Wall heat flux partitioning during subcooled flow boiling of NaCl solutions and pure water

Abstract

A careful evaluation on the wall heat flux partitioning is of great importance for the deep understanding the nucleate flow boiling heat transfer to saline solution. In this work, the portion of each heat transfer contribution was analyzed through wall heat flux partitioning model after model validation. The key parameters used in the model were discussed and the reasonable values were determined. The experimental data of bubble departure diameter, departure frequency, active nucleation site density, bubble waiting time and growth time, were combined into the model to eliminate the uncertainties of empirical closure sub-models. The comparison of heat flux partitioning of subcooled flow boiling between NaCl solution and pure water was presented under different operating conditions. The results showed that for the operating conditions of Qw > 180 kW/m2 or G < 400 kg/(m2·s), the contribution of single-phase liquid convection in the heat transfer of saline solution is greater than that in pure water, due to the bigger bubble diameter and more intensive bubble-induced turbulence. Quenching heat flux for NaCl solution is lower than that in pure water, owing to the smaller bubble departure frequency. For the lower heat flux or higher mass flux conditions, however, the contrary trend was observed. The dominant heat transfer mechanisms for solution and pure water during subcooled nucleate flow boiling were revealed. The interactions between bubble dynamic and heat transfer characteristics were carefully investigated.