Numerical simulation of nucleate pool boiling under high pressure using an initial micro-layer thickness model

Micro-layer evaporation is one of the main phase change mechanisms in nucleate pool boiling. However, the influence of pressure on micro-layer evaporation remains unclarified. The objective of this study is to establish an approach to calculate micro-layer evaporation at high pressure. Here, an analytical solution of the governing equations is applied to derive a semi-empirical correlation for the initial micro-layer thickness delta(0). After the calibration with measurement under atmospheric pressure, delta(0) becomes a function of fluid properties. A nucleation sites tracking method is then implanted in the micro-layer evaporation system for multi-bubble cases. In this study, two single bubble growing cases are employed to validate our initial micro-layer thickness model at high pressure (1.91 MPa, 4.47 MPa). The simulated bubble radius profiles show similar trends with experimental data. Furthermore, the entire multi-bubble evaporation system is also validated against a pool boiling experiment at high pressure (0.51 MPa). The simulated wall superheat is consistent with reported data, with the minimum deviation of about 20%. The contribution of evaporation during nucleate boiling from both the macro and micro region is demonstrated at various operating conditions. Micro-layer supplies about 70% vapor in nucleate pool boiling at 0.51 MPa.

Automated summary

This study aims to investigate the micro-layer evaporation mechanism at high pressure and establish a method to calculate it. Through the validation of two single bubble growing cases and a high-pressure pool boiling experiment, the accuracy of the initial micro-layer thickness model under high pressure environment is confirmed. The results demonstrate that micro-layer evaporation contributes to about 70% of the vapor in nucleate pool boiling.