| dc.description.abstract | This study develops a two-pass diverging microchannel heat exchanger to improve the two-phase flow instability in a microchannel heat exchanger used for the thermal management of high-power electronics. We totally designed three types of two-phase evaporative heat exchangers, including single-pass straight microchannel, two-pass straight microchannel, and two-pass diverging microchannel, and compared the performance of each type. Three types of microchannel have the same heat transfer area. Both single-pass and two-pass straight microchannel fin spacing and fin height are 1 mm and 3 mm, while the two-pass diverging microchannel fin spacing increase from 0.6 mm at the entrance to 1.4 mm at the exit with 0.449o diverging angle, and the height also 3 mm.
The experiment results show that a two-pass microchannel would increase the pressure drop of the heat exchanger at the same flow rate, because of the shorter channel length and lower mass flux of the single-pass microchannel. There is no significant pressure drop difference between two-pass straight and two-pass diverging microchannels.
Under the condition of high heat flux, the single-pass straight microchannel would be blocked by the large bubble causing the channel surface partial dry-out and decreasing the heat transfer performance. For the same condition in the two-pass microchannel. Due to the heat transfer between neighboring channels suppressing the bubble growth near the exit of the channel, the flow pattern can maintain bubble flow and increase the heat transfer performance. There is no obvious heat transfer performance difference between two-pass straight and two-pass diverging microchannel before partial dry-out happened. Owing to a more stable two-phase flow in the diverging microchannel, the two-pass diverging microchannel has the best heat transfer performance of the three types of microchannels.
In addition, using two-pass diverging microchannel to improve the single-pass straight microchannel has 27 % to 35 % increment of heat transfer coefficient, decreasing the minimum thermal resistance from 0.035 to 0.026 K/W, while with 126% increment of pressure drop. | en_US |