No abstract

Flow instabilities are one of the main challenges in the field of microchannel flow boiling. They modify the hydrodynamics and can lead to premature critical heat flux (CHF). To overcome these instabilities, geometrical adjustments such as inlet constrictions have proven to be very effective. Notwithstanding the effectiveness of these structures in preventing instabilities, so far only a few inlet restrictions have been discussed in the literature. For this reason, two different restrictions to suppress flow boiling instabilities were tested in this work and compared to a channel configuration without restriction. In addition, the single-phase pressure drop was measured to determine the impact of the restrictions on the pressure loss at the inlet. In all experiments, degassed DI water was used as working fluid and the mass flow rate ranged from 0.95 to 67.62 g/min. The heating power was 0 W for the adiabatic single-phase pressure measurements and 12 W for the flow-boiling instability studies. It was found that only one of the two inlet modifications could prevent flow boiling instabilities such as bubble clogging and flow reversal. At the same time, the part of this restriction that was crucial for flow stabilization had the least effect on the single-phase pressure drop in the microchannel.