The Study Of Particle Fouling Preventionand Cleanupin Vapor-Liquid-Solidmulti-Phase Evaporation Tube

In the boiling and evaporating process, scaling on the surface of boiling and evaporating is a standing and difficult problem. The fouling layer reduces the efficiency of heat transfer and increases energy consumption. Vapor-liquid-solid three-phase evaporation tube has far-ranging and particularly been paid attention for its outstanding present in anti-scaling and effecting heat transfer effect among the academic circles and industrial circles. But for the complexity in the process of heat transfer and the limit of experiment research, the mechanism that how the solid particle prevents the scaling formation is not clear and need for further research.This article is based on the actual structure of vapor-liquid-solid three-phase evaporation tube. Suppose that there is a fixed thickness calcium sulfate crystallizing layer covered the surface of tube inner wall, considering the coupling heat transfer between the scaling layer, boiling fluid heat transfer , the effective in that the denudation of gaseity or liquid state fluid to the crystallizing layer, and the Particle collisions wear to scale layer, I preliminarily established the vapor-liquid-solid three-phase evaporation tube anti-scaling model and use the STAR-CCM+ software to process in numerical simulation. Taking the affection of the solid particle to the anti-scaling covered the inline of the evaporate tube into selective analysis .I imitate the temperature of crystallizing layer and the spread field of thermal stress, I make a preliminary analysis for breakage of crystallizing layer in the vapor-liquid-solid three-phase evaporation tube and look forward to provide some reference in this field in vapor-liquid-solid three-phase fluidized bed evaporator design and industrial application.Simulation experiment results indicate that , the surface temperature of crystallizing layer and gas holdup, the rate of fouling denudation and the particles erosion rate to scale layer are the important factors to affect the the anti-scaling covered the inline of the evaporate tube. The joined solid particles reduced the surface temperature of crystallizing layer and gas scale, effectively reduce the degree of the surface of crystallizing layer superheat, stop the deposition on the crystallizing layer surface .These all are vapor-liquid-solid three-phase relative scale layers integrated function. If we ignore the solution scale layer deposition mechanism, The quality of scale layer surface removal rate for steam can be approximately expression liquid two-phase or liquid fluid to scale layer surface erosion rate and solid-phase particle on the scale layer surface caused by sum wear rate. Increase three-phase flow velocity and solid-phase particle apparent volume fraction can improve the quality of both removal rate. Particle volume fraction of relative to the apparent velocity scale layer surface dirt-remover quality rate less effect, Comprehensive removal rate and dirt-remover uniformity, evaporation tube appropriate operating conditions for apparent velocity 0.75 m/s, particle volume fraction 3% ~ 5%.