Numerical investigation of effective parameters in convective heat transfer of nanofluids flowing under a laminar flow regime

This article presents a numerical investigation on heat transfer performance and pressure drop of nanofluids flows through a straight circular pipe in a laminar flow regime and constant heat flux boundary condition. Al₂O₃, CuO, carbon nanotube (CNT) and titanate nanotube (TNT) nanoparticles dispersed in water and ethylene glycol/water with particle concentrations ranging between 0 and 6 vol.% were used as working fluids for simulating the heat transfer and flow behaviours of nanofluids. The proposed model has been validated with the available experimental data and correlations. The effects of particle concentrations, particle diameter, particles Brownian motions, Reynolds number, type of the nanoparticles and base fluid on the heat transfer coefficient and pressure drop of nanofluids were determined and discussed in details. The results indicated that the particle volume concentration, Brownian motion and aspect ratio of nanoparticles similar to flow Reynolds number increase the heat transfer coefficient, while the nanoparticle diameter has an opposite effect on the heat transfer coefficient. Finally, the present study provides some considerations for the appropriate choice of the nanofluids for practical applications.     

Unconfined laminar nanofluid flow and heat transfer around a square cylinder

The momentum and forced convection heat transfer for a laminar and steady free stream flow of nanofluids past an isolated square cylinder have been studied numerically. Different nanofluids consisting of Al₂O₃ and CuO with base fluids of water and a 60:40 (by mass) ethylene glycol and water mixture were selected to evaluate their superiority over conventional fluids. Recent correlations for the thermal conductivity and viscosity of nanofluids, which are functions of particle volumetric concentration as well as temperature, have been employed in this paper. The simulations have been conducted for Pe = 25, 50, 100 and 200, with nanoparticle diameters of 30 and 100 nm and particle volumetric concentrations ranging from 0% to 4%. The results of heat transfer characteristics of nanofluid flow over a square cylinder showed marked improvement comparing with the base fluids. This improvement is more evident in flows with higher Peclet numbers and higher particle volume concentration, while the particle diameter imposes an adverse effect on the heat transfer characteristics. In addition, it was shown that for any given particle diameter there is an optimum value of particle concentration that results in the highest heat transfer coefficient.     

Thermal Enhancement of Triangular Ducts Using Compound of Vortex Generators and Nanofluids

Laminar flow and heat transfer of three different types of nanofluids; Al₂O₃, CuO, and SiO₂ suspended in ethylene glycol, in a triangular duct using delta-winglet pair of vortex generator are numerically simulated in three dimensions. The governing equations of mass, momentum and energy are solved using the finite volume method. The effects of types, concentrations, and diameter of solid nanoparticles and Reynolds number on thermal and hydraulic performance of triangular duct are examined. The range of Reynolds number, volume fraction and nanoparticles diameters is 100–1200, 1–4%, and 25–85 nm, respectively. The results indicate that the average Nusselt number increases with the particles volume fraction and Reynolds number associated with an increase in the pressure drop. The heat transfer enhancement and pressure drop penalty reduce with increasing the particles diameters. However, a reduction in the pumping power required is observed to force the nanofluids when the volume fraction increases, assuming the heat transfer coefficient remains constant.     

Numerical study of turbulent flow and heat transfer characteristics of nanofluids considering variable properties

Turbulent flow and heat transfer of three different nanofluids (CuO, Al₂O₃ and SiO₂) in an ethylene glycol and water mixture flowing through a circular tube under constant heat flux condition have been numerically analyzed. New correlations for viscosity up to 10% volume concentration for these nanofluids as a function of volume concentration and temperature are developed from the experiments and are summarized in the present paper. In our numerical study, all the thermophysical properties of nanofluids are temperature dependent. Computed results are validated with existing well established correlations. Nusselt number prediction for nanofluids agrees well with Gnielinski correlation. It is found that nanofluids containing smaller diameter nanoparticles have higher viscosity and Nusselt number. Comparison of convective heat transfer coefficient of CuO, Al₂O₃ and SiO₂ nanofluids have been presented. At a constant Reynolds number, Nusselt number increases by 35% for 6% CuO nanofluids over the base fluid.     

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.     

Experimental investigation of heat transfer and friction factor with water–propylene glycol based CuO nanofluid in a tube with twisted tape inserts

Convective heat transfer and friction factor characteristics of water/propylene glycol (70:30% by volume) based CuO nanofluids flowing in a plain tube are investigated experimentally under constant heat flux boundary condition. Glycols are normally used as an anti-freezing heat transfer fluids in cold climatic regions. Nanofluids are prepared by dispersing 50 nm diameter of CuO nanoparticles in the base fluid. Experiments are conducted using CuO nanofluids with 0.025%, 0.1% and 0.5% volume concentration in the Reynolds numbers ranging from 1000 < Re < 10000 and considerable heat transfer enhancement in CuO nanofluids is observed. The effect of twisted tape inserts with twist ratios in the range of 0 < H/D < 15 on nanofluids is studied and further heat transfer augmentation is noticed. The increment in the pressure drop in the CuO nanofluids over the base fluid is negligible but the experimental results have shown a significant increment in the convective heat transfer coefficient of CuO nanofluids. The convective heat transfer coefficient increased up to 27.95% in the 0.5% CuO nanofluid in plain tube and with a twisted tape insert of H/D = 5 it is further increased to 76.06% over the base fluid at a particular Reynolds number. The friction factor enhancement of 10.08% is noticed and increased to 26.57% with the same twisted tape, when compared with the base fluid friction factor at the same Reynolds number. Based on the experimental data obtained, generalized regression equations are developed to predict Nusselt number and friction factor.     

Heat transfer augmentation in concentric elliptic annular by ethylene glycol based nanofluids

In this article, laminar mixed convective heat transfer at different nanofluids flow in an elliptic annulus with constant heat flux boundary condition has been numerically investigated. The three dimensional governing equations (continuity, momentum and energy) are solved using the finite volume method (FVM). The investigation covers Reynolds number and nanoparticle volume fraction in the ranges of 200–1000 and 0–4% respectively. In the present work, four different types of nanofluids are examined in which Al₂O₃, CuO, SiO₂ and ZnO are suspended in the base fluid of ethylene glycol (EG) with different nanoparticle sizes 20, 40, 60 and 80 nm. The results show that SiO₂-EG nanofluid has the highest Nusselt number, followed by Al₂O₃-EG, ZnO-EG, CuO-EG, and lastly pure ethylene glycol. The Nusselt number increased as the nanoparticle volume fraction and Reynolds number increased; however, it decreased as the nanoparticle diameter increased. It is found that the glycerine-SiO₂ shows the best heat transfer enhancement compared with other tested base fluids. Comparisons of the present results with those available in the literature are presented and discussed.     

Experimental study of Fe2O3/water and Fe2O3/ethylene glycol nanofluid heat transfer enhancement in a shell and tube heat exchanger

Heat transfer characteristics of Fe₂O₃/water and Fe₂O₃/EG nanofluids were measured in a shell and tube heat exchanger under laminar to turbulent flow condition. In the shell and tube heat exchanger, water and ethylene glycol-based Fe₂O₃ nanofluids with 0.02%, 0.04%, 0.06% and 0.08% volume fractions were used as working fluids for different flow rates of nanofluids. The effects of Reynold's number, volume concentration of suspended nanoparticles and different base fluids on the heat transfer characteristics were investigated. Based on the results, adding nanoparticles to the base fluid causes a significant enhancement of the heat transfer characteristics and thermal conductivity. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and temperature of fluids. In this paper, the effect of Fe₂O₃ nanoparticles on the thermal conductivity of base fluids like ethylene glycol and water was studied. The thermal conductivity measurement was made for different concentrations and temperatures. As the concentration of the nanoparticles increased, there was a significant enhancement in thermal conductivity and overall heat transfer due to more interaction between particles. It was also observed that there was an improvement in the thermal conductivity of the base fluid as the temperature increased. The measurements also showed that the pressure drop of nanofluid was higher than that of the base fluid in a turbulent flow regime. However, there was no significant increase in pressure drop at laminar flow.     

Investigation of Heat Transfer in Serpentine Shaped Microchannel Using Al2O3/Water Nanofluid

An experimental investigation was conducted to explore the maximum heat transfer in a serpentine shaped microchannel by varying the hydraulic diameter, flow rates and with influence of Al₂O₃ nanofluid. Microconvection is an important area in heat transport phenomena. Surface area is one of the important factors in high heat transfer in a microchannel heat exchanger. In this study, serpentine shaped microchannels of hydraulic diameters 810, 830, 860, and 890 μm are analyzed for the optimizing the hydraulic diameter to get enhanced thermal performance of the microchannel. A copper material microchannel having length a of 70 mm is used. Flow rate also varied from 1 lpm (Litres per minute) to 3.5 lpm for optimization with nanofluid as a medium. From numerical study it is observed that as the hydraulic diameter decreases from 890 μm to 810 μm the pressure drop increases with a decrease in hydraulic diameter. Also as heat input to the microchannel increases from 5 watts to 70 watts. From analysis it is observed that the hydraulic diameter of the microchannel is a major factor in microchannel heat transfer which is dependent on flow rate of fluid in the microchannel. The results also show that suspended Al₂O₃ nanoparticles in fluids have enhanced heat transfer when compared to the base fluid.     

Numerical Analysis of a Small Size Baffled Shell-and-Tube Heat Exchanger Using Different Nano-Fluids

In this study, numerical simulation was used to investigate the effect of adding different nano-particles into the fluid on the performance of a baffled shell-and-tube heat exchanger. A three-dimensional modeling approach was followed to analyze the effect of different nano-fluids, at various volume fractions, as applied in a baffled shell-and-tube heat exchanger. Once finished with validating the grid independency and results, we proceeded to obtain heat transfer rate, pressure drop, outlet shell temperature and exchanger effectiveness for different volume fractions and particle size of different nano-fluids. The studied nano-particles in the present work included Al₂O₃, CuO, Fe₂O₃, Cu, Fe, SiO₂, and Au, with water and ethylene glycol employed as base fluids. With constant mass flow rate for all cases, the results indicated that, the addition of nano-particles had reduced the heat transfer coefficient, pressure drop and the rate of heat transfer through the shell, even though it had increased outlet shell temperature. In other words, considering a constant heat transfer rate, the presence of nano-fluids in a baffled shell-and-tube heat exchanger is likely to be associated with increased outlet shell temperature. Another consequence presents that using ethylene glycol as base fluid leads to higher effectiveness compared with water as a base fluid in exchanger.     

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.     

Three‐Dimensional Numerical Investigation of Nanofluids Flow in Microtube with Different Values of Heat Flux

Forced convective laminar flow of different types of nanofluids such as Al₂O₃, CuO, SiO₂, and ZnO, with different nanoparticle size 25, 45, 65, and 80 nm, and different volume fractions which ranged from 1% to 4% using ethylene glycol as base fluids were used. A three‐dimensional microtube (MT) with 0.05 cm diameter and 10 cm in length with different values of heat fluxes at the wall is numerically investigated. This investigation covers Reynolds number (Re) in the range of 80 to 160. The results have shown that SiO₂‐EG nanofluid has the highest Nusselt number (Nu), followed by ZnO‐EG, CuO‐EG, Al₂O₃‐EG, and finally pure EG. The Nu for all cases increases with the volume fraction but it decreases with the rise in the diameter of nanoparticles. In all configurations, the Nu increases with Re. In addition, no effect of heat flux values on the Nu was found.     

Numerical Analysis of Heat Transfer and Nanofluid Flow in a Triangular Duct with Vortex Generator: Two‐Phase Model

Laminar forced convection heat transfer and nanofluids flow in an equilateral triangular channel using a delta‐winglet pair of vortex generators is numerically studied. Three nanofluids, namely; Al₂O₃, CuO, and SiO₂ nanoparticles suspended in an ethylene glycol base fluid are examined. A two‐phase mixture model is considered to simulate the governing equations of mass, momentum and energy for both phases and solved using the finite volume method (FVM). Constant and temperature dependent properties methods are assumed. The single‐phase model is considered here for comparison. The nanoparticle concentration is assumed to be 1% and 4% and Reynolds number is ranged from 100 to 800. The results show that the heat transfer enhancement by a using vortex generator and nanofluids is greater than the case of vortex generator and base fluid only, and the latest case provided higher enhancement of heat transfer compared to the case of a base fluid flowing in a plain duct. Considering the nanofluid as two separated phases is more reasonable than assuming the nanofluid as a homogeneous single phase. Temperature dependent properties model provided higher heat transfer and lower shear stress than the constant properties model.     

Numerical analysis of performance of water‐based nanofluid flowing through tube bent at 90°

The aim of the present study is to analyze the performance of CuO nanofluids with water as the base fluid in the flat tube bent at 90°. The analytical analysis has been performed under different Reynolds number as well as nanoparticle volume concentrations. Various thermophysical properties, that is, density, thermal conductivity, viscosity, and specific heat capacity have been estimated with well‐developed models of each, presented during previous studies carried out in the field of nanofluids. The simulation work has been performed with the help of the finite volume method. It was concluded from this study that heat transfer coefficient and Nusselt number of nanofluids at different volume concentrations between 0.1% to 0.5% v/v CuO is higher than that of the base fluids. The pressure drop obtained upon the use of nanofluids is found to be higher than the base fluid. The study also proves that nanofluids have a huge potential in playing an important role in decreasing sizes of heat transfer systems.     

Heat Transfer and Pressure Drop of Nanofluids in a Microchannel Heat Sink

The aim of this study is to determine the upper limitations of the particle volume fraction for heat transfer performance of TiO₂–water nanofluids in microchannels. Nanofluids were prepared by the addition of TiO₂ metallic nanoparticles into distilled water chosen as base fluid at five different volumetric ratios (0.25%, 0.5%, 1.0%, 1.5%, and 2.0%). The effects of the Reynolds number (100–750) and particle volume fraction at constant microchannel height (200 μm) on heat transfer and pressure drop characteristics were analyzed experimentally. Adding metallic oxide particles with nano dimensions into the base fluid did not cause excessive increase of friction coefficient but provided higher heat transfer than that of pure water. It was also observed that water–TiO₂ nanofluid increased heat transfer up to 2.0 vol%, but heat transfer decreased after 2.0 vol%. Furthermore, the thermal resistance was calculated and it was seen that adding nanoparticles with an average diameter smaller than 25 nm into the base fluid caused the thermal resistance to decrease.     

Thermal performance of U-shaped serpentine microchannel heat sink using various metal oxide nanofluids

This study aims to evaluate the thermal performance and friction factor characteristics of the U-shaped serpentine microchannel heat sink using three different nanofluids. Two distinct nanoparticles, namely Al₂O₃ (alumina) and CuO (copper oxide), were used for the preparation of nanofluids using water and ethylene glycol (EG) as base fluids. Three nanofluids, namely nanofluid I (Al₂O₃ + water), nanofluid II (CuO + water), and nanofluid III (CuO + EG), have been prepared. The results showed that the thermal conductivity of nanofluids was increased for all concentrations (from 0.01 to 0.3%), compared with base fluids. The theoretical values derived from the relationship between the Darcy friction factor showed a clear understanding of the fully developed laminar flow. Thermal resistance for nanofluid III was lower than other nanofluids, resulting in a higher cooling efficiency. The nanofluid mechanism and the geometry of the U-shaped serpentine heat sink have led to the improvement in the thermal performance of electronic cooling systems.     

Finned tube performance evaluation with nanofluids and conventional heat transfer fluids

The performance of hydronic finned-tube heating units with nanofluids is compared to their performance with a conventional heat transfer fluid comprised of 60% ethylene glycol and 40% water, by mass (60% EG) using a mathematical model. The nanofluids modeled are comprised of either CuO or Al₂O₃ nanoparticles dispersed in the 60% EG solution. The finned tube configuration modeled is similar to that commonly found in building heating systems. The model employs correlations for nanoparticle thermophysical properties and heat transfer that have been previously documented in the literature. The analyses indicate that finned tube heating performance is enhanced by employing nanofluids as a heat transfer medium. The model predicts an 11.6% increase in finned-tube heating output under certain conditions with the 4% Al₂O₃/60% EG nanofluid and an 8.7% increase with the 4% CuO/60% EG nanofluid compared to heating output with the base fluid. The model predicts that pumping power required for a given heating output with a given finned tube geometry is reduced with both the Al₂O₃/60% EG and the CuO/60% EG nanofluids compared to the base fluid. The finned tube with 4% Al₂O₃/60% EG has the lowest liquid pumping power at a given heating output of all the fluids modeled.     

Convective Heat Transfer and Fluid Dynamic Characteristics of SiO2 Ethylene Glycol/Water Nanofluid

Nanofluids comprised of silicon dioxide (SiO₂) nanoparticles suspended in a 60:40 (% by weight) ethylene glycol and water (EG/water) mixture were investigated for their heat transfer and fluid dynamic performance. First, the rheological properties of different volume percents of SiO₂ nanofluids were investigated at varying temperatures. The effect of particle diameter (20 nm, 50 nm, 100 nm) on the viscosity of the fluid was investigated. Subsequent experiments were performed to investigate the convective heat transfer enhancement of nanofluids in the turbulent regime by using the viscosity values measured. The experimental system was first tested with EG/water mixture to establish agreement with the Dittus-Boelter equation for Nusselt number and with Blasius equation for friction factor. The increase in heat transfer coefficient due to nanofluids for various volume concentrations has been presented. Pressure loss was observed to increase with nanoparticle volume concentration. It was observed that an increase in particle diameter increased the heat transfer coefficient. Typical percentage increases of heat transfer coefficient and pressure loss at fixed Reynolds number are presented.     

Convective boiling and particulate fouling of stabilized CuO-ethylene glycol nanofluids inside the annular heat exchanger

Thermal performance of convective flow boiling heat transfer and particulate fouling of CuO/EG nanofluids has been experimentally studied inside the annular heat exchanger. CuO nanoparticles were well-dispersed and stabilized using a new combinational method (adding surfactant, stirring, pH control and sonication) in ethylene glycol (EG) as the base fluid in different weight fractions of nanoparticles (0.1–0.4%). Despite stabilizing the nanofluids, a considerable boiling heat transfer reduction due to the fouling resistance has been reported. Subsequently, scale formation and particulate fouling of nanofluids in term of fouling resistance has experimentally been investigated. Influences of operating parameters on the fouling resistance and heat transfer coefficient are investigated and briefly discussed.     

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.