Thermal Performance Of Nanofluids Research Articles

Thermal performance of nanofluids in metal foam tube: Thermal dispersion model incorporating heterogeneous distribution of nanoparticles

This study presents the application of a modified single-phase method by thermal dispersion model incorporating heterogeneous distribution of nanoparticle concentration for evaluating thermal performance of a nanofluid in a circular porous metal foam tube. Numerical approach was conducted for Re=200–1000, mean concentration of 0.5–2%, and metal foam porosity of 0.7–0.9. It is observed that the predicted data by application of the thermal dispersion approach are in satisfactory agreement with those obtained experimentally, whereas applying the general homogeneous model results in an underestimation. The results reveal that the heterogeneity of the concentration distribution is directly proportional to nanoparticle mean concentration, Reynolds number, and the metal foam porosity. The velocity and temperature profiles at a cross section have been found to be flatter in dispersion model compared to those obtained from the homogeneous model. Furthermore, it is achieved that the Nusselt number varies directly relative to mean concentration and Reynolds number, whereas it inversely alters relative to the porosity. This reduction is found to be more profound at lower porosities.

Effect on Heat Transfer Characteristics of Nanofluids Flowing under Laminar and Turbulent Flow Regime – A Review

Heat transfer is a most important phenomenon that influence the performance of working device. To date several attempts have been made by researchers to minimize the size of heat exchangers in order to reduce the cost. Earlier we use some conventional fluids (water, air, engine oil etc.) for cooling of automobile, refrigeration and some other industrial applications. But it is observed here that by using these fluids there is curb and hindrance in heat transfer rate because of very low thermal conductivity. From last ten-years new generation fluid introduced known as nanofluid. To increase the thermal conductivity of base fluid some amount of nanoparticles is added. Nanofluid have combined properties of nanoparticles as well as base fluid. Researcher found that heat transfer rate fully dependent of the thermal conductivity of nanoparticles as well as nanoparticle size diameter and volume concentration. This review paper summarised the recent research on enhancement of heat transfer and thermal performance of nanofluid as coolant for industrial applications.

Experimental investigation of heat transfer and pressure drop in a straight minichannel heat sink using TiO2 nanofluid

In this paper, heat transfer and pressure drop characteristic associated with minichannel heat sink is investigated experimentally. TiO2 nanofluid with 15% weight concentration in water as base fluid is used as a coolant and its performance is compared with the distilled water at heating powers of 100W, 125W and 150W. The results indicate that TiO2 nanofluid thermal performance is strongly dependent on heating power and its usefulness heat transfer characteristic could be achieved more effectively at lower heating power. However, pressure drop is found to increase with the decrease of heating power and this decrement is more prominent for TiO2 nanofluid as compared to distilled water due to viscosity variation with temperature. Nusselt number is found invariant with increase or decrease of heating power and hence using distilled water, experimental Nusselt number satisfies Peng and Peterson empirical correlation at all heating powers within 20% accuracy. The lowest wall temperature is measured to be 37.05°C using TiO2 nanofluid at Reynolds number of 922 corresponding to heating power of 100W. Moreover, while passing through the minichannel, an axial rise of base temperature is observed from inlet to outlet of heat sink.

On mixed convection of two immiscible layers with a layer of non-Newtonian nanofluid in a vertical channel

Mixed convection in a vertical parallel plate channel is analyzed with one region filled with Newtonian fluids and another region with non-Newtonian nanofluids. Pseudo-plastic and dilatant fluids are used as working base flow of nanofluids. Power-law modelling is adopted to predict the effect of non-Newtonian behavior on the fluid flow and thermal performance of nanofluids, and the effective kinematic viscosity and thermal conductivity are determined using linear relations as functions of nanoparticle loading parameter. The velocity and temperature fields are investigated, considering the influence of power-law index n(0.6≤n≤1.4) and nanoparticle volume fraction ϕ(0≤ϕ≤4%). Two cases have been paid special attention in the present work, that is, Case I: in the absence of viscous dissipation (Br=0, GR≠0), and Case II: in the absence of buoyancy forces (GR=0, Br≠0) when purely forced convection happens. It is observed that the power-law index has a strong effect on the shape of velocity profile, and on the scale of temperature curves. The results reveal that the power-law effect on both velocity and temperature is more observable in shear-thinning fluids than that in the dilatant flow. These findings demonstrate that, in some potential applications, the shear-thinning fluid should be chosen for its higher effectiveness on fluid driving where the non-Newtonian fluid is used to drive Newtonian flow via interface shear.

Experimental Investigation of Al2O3-Polyethylene Glycol and TiO2-Polyethylene Glycol Nanofluids Flow through a Minichannel Heat Sink

Heat dissipation becomes a significant issue in the performance of various heat transfer systems. Thermal properties of liquids decide its heat transfer performance. Conventional fluids have inherently poor thermal conductivity which makes them not suitable for high heat loads and heat fluxes. Nanofluids are proposed as a promising challenger for advanced heat transfer fluids in a variety of engineering applications. Nanofluids are colloidal suspensions of nanometer-sized particles in various base fluids. Nanoparticles will improve the heat transfer characteristics of the base fluids effectively. In the present work, the forced convective heat transfer performance of copper mini channel heat sink has been carried out experimentally using Al2O3 polyethylene glycol and TiO2 polyethylene glycol nanofluids. The Al2O3 and TiO2 are converted into nanoparticles by using planetary ball mill and its shape was analysed. The nano particles then dispersed in polyethylene glycol base fluid by using a magnetic stirrer to form nano fluid for different volume concentration 0.5%, 1%, 1.5%, 2%, 2.5% without adding surfactant. The thermo physical properties thermal conductivity, density, viscosity, boiling point, flash and fire point, pH value, the heat transfer rate, heat transfer coefficient, heat flux of Al2O3 polyethylene glycol and TiO2 polyethylene glycol based nanofluids is evaluated. The comparative heat transfer performance of these two types of nanofluids for different volume concentration is analysed by passing it at a constant inlet velocity of 0.058m/s through a square shape copper mini channel heat sink (30x30mm) with seven passages by maintaining at constant heat supply. Further by varying the heat input of the minichannel heat sink the heat transfer phenomenon of these two types of nanofluid is analysed. The experimental evaluation conform the effective enhancement of heat transfer characteristics in nanofluid by the influence of volume concentration. The results showed that the Al2O3 polyethylene glycol nanofluid thermal performance increased significantly and out performs the TiO2 polyethylene glycol nanofluid. The highest improvement in the heat transfer occurred was 26% for 2.5 volume% Al2O3 polyethylene glycol nanofluid when compared to TiO2 polyethylene glycol nanofluid.

Effects of non-Newtonian behaviour on the thermal performance of nanofluids in a horizontal channel with discrete regions of heating and cooling

A numerical simulation is performed to investigate laminar forced convection nanofluid based non-Newtonian flow in a horizontal parallel plate with discrete regions of heating and cooling. Water, pseudo-plastic and dilatant fluids are used as working base fluids. Power-law modelling is adopted to predict the effect of non-Newtonian behaviour on the thermal performance of nanofluids in a channel with heating (cooling) regions placed symmetrically on walls, and the remaining surfaces are considered adiabatic. The velocity and temperature fields, heat transfer coefficient ratio, and pressure drop are investigated, considering the influence of power-law index n, nanoparticle volume fraction ϕ, Reynolds number, and generalized Prandtl number. It is observed that the velocity and temperature of nanofluids may increase or decrease considerably by changing the base power-law fluids. The results reveal that nanofluids based on dilatant flow are more sensitive to the environmental heat flux than those based on pseudo-plastic fluid. Furthermore, the pressure drop increases as the power-law index rises. The findings demonstrate that the presence of non-Newtonian effects in nanofluids can lead to improvement and optimization in the thermal performance of channels, which suggests the potential of nanofluid based power-law flow in industrial equipment heating and cooling applications.

Thermal performance of nanofluid in ducts with double forward-facing steps

The turbulent heat transfer to nanofluid flow over double forward-facing steps was investigated numerically. The duct geometry and computational mesh were developed with ANSYS 14 ICEM. Two-dimensional governing equations were discretized and integrated using finite volume technique. The k-ɛ turbulence model was used in the analysis. Al2O3 and CuO nanoparticles at volume fractions varying from 1% to 4% with water as the base fluid were employed for turbulent flow in a passage with a double forward-facing step. The effects of volume fraction and step height were compared with the base fluid thermal performance. The obtained results showed an increase in the Nusselt number with the increase in volume fraction of nanofluid, Reynolds number, and step height. A higher local Nusselt number value was found at the second step compared to the first step for all cases. Velocity contours were developed to visualize the recirculation regions before and after the first and second steps. The results also demonstrated enhanced heat transfer with the increase of nanoparticle concentration, and the largest thermal enhancement factor occurred for the highest nanoparticle volume fraction (4%) of Al2O3 considered in this investigation.

Viscous dissipative forced convection in thermal non-equilibrium nanofluid-saturated porous media embedded in microchannels

Under local thermal non-equilibrium and isoflux boundary conditions, the two-energy-equation model is employed to investigate the effect of viscous dissipation on the thermal characteristics of nanofluid flow through a porous medium embedded in a microchannel. Analytical closed-form solutions of the two-dimensional temperature distributions are obtained for the models with and without the viscous dissipation terms in the energy equation. The analysis emphasizes on the disparities induced by the viscous dissipation between the two models. The use of porous medium is capable to enhance the thermal performance up to 53%. When the viscous dissipation effect is neglected, the thermal performance of nanofluid is overrated as much as 60%, sufficiently serious to trigger an attention in the performance analysis. The heat transfer coefficient of nanofluid is found to be enhanced in the low-Reynolds-number flow regime but it declines in the high-Reynolds-number flow regime. By reducing the size of nanoparticle, the thermal performance can be enhanced as much as 70%. Furthermore, the thermal performance can be further augmented by increasing the channel aspect ratio as well as by increasing the thermal conductivity of the porous material. This study serves as a useful analytical tool for the design and performance characterization of an integrated system incorporating the use of nanofluid and porous medium into a microchannel.

Improvement of thermal performance of Ag nano fluid combined with carbon nano-tube

The thermal performance of nano fluid containing Ag NPs with different stabilizers was studied in detail. The wall temperature distributions of the heat pipe containing pure water and a small amount of PAN/Ag, PVP/Ag, L-cys/Ag, and OA/Ag were determined, respectively. With the addition of a small amount of Ag NPs in the pure water, the heat pipe wall temperature became lower than that of pipes filled with pure water. The efficiency under the same conditions was ranked as PVP/Ag > L-cys/Ag > PAN/Ag > OA/Ag. After adding a small amount of CNT in the mixture, the effect was enhanced further. As more CNT became dispersed in the working fluid, the opposite effect was observed. Therefore, the optimal amount is 4 mg/L CNT in nano-fluid. Ag nano fluid could form the multi-scaled surface with higher wettability and spreadability. The wettability of nano-fluid was improved with the addition of a small amount of CNT in the mixture. However, the spreadability of the mixture would decrease significantly in the presence of more CNT.

CFD and experimental investigation on the heat transfer characteristics of alumina nanofluids under the laminar flow regime

This study reports experimental and Computational Fluid Dynamics (CFD) investigations of the laminar convective heat transfer coefficient of Al2O3/water nanofluids in a circular tube under uniform and constant heat flux on the wall. Three different models including a constant physical properties single-phase (CP-SP) model, a variable physical properties single-phase (VP-SP) model and a discrete particles two-phase model were developed. Particle agglomeration and cluster size distribution were considered in the two-phase model. Experimental and simulation results showed that the thermal performance of nanofluids is higher than that of the base fluid and the heat transfer enhancement increases with the particle volume concentration and Reynolds number. Furthermore, higher heat transfer coefficients were detected in the case of the VP-SP model and the two-phase model. The results demonstrated that the two-phase model prediction and experimental data match significantly and that the model can be employed with confidence for the prediction of any type of nanofluid.

Improvement in Heat Transfer of a Two-Phased Closed Thermosyphon Using Silver-Decorated MWCNT/Water

Hereby, a comparative study of thermal and thermodynamic properties of nanofluids based on multiwalled carbon nanotubes (MWCNTs) and water is described. The first nanofluid includes pristine MWCNT while the second nanofluid prepared by MWCNT decorated with silver. To achieve the covalent functionalization, morphology of MWCNT-Ag was studied by transmission electron microscopy. Subsequently, the value of the entropy generation and thermal performance of nanofluids (MWCNT/water and MWCNT-Ag/water) were inspected in a two-phased closed thermosyphon (TPCT). The results suggested as the concentration and input power increased, the thermal resistance decreased. Also in different concentrations, the thermal efficiency of nanofluids obeyed the sequence: MWCNT-Ag (1 wt%) > MWCNT-Ag (0.5 wt%) > MWCNT (1 wt%) > MWCNT (0.5 wt%) > water. A variation of the vacuum pressure was also studied in the synthesized nanofluids as compared with pure water. The results were shown a lower pressure drop of MWCNT-Ag/water than MWCNT/water and the water. Also it was found that the higher thermal performance is produced using higher extent of covalent functional groups (with higher thermal conductivity). MWCNT-Ag/water can be an appropriate substitution for the water in the thermal equipment due to the intensive thermal efficiency and/or low thermal resistance compared with pure water.

Heat transfer enhancement in a hybrid microchannel-photovoltaic cell using Boehmite nanofluid

Experiments were conducted to investigate the cooling performance of water-based Boehmite (AlOOH·xH2O) nanofluid in a hybrid photovoltaic (PV) cell. A Perspex plate consists of 40 parallel rectangular microchannels with a hydraulic diameter of 783μm, a length of 24cm, a width of 1.8mm and a depth of 500μm attached to the back of the cell. Cooling performances of water, as the base fluid, and three different concentrations of nanofluid (0.01, 0.1 and 0.3wt.%) were compared. The nanofluid thermal performance has been assessed from the obtained results for outlet flow temperature and the average PV surface temperature. The average PV surface temperature decreased from 62.29°C to 32.5°C at zero and 300ml/min of flow rate for 0.01wt.% nanofluid, respectively. Moreover, the highest improving in the electrical efficiency was achieved about 27% for 0.01wt.% concentration of the nanofluid at this flow rate.

Heat transfer enhancement and pressure drop analysis in a helically coiled tube using Al2O3 / water nanofluid

In this experimental investigation, the heat transfer and pressure drop analysis of a shell and helically coiled tube heat exchanger by using Al2O3 / water nanofluids have been carried out under turbulent flow condition. The Al2O3/ water nanofluids of 0.1%, 0.4%, and 0.8% particle volume concentration have been prepared by using two step method. The tube side experimental Nusselt number of 0.1%, 0.4% and 0.8% nanofluids were found to be 28%, 36% and 56%, respectively higher than water. These enhancements are due to higher thermal conductivity of nanofluid, better fluid mixing and strong secondary flow formation in coiled tube. The pressure drop of 0.1%, 0.4% and 0.8% were found to be 4%, 6%, and 9%, respectively higher than water. The increase in pressure drop is due to increase in nanofluid viscosity while adding nanoparticles. The measurement of nanofluid thermal performance factor is found to be greater than unity. It is concluded that the Al2O3 nanofluid can be applied as a coolant in helically coiled tube heat exchanger to enhance heat transfer with negligible pressure drop.

An Experimental Study on Thermal Performance of Nano Fluids in Microchannel Heat Exchanger

An Experimental Study on Thermal Performance of Nano Fluids in Microchannel Heat Exchanger

Experimental study on turbulent convective heat transfer, pressure drop, and thermal performance characterization of ZnO/water nanofluid flow in a circular tube

In this experimental study heat transfer and pressure drop behavior of ZnO/water nanofluid flow inside a circular tube with constant wall temperature condition is investigated where the volume fractions of nanoparticles in the base fluid are 1% and 2%. The experiments? Reynolds numbers ranged roughly from 5000 to 30000. The experimental measurements have been carried out in the fully-developed turbulent regime. The results indicated that heat transfer coefficient increases by 11% and 18% with increasing volume fractions of nanoparticles respectively to 1% and 2% vol. The measurements also showed that the pressure drop of nanofluids were respectively 45% and145% higher than that of the base fluid for volume fractions of 1% and 2% of nanoparticles. However experimental results revealed that overall thermal performance of nanofluid is higher than that of pure water by up to 16% for 2% vol. nanofluid. Also experimental results proved that existing correlations can accurately estimate nanofluids convective heat transfer coefficient and friction factor in turbulent regime, provided that thermal conductivity, heat capacity, and viscosity of the nanofluids are used in calculating the Reynolds, Prandtl, and Nusselt numbers.

An Experimental Study on Thermal Performance of Nano Fluids in Microchannel Heat Exchanger

The enhancement of heat transfer performance in heat exchanger is achieved by reducing the size of the hydraulic diameter or by using a working fluid that has a better thermal conductivity compared to conventional working fluids. The application of a small hydraulic diameter can be found in the microchannel heat exchanger (MCHE). The design and the testing of the MCHE were done in this research. The MCHE was tested with several working fluids, such as the distilled water, the Al2O3-water nanofluids at 1%, 3% and 5% volume concentration, and the SnO2-water nanofluids at 1% volume concentration. The temperature of inlet and outlet were set at 50 o C and 25 o C, respectively. The variations of flow rate at the inlet were applied from 100 ml/min up to 300 ml/min. The addition of nanoparticle in the base fluid was proven to improve the heat transfer of the MCHE, the 5% Al2O3-water and 1% SnO2-water nanofluids are able to absorb the heat 9% and 12% higher than the base fluid. The overall heat transfer coefficient of MCHE with 5% Al2O3-water and 1% SnO2-water nanofluids were 13% and 14% higher than the base fluid.

Effect of nanoparticles size on thermal performance of nanofluid in a trapezoidal microchannel-heat-sink

This paper deals with spherical nanoparticles size effects on thermal performance and pressure drop of a nanofluid in a trapezoidal microchannel-heat-sink (MCHS). Eulerian–Eulerian two-phase numerical approach is utilized for forced convection laminar, incompressible and steady three dimensional flow of copper-oxide nanoparticles with water as base fluid at 100 to 200nm diameter and 1% to 4% volume concentration range. Continuity, momentum, energy and volume conservation equations are solved at whole of the computational domain via finite volume method. Obtained results signify that pressure drop increases 15% at Re=500 and 1% volume concentration while nanoparticles diameter increases from 100 to 200nm. By increasing volume concentration, nanoparticles size effect becomes more prominent and it is observed that increment rate of pressure drop is intensified for above 150nm particles diameter. Unlike the pressure drop, heat transfer decreases with an increase in nanoparticles diameter. Also, it is observed that with an increase in nanoparticles diameter, average Nusselt number of base fluid decreases more than that of the nanoparticles and this signifies that base fluid has more efficacy on thermal performance of copper-oxide nanofluid.

Thermophysical property-based evaluation of mixed convection performance and criteria of forced-mixed transition for nanofluids

This study investigates the hydrodynamic and thermal performance of nanofluids in the region of thermal developing laminar mixed convection. Single-phase approach was employed to evaluate the pumping power and heat transfer coefficient, i.e., no novel mechanism other than the renewing thermophysical properties of nanofluids was involved. An aggregation-mechanism-based methodology was introduced and verified to well unify the rheological and thermal properties of nanofluids. In comparing the pumping power savings, critical differences between forced convection and mixed convection were found: nanofluids are more favorable for application to mixed convection. Criteria for nanofluid forced-mixed transition have been discussed and presented to help the decision of whether a flow can be viewed as mixed flow.

Experimental study of forced convective heat transfer of nanofluids in a microchannel

The forced convective heat transfer for flow of water and aqueous nanofluids (containing colloidal suspension of silica nanoparticles) inside a microchannel was studied experimentally for the constant wall temperature boundary condition. Applications of nanofluids have been explored in the literature for cooling of micro-devices due to the anomalous enhancements in their thermo-physical properties as well as due to their lower susceptibility to clogging. The effect of flow rate on thermal performance of nanofluid is analyzed in this study. Variations of thermo-physical properties of the nanofluid samples were also measured. The experimental results show that heat transfer increases with flow rate for both water and nanofluid samples; however, for the nanofluid samples, heat transfer enhancements occur at lower flow rates and heat transfer degradation occurs at higher flow rates (compared to that of water). Electron microscopy of the heat-exchanging surface revealed that surface modification of the microchannel flow surface occurred due to nanoparticle precipitation from the nanofluid. Hence, the fouling of the microchannels by the nanofluid samples is believed to be responsible for the progressive degradation in the thermal performance, especially at higher flow rates. Hence, these results are observed to be consistent with previous experimental studies reported in the literature.

Thermal performance and pressure drop analysis of nanofluids in turbulent forced convective flows

In this research the enhancement of nanofluids convective heat transfer through a circular tube with a constant heat flux condition in the turbulent flow regime is numerically studied. All of the nanofluid properties depend on temperature and nanoparticle volume concentration. The incompressible and steady-state forms of continuity, Navier–Stokes and energy equations have been solved using finite volume approach with the SIMPLER algorithm. In order to demonstrate the validity and precision of the numerical procedure, calculated friction factors and Nusselt numbers have been compared with the experimental data and the well-known correlations. To attain the best prediction, the different turbulence models are examined and it has been observed that the best model to predict the near wall treatment is based on enhanced wall function in the κ–ɛ turbulence model. The effects of nanoparticle concentration (1–10% Al2O3) in EG/water mixture, Reynolds and Prandtl numbers on the heat transfer rate have been investigated. A dimensionless effectiveness quantity has been defined to measure the thermal performance of nanofluid in comparison with the base fluid with the same Reynolds number. But for a fixed pumping power, due to more increase of viscosity, the nanofluids heat transfer coefficient has been decreased by adding nanoparticle concentration. From the results, it can be deduced that for a fixed Reynolds number, increasing the particle concentration enhances convective heat transfer rate considerably. Moreover, there is a large pressure drop and pumping power when using nanofluids instead of base fluid with the same Reynolds number. Thus using nanofluids may be not a good candidate for the practical applications in turbulence region, in which an increase in pumping power is an important problem.