Experimental study of flow boiling characteristics in minigap channels over a wide heat flux range

The flow boiling characteristics in minigap channels were investigated by observing the two-phase flow patterns, measuring the two-phase pressure drops, and calculating the two-phase heat transfer coeffi-cients and critical heat fluxes in minigap channels with heights of 0.5-2 mm. The working fluid was deionized water with mass fluxes of 20 0-40 0 kg m-2 s -1. The results show that bubbly flow, sweep-ing flow, churn flow, and churn-annular flow occur in sequence with increasing heat fluxes. An unsta-ble two-phase flow regime was observed during the sweeping flow. The pressure drop varied in three regimes that were related to the flow patterns. The maximum pressure drops are 12.2, 3.8 and 1.6 kPa, respectively in 0.5 mm, 1 mm and 2mm channels at 400 kg m-2 s -1. The effect of gap height on the heat transfer coefficient first increases and then decreases with increasing heat flux. The heat transfer coefficients of all channels are at a high level when the heat flux is high. The maximum heat transfer coefficients are 7.3, 6.9 and 5.8 W cm-2 K-1 in the 0.5 mm, 1mm and 2mm channels at 400 kg m -2 s -1, which occurred before critical condition. The critical heat flux increased with increasing mass flux and gap height. In addition, a pressure drop correlation was developed to more accurately predict the pres-sure drop in microgap channels with an accuracy of 10.8%. The Liu-Winterton correlation and the Shah correlation give the best predictions for the subcooling boiling heat transfer coefficient. The Sun-Mishima correlation and the Kandlikar correlation provide the most accurate predictions for the saturated boiling heat transfer coefficients.(c) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The flow boiling characteristics in minigap channels were studied by analyzing the two-phase flow patterns, measuring pressure drops, and calculating heat transfer coefficients and critical heat fluxes. Results showed that different flow patterns occur with increasing heat fluxes. The gap height has an impact on the heat transfer coefficient. The critical heat flux is influenced by mass flux and gap height.