Simulation Study Of Vertical Tube Hfc-134a Low Pressure Over Subcooled Flow Boiling

On the consideration of environment protecting, HFC-134a is one of the most popular choices as the alternative refrigerants. So it is important to known heat transfer characteristics of it at different conditions. On the other hand, because the heat transfer coefficient of subcooled flow boiling is much larger than that of single-phase flow, subcooled flow boiling can enhance heat transfer and decrease heat transfer temperature difference. Owing to subcooled flow boiling usually arises at the front part of the flow; it could affect the other part of the flow. For example, it is reported that oscillation and pressure shakes in flow boiling are formatted at subcooled flow boiling area. Due to the intricacy of flow boiling and skimble-scamble mechanism, few research results are reported about subcooled flow boiling with HFC-134a.Base on the mechanism of water subcooled boiling at low pressure flow. The paper built up a physical model and a mathematical model for subcooled flow boiling of HFC-134a. On account of the partition of the wall heat flux, the Bowring's mechanism model is used. According to this mechanism, the inward wall heat flux is divided into three parts: the first is used to generate vapor, the second is to the superheated layer and nucleate boiling or surface quenching, and the third is to turbulent convection. The heat obtained by liquid is also considered as three parts accordingly: turbulent convection, surface quenching, and vapor condensation in subcooled liquid. The evaporation heat flux is proportional to the energy required for nucleation of a single bubble, the number of active nucleation sites per unit wall area and the bubble nucleating frequency.Based on the mechanism, the paper formed a simulated phase changing model, and the mixture multiphase model was used to simulate two-phase...