The Critical Heat Flux Condition With Water in a Uniformly Heated Microtube

The critical heat flux (CHF) condition needs to be well understood for designing miniature devices involving two-phase flow. Experiments were performed to determine the CHF condition for a single stainless steel tube having an inside diameter of 0.427mm subjected to uniform heat flux boundary conditions. The effects of mass flux, pressure, and exit quality on the CHF were investigated. The experimental results show that the CHF increases with an increase in mass flux and exit pressure. For all exit pressures, the CHF decreased with an increase in quality in the subcooled region, but with a further increase in quality (near zero quality and above), the CHF was found to have an increasing trend with quality (up to about 25% quality). CHF values in this region were much higher than those in the subcooled region. This suggests that even at very low qualities, the void fraction becomes appreciable, which results in an increase in the average velocity, thereby increasing the CHF limit.