Performance analysis of a minichannel-based solar collector using different nanofluids
Introduction
Among the solar energy technologies, flat-plate solar collectors are the most popular devices that can be used for heating of residential and public buildings. One of the aims which is considered by designers is the increase of outlet temperature of the solar collectors [1]. Using of nanofluids may be a solution to increase of outlet temperature in solar collectors. Nanofluids are mixtures of common fluids such as water and ultra-fine solid particles with the size of 1–100 nm. The application of nanofluids is developing day by day, especially in renewable energy systems. Here, a literature review is presented by focusing on the application of nanofluids in solar collectors. As one of the first studies on using of nanofluids in solar collectors, Yousefi et al. [2] conducted tests on a flat plate solar collector using Al2O3/water nanofluids with and without surfactant and in different weight fractions of nanoparticles, i.e. 0.2% and 0.4%. Their findings reveal that the weight fraction of 0.2% is the optimal weight fraction from the highest thermal efficiency viewpoint. They also found adding surfactant to the nanofluid will increase the efficiency considerably (by 15%). In the following of this work [2], Yousefi et al. [3] found that use of multi walled carbon nanotube/water nanofluids with the weight fraction of 0.4% leads to a higher efficiency compared to the concentration of 0.2%. In another work, Yousefi et al. [4] concluded that the pH of nanofluids can be an important factor in the increase of collector efficiency so that when the pH is close to the isoelectric point the efficiency is maximized. Tyagi et al. [5] investigated theoretically the potential of alumina/water nanofluids to improve the performance of non-concentrating direct absorption solar collectors. Their results show that the thermal efficiency of nanofluid-based direct absorption solar collector is about 10% higher than common flat plate collectors.
Khullar et al. [6] examined the efficiency of a nanofluid-based concentrating parabolic solar collector using aluminum nanoparticles and Therminol VP-1 as the base fluid. Their results show that the nanofluid based solar collector has higher efficiency (by 10%) compared to conventional collectors. In a numerical study, Nasrin et al. [7] solved the natural convection of Al2O3/water nanofluids in the space between the glass cover and sine-wave absorber of a flat plate collector. They concluded that the heat transfer can be enhanced by an increase in the number of waves on the absorber. The results of experiments conducted by Jamal-Abad et al. [8] show that using Cu/water nanofluids with weight fraction of 0.05 wt% instead of pure water leads to a higher efficiency as much as 24%. Faizal et al. [9] evaluated the potential of four different water based nanofluids, including CuO/water, SiO2/water, TiO2/water and Al2O3/water to reduce the size of solar collectors, and therefore economic and environmental benefits. They concluded that CuO/water nanofluids are the best option to reduce the size of solar collectors. In another work, Faizal et al. [10] studied the potential of Al2O3/water nanofluids to reduce the size of solar collectors using the data available in the literature. Nasrin and Alim [11] simulated the natural convection of two nanoparticles, including Ag and CuO suspended in water for application in solar collectors.
To solve the problem of sedimentation of nanofluids in the solar collectors, Colangelo et al. [12] designed a new flat plate collector. They stated that the heat transfer coefficient increases by 25% using Al2O3/water nanofluid and the new design. Rahman et al. [13] simulated the natural convection in a triangular shaped collector using three different nanofluids, including Cu/water, Al2O3/water, and TiO2/water. The study shows that the heat transfer rate is enhanced by 24% by using Cu/water nanofluid with volume concentration of 10% in comparison with water. Parvin et al. [14] analyzed the natural convection and entropy generation due to Cu/water and Ag/water nanofluids in a direct absorption solar collector. They found that with an increase in the volume fraction of nanoparticles and the Reynolds number the entropy generation increases. They offered correlations for Nusselt number and collector efficiency where the Reynolds number is less than 1000, and volume fraction of nanoparticles is less than 3%. Alim et al. [15] investigated the entropy generation due to the flow of four different nanofluids i.e. Al2O3/water, CuO/water, SiO2/water, TiO2/water with volume fractions up to 4% in a solar collector. Their results disclose that by using CuO/water nanofluid instead of water, the heat transfer coefficient rises up to 22.15% while the entropy generation is reduced by 4.34%. In this work, the pressure drop contribution to entropy generation is neglected. The readers also can refer to two review papers on the application of nanofluids in solar energy and solar collectors [16], [17]. Also, a review is conducted by Mahian et al. [18] on the entropy generation in thermal systems. The channels can be classified based on the size into three groups including conventional channels, minichannels, and microchannels. The channels with hydraulic diameter between 0.2 mm and 3 mm are called minichannels [19].
The main aim of the present work is to investigate the effects of using four different nanofluids including Cu/water, Al2O3/water, TiO2/water, and SiO2/water on the performance of a minichannel flat plate solar collector. The first and second laws of thermodynamics are considered to assess the collector where the mass flow rate is constant and diameter of risers is 2 mm. The contribution of pressure drop is taken into account in the entropy generation analysis. The results of this work elucidate that which type of nanofluids can be used to have the best performance and output in a minichannel based solar collector.
Section snippets
Problem description
A minichannel based solar collector is considered in this study. The specifications of the collector are given in Table 1. It is assumed that the risers are parallel and the centerlines of absorber plate and risers are located in the same line (see Fig. 1). The analysis is performed based on real meteorological data. Table 2 illustrates the values of solar irradiance, ambient temperature, and wind velocity for 1:00 PM in a typical day in Bangkok, Thailand. The mass flow rate is constant for all
First law analysis
When the solar radiation with the intensity of Gt falls on the glass cover of solar collector, a main part of the radiation, i.e. S = ηoGt, strikes to the absorber plate. A part of solar radiation is absorbed by the working fluid (Qu) and the remained part is dissipated through the edges, bottom, and top of the absorber plate to the surrounding. To calculate the outlet temperature and efficiency of the solar collector, first the heat losses to surrounding should be computed. The relation between
Pressure drop
To calculate the pressure drop, first the major and minor head losses should be calculated. Major head loss is produced due to the flow of fluid in pipes while the minor head loss is created due to fittings, entering and exiting of fluid, and so on. The major head loss in a solar collector having n parallel risers is obtained by [28]:
The total head loss (hL) is the sum of major head loss and minor head loss and its value is equal to:
Second law analysis
In this work, the total entropy generation, (W/K), has been obtained through the calculation of lost work. Lost work is the summation of leakage () and destroyed () exergy rates. The following relation states the relationship between the lost work and entropy generation rate [29]:
The destroyed exergy rate for a solar collector is determined as [30], [31], [32], [33]:where denotes the destroyed exergy rate due to the
Results and discussion
Fig. 2 shows the variations of the Nusselt number with volume fraction for different nanofluids and two mass flow rates of 0.1 and 0.5 kg/s. As seen, the Nusselt number decreases with an increase in volume fraction of particles. This happens because the Nusselt number is a function of Reynolds and Prandtl numbers. When the mass flow rate is constant, viscosity determines the value of the Reynolds number. It is obvious that adding nanoparticles increases the viscosity, therefore, based on the
Conclusion
A theoretical study is performed to assess the performance of a minichannel-based flat plate solar collector using four different nanofluids including Cu/water, Al2O3/water, TiO2/water, and SiO2/water. The study is carried out for mass flow rates of 0.1 and 0.5 kg/s. The results are presented for volume fractions up to 4% and nanoparticle size of 25 nm where the inner diameter of the risers of flat plate collector is assumed to be 2 mm. The findings of the study can be summarized as follows:
- •
Acknowledgements
The third author acknowledges the support provided by King Abdulaziz City for Science and Technology (KACST) through the Science and Technology Unit at King Fahd University of Petroleum and Minerals (KFUPM) through project No. 13-ENE1573-04 as part of the National Science, Technology and Innovation Plan. The fourth author would like to thank the Thailand Research Fund, the National Science and Technology Development Agency and the National Research University Project for the encouragement and
References (35)
- et al.
Parametric sensitivity studies on the performance of a flat plate solar collector in transient behavior
Energy Convers Manage
(2014) - et al.
An experimental investigation on the effect of Al2O3–H2O nanofluid on the efficiency of flat-plate solar collectors
Renew. Energy
(2012) - et al.
An experimental investigation on the effect of MWCNT–H2O nanofluid on the efficiency of flat-plate solar collector
Exp Therm Fluid Sci
(2012) - et al.
An experimental investigation on the effect of pH variation of MWCNT–H2O nanofluid on the efficiency of a flat-plate solar collector
Solar Energy
(2012) - et al.
Energy, economic and environmental analysis of metal oxides nanofluid for flat-plate solar collector
Energy Convers Manage
(2013) - et al.
A new solution for reduced sedimentation flat panel solar thermal collector using nanofluids
Appl Energy
(2013) - et al.
Augmentation of natural convection heat transfer in triangular shape solar collector by utilizing water based nanofluids having a corrugated bottom wall
Int Commun Heat Mass Transfer
(2014) - et al.
Heat transfer and entropy generation through nanofluid filled direct absorption solar collector
Int J Heat Mass Transfer
(2014) - et al.
Analyses of entropy generation and pressure drop for a conventional flat plate solar collector using different types of metal oxide nanofluids
Energy Build
(2013) - et al.
A review of the applications of nanofluids in solar energy
Int J Heat Mass Transfer
(2013)
Investigating performance improvement of solar collectors by using nanofluids
Renew Sustain Energy Rev
A review of entropy generation in nanofluid flow
Int J Heat Mass Transfer
Empirical correlating equations for predicting the effective thermal conductivity and dynamic viscosity of nanofluids
Energy Convers Manage
A critical synthesis of thermophysical characteristics of nanofluids
Int J Heat Mass Transfer
Exergetic optimization of flat plate solar collectors
Renew Energy
General theory of exergy balance analysis and application to solar collectors
Energy
A new solution for reduced sedimentation flat panel solar thermal collector using nanofluids
Appl Energy
Cited by (170)
Effects of anisotropic permeability on EMHD nanofluid flow and heat transfer in porous microchannel with wavy rough walls
2024, Chinese Journal of PhysicsEntry length correlations for alumina-water nanofluid in laminar pipe flow
2024, International Journal of Thermal SciencesPerformance boost of an integrated photovoltaic-thermal and solar thermal collectors using minichannel heat sink: Energy, exergy, and environmental analysis
2024, Case Studies in Thermal Engineering