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.     

Performance investigation of an automotive car radiator operated with nanofluid-based coolants (nanofluid as a coolant in a radiator)

Water and ethylene glycol as conventional coolants have been widely used in an automotive car radiator for many years. These heat transfer fluids offer low thermal conductivity. With the advancement of nanotechnology, the new generation of heat transfer fluids called, “nanofluids” have been developed and researchers found that these fluids offer higher thermal conductivity compared to that of conventional coolants. This study focused on the application of ethylene glycol based copper nanofluids in an automotive cooling system. Relevant input data, nanofluid properties and empirical correlations were obtained from literatures to investigate the heat transfer enhancement of an automotive car radiator operated with nanofluid-based coolants. It was observed that, overall heat transfer coefficient and heat transfer rate in engine cooling system increased with the usage of nanofluids (with ethylene glycol the basefluid) compared to ethylene glycol (i.e. basefluid) alone. It is observed that, about 3.8% of heat transfer enhancement could be achieved with the addition of 2% copper particles in a basefluid at the Reynolds number of 6000 and 5000 for air and coolant respectively. In addition, the reduction of air frontal area was estimated.     

Analytical analysis of heat transfer and pumping power of laminar nanofluid developing flow in microchannels

Thermal management issues are limiting barriers to high density electronics packaging and miniaturization. Liquid cooling using micro and mini channels is an attractive alternative to large and bulky aluminum or copper heat sinks. These channels can be integrated directly into a chip or a heat spreader, and cooling can be further enhanced using nanofluids (liquid solutions with dispersed nanometer-sized particles) due to their enhanced heat transfer effects reported in literature. The goals of this study are to evaluate heat transfer improvement of a nanofluid heat sink with developing laminar flow forced convection, taking into account the pumping power penalty. The phrase heat transfer enhancement ratio (HTR) is used to denote the ratio of average heat transfer coefficient of nanofluid to water at the same pumping power. The proposed model uses semi-empirical correlations to calculate nanofluid thermophysical properties. The predictions of the model are found to be in good agreement with experimental studies. The validated model is used to identify important design variables (Reynolds number, volume fraction and particle size) related to thermal and flow characteristics of the microchannel heat sink with nanofluids. Statistical analysis of the model showed that the volume fraction is the most significant factor impacting the HTR, followed by the particle diameter. The impact of the Reynolds number and other interaction terms is relatively weak. The HTR is maximized at smallest possible particle diameter (since smaller particles improve heat transfer but do not impact pumping power). Then, for a given Reynolds number, an optimal value of volume fraction can be obtained to maximize HTR. The overall aim is to present results that would be useful for understanding and optimal design of microchannel heat sinks with nanofluid flow.     

Heat transfer characteristics of multiwall carbon nanotube suspensions (MWCNT nanofluids) in intertube falling-film flow

Multiwall carbon nanotube suspensions (MWCNT nanofluids) are used in an intertube falling-film flow to explore the nanofluid effects on heat transfer characteristics. Water-based and ethylene–glycol-based nanofluids are prepared at concentrations of 0, 0.05, 0.14 and 0.24 vol%. Thermal conductivity and viscosity of these nanofluids is measured. Falling-film heat transfer behavior of these nanofluids is also investigated and the results are compared to those of the base fluids. Based on the same liquid feeding flow rate, it is observed that the heat transfer coefficients of the water-based nanofluids decreases then increases as the MWCNT concentration increases, and the heat transfer coefficient of the ethylene–glycol-based nanofluids decreases with an increased MWCNT concentration. A model is provided for predicting the heat transfer enhancement of the nanofluids in intertube falling-film flow, and an agreement between predictions and experimental data is obtained for nanofluids with larger MWCNT concentrations. When comparing the heat transfer coefficient based on the same Reynolds number, up to 20% or higher heat transfer enhancement can be observed for ethylene–glycol based nanofluids.     

Performance Enhancement for Wavy Fin Automotive Radiator Using Optimum PG Brine Based Nanofluids

In this study, optimum propylene glycol (PG) brine‐based nanofluids are being proposed as coolants for a wavy finned automotive radiator. Performance analysis is conducted and compared with conventional Ethylene Glycol (EG) brine and related nanofluids. A 25% PG brine has similar heat transfer characteristics to water at higher operating temperature ranges. The effects on radiator size, weight and cost, engine efficiency and fuel consumtion, and embodied energy saving and environmental impact are discussed as well. Compared to conventional coolant(EG water brine), for the same cooling capacity and radiator size, the coolant requirement and pumping power are reduced significantly by about 25% and 64%, respectively, whereas, for the same cooling capacity and mass flow rate, the radiator size and pumping power is reduced by 4.2% and 25.5%, respectively, with PG brine‐based Ag nanofluids.Furthermore, by using optimum PG brine‐based nanofluids, 3.5% of the embodied energy may be saved, which may yield reductions in radiator cost, engine fuel consumption and environmental costs.     

Investigation of heat transfer and pressure drop of a counter flow corrugated plate heat exchanger using MWCNT based nanofluids

The influence of different functional covalent groups on the thermophysical properties of carbon nanotube-base fluid was first investigated experimentally. To shed more light on this issue, cysteine (Cys) and silver (Ag) were covalently attached to the surface of the multi-walled carbon nanotubes (MWCNT). Functionality and morphology were studied by the aid of characterization instruments to confirm surface functionalization, as well. To calculate the thermal properties, different water-based nanofluids such as Gum Arabic-treated multi-walled carbon nanotubes (MWCNT-GA), functionalized MWCNT with cysteine (FMWCNT-Cys) and silver (FMWCNT-Ag) were employed as coolants to investigate the convection heat transfer coefficient, Nusselt number, friction loss, pressure drop and pumping power in a counter flow corrugated plate heat exchanger. Calculations were performed for Reynolds numbers ranging from 2500 to 10,000 (turbulent flow) and nanoparticle weight percentages of 0.0% to 1.0% using a FORTRAN code. Nanofluid properties were also measured through experimentation. It was found that increasing Reynolds number, Peclet number or fraction of nanomaterial would improve the heat transfer characteristics of the nanofluid. However, for a specific material, augmentation of Reynolds number or nanomaterial fraction would cause the required pumping power to rise but this penalty was relatively small. In all the investigated cases, heat transfer rate and power consumption were found to be less for water compared to nanofluids. Besides, heat removal in nanofluids was discovered to be higher than that of water for a specific pumping power. Therefore, performance of the plate heat exchanger can be enhanced by choosing MWCNT/water as the working fluid.     

Influence of nanofluids on parallel flow square microchannel heat exchanger performance

The effects of using various types of nanofluids and Reynolds numbers on heat transfer and fluid flow characteristics in a square shaped microchannel heat exchanger (MCHE) is numerically investigated in this study. The performance of an aluminum MCHE with four different types of nanofluids (aluminum oxide (Al₂O₃), silicon dioxide (SiO₂), silver (Ag), and titanium dioxide (TiO₂)), with three different nanoparticle volume fractions of 2%, 5% and 10% using water as base fluid is comprehensively analyzed. The three-dimensional steady, laminar developing flow and conjugate heat transfer governing equations of a balanced MCHE are solved using the finite volume method. The MCHE performance is evaluated in terms of temperature profile, heat transfer rate, heat transfer coefficient, pressure drop, wall shear stress pumping power, effectiveness, and overall performance index. The results reveal that nanofluids can enhance the thermal properties and performance of the heat exchanger while having a slight increase in pressure drop. It was also found that increasing the Reynolds number causes the pumping power to increase and the effectiveness to decrease.     

A review and analysis on influence of temperature and concentration of nanofluids on thermophysical properties,heat transfer and pumping power

The Prandtl number, Reynolds number and Nusselt number are functions of thermophysical properties of nanofluids and these numbers strongly influence the convective heat transfer coefficient. The pressure loss and the required pumping power for a given amount of heat transfer depend on the Reynolds number of flow. The thermophysical properties vary with temperature and volumetric concentration of nanofluids. Therefore, a comprehensive analysis has been performed to evaluate the effects on the performance of nanofluids due to variations of density, specific heat, thermal conductivity and viscosity, which are functions of nanoparticle volume concentration and temperature. Two metallic oxides, aluminum oxide (Al₂O₃), copper oxide (CuO) and one nonmetallic oxide silicon dioxide (SiO₂), dispersed in an ethylene glycol and water mixture (60:40 by weight) as the base fluid have been studied.     

Application of nanofluids in heating buildings and reducing pollution

This paper presents nanofluid convective heat transfer and viscosity measurements, and evaluates how they perform heating buildings in cold regions. Nanofluids contain suspended metallic nanoparticles, which increases the thermal conductivity of the base fluid by a substantial amount. The heat transfer coefficient of nanofluids increases with volume concentration. To determine how nanofluid heat transfer characteristics enhance as volume concentration is increased; experiments were performed on copper oxide, aluminum oxide and silicon dioxide nanofluids, each in an ethylene glycol and water mixture. Calculations were performed for conventional finned-tube heat exchangers used in buildings in cold regions. The analysis shows that using nanofluids in heat exchangers could reduce volumetric and mass flow rates, and result in an overall pumping power savings. Nanofluids necessitate smaller heating systems, which are capable of delivering the same amount of thermal energy as larger heating systems using base fluids, but are less expensive; this lowers the initial equipment cost excluding nanofluid cost. This will also reduce environmental pollutants because smaller heating units use less power, and the heat transfer unit has less liquid and material waste to discard at the end of its life cycle.     

Analysis of entropy generation and convective heat transfer of Al2O3 nanofluid flow in a tangential micro heat sink

Effect of using Al₂O₃–water nanofluids with different volume fractions and particle diameters on generated entropy, hydrodynamic performance and heat transfer characteristics of a tangential micro-heat sink (TMHS) was numerically investigated in this research. Results indicated that considerable heat transfer enhancement is possible when using Al₂O₃–water nanofluids as coolant and clearly the enhancement improves with increasing particles concentration and decreasing particles size. However, using nanofluid has also induced drastic effects on the pumping power that increases with particles volume fraction and Reynolds number. Finally, it was found that generated total entropy decreases with increasing volume fraction and Reynolds number and decreasing particles size.     

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.     

Enhanced heat transfer and friction factor of MWCNT–Fe3O4/water hybrid nanofluids

In the present experimental work, the convective heat transfer coefficient and friction factor for fully developed turbulent flow of MWCNT–Fe₃O₄/water hybrid nanofluids flowing through a uniformly-heated-at-constant-heat-flux circular tube are estimated. The MWCNT–Fe₃O₄ nanocomposite was prepared by in-situ method, which includes the dispersion of carboxylated carbon nanotubes in distilled water and mixing of ferrous chloride and ferric chloride. Sodium hydroxide was used as reducing agent to form MWCNT–Fe₃O₄ hybrid nanocomposite. The detailed surface and magnetic properties were performed by X-ray diffraction and scanning electron microscopy, and using a vibrating sample magnetometer. The stable hybrid nanofluids were prepared by dispersing nanocomposite in distilled water, and the heat transfer and friction factor experiments were conducted for particle loadings of 0.1% and 0.3%. The results indicate a maximum of 31.10% enhancement in Nusselt number with a penalty of 1.18-times increase of pumping power for the particle loading of 0.3% at a Reynolds number of 22,000 as compared to base fluid data. The empirical correlations were proposed for the estimation of Nusselt number and friction factor to match well with the experimental data.     

Exergy and energy analysis of a wavy fin radiator with variously shaped nanofluids as coolants

The present study deals with the energy and exergy analysis of a wavy fin radiator deploying various shapes of Al₂O ₃‐water as nanocoolant. The effects of radiator effectiveness, pumping power, heat transfer rate, and performance index with variously shaped nanoparticles, mainly spherical, brick, and platelet, on coolant flow rates and air velocities have been investigated. Also, the impacts of entropy, second law efficiency, entropy generation number, and irreversibility on radiator performance analysis have been considered with steady‐state assumptions. Theoretical analysis revealed that the spherical particle–based nanocoolant showed 21.9%, and 18.2% higher effectiveness than platelet and brick nanocoolants. However, minimization in the entropy generation is observed in the platelet shape of the nanoparticle. The second law efficiency is 13% higher for the spherical nanocoolant compared with the brick nanocoolant. An optimum entropy generation number is found at a coolant flow rate of 13 l/min and then gradually decreases with an increase in the coolant flow rate. For all the considered operating parameters, the spherical nanoparticle showed a better performance than brick and platelet nanofluids as a radiator coolant. Due to the enhanced overall performance for the spherical nanofluid, it may be considered as a potential candidate for a radiator coolant.     

Numerical Investigation of Forced Convection Flow of Nanofluids in Rotating U-Shaped Smooth and Ribbed Channels

The impact of the nanoparticles and ribs on the thermal performance of the rotating U-type cooling channel are investigated for turbulent forced convection flow of nanofluids. The nanofluids are provided by the inclusion of the nanoparticles of TiO₂ and Al₂O₃ in water as the base fluid, namely, water/Al₂O₃ and water/TiO₂ nanofluids mixtures. The simulations are performed for three-dimensional turbulent flow and heat transfer using an RNG k-? turbulence model for Reynolds number range of 5000 to 20,000. To show the effectiveness of the ribs and nanofluids, three criteria are employed: heat transfer enhancement, pressure drop or power consumed, and the thermal performance factor. It is found that the contribution of turbulence promotion in heat transfer enhancement of the ribbed channel is more effective than that of enlarging the heat surface area. The results show that using ribs at the lowest Reynolds number and utilizing nanofluids at the highest one provide high heat transfer rate and thermal performance. At the middle Reynolds numbers, the effects of these two methods on heat transfer enhancement are relatively close to each other. In this case, if the pumping power is the main concern, using nanofluids is recommended due to providing a smaller pressure drop penalty.     

Heat transfer enhancement in microchannel heat sinks using nanofluids

Heat transfer enhancement in a 3-D microchannel heat sink (MCHS) using nanofluids is investigated by a numerical study. The addition of nanoparticles to the coolant fluid changes its thermophysical properties in ways that are closely related to the type of nanoparticle, base fluid, particle volume fraction, particle size, and pumping power. The calculations in this work suggest that the best heat transfer enhancement can be obtained by using a system with an Al₂O₃–water nanofluid-cooled MCHS. Moreover, using base fluids with lower dynamic viscosity (such as water) and substrate materials with high thermal conductivity enhance the thermal performance of the MCHS. The results also show that as the particle volume fraction of the nanofluid increases, the thermal resistance first decreases and then increases. The lowest thermal resistance can be obtained by properly adjusting the volume fraction and pumping power under given geometric conditions. For a moderate range of particle sizes, the MCHS yields better performance when nanofluids with smaller nanoparticles are used. Furthermore, the overall thermal resistance of the MCHS is reduced significantly by increasing the pumping power. The heat transfer performance of Al₂O₃–water and diamond–water nanofluids was 21.6% better than that of pure water. The results reported here may facilitate improvements in the thermal performance of MCHSs.     

Heat transfer performance and exergy analyses of a corrugated plate heat exchanger using metal oxide nanofluids

Heat exchangers have been widely used for efficient heat transfer from one medium to another. Nanofluids are potential coolants, which can afford excellent thermal performance in heat exchangers. This study examined the effects of water and CuO/water nanofluids (as coolants) on heat transfer coefficient, heat transfer rate, frictional loss, pressure drop, pumping power and exergy destruction in the corrugated plate heat exchanger. The heat transfer coefficient of CuO/water nanofluids increased about 18.50 to 27.20% with the enhancement of nanoparticles volume concentration from 0.50 to 1.50% compared to water. Moreover, improvement in heat transfer rate was observed for nanofluids. On the other hand, exergy loss was reduced by 24% employing nanofluids as a heat transfer medium with comparing to conventional fluid. Besides, 34% higher exergetic heat transfer effectiveness was found for 1.5 vol.% of nanoparticles. It has a small penalty in the pumping power. Hence, the plate heat exchanger performance can be improved by adapting the working fluid with CuO/water nanofluids.     

An experimental study on the proper criterion to judge the thermal performance of the nanofluids

This work is dedicated to finding a suitable measure to judge thermal performance of nanofluids. The importance of this issue arises from misleading claim of excess heat transfer of nanofluids compared to the base fluid, neglecting the hydraulic effects such as increase in pressure drop. To clarify the issue, the experimental setup with capability to create constant Reynolds number and constant pumping power is constructed. Thermal behavior of nanofluids of silicon oxide/water and aluminum oxide/water and distilled water in developing region of laminar flow regime is investigated. In this regard, the convective heat transfer coefficient within the finned tube heat exchanger is evaluated. According to the results, the concentration of nanoparticle in the base fluid will have a significant impact on the amount of deflection of these two criteria, so that by increasing the nanoparticle's concentration the difference between these two measures becomes greater.     

Heat transfer of nanofluids in the mini-rectangular fin heat sinks

In the present study, the heat transfer characteristics of nanofluids cooling in the mini-rectangular fin heat sink are studied. The heat sinks with three different channel heights are fabricated from the aluminum by the wire electrical discharge machine with the length, width and base thickness of 110, 60, and 2 mm, respectively. The nanofluids are the mixture of de-ionized water and nanoscale TiO₂ particles. The results obtained from the nanofluids cooling in mini-rectangular fin heat sink are compared with those from the de-ionized water cooling method. Effects of the inlet temperature of nanofluids, nanofluid Reynolds number, and heat flux on the heat transfer characteristics of mini-rectangular fin heat sink are considered. It is found that average heat transfer rates for nanofluids as coolant are higher than those for the de-ionized water as coolant. The results of this study are of technological importance for the efficient design of cooling systems of electronic devices to enhance cooling performance.     

Experimental analysis of SiO2-Distilled water nanofluids in a Polymer Electrolyte Membrane fuel cell parallel channel cooling plate

An experimental report on the thermal performance of Silicone Dioxide (SiO₂) nanofluid coolants based on a PEM fuel cell cooling system is presented. The aim of this study is to evaluate the feasibility of applying these nanofluids coolants as an alternative to conventional distilled water through detailed analysis of thermofluids behaviour in a simulated cooling plate environment. SiO₂ nanoparticles were dispersed in distilled water at 0.1%, 0.3% and 0.5% volume concentrations and tested in a parallel channel cooling plate system. A constant heat load was supplied to simulate a fuel cell stack thermal condition. At inlet flow conditions from 750 to 900 Reynolds number, the SiO₂ nanofluids reduced the average plate temperatures by 15%–20% compared to conventional water coolant. The nanofluids also increased the cooling effectiveness by a similar margin, as well as improving the bulk heat transfer coefficient to a range between 2700 and 4400 W m⁻². ^oC⁻¹. However, the required pumping power was also increased due to the added viscous effect. Through the Advantage Ratio (AR) analysis, it was concluded that the enhancement in heat transfer mechanics was more significant than the penalties in fluid flow dynamics. Thus, the SiO₂ nanofluids and the cooling plate design are possible options for advanced PEM fuel cell thermal management practice in future stack designs.     

Effect of Vibration on Forced Convection Heat Transfer for SiO2–Water Nanofluids

In the process of heat transfer, the fluid type and external parameters have a significant impact on heat transfer performance. For this reason, the physical properties, pressure differences, and heat transfer rates of SiO₂–water nanofluids have been experimentally investigated in a straight circular pipe. Experimental results revealed a great difference in physical properties between SiO₂–water nanofluids and purified water. The friction factor of low-volume-concentration nanofluids was slightly increased for laminar flow and tended to be almost independent of the Reynolds number for turbulent flow. The heat transfer coefficient can be enhanced either by adding nanoparticles to purified water or by imposing a transverse vibration on the heat transfer surface. Using these two methods at the same time (compound heat transfer enhancement), heat transfer performance is much better than that with either method alone. The largest increase of about 182% was observed under conditions of compound heat transfer enhancement.