Heat Transfer Characteristics of Liquid-Solid Circulating Fluidized Beds

An experiment was conducted to obtain heat transfer data in liquid-solid circulating fluidized beds. In the experiment, two kinds of risers were provided, their inner diameter being 24 mm and 12 mm, respectively. Tested particles were of glass and ceramics, having a diameter range from 2.10 to 4.95 mm. Water at ambient conditions was used as the fluidizing liquid. The experimental data showed a trend where the heat transfer coefficient increases gradually with increasing liquid velocity approaching that for a liquid single-phase flow ("heat transfer enhanced region"), and finally coincides with that for a liquid single-phase flow ("liquid single-phase heat transfer region"). The heat transfer coefficient in the heat transfer enhanced region was found to be a function of the slip velocity between liquid and particles. Based on the experimental data, a correlation was proposed for predicting the heat transfer coefficient in the entire region from the heat transfer enhanced region to the liquid singlephase heat transfer region, which could reproduce the experimental data with an accuracy of +/- 15%. The proposed correlation agreed well with existing data. (C) 2008 Wiley Periodicals, Inc.