Effect of Heater Sizes on Critical Heat Flux and Enhancement using Discretized Heating Elements with Constant Temperature Wall Condition

Abstract

Considering the limitations of previous studies on heater size effects on CHF and the actual geometry of conventional chips, the rectangular-type heaters are fabricated and experimentally investigated. To exclude the effect of pressure, sub-cooling, and heater orientation, the experiments are conducted as saturated boiling under atmospheric pressure conditions using upward facing heaters. Seven different surfaces by changing the geometries of micro-pillar structures are fabricated and tested to further enhance CHF. In each surface, four different heater configurations are fabricated by changing both heating width (the shorter one of two side lengths) and length (the longer one). Among the experimental cases, maximum CHF of 3043 kW/m² (Surface: D40G20H20+SiO₂, 4X15 mm²) and minimum CHF of 696 kW/m² (Smooth SiO₂, 16X40 mm²) are experimentally confirmed. Among 7 groups, group 2 showed a minimum CHF difference of 232 kW/m², and group 7 showed a maximum CHF difference of 1316 kW/m² for give heater configurations. For surfaces with poor wettability, width shows dominant effect on CHF whereas samples with good wettability showed similar dependency of both heating length and width. Besides, we find different behavior of post-CHF condition for samples with small effective heater size. They maintain nucleate boiling phenomena for certain period without rupture and even go back to temperature before CHF in some case. Based on this, we thought the heating elements that can maintain constant temperature could enhance CHF further. We fabricated discretized heating elements (DHE) to induce constant temperature wall condition. Using DHE, we confirmed CHF enhancement of 16%.