Proceedings of Fluid Mechanics and Fluid Power (FMFP) 2023, Vol. 3

The incorporation of vortex generators in the microchannel proved to be effective in dissipating heat and has become a hot topic for decades. This numerical study compares the heat dissipation performance of eight vortex generators (VGs) incorporated in microchannels with water as the coolant. The thermo-hydraulic performance of the channel with selected VGs were studied. Microchannel with hydraulic diameter of 500 μm was used with 13 pairs of VGs of each type arranged in the flow direction, respectively. The heat transfer analysis with coolant flow was conducted on each of these microchannel at Reynolds numbers 100, 200, 300, 400, and 500. Two arrangements: bottom wall and sidewall arrangements were studied separately. The results indicated that all vortex generators enhanced the heat dissipation performance with Reynolds number with the penalty of pressure drop. The studies proved that both bottom and side wall arrangements of VGs significantly improved Nusselt number of the channel but the side wall fetched the highest pressure drop of 49.29% at Re = 500.

Young’s piecewise-linear interface construction is a volume-of-fluid (VOF)-based numerical algorithm used for accurate intrinsic volume conservation and interface representation for multiphase simulation. The numerical model solves the complex Navier–Strokes equations along with the hyperbolic volume fraction advection equation. The major challenge that lies in Piecewise-Linear Interface Construction Volume of Fluids (PLIC-VOF) is to achieve a volume-preserving advection and an accurate reconstruction of the interface in solenoidal velocity fields. In the present work, a redistribution-based PLIC-VOF algorithm is developed and is first applied to an inertial frame of reference for simulating a cavitation bullet. The algorithm after appropriate modification for non-inertial frame of reference is used to simulate tank sloshing phenomena. To include the non-linearity a moving coordinate system is used which also avoids the complexities of moving wall boundary conditions of the tank. Kinematic stability equation is used to ensure kinematic compatibility when implementing in a non-inertial frame by defining the datum at the horizontal center of the interface at the initial time (t = 0). Comparison of the present simulation for the tank sloshing benchmark problem with the results reported in literature using Smoothed Particle Hydrodynamics (SPH) (Bota-Vera et al. 2010) shows good agreement for both non-impact and impact type slosh loads.

This study examines the effects of contact angle, surface tension, and heat flux on bubble growth rate, bubble departure time, and bubble departure radius using a comprehensive numerical simulation approach. The study uses a computational fluid dynamics (CFD) approach based on volume of fluid (VOF) to capture the dynamic behavior of the liquid-vapor interface during boiling. The simulations provide significant information on the mechanisms that control the boiling process by varying the contact angle, surface tension, and heat flux. According to the findings, slower bubble growth leads in bubbles taking longer to reach their maximum size. Additionally, longer time intervals before bubbles detach are a result of increasing surface tension. The simulations also show that heat flux has an impact on the size of the bubbles that detach as well as the time it takes for them to do so. Higher heat fluxes hasten bubble detachment, resulting in a reduction in bubble size and detachment time. These findings offer crucial knowledge for heat transfer system design and optimisation, enhancing boiling heat exchangers and cooling mechanisms across several sectors. The information gained from this inquiry creates possibilities for more effective temperature control and better heat transmission.

We numerically probe the transient evaporation dynamics of wettability influenced capillary bridges. For this purpose, first the profile of capillary surface is numerically obtained using Level Set (LS) method. Then this profile is used as input for the transient evaporation model. The corresponding governing differential equations for mass, momentum, and energy transfer are solved in a fully coupled manner based on Arbitrary Lagrangian–Eulerian (ALE) framework. We vary the contact angles at solid–liquid interface over a wide range to portray the role of wetting state on evaporation kinetics. Results show that, large contact angles manifest upscaled mass loss rate due to alleviated vapor confinement effect around the capillary surface. During the initial transient regime, the interfacial temperature evolves in a non-linear manner due to internal heat advection. This leads to formation of multi-vortex pattern during initial stages. Also, the evaporative mass flux for large contact angles (low wetting conditions) is significantly higher near the bulge region. As a result, the evaporation-induced cooling and the corresponding internal velocity scales are significantly amplified in such cases than the hydrophilic surfaces. This upscaled internal velocity facilitates the temperature homogenization process thereby causing the stable conditions to be reached at much early stages than high wetting conditions.

Gravity currents are predominantly horizontal flows driven by density differences. In the context of porous media, they occur in environmental applications such as carbon sequestration and geothermal energy recovery, where flow arises from the density contrast between two fluids, such as liquefied CO2 and denser brine. While there has been substantial research on gravity currents in porous media, most of the emphasis has been on studying two-dimensional rectilinear flows due to their ease of visualization and analytical modeling. Consequently, only a limited number of studies have investigated axisymmetric gravity currents. Moreover, earlier research on gravity currents has often assumed the presence of a sharp interface between the gravity current and the ambient fluid, which is not a realistic assumption. In this study, we developed a depth-averaged model of mass and concentration to account for the dispersive entrainment of ambient fluid by the axisymmetric gravity current. Our findings demonstrate that, under the condition of a constant and continuous flux release from a point source, the buoyancy of the current exhibits self-similar behavior, while the height and spread of the gravity current increase in a non-self-similar manner, proportional to t1⁄2 (where t represents time). Similarly, the depth-averaged concentration of the gravity current also displays non-self-similar behavior. Through this study, we have eliminated the assumption of a sharp-surface interface and established that an axisymmetrically flowing gravity current can be effectively modeled using a dispersive entrainment approach.

This paper explores the complex phenomena of viscous fluid flow through layered porous medium. In nature, there are several instances where viscous flows occur through high permeable channels, e.g., oil recovery, CO $$_2$$ 2 sequestration, and water soil infiltration. In the current work, Dye-attenuation technique is used to investigate the flow behavior of viscous fluid injected into a fully saturated layered porous medium. The research focuses on understanding the flow patterns developed through image visualization and post-processing in MATLAB. Experimental investigations are conducted in a two-layered porous medium using a glycerin-salt-water mixture as the viscous fluid and a salt-water mixture as the ambient fluid. The study examines flow profiles, front, height patterns, self-similarity of front propagation ( $$x_f$$ x f ) with respect to time (t), and the best fit on the data represented by a power law. We have also calculated the frictional losses in the pipe network at the inlet. In the future, we could validate this experimental study with numerical or analytical models and perform further experiments for multiple layers of porous medium.

Present work is focused on the investigation of shear layer atomization of thin film of mucosalivary fluid in the presence of unsteady pulsed airflow mimicking cough events. The fluid dynamics of thin film atomization is numerically studied, and a comparison is made between two flow cases, namely laminar and LES turbulence modeling approach. In the initial stage, the deformation of the thin liquid film in shear flow shows qualitative similarity, and a prominent wavy Kelvin-Helmholtz instability-like structure is observed to form in results obtained using both the approaches. Whereas, in the later stage, deformation of liquid film into bag-like structure due to pulsed air velocity was observed to appear with LES approach, unlike laminar approach. Overall, it is observed that investigation of the liquid film atomization using LES approach has provided relatively better insights such as inflation of deformed liquid film into bag like structure, its rupture and fragmentation into tiny-sized droplets compared to that of laminar approach, which are essential and important aspects in the physics of coughing phenomena.

Since past years, the study of formation of free surface vortex at intake of hydropower plants has been a trendy and interesting subject among engineers and researchers. The one of the important and main problem encountered in hydraulic engineering is air entrainment by means of formation of free air-core vortex at water intake pipe when the submergence over the intake is not enough. Thus, in order to prevent the formation of vortex over intake mouth, a minimum submergence has to be kept over it, which is called as critical submergence. Numbers of formulae are present which predict the critical submergence for vertical intakes for axial flow condition but study is required on how critical submergence is affected by flow non-axiality. In present study, a potential solution was developed for critical submergence by combining the inclined uniform flow and point sink flow. It was observed that in case of non-axial flow, critical submergence required was more than what is required with the axial flow condition. The derived analytical equation of circular intake predicts the critical submergence within the error margin of ±20%. Also in the present study, the regression analysis was performed to propose a functional relationship for prediction of critical submergence for non-axial flow.

Forced convective heat transfer with nanofluid flow over a circular cylinder has been numerically studied using the single- phase dispersion model. The cylinder has a constant wall temperature of 350 K and is exposed to a free stream of nanofluid (Al2O3–H2O) at ambient temperature for Reynolds number in the range of 20–160. A steady-state analysis uses a 2-D domain, and governing equations are solved using a finite volume method based on the SIMPLE algorithm. Effect of volume fraction (0.05 < ϕ < 2) and Reynolds number on the heat transfer characteristics are studied. Nanofluid exhibits a higher heat transfer rate than base fluid for all volume fractions and Re. The highest Nusselt number is obtained near the front stagnation point and decreases toward the rear stagnation point. It is observed that for a given volume fraction, the heat transfer enhancement ratio increases up to Re = 120, and then there is no significant change.

The impact of a single droplet on various surfaces is widespread in nature and prevalent across numerous industries such as pharmaceuticals, chemicals, spray drying, coating, ink-jet printing, jet cleaning, self-cleaning surfaces, anti-icing, forensic science, and others. This study presents a Volume-of-Fluid (VOF)-based multiphase simulation of a single droplet impacting a hydrophobic solid surface in a quasi-steady air medium at atmospheric pressure. The droplet’s shape transitions from spherical to ellipsoidal (by varying the ratio of major to minor axes) to explore how shape of the droplet affects spreading and retraction dynamics during post-impact. A novel image processing algorithm is introduced to model the dynamic contact angle (DCA). Present study investigates the temporal and spatial evolution of spreading factor, apex height, and shape factor. Using a finite volume-based solver in ANSYS FLUENT, simulations were conducted at specific Weber (We) and Reynolds (Re) numbers of 10 and 1575, respectively. This research offers unique insights into droplet dynamics and morphology during spreading and retraction, which could enhance understanding of related natural and industrial phenomena.

Droplet impact on a ribbed surface finds broad applications in both natural and industrial settings. This study aims to investigate the fundamental physics governing droplet dynamics upon impact with ribbed surfaces. Three types of rib surfaces—square, truncated cone, and discrete cylindrical ribs—were used to examine the effect of rib surfaces on the post-impact dynamics of a spherical droplet. The numerical simulations were performed on a finite volume solver in ANSYS FLUENT software, employing the Volume-of-Fluid (VOF) method at specific Weber number ( $$We$$ We ) of 5 and Reynolds number ( $$Re$$ Re ) of 875 numbers based on the droplet properties. The simulation tracks the time-dependent evolution of the droplet spreading factor (the ratio of instantaneous diameter to the initial droplet diameter). The study demonstrates a notable reduction (~29.5%) in contact time for the droplet impacting on the truncated cone rib surface, whereas no significant improvement was observed with cylindrical ribs compared to the standard square rib case. Additionally, the dynamics of droplets over different rib geometries were analyzed, including the Wenzel and Cassie–Baxter states, highlighting the role of a rib surface on droplet dynamics at constant Weber and Reynolds number conditions. The present work explores the possibility to enhancing the efficiency and effectiveness of surfaces used in self-cleaning, anti-corrosion, anti-icing, and heat transfer applications.

Hydropower is an important supplement to intermittent renewables such as wind and solar power. Because of its flexibility, it contributes to grid stability. However, when used in off-design condition, this flexibility presents challenges in turbine operation. Cavitation is one of such issue in reaction turbines, i.e., Francis turbine. Increase in velocity combined with flow separation on the suction surface of runner blade as well as guide vane results in pressure to fall below vapor pressure and thus development of cavitation. Guide vane and runner blades are basically extension and combination of the NACA 65-021 hydrofoils, therefore a single three-dimensional NACA 65-021 hydrofoil is investigated for cavitation to develop a theoretical understanding of cavitation dynamics. ANSYS ICEM is used to create a three-dimensional structural mesh of a single hydrofoil. Unsteady Reynolds Averaged Navier–Stokes simulations are performed for cavitation investigation. RNG k-ε model is used with mixture modeling. Overprediction of turbulent viscosity in the cavity presents a major challenge in cavitation prediction with the current modeling approach. So, the correction in turbulent viscosity is attempted by incorporating density correction in cavity region, in the formulation of turbulent viscosity (DCM). The pressure coefficient over suction surface in cavity region is in good agreement with earlier experimental study. Further, pressure fluctuation over hydrofoil surface is discussed. FFT of drag coefficient reported two dominant frequencies. DCM model also predicted re-entrant jet formation near trailing edge of hydrofoil.

A numerical attempt is made to explore the time variation of two-phase nitrogen flow regimes in a microchannel in the presence of a heat interaction between the ambient and the cryogen across the tube wall due to the existence of a huge temperature gradient. The FVM-based VOF model coupled with Lee’s phase change model is employed to get the numerical results. To study the generated flow regimes and the associated flow characteristics, three different mass flow rates are considered, and for each, three different heat fluxes across the wall are chosen. The bubbly flow regime is observed just at the start of the boiling, and gradually it is converted to slug flow with a short transitional period of confined bubble flow. The transition from bubbly flow to slug flow is delayed at higher mass flow rates.

In this article, we perform a semi-analytical investigation of two-dimensional transient analysis of combined electroosmotic and electro-magneto-hydrodynamic flow of a Newtonian electrolytic fluid through a circular micropipe. The fluid is exposed to pulsatile electric fields in the azimuthal direction, and an axial electric field consisting of both steady and pulsatile component. Additionally, a constant magnetic field in the radial direction has also been applied. By considering the collective influence of all the participating forces, we present a comprehensive mathematical model to capture the flow dynamics under the assumption of Debye–Huckel approximation of thin electric double layer (EDL) for low surface zeta potential. In this study, we particularly underscore the consequence of the applied magnetic field and the transient axial electric field strength on the flow behavior. Interestingly, we observe that for some combination of the participating forces at one time, enhancing the strengths of (electric and magnetic) fields augments the flow, whereas, at another time, increasing the field strengths attenuates the flow. This examination is predicted to advance our knowledge of flow behavior under the influence of these forces, and yield valuable perspectives on flow enhancement and regulation.

Heat pipes have emerged as passive devices that utilize the phase change of a working fluid to efficiently transfer heat between two surfaces. In recent years, they have gained considerable attention for thermal management in electronic devices. This study focuses on numerical investigations of a wickless heat pipe (thermosyphon) having its adiabatic section covered with Paraffin Wax Phase Change Material (PCM). Deionized (DI) water serves as the base fluid for comparison. The heat input to the heat pipe is varied from 10 to 50 W for 3640 s. It is observed that the heat pipe with paraffin wax achieved a maximum reduction of 55.79% in the evaporator wall temperature at 10 W. Additionally, the incorporation of paraffin wax led to a significant reduction, with the wall temperature along the evaporator being up to 10% lower compared to the non-coated heat pipe at 10 W. It is found that incorporating paraffin wax into the heat pipe enhances its ability to manage elevated thermal loads, indicating its effectiveness in electronic thermal management. Thus the utilization of paraffin wax is a valuable strategy for achieving efficient and reliable thermal control in electronic devices.

Slug flow through pipe can lead to pressure surge, erosion, and corrosion in pipe thereby pipe thinning in the long run. Continuous pipe thinning results in cracks in the pipe which have been reported as the cause of several fatal accidents in literature. In this article, analysis is reported first for slug characteristics which include slug frequency, slug velocity, and slug length. This is followed by a literature review on how these slug characteristics influence different kinds of stress, erosion, and corrosion of pipe. At the end a detailed discussion is provided on non-linear analysis to identify slug flow through industrial pipe and hence to avoid associated disasters.

In present numerical study we look at the effect of different forces on dynamics of a rising bubble in a confined channel with no external pressure gradient in incompressible flow regime. This study is conducted for five different cases. With surface tension (S.T.), buoyancy and viscosity dominance effects as primary cases followed by two other cases where combination of buoyancy with S.T. and viscosity with S.T. are considered to be dominating. It is observed that the rise of bubble, when it flows close to wall in a channel, is greatly affected by strength of competing inertial and surface tension forces along with shear exerted by walls. The simulations are performed using an in-house Navier-Stokes solver coupled explicitly with Level Set advection and a Re-initialization procedure. The flow solver uses first order upwind convective scheme with implicit Euler time stepping in SIMPLE algorithm for pressure velocity coupling. Converged velocities thus obtained are passed to Level Set advector which uses WENO-5 with RK-4 time stepping in explicit fashion. The advected level set function is then passed to Re-initialization subroutine which uses WENO-5 and TVD RK-3 scheme for discretization of Re-initialization equation recursively till steady state is reached. In our method, surface tension has been added as a body force on Collocated grid point directly.

This study focuses on the impact of droplets on a horizontal solid substrate using distilled water droplets. Due to initial kinetic energy, the droplet rapidly spreads outward upon impact until the viscous dissipation, along with the surface tension force, slows down the spreading. After a period, the droplet continues to spread at a slower rate while the film thinning rate becomes stagnant, resulting in a residual thickness. The primary objective of this work is to measure the residual lamella thickness formed on the surface after droplet impact. A measurement technique using a Chromatic Confocal Sensor is used here for the thickness measurement. This sensor allows to measure droplet thickness with high precision. Experiments are performed within a Reynolds number range of 6900 to 10300. Results from the experimental data are compared with an existing theoretical model, and the model is found to overpredict the residual thickness by up to 10.3%.

In this study, a numerical simulation was conducted to analyze the hydrodynamics of flow using a dual Rushton impeller, operating at a rotation speed of 550 rpm and a constant flow rate of 0.3 vvm [volume of gas per volume of liquid per minute]. An Eulerian–Eulerian multiphase and turbulence k-ϵ model with a dispersed phase has been applied in ANSYS Fluent 2020R1. Using the population balance model, the hydrodynamic parameter has been focused on bin size air distribution. Multiple frame rotation model will be used for rotation of the impeller, which is good for mixing. Flow behavior has been validated with numerical simulation. The flow behavior near the impeller and the gas hold-up fraction distribution is observed. It is seen that the air-bin size affects the gas hold-up distribution, which enhances the biomass growth in the bioreactor.

This study investigates the spatiotemporal behaviour of laminar plumes in a porous medium, focusing on Darcy regime with $$Pe\gg \!\mathcal {O}(1)$$ P e ≫ O ( 1 ) . The objective is to identify the plume morphology and analyze the dilution of injected fluid mimicking contaminant concentration. Laboratory experiments were conducted using dyed saltwater to visualize the flow. This was achieved through the dye attenuation technique, which involved establishing a relationship between dye concentration and light intensity through calibration experiments. With the help of this relationship and image processing in MATLAB, we found the interface between the injected fluid and the surrounding medium in our plume experiments. The parameters of interest, namely the length and volume, were then used to derive semi-empirical correlations, which exhibited power-law behaviour and showed a good agreement with the experimental values. These findings can contribute to understanding geological plumes, such as those resulting from $$CO_2$$ C O 2 injection in deep saline aquifers for carbon sequestration and the spread of contaminated fluid through real geological formations, particularly in cases of groundwater contamination.

This work presents a comparative numerical study of the initial bounce of power-law droplets during superhydrophobic surface interaction. The numerical modeling of the specified droplet impact employs the finite volume method (FVM) in conjunction with the volume of fluid model (VOF) employing dynamic contact angle boundary conditions for the surface. The non-Newtonian behavior of droplets is modeled using the power law. Varying Weber number ( $$2 \le We\le 5$$ 2 ≤ W e ≤ 5 ) and viscosity indices ( $$0.6 \le n \le 1.4$$ 0.6 ≤ n ≤ 1.4 ) of the impinging droplet are investigated to understand the rheological variations influencing rebound dynamics. Power-law fluid droplets at identical Weber numbers show unique spread, retraction and rebound characteristics due to enhanced shear dependent viscosity variations. Contact times extend particularly for droplets with $$n>1$$ n > 1 , reflected in morphological changes that emphasize amplified internal flow dynamics. Droplet kinematics, investigated through vertical and parallel velocities, reveal significant viscosity index induced alterations in spreading and retraction while maintaining a consistent vertical velocity trend across cases for the same We number conditions.

Understanding droplets aerodynamics and collision efficiency in fluid flow is crucial in various applications, including environmental science, industrial processes, and respiratory health studies. This research aims to numerically characterize interception-based deposition of finely divided liquid droplets—like in a fog—on a cylindrical fiber in a cross-flow. The solver is specifically designed to simulate the behavior of liquid droplets within the Lagrangian Particle Tracking (LPT) framework, and it has been implemented in OpenFOAM. The paper presents a rigorous validation study of the modified solver dedicated to investigating droplet behavior within fluid flow. A thorough validation has been conducted using established experimental data to assess the solver's accuracy and reliability. Additionally, the study explores the influence of Stokes number on particle flow, providing valuable insights into droplet collision with surfaces. The findings highlight the significance of the solver in predicting droplet–surface interactions and its potential applications in diverse fields. The validated solver holds promising potential for computing the performance of fog harvesting meshes and filters that are routinely deployed in environmental studies, industrial processes, and respiratory health research.

This research presents an exploration of a demountable gasketed vapour chamber. The utilization of a gasketed vapour chamber assembly technique offers considerable flexibility in the assembly and disassembly processes, ensuring that the thermal performance of the vapour chamber remains uncompromised. Moreover, modifications to the wick structure, such as altering the wick type or adjusting surface wettability, can be easily implemented on the same sample of the vapour chamber. This advantage greatly enhances the prospects for lab-scale research. Prior to conducting the performance testing trials, the vapour chamber underwent vacuuming and filling processes. An absolute vacuum of 30 mm of Hg was established inside the chamber, and the vacuum level was continuously monitored. Comparing performance of different configurations, the thermal resistance of the aluminium grooved wick vapour chamber with a 150% filling ratio of acetone was found to be the lowest at 1.416 °C/W, while the aluminium solid plate of the same size, exhibited a thermal resistance of approximately 2.45 °C/W at 20 W, making it roughly 74% higher than the vapour chamber. Increasing the heat load resulted in improved cooling performance. Moreover, the aluminium grooved wick vapour chamber with a 150% filling ratio demonstrated superior temperature uniformity compared to the solid plate.

A severe accident in a fast reactor can lead to melting of core. Though extremely rare, phenomenology related to severe accidents are of interest to allow placement of appropriate mitigation measures. The main vessel of a pool type reactor can be breached in case molten corium comes in contact. In order to avoid this, an in-vessel core catcher is placed to collect the molten corium, dissipate heat produced and avoid re-criticality. Core catchers can have multiple plates including sacrificial ones that can melt partially. As part of the present work, the melting of a typical sacrificial plate in a core catcher is studied. A two-dimensional numerical model with capability of capturing phase change (melting/solidification) has been developed. Especially, the effect of buoyancy driven flow within the molten material on the melt front is captured. Effect of parameters like angle of inclination and non-uniformity in heat flux is estimated and reported.

This research work aims to explore the potential of latent heat thermal energy storage (LHTES) using a prototype of four-pass vertical heat exchangers. The LHTES system incorporates the energy storage mode as paraffin wax savE® OM-42 (make: PLUSSTM) and for the heat transfer liquid water is used. Both numerical simulations using ANSYS Fluent and for the analysis of the influence of heat exchanger design on the charging characteristics of the phase change material (PCM), experimental studies were performed. The 3D models of the four-pass heat exchangers were created, and simulations were performed in the transient state to investigate the impact of orientation, number of passes, and relative position of the tube, i.e., heat transfer fluid (HTF) tubes. Varying the HTF inlet temperatures allowed for studying its effect on the melting characteristics. Key parameters under consideration included the melting time of PCM during the charging cycle, the average liquid fraction of PCM, middling value temperature for the PCM domain, inlet and outlet temperatures of the HTF, and visual observations of melting and solidification patterns during charging. The computational results emphasized the significant roles of HTF inlet temperature, the relative position of the HTF tubes, and the orientation of heat exchanger (HEX), affecting the time of complete PCM melting and the energy storage rate.

This study focuses on the dynamics of droplet impact and spreading on a superhydrophobic wedge surface. Understanding these processes is crucial for various natural and technological applications. The numerical investigation considers factors such as Weber number, wedge inclination, and surface wettability. The droplet's impact results in spreading on the superhydrophobic surface, minimizing surface energy. Kistler’s dynamic contact angle model is employed to characterize the superhydrophobic nature of the wedge surface. The simulation is conducted in a 2D planar domain, showing symmetric volume distribution for the droplet fractions impacting the symmetric wedge face. Higher Weber numbers lead to increased average droplet velocity and a faster rate of fall for the centroid. Likewise, greater wedge inclination promotes faster droplet movement on the steeper face compared to the less inclined one. This study provides valuable insights into droplet impact dynamics, contributing to the understanding and control of processing parameters in day-to-day technological applications such as spray cooling, anti-icing, and printing.

The present work employs pore-scale simulations by constructing true porous shape in order to reduce the uncertainties associated with porous transport models. For a fixed value of porosity, the rib height is varied, while the flow rate is maintained at the lower Reynolds number range (Re = 1 and 10). For various rib heights and flow rates, pressure drop and heat transfer coefficient are determined. It has been showed that as height rises (blockage fraction increases), the resistance to flow created by the porous ribs increases continuously, leading to a greater pressure decrease across the channel. In addition, as the rib height increases, the magnitude of the effective heat transfer coefficient (shown by Nusselt number) increases. Since the Thermal Performance Factor (TPF) can reach to 20.2 and 10.5, respectively, at Re = 1 and 10, the channel with ribs is observed to be improving the overall thermo-hydraulic performance as compared to the empty channel. As a result, inserting the porous rib into the channel may have the intended outcomes of enhancing thermo-hydraulic performance, reducing the maximum temperature of the heated zone and promoting temperature uniformity.

The current study investigates the behavior of a constricted drop engrossed in dissimilar dielectric medium, with a precise effort on the effects of the electromagnetic (E-M) field that are applied externally. The research examines a system involving a suspended drop that exhibits higher electrical conductivity compared to the contiguous liquid pool. By employing the small shape evolution approximation in the immiscible, leaky dielectric, and Newtonian fluid framework under the creeping flow condition, we analyze how E-M field affects drop shape evolution. This shape evolution depends on factors such as the magnitude and relative orientation of the E-M field, as well as thermophysical properties and the degree of confinement. The E-M field induces hydrodynamic forces due to field coupling, which alters drop shape evolution compared to scenarios involving solely an electric field. Furthermore, in the manifestation of a magnetic field, the shape reversal phenomenon is observed which is not achievable with only electric field. The flow contours behavior in inside the drop and contiguous pool are also modified by the magnetic field. Our findings suggest that combining E-M fields could provide an alternate approach for controlling, adjusting, and enrapturing drops in numerous microfluidic expedients, thereby enhancing mixing processes.

The droplet impact kinetics on super-hydrophobic surfaces are a crucial, multifaceted interfacial phenomenon. Many science-based technological and industrial applications are based on this interfacial phenomenon. Some examples are coating, printing, the food industry, bio or tissue engineering, and printed circuits, etc. After impact on solid surfaces, a droplet may spread, splash, bounce, or deposit. It depends upon the fluid properties, flow conditions, and characteristics of the solid substrate. The process of tuning surface properties, preparation of non-Newtonian fluids of different desirable properties and their characterization, and visualization-based experiments to capture the length scales involved, is extremely time-consuming and challenging. Therefore, numerical simulations serve as a good technique to investigate such a phenomenon. In this research work, an open-source framework OpenFOAM is used to perform the numerical simulations of non-Newtonian fluid droplets on super-hydrophobic surfaces. Xanthan polymer at different concentrations with DI water, exhibiting non-Newtonian fluid behavior, is used.

During tertiary phase of oil production, the interactions between reservoir rock and fluids (i.e., oil and brine) are intentionally modified to favor oil flow through porous rocks and recover more oil from reservoirs. Wettability of rock surface plays an important role in deciding oil recovery from oilfields. This work presents an experimental investigation of wettability alteration of natural sandstone and carbonate rock surfaces by silica nanoparticles in high salinity conditions. Commercial silica nanoparticles (SNP) were first chemically modified for its stability in high salinity conditions and subsequently were employed for wettability alteration studies. Wettability was evaluated by measuring contact angles between natural and model surfaces and oil in brine environment. The results showed that neutral-wet surfaces were turned water-wet and substantial change in contact angles of oil with rock surfaces were observed.

For prolonged working of microstructured devices such as integrated circuits and micro-electro-mechanical devices (MEMS), effective cooling solutions are mandatory. This utilizes two phase cooling strategies employed in micro-heat pipes, capillary pump loops, thermosiphons, etc. The evaporating thin film meniscus is observed in the domain of the aforementioned. It harbors potential for high evaporative mass flux and heat flux. The fluid flow and heat flow characteristics of the thin film meniscus can be evaluated by determining its thickness profile. The existing work explicitly measures the thickness profile of octane in the micro region. This work chiefly explores the effect of introducing surface acoustic wave (SAW) for different cases (Wea = 92.87, 120.01) on the working liquid meniscus. The generation of small droplets near the thin film meniscus is noticed pertaining to the piezoelectric transducer below the substrate. The observation suggests transformation of the acoustic energy from the transducer into kinetic energy in the fluid causing strong capillary waves at the interfacial region near adsorbed region that results in generation/ejection of droplets. The followed-up discussion deduces the replenishment of flow towards the transition region from the intrinsic meniscus based on the curvature profile. The calculated pressure gradient responsible for driving the liquid flow proclaims an increase in the liquid flow with increasing SAW.

The market share of electric vehicles has been growing at a faster pace in passenger vehicle segment to reduce automotive pollution. There are many variants of electric vehicle but of late battery powered electric vehicle gained attraction. The battery, the major source energy storage, is available in different types. Lithium-Ion batteries got wide acceptance due to imminent better properties relatively. However, its performance is sensitive to temperature variations due to high discharge rate and high ambient temperatures. To maintain batteries without thermal runaway, battery thermal management has become essential and forms an integral part of electric vehicle. Of late external and passive cooling with Phase Change Materials has gained attraction by researchers. The present work deals with the computational simulations, using ANSYS R21, carried out on a prismatic battery cell with varying cell thicknesses under high discharge rates with and without PCM. It is noted that PCM could bring down the temperature with increase in thickness of PCM satisfactorily. In addition, to PCM thickness, the battery cell thickness and cell’s overall volume, plays a vital role. Among the variations tried out, the lowest peak temperature is seen to be 316 K with 4 mm thick PCM under 5C discharge rate, for a thin cell or higher volume.

This work aims to study the phase change heat transfer of a Latent Heat Energy Storage System (LHESS) which consists of a sealed cylindrical capsule filled with a phase change material (PCM) placed at the focus of a concentrating solar collector. A numerical model was created using enthalpy porosity formulation and was validated by comparing the results to a similar study. This model was then applied to the current problem to study the phase change transfer of paraffin wax in a parabolic trough. A constant heat flux boundary condition was applied to different sections of the circumference of the absorber tube which varied along the circumference to account for the different values of flux at different parts of the tube. Values of the melt fraction and temperature were recorded at regular intervals of time to analyze the melting process of the PCM during the charging process of the LHESS.

Entrainment develops during the adiabatic synergy of components such as air and water, and it can also emerge during boiling and condensation. The interface is the physical border that allows specific entities to be exchanged between gas and liquid phases which is commonly known as interfacial phenomenon (Rana et al. in Langmuir 31:9870–9881, 2015; Rana et al. in Chem Eng Sci 161:316–328, 2017; Rana et al. in Chem Eng Sci 168:41–54, 2017; Rana et al. in Phys Fluids 28, 2016; Sharma et al. in In Proc. Indian Natl. Sci. Acad. 82:1293–1301, 2016; Sahoo et al. in Phys Fluids 34, 2022; Rana et al. in Multiph Sci Technol 28:173–191, 2016; Dhabekar et al. in European Journal of Mechanics-B/Fluids 100:52–66, 2023; Sahoo et al. in Langmuir 38:14,891–14,908, 2022). The layer of stability between phases that allows for the progressive transmission of enclosed entities established as the outcome of a particular emphasis on the predominant influence is the location, where it primarily emerges. The present investigation deals with cusp-induced air entrainment because of forward and reverse horizontal crossflow employed in air medium only. Here, we allocated a solid roller placed in between the interface of the gas–liquid fluid pair and 50% of the roller is submerged in liquid. For this investigation, we have chosen an open-source Gerris software that follows the VOF (volume of fluid) method for reorientation of the interface. This investigation demonstrates the alteration in the interfacial dynamics and steady wrapping film thickness due to these forward and backward horizontal crossflows. A non-dimensional number, Reynolds number $$\left({Re}_{flow}\right)$$ Re flow , has been used to express horizontal crossflow of gaseous medium. In the present investigation, we displayed velocity vector diagram for both forward and backward horizontal crossflows to analyze the flow patterns near the roller. Finally, we proposed a scaling analysis to identify discrepancy in steady liquid film thickness number $$\left({T}_{h}^{*}\right)$$ T h ∗ and steady air entrained thickness number $$\left({T}_{H}^{*}\right)$$ T H ∗ with characteristics angular position $$\left({\theta }^{*}\right)$$ θ ∗ .

This research investigates the percolation characteristics of fine spherical particles through static packed beds composed of larger particles. For our experiments, glass beads with a diameter of 0.5 mm are used as the smaller particles, and the diameter of the larger particles is adjusted to achieve a desired size ratio (R) ranging from 8 to 16. Experimental studies are conducted in a rectangular tank, which is filled with larger particles to form the packed bed and the fine particles are introduced from the top of the tank. During experiments, we capture high resolution images using a DSLR camera which are later processed in MATLAB for extracting data and analysis. By varying these listed parameters systematically, this study aims to identify the conditions under which percolation occurs. The primary objective of this research is to establish a relationship between the flow rate, bead size ratio, and their impact on percolation through the packed beds. This investigation holds significant importance for understanding granular material behavior and has implications for fluidization, filtration.

An automobile radiator is an important component of an automotive cooling system that have an intricate design and is crucial in transporting heat from the engine’s internal components to the outside air. This study presents a performance analysis of an automotive radiator using Al2O3 and CuO nanoparticles as coolants, conducted solely through simulation using the Ansys software. We have calculated and compared the heat transfer coefficients of mixture of Al2O3, CuO and water with nanofluid. Nanofluid preparation is done using 0.15 and 0.3% concentration Al2O3 and 0.15 and 0.3% concentration CuO, remaining using water and glycol having equal proportion. The objective of this study is to evaluate the impact of these nanoparticles on the thermal characteristics and heat transfer properties of the radiator. It was observed that nanofluid having CuO nanoparticles shows higher heat transfer coefficient than the others. A three- dimensional computational model of the automotive radiator was developed in SolidWorks and analyzed in Ansys Fluent.

This work attempts to investigate the melting behavioral pattern and heat transfer performance of phase change materials (PCM) in an oriented rectangular geometry filled with paraffin wax (P-52). The geometry mimics a solar thermal energy storage unit, which can store thermal energy during the daytime. The top wall of the unit is heated with a constant heat flux (600 w/m2) and all other walls are insulated. The total area of the heated surface is kept constant so that the volume of the PCM remains the same for the different cases. The evolved transport equations are solved numerically using the finite volume-based solver and for validation of the numerical model, the melting behavior is compared with the in-house experimental results for the 0º inclination position of the geometry and the comparison displays an outstanding matching among the two outcomes. Then the validated numerical model is utilized to extensively investigate the impact of various inclination angles of the geometry (ϕ = 0º, 30º, and 60º). The outcomes show that the melting performance of the PCM is conduction-dominated initially and contributes to the major portion of the heat transfer. With the progress in time, the buoyancy effect overcomes the viscous force and natural convection takes control of the heat transfer. Results also demonstrate that the initial liquid fraction for a ϕ = 60º inclination is greater than ϕ = 0º or 30º inclination. Furthermore, the case with ϕ = 0º takes less time to melt, and 60º inclination takes the longest time. It implies that, as the inclination rises from 0º to 60º, total melting time increases.

Startup and steady-state experiments are performed on a cylindrical evaporator miniature loop heat pipe (MLHP) at different heat loads from 5 to 148 W. The startup studies are conducted for various parameters of heat load and sink temperature. Thermal oscillations are observed for the input power range of 40 to 60 W at 10 °C sink temperature. The condenser outlet temperature shows large oscillations of about 2.5 °C amplitude and 80 s time period for 40 W heat load. From the steady-state studies, it is found that the MLHP removed a heat of 148 W power input while maintaining the evaporator temperature of 52 °C at 10 °C sink temperature. The device is found to be capable of startup at a low heat load of 4.8 W for the sink temperature of 10 °C. The trends observed in the experiments are similar to those reported in the literature.

The velocity of steam introduced into a turbine is a critical factor in power generation. Varying steam velocities can impact kinetic energy, thereby affecting turbine efficiency and performance. Higher velocities can enhance efficiency but may lead to erosion and inefficiencies, while lower velocities might reduce power output. This study explores the influence of different steam velocities on power generation in turbines. The investigation focuses on the effects of various steam flow rates on turbine operation, efficiency, and overall power output. By conducting a comprehensive analysis and experimentation, this research aims to determine the optimal steam velocity for maximizing power output in turbines, highlighting the difference between wet and dry steam’s impact on power generation.

The rapid pace of industrialization and urbanization has brought about significant environmental challenges, especially in densely populated areas where air pollution poses serious health risks. This paper conducts a comprehensive investigation into the influence of electrostatic enhancement on air filter performance, focusing on the removal of fine particles. The research addresses the critical need for effective air filtration systems due to the adverse impact of air pollutants on human health and indoor air quality. Through an extensive review of relevant literature, we present a series of parametric studies carried out by various researchers, emphasizing developments in electrostatically enhanced filtration methods, hydro-charged filters, and electric field-assisted cyclones. These studies delve into the challenges of maintaining high filtration efficiency while optimizing operational parameters. In light of this context, our study aims to explore the advantages of electrostatically enhanced air filters for fine particle removal through rigorous Computational Fluid Dynamics (CFD) simulations. Our investigation delves into the influence of electrostatic enhancement on filtration efficiency, the relationship between electrostatic field strength and filtration improvement, the impact of applied voltage and discharge wire position, and the effects of varying inlet velocity. The findings establish a direct connection between electrostatic enhancement and improved filtration efficiency, providing insights into optimal operational parameters. This study underscores the significance of fine- tuning electrostatic parameters to attain superior air filtration results, contributing to cleaner indoor air and enhanced environmental sustainability.

Dip coating is a widely used technique in the industry for coating various products. This study presents findings from experiments and numerical simulations of the dip-coating process using a two-fluid layer system. This system holds practical significance for continuous dip-coating applications, such as galvanizing [10], or producing optical fibers with multiple layers of coating [5]. In this two-liquid system, the liquid in the upper layer (oil) is lighter and dense compared to the bottom liquid layer (water). A wire is drawn into the water layer from the oil layer at a constant velocity, and experimentally film thicknesses are measured from captured videos using image processing techniques. Numerical simulations are set up in the laminar regime with interface tracking done by the level set method in COMSOL Multiphysics. Experiment results are found to be in good agreement with the final film thickness from simulation results. Following five parameters, namely the velocity of the wire, the radius of the wire, the density difference and ratio of kinematic viscosity of liquids, and the height of the top liquid layer are explored for their impact in determining the coated oil film thickness and various regimes of film coating have been identified.

Numerical simulations have been performed for a vertical jet impinging on a flat and conical surface for elucidating the effect of initial momentum flux on the jump radius. The Reynolds number, Re, based on jet inlet radius in the simulations was varied in the range from $$10^2$$ 10 2 to $$2\times 10^3$$ 2 × 10 3 . By varying the jet-nozzle radius from 4.6 to 1.6 mm (for a fixed flow rate), the impact of initial momentum flux was investigated. Simulation results indicate a strong correlation between initial momentum flux and the jump radius, apart from other governing parameters. However, surface tension was observed to have a negligible impact, consistent with the findings of Wang et al. [12]. The simulation data set was well-matched using a modified scaling approach based on energy dissipation arguments as presented in Vishwanath et al. [11].

In this paper, we experimentally investigated the dynamics of droplet impacts on liquid films to explore the influence of different fluid properties. We have altered the fluid of the film in which water drops impacted, using various liquids, such as water, silicon oil, glycerol, and ethanol. The aim was to observe how different fluid properties, including surface tension, viscosity, and miscibility, affected the drop impact behavior. We discovered distinct mechanisms for each combination of droplet and film liquid, highlighting the importance of fluid properties in drop impact phenomena. We have observed two types of interesting fluid dynamics: crown formation and central jet formation, depending on the miscibility of the fluids involved. We have observed that miscibility plays a major role in understanding and predicting the behavior of dynamics.

Boiling is a complex phenomenon, as it is affected by many variables. Here, we investigate how changing equilibrium contact angle $$\phi $$ ϕ , surface tension $$\sigma $$ σ and heat flux q influences bubble departure radius $$r_{d}$$ r d and bubble departure time $$t_{d}$$ t d . In this work, we have studied the nucleation and growth of a single bubble in a pool of saturated liquid in contact with a flat plate acting as a heat source. We have used a Volume of Fluid (VOF) method to numerically model the two-phase fluid system. A wedge-shaped domain has been used to take advantage of symmetry to reduce the size of the domain. Adaptive meshing has been applied to this domain in order to obtain highly accurate results with minimum computational cost. The results indicate that as equilibrium contact angle increases, so do the bubble departure radius and bubble departure time. Likewise, it is found that an increase in surface tension leads to an increase in both bubble departure radius and bubble departure time. As heat flux increases, bubble departure radius does not change significantly, while the bubble departure time decreases. The results presented here can be used to optimize variables to allow for maximum enhancement of heat transfer.

Determination of residence time distribution is essential to ascertain the performance of fluid flow through systems. In the current work, flow through serpentine microchannels was simulated using a steady-state two-dimensional model. A parametric study was also performed by varying the amplitude of the walls of the microchannel. Further tracer studies were done to determine the residence time distribution in the channel. The 2D model was developed using free and open-source software, OpenFOAM version 2012.

Boiling is a very efficient mode of heat transfer that is crucial to many technical processes and applications. Heat transfer during boiling relies on the bubble departure. Accordingly, various studies have been performed to investigate bubble departure to model and predict the heat transfer during boiling. Various models and empirical correlations have been developed; however, they are valid only over a limited range of parameters, beyond which they are unable to predict heat transfer. Despite numerous efforts, boiling is still not well understood. This is primarily due to the involvement of various physical parameters and hidden mechanisms that govern the boiling process. One such hidden mechanism is coalescence-induced bubble departure, which usually remains hidden due to the prevailing buoyancy in terrestrial gravity conditions. Microgravity condition offers an ideal condition to study such hidden mechanism in detail due to the absence of buoyancy. In this work, we demonstrate coalescence-induced bubble departure from the heated substrate in shear flow in microgravity condition. Dynamics of two-bubble and three-bubble coalescence is investigated. Dynamics of coalescence is similar in both the cases before departure/lift-off from the substrate; however, in spite of similar bubble departure diameter there is a significant difference between the departure velocity and jumping height. This is primarily due to the difference in the conversion of excess surface energy into the kinetic energy required for departure. This suggests that by increasing the number of bubbles, the coalescence-induced departure can be made more effective. The physical insights presented in this work are of significant importance to the design of multiphase energy systems for terrestrial and space applications.

Two-phase flow can show different flow patterns in a microchannel based on the flow rates of phases. Some of the major flow patterns are bubbly/fine droplets, slug or Taylor, and annular flow. Different flow patterns are desirable in different kinds of processes, such as mixing, heating, cooling, and reactions. Annular flow regime typically occurs when the flow rate of dispersed phase is significantly high. In annular flow, a gas or liquid core is surrounded by a thin liquid film. The change in film thickness affects heat and mass transfer rates, mixing, and overall reaction rate. The introduction of a U-bend is often done to achieve a longer flow path and high residence time in microchannels. In this work, we study the effect of U-bend on film thickness analytically and derive a two-dimensional analytical solution for smooth interface two-phase annular flow at a circular bend in microchannels. Flow is assumed to be steady and fully developed. The momentum conservation equation is solved in cylindrical coordinates for three regions of annular flow: inner liquid, core gas or liquid, and outer liquid. Using the six boundary conditions, no-slip at the inner and outer walls, velocity continuity, and two shear stress continuity at the two interfaces, expressions are derived to obtain velocity profile in the three regions.

Nucleate pool boiling is a super-effective way to cool down machines with a lot of heat. Changing from liquid to vapor and using the hidden heat in the liquid leads to better heat transfer through the medium. Many sources say that mixing of NaCl with water is good for enhancement of heat transfer. In our experiment, we used a 3 weight % aqueous solution of NaCl for pool boiling studies at atmospheric conditions. We have investigated the bubble dynamics in terms of their size, shape, and the time duration they took to grow in liquid maintained at 5 K subcooling temperature. We varied the heat flux of heater from 54 to 120 kW-m−2. The results showed that when we mix NaCl with water in the pool, bubbles size increases approximately by 55% and it took more time to grow as compared to its growth in a pure water pool.

In this paper, we develop a mathematical model for viscoelastic fluid flowing through a constant wall temperature slit type parallel plate microchannel. The flow is driven by mixed electroosmotic and pressure forces, respectively, and the rheological behavior of viscoelastic fluid is described by the simplified Phan–Thien–Tanner (sPTT). Analytical solutions for the potential distribution, flow velocity, and volumetric flow rate based on the full-scale solution for Poisson–Boltzmann equation. A comprehensive parametric analysis is conducted to examine the impact of flow parameter such as electrokinetic parameter, viz., surface potential $$\left(\overline{\zeta }\right)$$ ζ ¯ , EDL thickness $$\left(\overline{k }\right),$$ k ¯ , and viscoelastic parameter $$\left(\varepsilon {Wi}_{k}^{2}\right)$$ ε Wi k 2 on hydrodynamic behavior of sPTT flow. Significant augmentation in flow rate is observed for the high zeta potential, thin EDL thickness $$\left(\overline{k }=10\right)$$ k ¯ = 10 , and the shear thinning characteristic of $$\varepsilon {Wi}_{k}^{2}$$ ε Wi k 2 under favorable pressure gradient. We anticipate that this research will offer a thorough theoretical understanding of the electrokinetic transport mechanism, which will be essential for designing microfluidic systems and devices.

High-heat hydrophobic surfaces are designed to repel oil droplets, improving heat transfer, and reducing energy consumption. These surfaces have gained significant attention in industrial applications. The paper attempts to understand the evaporating dynamics of oil sessile droplets on hydrophobic (water-repelling) surfaces in the boiling regime. We examine the variation of contact angle, contact line, and droplet lifetime during evaporation. The size of the oil droplets used in the study is $$2.5\,\upmu $$ 2.5 μ l, and the temperature of the hydrophobic surface is set at $$250\,^{\circ }$$ 250 ∘ C. The study results show that the droplets’ evaporation time is positively correlated with the initial volume of the droplets and the hydrophobicity of the surface. The study also found that high heat energy causes a volume bulge, leading to droplet spreading due to the transient heating of the sessile droplet. However, as the equilibrium evaporation process continues, the droplet’s shrinking and spreading are opposed by the viscous force. The stable evaporation stage indicates the loss of capillary force over the dominance of the viscous force with stable evaporation flux.

Multiphase flow in porous media is crucial for many energy and environmental processes, including hydrocarbon recovery, CO2 sequestration, groundwater contamination, etc. Prediction of flow properties such as permeability and tortuosity is challenging as internal structures, including pore geometry and connectivity, directly affect fluid flow. The natural porous media may consist of fractures and cracks, etc. Dual-porosity models often explain transport and flow in heterogeneous media, envisioning high- and low-permeability zones with limited pore connections. In our present study, we have studied single-phase and two-phase flows in a dual-porosity model to investigate the effect of heterogeneity on flow properties and immiscible displacement. The pressure drop was identical when the low- and high-permeable regions were parallel to the flow direction. However, when the fluid flows from a high-permeable zone to a low-permeable zone, it gives a higher pressure drop as compared to when fluid flows from the low-permeable zone to the high-permeable zone. The effect of dual porosity on immiscible displacement was also investigated, and a breakthrough change was observed for different dual-porosity models.

Some of the crucial issues in cryogenics industries are handling, transporting, and storing cryogens. Chill-down is the first stage in the cryogen transportation process, and it involves multiphase flow. Before single-phase liquid can flow through the connecting transfer line, it must first be chilled down to cryogenic temperatures. The present study attempts to explore the transient three-phase flow characteristics during chill-down in a long circular pipeline carrying LN2 flow where the pipeline is initially filled by air. LN2 flows of various Reynolds number (Re) values are considered at the inlet of the pipe. The FVM-based VOF model coupled with the Lee model of phase change is employed for the present transient numerical simulation. k-ω model is employed for turbulence modeling. The study focuses on exploring flow characteristics in terms of the spatial distribution at different time instants for the air volume fraction (VF), gaseous N2 VF, pressure, velocity magnitudes, etc. Time variations of area-weighted average (AWA) air VF, gaseous N2 VF, pressure, velocity magnitude, and temperature at different cross-sectional planes are also extracted to depict the results.

In this study, the performance of Plain Walled Microchannel (PWMC) and Oblique Finned Microchannel (OFMC) is studied under the influence of varying magnetic fields (Ha = 0, 10, 20, 30) with constant coolant flow and heat flux. 2% Alumina-water nanofluid is utilized as a coolant. While the thermal performance of both the PWMC and OFMC increases, the hydrothermal performance of PWMC reduces by up to 49% over a base case, while in the case of OFMC maximum 10% increase is observed. This is due to a significantly greater pressure drop observed in the case of PWMC. The velocity profile is seen to be flattened with the increase in applied magnetic fields. This results in the acceleration of flow toward the walls of the microchannel with a corresponding reduction in the core velocity.

The Onset of Nucleate Boiling (ONB) marks the start of boiling heat transfer in a system designed for boiling heat transfer. ONB is dependent on the way the heat is generated within the heater. In applications such as nuclear reactors, during reactivity-initiated accidents, the heat generation is exponential, and hence an excursion in the heater temperature is observed. Similarly, in applications such as immersion cooling of microelectronics, the heat generated within the chip is a function of the load it is subjected to. In such cases, the point of ONB can shift and lead to an increase in the chip temperature. To avoid such an event and effectively design the chip cooling system, the knowledge of the change in the superheat at ONB with the heating rate is essential. In this work, ONB conditions are predicted by a model based on transient conduction and Hsu’s nucleation criterion. Numerical solutions are obtained for exponentially increasing heat flux. Different heating rates and bulk temperatures are explored. It is found that ONB heat flux and wall superheat increase with an increase in heating rate, whereas the total heat added till ONB decreases with an increase in heating rate. Subcooling increases the ONB wall superheat, ONB heat flux, and total heat added till ONB.

Lee Model is widely used to model mass transfer in two-phase flow. The phase change model involves a time relaxation coefficient, which has a significant impact on numerical simulation. Two benchmark problems related to two-phase flow have been numerically simulated using the volume of fluid (VOF) approach with a customized solver in OpenFOAM 9. The influence of the time relaxation coefficient for 1-D Stefan and 2-D film boiling problems is studied, and the same is discussed here. The results indicate that for different fluids, the time relaxation parameter yields accurate results within certain ranges; however, outside these ranges, the precision of the numerical simulation diminishes significantly. While analyzing various fluids, it was found that good numerical simulations are achieved with a time relaxation coefficient ranging between $$10^3$$ 10 3 and $$10^7$$ 10 7 . For this range of $$r_e$$ r e , the error is less than $$1.5\%$$ 1.5 % for the Stefan problem and within $$15\%$$ 15 % with correlations for 2-D film boiling. The time relaxation coefficient is influenced by the phase initiating the transition, which shows variations in bubble growth during the simulation of 2-D film boiling with different values of $$r_e$$ r e . This variation is also mirrored in the periodicity of the average Nusselt number.

Carotid artery stenosis (CAS) can have a variety of shapes at the stenosis region. Generally, the severity of CAS is judged by the blockage percentage regardless of stenosis shape. However, certain studies on coronary artery stenosis suggest that the shape of stenosis significantly affects the various hemodynamic parameters due to altered flow structures arising as the shape of stenosis changes. Hence, a comparative study is carried out comparing two different stenosis shapes namely eccentric and axisymmetric stenosis for CAS in internal carotid artery. We observe significant variations of flow structures as the shape of stenosis changes. These variations in flow structures lead to higher time-averaged wall shear stress (TAWSS) for eccentric stenosis compared to axisymmetric stenosis. Hence, eccentric stenosis is much more susceptible to plaque rupture than axisymmetric stenosis with the same blockage.

In the present work, copper and nickel bi-porous capillary wicks were fabricated by cold press sintering process using silicon oil as a binder and sodium chloride as a pore former. The fabricated wick sample has a diameter of 30 mm and a thickness of 10 mm. The experimental investigation of sintered wicks was performed for the evaluation of permeability, surface wettability, capillary rise rate, surface morphology, and porosity. The permeability of nickel and copper wicks were calculated experimentally using falling head method and was found to be 1.346 × 10–10 m2/s and 9.67 × 10–11 m2/s, respectively. The surface wettability of the wick surface was evaluated using dynamic contact angle measurements using high-speed camera. The dynamic contact angle measurements showed that the nickel wick had a better wettability compared to copper wick using methanol as working fluid. The capillary rise rate measurements showed that the nickel wick had a better capillary performance as compared to the copper wick. The surface morphology analysis using SEM shows the presence of small pores and pore connectivity of the sintered wick surface. The porosity measurement was performed using Archimedes’ method and found to be 65% and 50% for nickel and copper wicks, respectively.

In this paper, immiscible fluid flow in a square microchannel was studied numerically and experimentally, with an emphasis on the slug flow regimes. Accurate calculation of the slug length and slug length distribution plays a crucial role in designing separation facilities quantitatively. The presented work examines how various variables, namely, inlet velocity, channel dimensions, and contact angle, affect slug formation. To accurately track the interface between the water and toluene, the volume of fluid model (VOF) was used to simulate the flow. The inlet velocity of water was varied from 0.02 to 1.28 m/s, while the inlet velocity of toluene was kept constant at 0.08 m/s. From the numerical study, it was observed that the length of the slugs decreases up to 5 times as the water inlet velocity increases. The results are experimentally validated. The effect of wall shear stress and microchannel wettability was observed in slug formation.

This research paper explores the intricate challenges presented by hypersonic flow over a ramp surface. Its primary focus is on the significance of Shock Wave Boundary Layer Interaction (SWBLI) and the utilization of unsteady transient analysis of flow over a ramp under Mach 6 conditions. To comprehend the unsteadiness of the separation and SWBLI, the study employs transient fluid flow simulations. Further, the investigation is centered around regions where SWBLI significantly impacts the pressure and aerodynamic loads on the ramp surface, leading to the formation of a separation bubble. The results are subsequently compared with the existing literature. The outcome of this research provides deeper insights into the unsteady separation and SWBLI aerodynamics of scramjet ramps.

We investigate the temperature aspects of evaporating salt droplets by studying the nucleation and deposition dynamics through an infrared (IR) camera. Two different salt types were used for this purpose: NaCl and MgSO4, both with 1 M initial concentration. Crystallization is an exothermic process, and we found such evidence in both cases, where the crystals were 0.50–1.50 °C hotter than the solution itself. However, in the case of NaCl, a relatively colder region was observed surrounding the growing crystals, which is fascinating in its own aspect. With the other salt type, no such surrounding colder region was observed, but here, the deposition was extremely fast compared to the NaCl case. We believe that these findings would improve the understanding of connected phase change systems as well as the available models.

This study investigates scouring beneath a submarine pipeline, specifically analyzing how varying particle Reynolds numbers affect sediment transport using the two-phase flow model, SedFOAM. It explores the impact of particle grain size and fluid bulk velocity under subaqueous conditions. The research provides valuable insights into the complexities of sediment transport and emphasizes the need for enhanced modeling to ensure accurate risk assessment of underwater structures.

Soot generation in a turbulent diffusion flame generated during methane gas combustion is numerically explored. Moss-Brooke’s soot methodology is used for this purpose. The temperature field, mass fraction of soot, rate of soot surface growth, and soot formation were investigated in detail. This method takes into account several sub-processes, containing coagulation, nucleation, oxidation, and surface growth. The radiative transfer equation is approximated by employing the P1 method which involves the truncating series expansion in terms of spherical harmonics. The equilibrium-based method is applied to investigate the role of OH on soot oxidation and concentration on soot production using the Fenimore-Jones and Lee soot oxidation models. The obtained results indicate a higher estimation of soot generation from the Lee oxidation model as compared to the Fenimore-Jones model. Furthermore, neglecting the radiation from the wall results in significant temperature overestimations, which could potentially affect the distribution of species.

This study presents the investigation of pressure drop with mass flow rate in PDMS microchannels with varying elasticity. Four microchannels with constant diameter of 0.289 mm were fabricated with different ratios of PDMS to curing agent (i.e. 5:1, 10:1, 15:1 and 20:1) and deployed for this study. Pressure drop has been measured in each channel for the range of mass flow rates varying from 1 to 20 ml/min (Re = 80–1440) using peristaltic pump in order to introduce the pulsating flow. Experimental results reveal distinctly contrasting trends in both sets of channels, with the soft-walled channels notably exhibiting a decrease in pressure drop with increase in softness. This can be attributed to deformations in the walls, which when observed using an inverted microscope, reveal significant expansions in soft walled channels, illustrating increasing effects under different flow rates. Our results reveal the clear differences caused by different flexibilities of PDMS samples on pressure drop for Newtonian Fluids under pulsating flow condition.