An Analysis of Saturated Critical Heat Flux in Micro/Mini-Channels

This paper verified the macro-to-micro-scale transitional criterion $BoRel0.5$ = 200 proposed by Li and Wu [W. Li, Z. Wu, A general criterion for evaporative heat transfer in micro/minichannels, International Journal of Heat and Mass Transfer 53 (2010) 1967–1976] because data points where $BoRel0.5$ ≤ 200 and $BoRel0.5$ > 200 show very different trends for the entire database (1,672 data points). For the 859 data points with $BoRel0.5$ ≤ 200, the boiling number at CHF decreases greatly with length-to-diameter ratio L_h/d_he when L_h/d_he is small, while L_h/d_he presents negligible effect on the boiling number when L_h/d_he > 150. For the region where L_h/d_he ≤ 150 and $BoRel0.5$ ≤ 200, a simple saturated CHF correlation was proposed by using the boiling number, length-to-diameter ratio, and exit quality. Heated length and heated equivalent diameter were adopted in the length-to-diameter ratio, considering the actual heat transfer conditions. A combined dimensionless number $WemCal0.8$ was introduced to correlate the micro/mini-channel database for the region: L_h/d_he > 150 and $BoRel0.5$ ≤ 200. The new method can predict the overall micro/mini-channel database accurately on the whole. It can predict almost 95.5% of the non-aqueous data and 93.5% of the water data within the ± 30% error band.