Flow boiling performance and bubble behaviors of non-closed droplet micro pin-fin arrays

Abstract

Bubble characteristics are closely related to the thermal-hydraulic performance of working fluid in micro scale. This study aimed to investigate the flow boiling performance of non-closed droplet micro pin-fin arrays and bubbles behaviors in three different regions around micro pin-fins. Deionized water was selected as coolant, circulating under heat flux in the range of 2.51–144.64 W/cm2, of which high-speed images were attained, showing the flow field behaviors of coolant and the growth characteristics of bubbles at nucleate boiling. The experiments were carried out as mass flow rate ranging from 53.41 to 266.92 kg/(m2·s), and comparative analysis on flow and thermal performance were conducted. The visualization results presented that the flow boiling behavior of coolant could be divided into four states: single-phase flow, sub-cooled boiling, nucleate boiling and transition boiling state. The waiting time and growth time of bubbles in region III were smaller than that in region II, which was shown closely related to the larger flow velocity of coolant. The pressure drop of non-closed droplet micro pin-fin arrays underwent three stages as the rise of heat flux. The heat transfer coefficient could be ascended by increasing the mass flow rate during flow boiling.