Effect of wall cooling with condensation on depressurization of a steam-prefilled chamber

Depressurization can be realized by condensing saturated vapor of a pure substance inside a thermodynamically-closed system such as a confined chamber. The depressurization rate depends directly upon the effectiveness of cooling to the condensing vapor. This study is to investigate the transient characteristics of heat and mass transfer during the condensation-controlled depressurization process. Specifically, the objectives of the study include the transient changes in pressure, temperature and their distributions within the chamber. The representations of pressure and temperature in terms of the corresponding in-situ measurements are also of utmost interest. To this end, this study adopts a research methodology of combined modeling-simulation-experiment approaches, including (1) a pseudo-Thermodynamics model to provide the limiting characteristics of depressurization and a quick parametric analysis, (2) a full-field numerical simulation to explore the phase non-equilibrium in momentum and heat transfer, (3) an experimental system to provide measurements for model validations, and (4) a heat transfer model to interpret the transient relationship between thermocouple measurements and vapor temperatures. Our study shows that the pressure in chamber is almost uniformly distributed, with a non-equilibrium margin less than 0.4% of the averaged chamber pressure. The vapor temperature distribution, however, can be highly non-uniform. The local vapor temperature is influenced by multiple factors, including nearby vapor condensation, heat conduction and convection from vapor movement, and convective heat transfer from cooling pipe and chamber wall. The transient thermocouple measurements can be significantly deviated from that of vapor, due to the thermal capacity of the thermocouple as well as the thermal radiations from cooling pipe and chamber wall. The deviation margin in temperature measurements can be thermocouple-location sensitive.