Abstract：

A numerical simulation study is carried out to investigate the heat transfer characteristics of the flow boiling in a vertical rectangular narrow channel applied to a rising film heat exchanger, to clarify the heat transfer characteristics of the flow boiling at each stage in the channel, and to provide a reference for the design of efficient heat transfer equipment. A vertical rectangular narrow channel model with a size of 1 400 mm×250 mm×3 mm is established, and the multiphase flow VOF model is used to obtain the temperature, vapor phase and velocity distributions in the channel at different heights. The two-phase flow is divided into sub-regions, and the bubble motion is analysed. The heat transfer characteristics and the influencing factors in each sub-region are also quantitatively analysed in combination with the flow pattern. The results show that the flow pattern during flow boiling mainly includes bubble flow, slug flow, churn flow and stirred flow. Increasing the inlet temperature can enhance the local heat transfer in the partially developed nucleate boiling phase, but has less effect on the fully developed nucleate boiling phase. Increasing the mass flux can weaken the heat transfer in the initial nucleate boiling phase, but enhances the heat transfer in the region far from the vaporization core. The heat transfer characteristics of different regions vary with the trend of the vapor quality.

Keywords:narrow channel; flow boiling; heat transfer characteristic; surface heat transfer coefficient; flow pattern; vapor quality; plate heat exchanger