Flow boiling heat transfer performance in phase separation structure countercurrent microchannel under the action of pin electrodes

The purpose of this study is to explore the boiling heat transfer performance of microchannel flow under the combination of two enhanced technologies of pin electrodes and phase separation structure. Therefore, a parallel bidirectional microchannel heat sink was proposed to realize the gas-phase separation by switching high and low pressure for the downstream and countercurrent microchannels. Ethanol was taken as an experimental working fluid, while the modified polyvinylidene fluoride (PVDF) was as a gas-liquid phase separation tool. Then the flow boiling experiment was carried out under the conditions of inlet supercooling at 10 °C and effective heat flux range of 48.08 - 87.29 kW/m², where other experimental conditions remained the same. Furthermore, the heat transfer enhancement factor of saturated boiling heat transfer coefficient (F_ht) was introduced to investigate the boiling heat transfer mechanism in the microchannel under the combination of the number of pores in different phase separation structures (4-hole PSS-1, 6-hole PSS-2, 10-hole PSS-3) (phase separation structure, PSS) and different electric field strengths (200, 400 and 600 V). The results show that the heat transfer performance of the microchannel under the action of the single-phase separation structure and the pin electrodes was effectively improved under the same working conditions, compared with the ordinary microchannel (0 V without electric field and 0-hole PSS-0 without phase separation structure). The number of opening holes shared a strong correlation with the enhanced heat transfer of the phase separation structure. The maximum Fht of the phase separation structure was 1.14 at a heat flux of 80 kW/m², with an increase in the number of opening holes. There was the strengthening effect of the electric field on small or confined bubbles, with small lengths and diameters. An outstanding strengthening was found under the condition of low and medium heat flux, such as the maximum Fht under pin electrodes was 1.20 at a heat flux of 65 kW/m². The heat transfer performance of the microchannel was further improved under the combined role of phase separation structure and pin electrodes, in which the maximum F_ht was 1.29. In addition, the electric field was introduced to improve the strengthening effect of the phase separation structure at low heat flux density. The phase separation structure also effectively enhanced the strengthening effect of the electric field at high heat flux density, indicating the synergistic effect. In addition, the comparison was made on the effects of phase separation structure and electric field enhancement on the heat transfer of micro-channel boiling under the condition of mass flow rate (86.11 and 172.11 kg/(m²·s) of the two groups. The results show that the strengthening effect of phase separation during the boiling heat transfer of the microchannel was weakened at the high mass flow rate, compared with the low one. The strengthening effect of the electric field was enhanced, according to the influence of fluid flow rate. And there was little difference in the enhanced effect of boiling heat transfer under the two mass flow rates. The finding can provide a strong reference for the phase separation structure combined with the electric field.