Heat transfer performance of a vapor–liquid–solid three-phase circulating fluidized bed evaporation system with different concentrations of Na2SO4 solutions

Abstract

A vapor–liquid–solid three-phase circulating fluidized bed evaporation system is designed and bulit to investigate the heat transfer performance of different concentrations of Na2SO4 solutions. Glass beads particles are selected as the inert solid particles. Liquid–solid two-phase and vapor–liquid–solid three-phase flow experiments are conducted by varying the particle volume fraction (0.5%–2.0%), circulating flow velocity (0.38–2.07 m∙s−1), and heat flux (6.47–11.22 kW∙m−2). The effect of the solution concentration on heat transfer performance is analyzed. Results show that the convective heat transfer coefficient of the high-concentration solution is lower than that of the low-concentration solution under the same operating conditions due to the difference in physical properties. The addition of the glass bead particles not only effectively enhances the heat transfer but also reduces the difference in heat transfer performance between the different concentrations of Na2SO4 solutions. The maximum heat-transfer enhancing factors are 8.8% and 10.7% within the experimental range for 16.7 wt% and 33.3 wt% Na2SO4 solutions, respectively. Three-dimensional diagrams are established to display the variation ranges of the enhancing factor under different operating parameters.