Heat Transfer Characteristics And Pressure Drop In Vapor-liquid-solid Horizontal Circulating Fluidized Bed Evaporator

The circulating fluidized bed heat transfer technology can enhance heat transfer by combining the fluidized bed technology with the heat transfer process.A vapor-liquid-solid three-phase horizontal circulating fluidized bed evaporator is designed and built to investigate the heat transfer performance and pressure drop.The polyformaldehyde(POM)particles are selected as inert solid particles.The heat transfer characteristics and pressure drop are analysed by varying the amount of added particles,circulation velocity,heat flux and particle size.The difference of heat transfer performance among different vertical heights of the horizontal bed is also studied systematically.The results show that the addition of POM particles significantly improves the heat transfer efficiency of the horizontal circulating fluidized bed evaporator.The maximum enhancement factors are 60.14%,59.89%,71.5% and 66.71% for four sizes of different POM particles,respectively.The corresponding pressure drop ratios are35.7%,58.9%,60.3% and 78.3%,respectively.The effects of various operating parameters on the heat transfer enhancement are different.With the increase in the amount of added particles,the heat transfer enhancing factor generally initially increase and then decrease,but the pressure drop ratio increases or fluctuates.The effect of the amount of added particles on heat transfer performance has been analyzed by using the existing visualization experiments.The enhancing factor fluctuates and the pressure drop ratio decreases with the increase in circulation velocity.The effect of the circulation velocity on heat transfer performance has been analyzed by using the existing visualization experiments.The increase in heat flux is not conducive to heat transfer enhancement.With the increase of heat flux,the convective heat transfer coefficient and enhancing factor decrease,but the pressure drop ratio gradually decreases.With the increase in particle size,the enhancing factor initially increases and then decreases but the pressure drop ratio gradually fluctuated.POM3 particles have the optimal heat transfer enhancement effect within the experimental range.The results on the heat transfer performance of horizontal bed at different vertical heights and their difference is presented as follows: the variation trend of convective heat transfer coefficients at different vertical heights with operating parameters is consistent with the average convective heat transfer coefficient.The difference of convective heat transfer coefficient between different vertical heights of the horizontal circulating fluidized bed increases with the increase of the amount of added particles.However,the difference decreases slightly with the increase of circulation fluidized velocity.The difference fluctuates with the increase of heat flux.With the increase of particle size,the difference first increases and then decreases.The convective heat transfer coefficient at the bottom of the horizontal bed is the greatest at low heat flux,but that at the top of the horizontal bed is the greatest at the high heat flux.The research results of three-phase horizontal circulating fluidized bed evaporator on the heat transfer characteristics are helpful to promote its large-scale application in industry.