The Effects of Microchannel Geometry on Phase Transition for Two Phase Flow in Microchannel Heat Sinks

Abstract

Abstract. The effects of microchannel geometry on the phase transition between liquid and vapour for the two phase flow were investigated both numerically and experimentally. In the study the rounded edge rectangular microchannel heat sink was found to have the phase transition earlier than the rectangular one in both numerical simulation and experimental data by about 1.5 seconds. The outlet temperature and vapour quality of the rounded edge rectangular microchannel heat sink was higher than those obtained from the rectangular microchannel heat sink. Also, the phase transition curves achieved in the evaporation were parabolic in shape. The output vapour temperature achieved a steady state with the maximum value at around 2 minutes, 30 seconds. In addition the numerical results matched well with the experimental data. These numerical results have not yet been seen in literature reviews.Keywords: Microchannel, two phases, temperature, numerical simulation, experiment. IntroductionIn recent years the heat transfer behaviour of the two phase flow in microchannels has become an interesting topic. Regarding the microchannel heat transfer fields, Yun et al.[1] investigated in the boiling heat transfer coefficients and the two-phase pressure drops of rectangular microchannels. The microchannels have a hydraulic diameter of 1.36 and 1.44 mm. R410A was used as the working fluid and the heat flux obtained was from 10 to 20 kW/m2. The results showed that the boiling heat transfer coefficients in the microchannels were much higher than those in single tubes under similar test conditions. In addition, they also showed that the pressure drop accelerated with the increasing mass flux at a constant saturation temperature. Also in addition, the pressure drop decreased with an increasing saturation temperature at a given mass flux, Schilder et al.[2] studied the pressure drop and the convective heat transfer characteristics in a circular tube with a diameter of 600 µm and with the working fluid being ethanol. The experiments were carried out for both the two phase flow and single phase flow. The results showed that the mean pressure drop for two phase flow was about three times higher than that for the single phase flow. The Nusselt number for the two phase flow was not dependent on the heat flux and increased with raising the mass flux. The alternating slanted passage in the channel wall as a secondary flow was investigated by Kuppusamy et al. [3]. The results showed that when comparing the alternating slanted passage microchannel heat sink with the conventional one the overall performance of the microchannel heat sink with alternating slanted passage increased by 146% and the thermal resistance reduced to 76.8%. Ergu et al.[4] studied the pressure drop and local mass transfer of the rectangular microchannel with a hydraulic diameter of 208 µm. The microchannels have a width of 3.70 mm, a height of 0.107 mm and a length of 35 mm. Distilled water was used to measure the pressure drop and was also used as the working fluid. Reynol...