Cooling performance investigation of electronics cooling system using Al2O3–H2O nanofluid

In this study, the cooling performance of Al₂O₃–H₂O nanofluid was experimentally investigated as a much better developed alternative for the conventional coolant. For this purpose the nanofluid was passed through the custom-made copper minichannel heat sink which is normally attached with the electronic heat source. The thermal performance of the Al₂O₃–H₂O nanofluid was evaluated at different volume fraction of the nanoparticle as well as at different volume flow rate of the nanofluid. The volume fraction of the nanoparticle varied from 0.05 vol.% to 0.2 vol.% whereas the volume flow rate was increased from 0.50 L/min to 1.25 L/min. The experimental results showed that the nanofluid successfully has minimized the heat sink temperature compared to the conventional coolant. It was noticed also that the thermal entropy generation rate was reduced via using nanofluid instead of the normal water. Among the other functions of the nanofluid are to increase the frictional entropy generation rate and to drop the pressure which are insignificant compared to the normal coolant. Given the improved performance of the nanofluid, especially for high heat transportation capacity and low thermal entropy generation rate, it could be used as a better alternative coolant for the electronic cooling system instead of conventional pure water.     

Experimental Assessment of the Thermo-Hydraulic Performance of Automobile Radiator with Metallic and Nonmetallic Nanofluids

Abstract

The overall heat transfer of a cross flow heat exchanger can be enhanced by using the nanofluids as coolant, which finds application in reducing the size and weight of automobile radiator. However, improving the heat transfer using nanofluids can be accompanied by simultaneous variations in the required pumping power. This study experimentally evaluates the thermo-hydraulic performance of three nanofluids—metallic (copper, aluminum) and nonmetallic (multiwalled carbon nanotube (MWCNT))—as coolant for an automobile radiator by utilizing an in-house test rig. An enhancement in overall heat transfer coefficient can be observed with nanocoolants (nanofluid as coolant), compared to the de-ionized water at the same Reynolds number. The maximum enhancement in the overall heat transfer coefficient was observed to be 40, 29, and 25% for MWCNT, copper, and aluminum nanofluids, respectively. The thermal performance of coolants was also compared with the same pumping power criterion. The overall heat transfer coefficient of nanofluids were higher than basefluid at low pumping power range and the trend changes with increase in the pumping power. The present study shows that the heat transfer characteristics at the same Reynolds number as well as at the same pumping power needs to be considered for the selection of appropriate nanocoolant for automobile radiator application.     

Performance Analysis of a Louvered Fin Automotive Radiator Using Hybrid Nanofluid as Coolant

This study deals with the theoretical enhancement of thermal performance using water‐based (50/50) volume fraction of Fe₂O₃, CuO, TiO₂, Ag, Cu in Al₂O₃ hybrid nanofluids as coolants for a louvered fin automobile radiator. The effects on thermophysical properties and various performance parameters, i.e., heat transfer, effectiveness, and pumping power of hybrid nanofluids have been compared with water. Among all studied hybrid nanofluids, Al₂O₃‐Ag/water hybrid nanofluid has higher effectiveness, heat transfer rate, pumping power, and pressure drop of 0.8%, 3%, 6%, and 5.6%, respectively, as compared to water and is followed by (50/50) volume fraction of Cu, CuO, Fe₂O₃, TiO₂ hybrid nanofluids as radiator coolant. For the same radiator size and heat transfer rate, coolant flow rate and pumping work decreases by 3%, 4%, respectively, for Al₂O₃‐Ag/water hybrid nanofluid and for the same coolant flow rate and heat transfer rate the radiator size decreases by 3% and pumping power increases by 3.4% for Al₂O₃‐Ag/water hybrid nanofluid as compared to water. Reduction in radiator size may lead to a reduction in radiator cost, engine fuel consumption, and environmental benefit.     

Entropy generation in transpiration cooling of concentric spherical shells

The present paper deals with transpiration cooling of two concentric spherical shells. The analysis includes the calculation for the radial distribution of temperature and volumetric entropy generation, and the total rate of entropy generation in the thermal system. Standard air is considered as the cooling fluid. Results showed that the entropy generation increases with increasing temperature difference between the sphere surfaces. Variation of either mass flow rate or radius ratio affects volumetric entropy distribution and the total rate of entropy generation of the processes. The increase of mass flow rate or radius ratio increases the total rate of entropy generation. The performance of the system is analyzed by calculating irreversibility to heat transfer ratio at both inner and outer sphere surfaces. It was found that irreversibility to heat transfer ratio at the inner sphere surface increases with increasing mass flow rate, or decreasing radius ratio. The opposite is true for the outer sphere surface.     

Experimental investigation of convective heat transfer coefficient of Al2O3/water nanofluid at lower concentrations in a car radiator

For many years, water and ethylene glycol were used as conventional coolants in automotive car radiators, but these coolants offer lower thermal conductivity than is required. This study is focused on the application of water‐based Al₂O₃ nanofluid at lower concentrations in a car radiator. The Al₂O₃ nanoparticles with an average diameter of 50 nm are dispersed in demineralized water at four different volume concentrations (0.1 vol. % to 0.4 vol. %) without any dispersant or stabilizer. Flow rate is varied in the range of 2 l/min to 5 l/min and inlet coolant temperature to the radiator is set to 50 °C, 60 °C, and 70 °C. The results show that the heat transfer coefficient increases with an increase in particle concentration, flow rate, and inlet temperature of coolant and the maximum increase in heat transfer coefficient is 45.87 % compared to pure water. However, the Nusselt number increases with the increase in particle concentration, Reynolds number, and inlet temperature of the coolant. In addition with the experimental study, a regression analysis is performed by using the ANOVA method and generates a correlation for the convective heat transfer coefficient.     

Experimental and analytical investigation on an automobile radiator with CuO/EG‐water based nanofluid as coolant

In the present study, experimental and analytical thermal performance of automobile radiator using nanofluids is investigated and compared with performance obtained with conventional coolants. Effect of operating parameters and nanoparticle concentration on heat transfer rate are studied for water as well as CuO/EG‐water based nanofluid analytically. The results are presented in the form of graphs showing variations of net heat transfer rate for various coolant flow rate, air velocity, and source temperature for various CuO/EG‐water based nanofluids. Experimental results indicate that with the increase in coolant flow rate and air velocity, heat transfer rate increases, reaches maximum and then decreases. Experimental investigation of a radiator is carried out using CuO/EG‐water based nanofluids. Results obtained by experimental work and analytical MATLAB code are almost the same. Maximum absolute error in water and air side is within 12% for all flow condition and coolant fluids. Nusselt number of nanofluid is calculated using equation number 33[9]. The results obtained from experimental work using 0.2% volume CuO/EG‐water based nanofluids are compared with the results obtained from MATLAB code. The results show that the maximum error in the outlet temperature of the coolant and air is 12% in each case. Thus MATLAB code can be used for different concentration of nanofluids to study the effect of operating parameters on heat transfer rate. Thus MATLAB code developed is valid for given heat exchanger applications. From the results obtained by already validated MATLAB code, it is concluded that increase in coolant flow rate, air velocity, and source temperature increases the heat transfer rate. Addition of nanoparticles in the base fluid increases the heat transfer rate for all kind of base fluids. Among all the nanofluid analyzed in this study, water‐based nanofluid gives highest value of heat transfer rate and is recommended for the heat exchanger applications under normal operating conditions. Maximum enhancement is observed for ethylene glycol‐water (4:6) mixture for 1% volume concentration of CuO is almost equal to 20%. As heat transfer rate increases with the use of nanofluids, the heat transfer area of the radiator can be minimized.     

Experimental study of heat transfer enhancement using water/ethylene glycol based nanofluids as a new coolant for car radiators

Traditionally forced convection heat transfer in a car radiator is performed to cool circulating fluid which consisted of water or a mixture of water and anti-freezing materials like ethylene glycol (EG). In this paper, the heat transfer performance of pure water and pure EG has been compared with their binary mixtures. Furthermore, different amounts of Al₂O₃ nanoparticle have been added into these base fluids and its effects on the heat transfer performance of the car radiator have been determined experimentally. Liquid flow rate has been changed in the range of 2–6 l per minute and the fluid inlet temperature has been changed for all the experiments. The results demonstrate that nanofluids clearly enhance heat transfer compared to their own base fluid. In the best conditions, the heat transfer enhancement of about 40% compared to the base fluids has been recorded.     

Effect of nanoparticle shape on the heat transfer and thermodynamic performance of a shell and tube heat exchanger

Nanofluid is a heat transfer fluid that can improve the performance of heat exchanger systems. Different parameters such as particle size, shape, and volume concentration affect the performance of these systems. The objective of this paper is to study the effect of different nanoparticle shapes (such as cylindrical, bricks, blades, platelets, and spherical) on the performance of a shell and tube heat exchanger operating with nanofluid analytically. Boehmite alumina (γ-AlOOH) nanoparticles of different shapes were dispersed in a mixture of water/ethylene glycol as the nanofluid. The thermodynamic performance of the shell and tube heat exchanger that is used in a waste heat recovery system was analysed in terms of heat transfer rate and entropy generation. Established correlations were used to measure the thermal conductivity, heat transfer coefficient and rate and entropy generation of nanofluid. The results show an increase in both the heat transfer and thermodynamic performance of the system. However, among the five nanoparticle shapes, cylindrical shape exhibited better heat transfer characteristics and heat transfer rate. On the other hand, entropy generation for nanofluids containing cylindrical shaped nanoparticles was higher in comparison with the other nanoparticle shapes. However, the increased percentage of entropy was below 1%. Therefore, this greater entropy generation could be deemed negligible and cylindrical shaped nanoparticles are recommended to be utilized in heat exchanger systems working with nanofluids.     

Novel and optimal integration of SOFC-ICGT hybrid cycle: Energy analysis and entropy generation minimization

Integrating fuel cells with conventional gas turbine based power plant yields higher efficiency, especially solid oxide fuel cell (SOFC) with gas turbine (GT). SOFCs are energy efficient devices, performance of which are not limited to Carnot efficiency and considered as most promising candidate for thermal integration with Brayton cycle. In this paper, a novel and optimal thermal integration of SOFC with intercooled-recuperated gas turbine has been presented. A thermodynamic model of a proposed hybrid cycle has been detailed along with a novelty of adoption of blade cooled gas turbine model. On the basis of 1st and 2nd law of thermodynamics, parametric analysis has been carried out, in which impact of turbine inlet temperature and compression ratio has been observed on various output parameters such as hybrid efficiency, hybrid plant specific work, mass of blade coolant requirement and entropy generation rate. For optimizing the system performance, entropy minimization has been carried out, for which a constraint based algorithm has been developed. The result shows that entropy generation of a proposed hybrid cycle first increases and then decreases, as the turbine inlet temperature of the cycle increases. Furthermore, a unique performance map has also been plotted for proposed hybrid cycle, which can be utilized by power plant designer. An optimal efficiency of 74.13% can be achieved at TIT of 1800 K and r_p,c 20.     

Analysis of entropy generation using nanofluid flow through the circular microchannel and minichannel heat sink

In this paper, different types of entropy generations in the circular shaped microchannel and minichannel are discussed analytically using different types of nanoparticles and base fluids. In this analysis, Copper (Cu), alumina (Al₂O₃) as the nanoparticle and H₂O, ethylene glycol (EG) as the base fluids were used. The volume fractions of the nanoparticles were varied from 2% to 6%. In this paper, the irreversibility or entropy generation analysis as the function of entropy generation ratio, thermal entropy generation rate and fluid friction entropy generation rate for these types of nanofluids in turbulent flow condition have been analyzed using available correlations. Cu–H₂O nanofluid showed the highest decreasing entropy generation rate ratio (36%) compared to these nanofluids flow through the microchannel at 6 vol.%. The higher thermal conductivity of H₂O causes to generate much lower thermal entropy generation rate compared to the EG base fluid. The fluid friction entropy generation rate decreases fruitfully by the increasing of volume fraction of the nanoparticles. Cu–H₂O and Cu–EG nanofluid gave the maximum decreasing rates of the fluid friction entropy generation rate are 38% and 35% respectively at 6% volume fraction of the nanoparticles. Smaller diameter showed less entropy generation in case of all nanofluids.     

Performance prediction of plate-fin radiator for low temperature preheating system of proton exchange membrane fuel cells using CFD simulation

The objective of this paper is to analyze the heat transfer characteristics of plate-fin radiator for the cold air heating system of a PEMFC engine and to find the optimal parameter combination in order to reduce the power consumption. The effect of the coolant mass flow and temperature on the heat exchange performance of the radiator was investigated based on 3D porous medium model. The results, including the amount of heat transferred and temperature change and heat exchanger effectivity with the increasing of the air flow rate at different coolant flow rate were obtained using CFD method. Good agreement is found by comparing the simulation values with the test data and the deviation is less than 7% which indicate simulation model validation and research method feasibility used in this study. The simulation results indicate that bigger coolant flow rate and temperature result in higher outlet air temperature and the amount of heat transferred. The variation of the heat exchanger effectivity is predicted for different working conditions. Based on the Taguchi method, the influence of structural parameters of the corrugated fins on the heat transfer and pressure drop of the radiator is analyzed qualitatively. It is shown that fin length has the greatest impact on the comprehensive heat transfer performance of the radiator. This research provides a guide for optimizing the air preheating system and improving the amount of heat transferred.     

Entropy generation of vapor condensation in the presence of a non-condensable gas in a shell and tube condenser

This article investigates the entropy production of condensation of a vapor in the presence of a non-condensable gas in a counter-current baffled shell and one-pass tube condenser. The non-dimensional entropy number is derived with respect to heat exchange between the bulk fluid and condensate, as well as heat exchange between the condensate and coolant. Numerical results show that heat transfer from the condensate to the coolant has a dominant role in generating entropy. For example, at an air mass flow rate of 330 kg/h, 93.4% of the total entropy generation is due to this source. The resultant profiles during the condensation process indicate that a higher air mass flow rate leads to a lower rate of entropy production. For example, as the air mass flow rate increases from 330 kg/h to 660 kg/h and 990 kg/h, the total entropy generation decreases from 976 J/s K to 904 and 857.2 J/s K, respectively. By introducing a new parameter called the condensation effectiveness, a correlation is also developed for predictions of the entropy number, and an illustrative example is presented.     

Entropy generation of viscous dissipative nanofluid flow in microchannels

An analytical study on the viscous dissipation effect on entropy generation in laminar fully developed forced convection of water–alumina nanofluid in circular microchannels is reported. In the first-law analysis, closed form solutions of the temperature distributions in the radial direction for the models with and without viscous dissipation term in the energy equation are obtained. The results show that the heat transfer coefficient decreases with nanoparticle volume fraction largely in the laminar regime of nanofluid flow in microchannel when the viscous dissipation effect is taken into account. In the second-law analysis, the two models are compared by analyzing their relative deviations in entropy generation for different Reynolds number and nanoparticle volume fraction. When the viscous dissipation is taken into account, the temperature distribution is prominently affected and consequently the entropy generation ascribable to the heat transfer irreversibility is significantly increased. The increase of entropy generation induced by the increase of nanoparticle volume fraction is attributed to the increase of both the thermal conductivity and viscosity of nanofluid which causes augmentation in the heat transfer and fluid friction irreversibilities, respectively. By incorporating the viscous dissipation effect, both thermal performance and exergetic effectiveness for forced convection of nanofluid in microchannels dwindle with nanoparticle volume fraction, contrary to the widespread conjecture that nanofluids possess advantage over pure fluid associated with higher overall effectiveness from the aspects of first-law and second-law of thermodynamics.     

Experimental study on thermal performance of optimum PG brine as a radiator coolant

The present study deals with the experimental impact of an alternative heat transfer fluids for overall performance improvement for radiators. Water and water mixed with anti‐freezing agents such as ethylene glycol (EG) and propylene glycol (PG) are the traditional coolants for an automotive radiator. Comparison of experimental and numerical analysis of optimum brine solution, that is 25% of propylene glycol and water as coolant for the rectangular fin radiator, has been well discussed. A closed loop test rig was designed, and fabricated with a wind tunnel section to achieve uniform velocity at the test section of the rectangular radiator and was tested for performance. Experimental runs were conducted at varying operating temperatures which included the runs for water, and an optimum propylene glycol brine solutions at 70 °C and 80 °C with various flow rates. Results show the energy performance of an optimum brine solution was nearly similar to that of water at high temperatures. The Nusselt number, heat transfer coefficient, and heat transfer rate for an optimum propylene glycol brine is nearly the same as water at 80 °C with a maximum deviation of 15%, 5.7%, and 6.6%, respectively, for theoretical and experimental result comparisons. Air side and coolant side pressure drops had a maximum deviation of 3.66% and 6.6%, respectively. Air and coolant exit temperatures had a deviation of 5% and 3.5%, respectively, with an air frontal velocity of 4.6 m/s in a rectangular fin radiator for an optimum brine solution used as coolant for the automotive radiator. The optimum propylene glycol brine may be environmentally beneficial.     

Entropy generation analysis of nanofluids flow in various shapes of cross section ducts

The selection of flow passage's cross section shape is important in thermal system design such as compact heat exchanger. A variety of duct's shapes can be used to enhance the thermal performance. However, it must be noted that different thermal and friction characteristics can be initiated due to this approach. Therefore this paper investigates the entropy generation characteristics of three types of duct's cross section subjected to constant heat flux. The considered shapes are circular, square and triangle (equilateral). Al₂O₃ and MWCNT based nanofluids are used as working fluids in the analysis. The study found that the total entropy generation of Al₂O₃ based nanofluids decreases with the increase of particle volume fractions. However, this parameter increases when working fluid's mass flow rate and heat flux applied to the duct increase. On the aspect of cross section's shape, circular duct exhibits lowest total entropy generation compared to other considered shapes. Moreover, it was also found that MWCNT based water nanofluids exhibit lower total entropy generation compared to Al₂O₃ based nanofluids due to its high thermal conductivity value.     

Entropy generation during the quasi-steady burning of spherical fuel particles

Entropy generation during the quasi-steady combustion of spherical liquid fuel particles has been presented in detail. The effects of freestream velocity, particle diameter, ambient temperature and gravity, on the entropy generation rate, have been discussed in detail. In the range of sub-critical freestream velocity, where an envelope flame is present, the entropy generation rate presents a minimum value. At a critical velocity, where the flame transition occurs, the entropy generation rate reaches a maximum value. Flame transition significantly affects the entropy generation rate, which suffers a sharp decrease in its value after the transition. Heat transfer and chemical reaction contribute almost equally to the total entropy generation rate. When normal gravity is considered in an upward flow configuration, there is an increase in the entropy generation rate as compared to the zero gravity case. The effect of gravity poses a complex variation pattern in the entropy generation rate, for a downward flow configuration. The entropy generation rate decreases with increasing ambient temperature. The entropy generation rate increases with the particle diameter. A correlation has been presented for the non-dimensional entropy generation number as a function of Froude number.     

Entropy generation due to flow and heat transfer in nanofluids

Present study provides a theoretical investigation of the entropy generation analysis due to flow and heat transfer in nanofluids. For this purpose, the most common alumina–water nanofluids are considered as the model fluid. Since entropy is sensitive to diameter, three different diameters of tube in their different regimes have been taken. Those are microchannel (0.1 mm), minichannel (1 mm) and conventional channel (10 mm). To consider the effect of conductivity and viscosity, two different models have been used to represent theoretical and experimental values. It has been found that the reduced equation with the help of order of magnitude analysis predicts microchannel and conventional channel entropy generation behaviour of nanofluids very well. The alumina–water with high viscosity nanofluids are better coolant for use in minichannels and conventional channels with laminar flow and microchannels and minichannel with turbulent flow. It is not advisable to use alumina–water nanofluids with high viscosity in microchannels with laminar flow or minichannels and conventional channels with turbulent flow. Also there is need to develop low viscosity alumina–water nanofluids for use in microchannel with laminar flow. It is observed that at lower tube diameter, flow friction irreversibility is more significant and at higher tube diameter thermal irreversibility is more. Finally, for both laminar and turbulent flow, there is an optimum diameter at which the entropy generation rate is the minimum for a given nanofluid.     

Experimental investigations on overall cooling effect of ribbed channel with air bleeds

An experimental investigation on overall heat transfer performance of a rectangular channel, in which one wall has periodically placed oblique ribs to enhance heat exchange and cylindrical film holes to bleed cooling air, has been carried out in a hot wind tunnel at different mainstream temperatures, hot mainstream Reynolds numbers, coolant Reynolds numbers and blowing ratios. To describe the cooling effect of combined external coolant film with the internal heat convection enhanced by the ribs, the overall cooling effectiveness at the surface exposed in the mainstream with high temperature was calculated by the surface temperatures measured with an infrared thermal imaging system. The total mass flow rate of cooling air through the coolant channel was regulated by a digital mass flow rate controller, and the blowing ratio passing through the total film holes was calculated based on the measurements of another digital-type mass flow meter. The detailed distributions of overall cooling effectiveness show distinctive peaks in heat transfer levels near the film holes, remarkable inner convective heat transfer effect over entire channel surface, and visible conductive heat transfer effect through the channel wall; but only when the coolant Reynolds number is large enough, the oblique rib effect can be detected from the overall cooling effectiveness; and the oblique bleeding hole effect shows the more obvious trend with increasing blowing ratios. Based on the experimental data, the overall cooling effectiveness is correlated as the functions of Re_m (Reynolds number of hot mainstream) and Re_c (Reynolds number of internal coolant flow at entrance) for the parametric conditions examined.     

Effect of nanoparticle shapes on irreversibility analysis of nanofluid in a microchannel with individual effects of radiative heat flux,velocity slip and convective heating

In this study, the flow of a nanoliquid in a microchannel is examined. Two distinct metallic nanoparticles, titanium and silver, are used in this study. The slip regime and convective boundary are considered to compute the momentum and energy balance equation. The mathematical expressions are made dimensionless by using nondimensional quantities. A numerical approach called Runge‐Kutta‐Fehlberg scheme is employed to obtain the solution. Effects of the internal heat source and radiative flux on fluid model are examined. The upshots of the pertinent flow parameter and the physical features are visualized through graphical elucidations. The effect of flow constraints on the second law analysis for the described physical phenomenon is predicted. Conclusion indicates that lowering of temperature of the nanofluid is obtained by higher values of nanoparticle volume fraction. The causes of irreversibility in a thermal system is explored in this investigation. The results indicate that nonspherical nanoparticles has higher thermal conductivity ratio as compared with spherical nanoparticles. Minimization of entropy can be attained through increasing volume fraction of titanium and silver nanoparticles. Besides, it is emphasized that entropy generation is high in case of disc‐shaped nanoparticles, followed by needle and sphere shapes.     

Entropy generation analysis in a uniformly heated microchannel heat sink

Present investigation analyzes the issue of entropy generation in a uniformly heated microchannel heat sink (MCHS). Analytical approach used to solve forced convection problem across MCHS, is a porous medium model based on extended Darcy equation for fluid flow and two-equation model for heat transfer. Simultaneously, closed form velocity solution in a rectangular channel is employed to capture z-directional viscous effect diffusion and its pronounced effect on entropy generation through fluid flow. Subsequently, governing equations are cast into dimensionless form and solved analytically. Second law analysis of problem is then conducted on the basis of obtained velocity and temperature fields and expressions for local and average entropy generation rate are derived in dimensionless form. Average entropy generation rate is then utilized as a criterion for assessing the system performance. Finally, the effect of influential parameters such as, channel aspect ratio (α_S), group parameter (Br/Ω), thermal conductivity ratio (C) and porosity (ε) on thermal and total entropy generation is investigated. In order to examine the accuracy of the analysis, the results of thermal evaluation are compared to one of the previous investigations conducted for thermal optimization of MCHS.