Numerical investigation into the vapor-liquid flow in the mixer of a liquid metal Magneto-Hydro-Dynamic system

Abstract

Liquid Metal Magneto-Hydro-Dynamic (LMMHD) power generation is a promising technology for waste heat recovery, solar thermal utilization, etc. In this system, a high-temperature liquid metal is mixed with a low-boiling point working fluid, which will evaporate and push the liquid metal to flow through the MHD generator channel. The characteristics of mixing and the vapor–liquid two phase flow will greatly affect the power generation efficiency and effectiveness. This paper firstly proposed a spherical mixer tank for the entire LMMHD system. Then CFD simulation was employed to investigate the above process, with liquid tin as the liquid metal and trifluorotrichloroethane (R113) as the low-boiling point working medium. The findings indicate that an appropriately higher inlet velocity of liquid tin can lead to both higher outlet velocity and larger volume fraction of liquid tin, which is beneficial to MHD power generation. Increasing the initial temperature of liquid tin or inlet velocity of R113 will, on the one hand, elevate the outlet velocity of liquid tin; on the other hand, it will reduce the outlet volume fraction of liquid tin, which was suggested be kept above 20% to avoid the undesirable annular flow. In addition, the inlet velocity of R113 should be kept above 0.05 m s⁻¹; otherwise, liquid tin may flow downwards into its inlet pipeline and cause blockage. The present results will help guide the design, operation and optimization of the mixer, and improve the basic theory of multiphase flow in a LMMHD system.