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Showing 2 results for Microchannels
Hamidreza Ermagan, Roohollah Rafee,
Volume 17, Issue 7 (9-2017)
Abstract
In the present study, thermal performance of a microchannel heat sink with superhydrophobic walls is studied for different ratios of the wall convergence. To this end, three-dimensional Navier-Stokes equations and energy equation subject to the slip boundary conditions, viz. velocity slip and temperature jump, are numerically solved using the finite volume method. Then, the variations of thermal resistance of the heat sink with the number of channels, width- and height-tapered ratios, are studied for a fixed pumping power. The results show that by utilizing the superhydrophobic walls, the optimum width-tapered ratio of the channel is higher than that of the hydrophilic walls. The accentuated effect of the number of channels on thermal performance in the presence of liquid-solid interfacial slip weakens the effect of converging the width of the channel. It is also revealed that the optimum number of channels also increases to give prominence to the effect of interfacial slip by diminishing the smallest dimension of the channel. Finally, it is shown that for a pumping power of 0.05 W, using a heat sink with converging microchannels and superhydrophobic walls, reduces the overall thermal resistance by 28 percent, compared to that with conventional microchannels. In fact, the increase in fluid flow rate resulting from the use of converging microchannels with superhydrophobic walls outweighs the undesirable effect of temperature jump on heat transfer, in a sense that the heat sink performance augments considerably.
M. Khayat, M. Mohebie,
Volume 19, Issue 11 (11-2019)
Abstract
This study aims to investigate the effect of nanoparticle deposition on the boiling surface in the presence of microchannel on the characteristics of boiling heat transfer. In this experimental study, the copper boiling surfaces including polished circular surface, rectangular and trapezoidal microchannels were used. The microchannels include feeding sub-channels perpendicular to the main channel, which increases the boiling surface and separates the downward cool fluid flow and upward hot bubbles. Nuclear boiling experiments on microchannel surfaces in the presence of a hybrid water-based nanofluid containing 70% titanium oxide and 30% OH-based multi-wall carbon nanotubes in volumetric concentrations of 0.1% and 0.5% have been conducted. The results of nanofluid boiling experiments on both microchannel surfaces show that with increasing concentrations, critical heat flux and heat transfer coefficient increases and the highest increase in critical heat flux and heat transfer coefficient is related to the hybrid nanofluid with 0.5 % volumetric concentration on the surface with trapezoidal microchannel and their values are 64.64% and 344.76%, respectively, compared to pure water boiling on the polished copper surface. Also, in boiling of pure water on the deposited surfaces with nanoparticles, the greatest increase in critical heat flux and heat transfer coefficient is related to the surface with trapezoidal microchannels with 0.1% volumetric concentration and 0.5% and volumetric concentration and their values are 120.16% and 149.4% respectively, compared to pure water boiling on the polished copper surface.
