The effect of heater dimensions with different liquid penetration lengths to dry spots on critical heat flux

Abstract

• Depending on heater dimension, CHF increased 106% for water and 46% for Novec TM 7100. • Growth and rewetting time scale of dry spot at the center are compared for the CHF. • Width, the shorter of two side lengths, affect the velocity within macrolayer. • The average velocitiy within macrolayer affect the rewetting velocity and CHF. The Critical Heat Flux (CHF) on different heater dimensions for two different working fluids were experimentally evaluated. For a given boiling surface (SiO 2 ), the CHF differences were 107% for water and 46% for NOVEC TM 7100 under different heater dimensions. These differences were not describable with previous studies correlating the CHF with the characteristic length for a given heater dimensions. To understand the effect of the heater dimensions on the CHF, we compared the dry-spot growth time-scale and rewetting time-scale of the dry spot created at the center of the heating surface. The analysis showed that the average velocity in the macrolayer depends on the liquid penetration length, which is the shortest flow path from the end to the center of the heater. The average velocity in macrolayer affect the rewetting velocity and finally the CHF. Based on the analysis considering the dry-spot rewetting phenomena, the dependence of CHF on heater dimension for two different working fluids was well described in this study.