Effect of straight bend ratio of lower elbows on the stable fluidization performance of a new type of closely spaced liquid-solid circulating fluidized bed heat exchanger
In a heat exchanger operating on a liquid-solid circulating fluidized bed,the essential fluidization stability of the liquid-solid two-phase flow and the uniformity of the particle distribution are paramount.These aspects not only represent the descaling capability of the heat exchanger but also have a direct influence on its heat transfer efficiency.Maintaining an equitably spread out particle distribution pattern in the rising tube enhances the interaction of particles with the inner wall,leading to optimum efficiency for both scale prevention and removal.A novel dense-row lower fluidization box structure is incorporated into the conventional experimental setup of the heat exchanger to augment its heat transfer efficiency and explore the intricate dynamics of particle flow in the rising tube.A stable operation of bed fluidization is achieved through experimental research,and subsequent measurements of the rising tube's pressure drop at three distinct flow rates are consistent with the theoretical forecasts.Building upon the stable operation experiments of the newly fashioned dense-discharge liquid-solid circulating fluidized bed heat exchanger,the validity of the computational particle fluid dynamics(CPFD)method in simulating particle distribution is assessed.The deviation between experimental findings and simulation outcomes falls within a reasonable range of 10％,endorsing the reliability of the CPFD simulation approach and its promise of efficiency enhancement in future research.An optimization simulation of the ratio of the straight section's length to the bending radius of the lower elbow tube,a critical factor in flow dynamics,is executed using the CPFD method.The data suggest that a 5:1 ratio for the straight section to the bending radius offers the most uniform particle distribution in the heat exchanger.At this ratio,particle collisions against the rising tube's inner surface are at their highest efficiency,yielding optimal descaling results and leading to peak heat transfer efficiency.
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