A phase field method for simulation of subcooled flow boiling in a rectangular channel

A Cahn-Hilliard phase-field method, in the context of the spectral element method, has been developed to simulate boiling heat transfer in practical engineering problems, where the density ratio between the liquid and vapor phases can exceed 1000. In our method, the boiling model is applied only to mesh elements across the liquid/vapor interface and their neighboring elements, to avoid the non-physical generation of bubbles due to numerical errors. Additionally, a smearing technique based on the Helmholtz equation derived from the semi-discretized Cahn-Hilliard equation is employed to ensure numerical stability, especially in cases with high heat flux. To simulate flow boiling with subcooling, we adopt a nucleation site density correlation model based on experimental data, which determines when and where new bubbles should be generated. Furthermore, a micro-layer boiling model is developed to account for vaporization in the thin film between the bubble and the heated solid wall. Our method has been validated through simulations of subcooled HFE-7200 flow in a 3D micro-channel with the top wall heated at a constant heat flux. Compared to the visualization experiment, our simulation can accurately predict the wall temperature and qualitatively capture bubble evolution.