced primarily by flow instabilities. An in-house force balanced two-phase flow solver, namely THYC-MP has been used to study the behavior of two-dimensional jets of corium and simulant material namely wood’s metal within liquid sodium. The expected physics and jet breakup behavior is studied and described.

Nowadays Phase Change Materials (PCM) have been utilized for different thermal applications and thermal management of electronic systems. However, the poor thermal conductivity in PCM reduces the heat transfer results in a poor performance. Therefore, heat transfer augmentation methods have to be employed for improving the heat transfer in PCM based systems. In the present study, a novel heat transfer enhancement technique, that is, copper porous-fin has been introduced for improving the melting performance of the PCM. In order to perform a numerical study, a 2-D axisymmetric numerical model has been developed. Further, liquid fraction and thermal behaviour of porous-fin TES was evaluated and compared with the without-fin TES system. Based on the studies, it was found that porous-fin TES has uniform temperature distribution and shorter melting time than the without-fin TES. This shows that porous-fin TES can be recommended for thermal management of electronic systems which needs uniform and faster cooling.

For an asymmetrically confined rotating cylinder placed at the axis of a channel, surrounded with the flow of power-law fluid has been numerically investigated here. The dimensionless parameters used to solve the governing equations numerically are Reynolds number, Prandtl number and power law index which have the values as 0.1 ≤ Re ≤ 40, 0.7 ≤ Pr ≤ 100, 0.3 ≤ n ≤ 1 respectively, the value of asymmetrical ratio and blockage ratio varies as 0.1 ≤  $$\Upsilon$$ Υ  ≤ 1 and 0.2 ≤ β ≤ 0.6 respectively. For keeping the two Reynolds number equal, at the inlet section average velocity should be same as that of angular velocity. Streamlines are used for the visualization of flow and isotherms represent the temperature profile at different positions of the cylinder. In most cases, the flow is made more stable by having a moderate degree of cylinder confinement. However, arrangement of the high Reynolds number, the high shear-thinning behaviour of the fluid and the degree of symmetry become more promising than the cylinder confinement to determine the flow behaviour, and resulting to shift the flow field from being steady to being time-dependent. Although, the extent of transition takes longer to take place as the cylinder gets closer to one of the channel walls.

This chapter deals with comparison of heat transfer performance of rectangular and circular mini channels liquid heat sink for cooling of real Insulated Gate Bipolar Transistor (IGBT) module. A three-dimensional steady-state simulation using Ansys Icepak is implemented for this investigation. In this chapter, IGBT module- SKM75GB12T4 made by SEMIKRON is used. The IGBT module is made of multilayers, in which a power of 200 W is dissipated on the silicon diode chip. Water as a coolant is passed through the mini channel at an inlet temperature of 305 K for different values of Reynolds numbers (396 to 989). It is observed that the heat transfer performance of rectangular channels is always better than that of circular channels both in terms of baseplate and junction temperature because the surface area to cross-sectional area ratio is higher in case of rectangular channels. Further, the aspect ratio of rectangular channel is varied in a range of 0.8–1.6 at different Reynolds numbers (396–989). A higher aspect ratio confirms better heat dissipation, although at higher Reynolds number (Re > 700) baseplate temperature is insensitive to the aspect ratio of the mini channel. Thermal resistance for rectangular and circular mini channel is obtained and its variation with channel height is also analysed. It is found to have lower thermal resistance in rectangular channel than circular. Results have shown lower thermal resistance with higher mini channel height. As per the requirements of junction to case thermal resistance value of 0.38 K/W provided by the manufacturer for safe operation of the IGBT, a rectangular mini channel with aspect ratio of 1.5 at Reynolds number of 989 gave the thermal resistance value of 0.39 K/W.

This study investigates the effect of introducing fillets at various sharp edges in a unidirectional flow to explore flow behavior and heat transmission. This study utilizes a finite volume approach with Ansys Fluent, a commercial package that employs the face meshing approach, to investigate the impact of fillets on fluid flow characteristics and heat transmission in a grooved channel. The validation of the numerical simulation solver involved a comparison with previous studies, and a grid-independence test was conducted to confirm the independence of the solution on mesh resolution. The results demonstrate that fillets effectively direct fluid flow toward the channel walls, reducing the downstream reversed flow zone caused by flow contraction. The research aims to thoroughly investigate the physics of flow and engineering parameters that are relevant. The introduction of fillets at sharp corners in the grooved channel enhances heat transfer efficiency by over 34%, benefiting from the increase in heat transmission. This study investigates the effect of fillet placement on the heat transfer coefficient and pressure drop in grooved channels. Results show that introducing fillets in the outer corner of the groove yields a higher heat transfer coefficient than fillets in the inner corner. Moreover, while different fillet configurations do not significantly affect the pressure drop, it is approximately 60% lower compared to conventional grooved channels. These findings provide valuable insights for optimizing grooved channel designs in various engineering applications, where heat transfer and pressure drop are important considerations.

The present study is a numerical investigation on the thermal and flow characteristics of flow over cylinders in the presence of vortex generators acting also as flow guides. This is proposed as a method to enhance the heat transfer from the Li-ion battery by air cooling in electric vehicle battery arrangement. The flow guides placed upstream of the cylinder divert some mainstream flow towards the cylinder surface and therefore enhance the heat transfer from the cylinder. The location, angle of attack and number of diverters are varied. The results are presented in terms of local Nusselt number along the circumference of the cylinder, and it is found that vortex generators increase the rate of heat transfer for all configurations. It is also observed that placing a vortex generator only on one side of the cylinder is more effective than placing vortex generators on both sides. The heat transfer characteristics are explained with aid of flow behaviour observed.

Baking of bread is a major global activity, largely carried out using traditional wood-fired furnaces, particularly in the Africa and Indian continent. Literature shows that the specific wood consumption for traditional design of a wood-fired bakery is around 0.9 kg of wood/kg of wheat bread baked, which is very high. This can be reduced by reducing the heat losses from furnaces during intervention of operators, e.g. frequent opening and closing of the door, mainly to decide the cycle time by checking the quality of the baking of bread. A typical frequency of door opening reported in the literature is ‘three’ for any batch. The baking time for a particular batch is influenced by the total heat possessed and radiated by walls of the baking furnace. Hence, the total time for baking varies for each subsequent batch of baking. This makes it difficult to determine a standard baking time. The present work is aimed at improving the baking efficiency of the furnace. Under this a mathematical determination of the time required for a standard baking cycle, which can reduce the frequency of the door opening. This way of operation can also reduce the carbon footprint and cost of baking of bread.

Impinging air-jet cooling using open-cell metal foam is found to be a viable option for the removal of concentrated heat loads. An experimental study has been conducted for the air-jet cooling of the copper metal foamed flat plate using an elliptical nozzle of aspect ratios 1 and 4, respectively. The operational parameters include Reynolds number 40000 and 50,000, respectively, and the impinging distance is varied from 3 to 7. The nozzle's average and local thermal performance with a higher aspect ratio are found to be better. The enhancement in the peak value of the Nusselt number is found to be 35% for the Reynolds number 50000 by increasing the aspect ratio from 1 to 4.

In the last few decades, nanotechnology has played a vital role in introducing heat transfer into the industry. Currently, maximum research has been conducted on heat transfer to increase the rate of heat transfer and to increase the efficiency of heat transfer devices pertaining to vehicles, such as heat exchangers and automobile radiators. In this study, the numerical investigation has been performed to analyse the heat transfer of the nanofluid ZnO and a novel Ag/ZnO flowing through the radiator. The analysis is performed for pressure drop and Nusselt number for each simulation. The results were presented, including temperature distribution, pressure drop, Nusselt number, Reynolds number, and heat transfer rate. HTC of Ag/ZnO is enhanced by 34.68% more than ZnO at 0.1% volume concentration. At same volume concentration, pressure drop of Ag/ZnO nanofluid is reduced by 18.03%. It is observed Ag/ZnO nanofluid appears to be more effective than ZnO nanofluid.

Supercritical fluid (SCFs) may have normal heat transfer (NHT), enhanced heat transfer (EHT) or deteriorated heat transfer (DHT) as they pass through the pseudo-critical region. It is the DHT which poses threat to safe operation of reactor as DHT results in higher surface temperature which may lead to the failure of the fuel clad and cause further detrimental complexities. Literature suggests the buoyancy and acceleration parameters as the main factors causing the DHT in SCFs. There have been many studies in the literature for forced convection systems for investigating DHT, still, there is lack of clarity for DHT criteria to be adapted for safety studies of the reactors. Nonetheless, such studies for natural circulation systems are rare. In the present paper, experiments have been conducted with supercritical carbon-dioxide (SC-CO2) to study the DHT under natural circulation (NC). Experimental results obtained for vertical flow of SC-CO2 at different pressure and cooler orientation have been reported, and the role of buoyancy and acceleration parameters in the DHT has been discussed for NC systems.

Thermal contact conductance is an important concern in the heat transfer applications such as electronic packaging, engine cooling, nuclear cooling, and thermal control. The characterization of thermal contact conductance between the two solid plates is an important parameter in the designing of heat sinks in various industrial applications, where suitably different thermally conducting interface materials are employed. In the present investigation, glycerin and a commercially available thermal paste are used with and without the nanoparticles in the different particle concentrations. The effects of heat fluxes and interface materials on thermal conductance and heat transfer are estimated, experimentally. A reduction in the resistance to heat transfer at the interface of solid surfaces subjected to constant pressure is found for the higher concentration of nanoparticles. The effects of all the materials and temperature differences are duly reported and discussed.

In rocket motors, propellants are utilized to undergo combustion and generate thrust. In the case of solid rocket motors, this is accomplished with solid propellant grain, which is the mixture of solid fuel and/or oxidizer cast and cured inside the combustion chamber to a semi-solid state. For the purpose of achieving various types of combustion, numerous designs have been created. There are four distinct types of combustion: progressive, neutral, regressive, and multi-stage thrust. Although these geometries have been designed since the earliest days of rocket manufacturing, they perform as intended despite not being optimized. This research investigates and analyzes the creation of new and optimized designs with differential calculus method and finite element analysis in order to increase surface area and propellant volume within the combustion chamber. Two models are theorized, designed, and analyzed in software for their various parameters, including internal surface area, volume, and pressure versus time curves.

The present study investigates the effect of piezoelectric coupling factor of a piezoelectric flag where the energy can be harvested through flow-induced oscillations. The flexible filament structure is placed in an incoming viscous fluid at a low Reynolds number of 200. An in-house immersed boundary method (IBM)-based fluid–structure–energy equations solver has been used for the simulations. It is observed that for a wide range of bending rigidity $$\left( \gamma \right)$$ γ and mass ratio $$\left( \beta \right), $$ β , the dynamics of the flow-induced oscillations are not affected by the piezoelectric coupling factor $$\left( \nu \right). $$ ν . However, for a lower $$\gamma$$ γ and $$\beta$$ β , the oscillation states of the system are significantly affected; for $$\beta = 0.05$$ β = 0.05 and $$\gamma = 10^{ - 3}$$ γ = 10 - 3 , the system exhibits self-sustained oscillations at higher ν; otherwise, it was a damped oscillation. In contrast, for higher $$\beta$$ β values $$\left( {\beta = 5.0} \right)$$ β = 5.0 , the periodic oscillations of the flexible filament transitions into an aperiodic state in the presence of piezoelectric coupling. The present findings may provide the insights into the design of efficient FIV-based energy harvesting of a piezoelectric flag by identifying the parametric regimes, where the dynamical state is either conducive for energy harvesting or is detrimental.

The present study concerns the numerical investigation of placing a propeller upstream of a thin disk flow. The investigation is performed with an unsteady Reynolds averaged Navier–Stokes (URANS) simulation approach using the open-source code OpenFOAM. Three different simulations are performed: disk flow, propeller flow, and propeller–disk flow. A widely used marine propeller, INSEAN E779A, is employed for the current study, and the propeller flow is simulated using the cyclic arbitrary mesh interface (Cyclic AMI) approach. The propeller wake dynamically interacts with the disk shear layer and changes the flow in front of the disk. The symmetry of the flow gets broken, and the size of the bubble also increases due to the propeller wake. The interaction between recirculating vortex rings as the flow develops is examined using three-dimensional flow features. The present study may be relevant to propeller–body interactions in aerospace and marine applications as well as finding approaches for enhancing mixing.

Ocean energy offers enormous potential compared to the other forms of renewable sources like wind and solar to move toward a sustainable energy source and decrease our reliance on fossil fuels. Wave energy converter is a device that converts ocean energy into electrical energy. Power take-off (PTO) systems convert the energy absorbed by the wave energy devices into electrical energy. Out of the various method of PTO, hydraulic PTO is the most widely used PTO system. The current research focuses on selecting hydraulic fluid for wave energy converter. Two hydraulic fluids, namely HLP-68 and HLP-46, are tested in the present hydraulic PTO setup. The variation in pressure, temperature, and Vrms generated by the generator is noted. Hydraulic fluid HLP-68 shows better performance as compared to HLP-46. Temperature increases more in HLP-68 as compared to HLP-46 of hydraulic fluid.

This paper reviews the status of micro-hydropower in relation to different methods. Micro-hydropower uses either turbines or reactions, depending on what your site can offer. There could be some dependency on fuel if you do not have a renewable energy source but it is still much less than fossil fuels. It is important to consider how developing countries can use renewable energies for their short-term economic planning. Hydroelectricity is the most reliable and affordable of all renewable energy sources, because of its advantages over other source of energy. However, an environmental and financial concerns, a large hydropower plant is less attractive in the current economy, whereas a micro-hydropower plant has a huge potential to develop. Many small and shallow rivers can be used for hydropower to generate electricity: includes pico-hydro and micro-hydro technologies. India is a developing country with a population of 1.35 billion people who live in different socioeconomic strata. Thus, the energy demand is constantly adding in a trouble to accelerate artificial conditioning and boost the frugality. Reactive energy provides a significant portion of the nation’s electricity needs. Small hydropower (SHP) should be prioritized because large hydropower projects require significant capital investments and have complex social and economic implications.

The unsteadiness caused by relative motion between stator and rotor of a turbine stage and its effect on performance is still an active research area. For better understanding of flow and performance, a highly loaded low aspect ratio HP transonic turbine stage with application to a small engine is considered for the present study. The geometry has a stator-to-rotor pitch ratio of 2.63 and is designed to operate at a total-to-total pressure ratio of 2.78. Unsteady three-dimensional CFD simulations were performed with the help of the commercial software ANSYS CFX. Cases were simulated at five different operating conditions to study the influence of pressure ratio and rotor speed on the rotor–stator interaction. Simulations are performed at design speed for design point (DP), low and high pressure ratios (LP and HP, respectively), and two cases at the design pressure ratio, but at rotor speed higher (105%) and lower (90%) than that of design speed (named HS and LS). The stator and rotor in the LP case are unchoked at midspan and at a high subsonic condition, whereas they remain choked in the rest of the cases. The HP case represents an operating point where the turbine is close to the limit load condition. It is observed that the stator exit flow field is affected by the moving blade row, causing total temperature fluctuations upstream of the rotor, of about 10% of the stage total temperature drop locally. The magnitude of this fluctuation is determined by the pressure ratio and rotor speed. The magnitude of fluctuations of total temperature averaged over the interface plane remains relatively smaller; for the case of LP, these fluctuations are observed to be marginal.

A numerical investigation of the species separation of a mixture of argon (Ar) and helium (He) flowing through the micro-nozzle at different divergent angles and in the presence of different concentrations of carrier gases (nitrogen and krypton) is reported. The study of varying back pressure effect on species separation is also included in the current literature. The Direct Simulation Monte Carlo approach has been adopted for the research, and the methodology was validated with the experimental study of Hao et al. (J Micromech Microeng 15:2069, 2005 [12]). Nozzle inlet is kept at a pressure of 120 kPa, while the exit is kept at hard vacuum. An equimolar mixture of argon and helium is inserted at the inlet of the nozzle with an inlet temperature of 300 K. The highest centerline argon mole fraction is obtained for a 45° divergence angle. The separation is found to be decreased with an increase in the concentration of carrier gases, and the heavier carrier gas (Kr) was found to further inhibit the separation. The species separation is found to be decreased with an increase in back pressure.

Double-divergent nozzle (DDN) is an altitude adaptable rectangular nozzle which has no mechanical elements to gain altitude compensating property, which results in a lighter nozzle. In this work, the thrust vectoring using a secondary hot gas injection in a DDN is investigated. The effects of injection pressure, injection location, injection angle, inflection angle, and nature of injectant on thrust vectoring performance are investigated using numerical simulation. Initially the effect of different propellant is studied under hot flow conditions. It is observed that, H2O2 shows better performance compared to other mixtures, and it is used for remaining studies. Further, the thrust angle is affected by both the injection pressure and the injection site. The lateral thrust is increased with higher injection pressure and the injection closer to the exit of the nozzle. When the injector slot angle is high, the primary downstream vortex vanishes and a strong secondary upstream vortex is created. This shift in the primary upstream vortex away from the core flow advances the shock separation. More deflection of propellants is obtained at higher injection angle. Finally, it is noted that, as the inflection angle increases the deflection of combustion gas also increased to ensure better thrust vectoring.

Most tasks connected to departing a flow as well as adjusting flow rate, velocity, pressure, and temperature can all be controlled via the nozzle. Accordingly, accuracy and total control that is hand-in the nozzle are based on this observation. Therefore, the primary function of the nozzle and any modifications to its shape or geometry will directly impact the system's current value and performance. The major goal is to attempt to alter nozzle geometry, and while these changes have been thoroughly examined using analysis software, they are not entirely accurate; rather, they are intended to provide a general notion of what might happen if all modifications were made to the divergent section. Surprisingly, compared to RS-25, it received an improvement in new adjustments. Finding out all the information about the RS-25 is another crucial step because, in comparison with these alterations, this engine is used as a paradigm, and meshing adjustments during the study have an impact on the outcomes.