A non-equilibrium relaxation model for fast depressurization of pipelines

Abstract

In this paper, transient depressurization of high pressure pipelines containing initially subcooled liquid is simulated numerically by using thermodynamic non-equilibrium and choking condition model. The numerical method relies on finite volume. The convective terms of cell boundaries are discretized by Advection Upstream Splitting Method (AUSM+ - up) with a proposal of partially implicit approach for source terms. Different void fraction correlations are applied to simulate two phase shock tubes as well as the depressurization process. By comparison between the present results and previous experimental data, the best void fraction correlation is introduced. The results indicate that the propagation of a strong evaporation wave toward the closed end drops the inside pressure of the pipe to a value below the initial saturation pressure. As the wave is reflected from the closed end, a slight pressure undershoot is developed. At the late stage of the depressurization, the pressure along the pipe reduces at a moderate rate. Maximum heat transfer rate and minimum pipe wall temperature occur at the open end.