OBSERVATIONAL STUDIES ON AXIAL HYDRODYNAMIC IN VAPOR-LIQUID-SOLID BOILING FLOW WITH CCD MEASUREMENT

摘要

The vapor-liquid-solid (V-L-S) flow boiling evaporator has the features of fouling preventing and heat-transfer enhancing. However, the mechanisms of flow and heat transfer are still not well understood due to the system complex and the limitation of the measuring methods due to the characteristic of opaque of the system in practice. In this paper, a CCD (charge coupled device) measuring system is developed to investigate the hydrodynamics including axial profiles of solid holdup and of solid velocity in a V-L-S three-phase natural circulating flow boiling system. The main results are as follows. In heating tube, the distributions of holdup and velocity of solid particles are not uniform along the axial direction, and the solid velocity in V-L-S three-phase region is higher than that in liquid-solid two-phase region. When increasing the heat flux, the solid holdup decreases and the solid velocity increases in heating tube. However, both solid holdup and solid velocity increase in circulating tube. The solid holdup in heating tube is larger than that in circulating tube and the solid velocity in heating tube is lower than that in circulating tube.