Simulation on direct contact heat transfer in gas-molten salt bubble column for high temperature solar thermal storage

Abstract

The charging and discharging of molten salt thermal storage is of great importance to the operation and maintenance of the solar power plant. The molten salt bubble column is proposed for solar thermal storage, which is regarded as direct contact heat exchanger. The gas from the solar field is directly injected into the molten salt bubble column. High heat transfer rates can be achieved between the gas and the molten salt due to the direct contact. The hydrodynamics and heat transfer characteristics of the gas molten salt bubble column are numerically analyzed based on the two fluid model, which incorporating the interfacial area transport equation. Simulation results are compared with experimental data from previous literature and our lab. The predictions of lateral profiles of the axial liquid velocity, overall gas holdup and temperature rising rate are in well agreement with the experimental data. Therefore, the models can be used to simulate the behaviors of gas-molten salt bubble column. The effect of superficial gas velocity, static liquid height, operation pressure and inlet gas temperature are discussed. Numeric results show that the volumetric heat transfer coefficient and rising rate of average molten salt temperature increase by increasing superficial gas velocity or operation pressure, and decrease by increasing the static liquid height. The molten salt temperature decreases along the height gradually and the distribution of molten salt temperature in the bubble column is almost uniform during the process.