Pressure Drop of Liquid–Solid Two-Phase Flow in the Vertical Tube Bundle of a Cold-Model Circulating Fluidized Bed Evaporator

Abstract

A cold-model vertical multi-tube circulating fluidized bed evaporator was designed and built to conduct a visualization study on the pressure drop of a liquid–solid two-phase flow and the corresponding particle distribution. Water and polyformaldehyde particle (POM) were used as the liquid and solid phases, respectively. The effects of operating parameters such as the amount of added particles, circulating flow rate, and particle size were systematically investigated. The results showed that the addition of the particles increased the pressure drop in the vertical tube bundle. The maximum pressure drop ratios were 18.65%, 21.15%, 18.00%, and 21.15% within the experimental range of the amount of added particles for POM1, POM2, POM3, and POM4, respectively. The pressure drop ratio basically decreased with the increase in the circulating flow rate but fluctuated with the increase in the amount of added particles and particle size. The difference in pressure drop ratio decreased with the increase in the circulating flow rate. As the amount of added particles increased, the difference in pressure drop ratio fluctuated at low circulating flow rate but basically decreased at high circulating flow rate. The pressure drop in the vertical tube bundle accounted for about 70% of the overall pressure drop in the up-flow heating chamber and was the main component of the overall pressure within the experimental range. Three-dimensional phase diagrams were established to display the variation ranges of the pressure drop and pressure drop ratio in the vertical tube bundle corresponding to the operating parameters. The research results can provide some reference for the application of the fluidized bed heat transfer technology in the industry.

Keywords

Pressure drop / Liquid–solid two-phase flow / Circulating fluidized bed evaporator / Vertical tube bundle / Heat transfer enhancement / Fouling prevention / Descaling

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