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Abstract This work investigates experimentally the cooling performance of Al 2 O 3 /water nanofluid with 8 wt% concentration flowing through a minichannel heat sink with a MEPCM layer in its ceiling. The hydrothermal characteristics of the nanofluid-cooled minichannel heat sink are analyzed and the dimensionless wall temperature distribution, Nusselt number, heat transfer effectiveness, coefficient of performance, figure of merit, and wall temperature thermal resistance are assessed. The measured results show that the dispersion of alumina nanoparticles inside pure water declines the wall temperature and consequently enhances the heat transfer effect and Nusselt number augments. The maximum values of average heat transfer effectiveness and FOM at the inlet of the MCHS are achieved 1.4 and 1.27 by flowing nanofluid with 8 wt% nanoparticle concentration and Re = 1549, respectively. The results revealed that embedding MEPCM layer in the ceiling of the MCHS has little influence on the cooling performance of Al 2 O 3 /water nanofluid in the minichannel heat sink. [ABSTRACT FROM AUTHOR]

Abstract The present study demonstrates, via a numerical simulation, the feasibility of achieving enhanced forced convection heat transfer of laminar water flow in an isoflux heated circular tube by inserting a concentric circular tube and controlling the concurrent flow distribution through the resulting concentric double-tube duct. Under identical operation conditions to those for the parent single-tube flow configuration, including the inlet fluid temperature, the total volumetric flow rate, the length of heated section, as well as the wall heat flux imposed, numerical simulations have been undertaken for the thermally developing convective heat transfer characteristics of water flow in the concentric double-tube duct featuring geometrically by three different relative radius ratio r o (= 1.2, 1.5, 1.8), compared with its parent single-tube duct of l h,ST = 0.1 at Re ST = 100, 500, and 1000, respectively. In terms of the local and length-averaged heat transfer effectiveness gauged against that obtained for the parent single-tube duct, numerical results clearly demonstrate that the double-tube duct of smaller r o operating with relative larger flow rate than that in the inner tube can serve as highly effective heat transfer enhancement configuration. [ABSTRACT FROM AUTHOR]

In this work, the augmentation in the hydrothermal performance of parallel and divergent minichannel heat sinks (MCHSs) containing microencapsulated phase change material (MEPCM) suspensions is investigated. Accordingly, the effect of diverging minichannels with the angles of 1.38° and 2.06° on the pressure drop and heat transfer performance in the presence of 2%, 5%, and 10% MEPCM particles at different Reynolds numbers from 238 to 1375, under various different heat fluxes of 3.2 × 10 4 , 4 × 10 4 , and 4.8 × 10 4  W/m 2 , with the inlet temperature of 34 ± 0.2 °C is evaluated. The results also compared with the corresponding data in a parallel MCHS. It was found that the implementation of MEPCM suspension yielded to the increase of both the heat transfer and pressure drop. Diverging the minichannels and incrementing its angle significantly reduced the pressure drop penalty, especially at higher Reynolds number and greater mass fractions. The heat transfer effectiveness was also increased by diverging the minichannels with the angle of 1.38°, especially for higher concentrations and higher heat fluxes. The increment of the divergence angle to 2.06° had a detrimental impact on the thermal performance of the suspension and decreased the heat transfer coefficients to even less that that in the parallel MCHS. The results reveal that diverging the minichannels can effectively intensify the contribution of MEPCM suspensions in heat sinks in a certain range of parameter combinations. [ABSTRACT FROM AUTHOR]

In the present study, experimental efforts have been performed to explore the forced convection heat transfer using water-based suspension of Al 2 O 3 nanoparticles (nanofluid) to replace the pure water as the working fluids in circular tubes. The nanofluid was prepared as a functional forced convection fluid and the thermal properties including the density, thermal conductivity, and dynamic viscosity were investigated experimentally. Besides, forced convection heat transfer in circular tubes was investigated with water-based nanofluid containing various mass fractions of the Al 2 O 3 nanoparticles (2, 5, and 10 wt%) under the following operating conditions: the volume flow rate Q f = 23.6–183.5 cm 3 /min (the Reynolds number Re f ,0 = 188–2095), the heating power applied at the outer wall of the tube q o , eff . ″ = 1908–7362 W/m 2 , and the inlet fluid temperature T in = 24.5–25.5 °C or 49.5–50.5 °C. Measured data showed that the dispersion of increasing mass fraction of Al 2 O 3 nanoparticles can effectively improve the thermal conductivity relative to the pure water. Besides, higher average heat transfer effectiveness ε − h , btd and figure of merit FOM are noted for the cases with higher inlet fluid temperature T in . [ABSTRACT FROM AUTHOR]

This paper aims to investigate the Rayleigh–Bénard convection of Al 2 O 3 /water nanofluids in a cavity considering the sedimentation, thermophoresis, and Brownian motion. For this purpose, a numerical simulation is carried out using finite volume method to obtain the flow patterns and heat transfer characteristics of nanofluid flow inside the cavity. The results are presented for volume fractions up to 4%, Rayleigh numbers between 10 4 and 8 × 10 4 where the temperature difference between top and bottom walls is between 2 and 10 °C. To validate the numerical solution, comparisons are made between the numerical results and experimental data available in the literature. The comparisons unfold that the results of numerical work are in a good agreement with the previous experimental results. [ABSTRACT FROM AUTHOR]

The present study aims to explore experimentally the influence of elevated inlet fluid temperature on the turbulent forced convective heat transfer effectiveness of using alumina–water nanofluid over pure water in an iso-flux heated horizontal circular tube at a fixed heating power. A copper circular pipe of inner diameter 3.4 mm was used in the forced convection experiments undertaken for the pertinent parameters in the following ranges: the inlet fluid temperature, T in = 25 °C, 37 °C and 50 °C; the Reynolds number, Re bf = 3000–13,000; the mass fraction of the alumina nanoparticles in the water-based nanofluid formulated, ω np = 0, 2, 5, and 10 wt.%; and the heating flux, q o ″ = 57.8–63.1 kW/m 2 . The experimental results clearly indicate that the turbulent forced convection heat transfer effectiveness of the alumina–water nanofluid over that of the pure water can be further uplifted by elevating its inlet temperature entering the circular tube well above the ambient, thereby manifesting its potential as an effective warm functional coolant. Specifically, an increase in the averaged heat transfer enhancement of more than 44% arises for the nanofluid of ω np = 2 wt.% as the inlet fluid temperature is increased from 25 °C to 50 °C. [ABSTRACT FROM AUTHOR]

Abstract: A hybrid water-based suspension of Al2O3 nanoparticles and microencapsulated phase change material (n-eicosane) particles (MEPCM) was prepared as a functional forced convection fluid and the thermal properties of the resulting ternary suspension including the density, specific heat, thermal conductivity, latent heat of fusion, and dynamic viscosity were investigated experimentally. It was found that the dispersion of increasing fraction of Al2O3 nanoparticles can effectively improve the intrinsic characteristics of low thermal conductivity of the pure PCM suspensions, resulting even in significantly enhanced thermal conductivity relative to the pure water. [Copyright &y& Elsevier]

Abstract: In this study, phase change material (PCM) embedded by nanoparticles was prepared by emulsifying alumina (Al2O3) nanoparticles in paraffin (n-octadecane) by means of a non-ionic surfactant. The formulated nanoparticle-in-paraffin emulsions contain the nanoparticles of 5 wt.% and 10 wt.%, respectively; their effective thermophysical properties, such as latent heat of fusion, density, dynamic viscosity, and thermal conductivity, were investigated experimentally. The experimentally measured density of the emulsions agrees excellently with that predicted based on the mixture theory. The measured thermal conductivity and dynamic viscosity for the nanoparticle-in-paraffin emulsions formulated show a nonlinear increase with the mass fraction of the nanoparticles compared with that for the pure paraffin, depending on the temperature. [Copyright &y& Elsevier]

In this paper, an experimental investigation is carried out to evaluate the heat dissipation performance of the parallel mini-channel heat sink with the latent heat cooling ceiling. The heat sink is under the influence of an isothermal heating from the below. To enhance the cooling capacity of the system, the alumina/water nanofluid with various mass fractions of nanoparticles is considered as the working fluid. A micro-encapsulated phase change material layer is installed on the ceiling of the heat sink to cool down the fluid along the length of the heat sink. The experiments are performed for different values of mass fraction of nanoparticles, Reynolds number, mean temperature of bottom wall, inlet temperature of fluid, and mean temperature of cooling upper plate. The effects of these parameters on the friction factor, the mean Nusselt numbers dependent on the inlet and bulk temperatures difference, and the coefficient of performance are investigated. The experimental results indicate that the inlet temperature of the nanofluid has negligible effects on the friction factor for the base fluid Reynolds numbers of 483 and 968. However, the friction factor decreases as the inlet temperature increases for the base fluid Reynolds number of 161. The mean Nusselt numbers dependent on the inlet and bulk temperatures difference decrease by using a working fluid with the higher inlet temperature. The coefficient of performance increases with increasing the mean temperature of bottom wall from 50 °C to 55 °C. Finally, the mean temperature of cooling upper plate has negligible influences on the coefficient of performance. [ABSTRACT FROM AUTHOR]

The minichannel heatsink is one of the small heat exchangers, having high heat capacity and being able to remove substantial heat within a very small volume, in line with the current demand for heat dissipation of electronic components. In the present study, the convection cooling characteristics in a rectangular minichannel considering wall conduction effect was investigated numerically. Numerical simulations are performed under 2% and 10% volume fractions of PCM particles (n-eicosan). The results reveal that the axial wall conduction plays a more pivotal role in the minichannels at the lower Reynolds number. Besides, the employment of phase change nano-emulsion in the working fluid in the rectangular minichannel suppresses the wall temperature and improves the heat transfer performance up to 4.23% and 9.36%, respectively, compared with the application of pure water. In addition, it is demonstrated that a high concentration of PCM particles may have detrimental effect on pressure drop and extended wall heat dissipation efficiency under certain circumstances thus the concentration of PCM particles needs careful selection. [ABSTRACT FROM AUTHOR]