Visualization study on double-diffusive convection during a rollover in liquid energy storage tanks

Abstract

The growing global energy consumption and the transition to the renewable era highlight the urgent need for safe and energy-efficient liquid energy storage tanks. Rollover has been a severe hazard to the efficiency and safety of the storage tank accompanied by significantly enhanced mass and heat transport across the stratified layers, and rapid evaporation and mixing of the layers happen. However there is a lack of experiments sophistically designed for cryogenic storage applications, which leads to a lack of visualized and quantitative experimental data to understand the physics of rollover in energy storage tanks. In this study, a Z-type Schlieren system is established to visually reveal the double-diffusive convection patterns in a cylindrical experimental chamber. The concentrations of salt-water solutions are adjusted to simulate the density difference between the multi-component cryogenic fluids. Cross-correlation algorithm is adopted to analyze the transient velocity distributions in the stratified system. The rollover process is divided into four stages, namely the initial, transition, mixing, and stable stages. Effects of heat flux, concentration difference, and heating location on the rollover characteristics are parametrically investigated. Correlations are proposed with rescaled buoyancy ratio and density gradient, and satisfactory agreement with experimental data is achieved.