Heat Transfer Characteristics and Particle Microscopic-Behavior around a Horizontal Tube Bundle in Fluidized Bed

以平均直径为0.42 mm和1.0 mm的玻璃微珠为流态化颗粒，在流态化床管表面的同一位置同时测量了管内的瞬时换热系数、颗粒体积分数和颗粒速度。在薄箔和酚管之间插入直径为0.012 mm的铬-康铜热电偶。根据测量的热电偶温度，采用逆热传导分析方法估算了瞬时换热系数。该测量系统能对频率低于40~50 Hz的脉动换热系数做出响应。通过粘贴在管子表面的光纤探头测量了管子周围的颗粒体积分数和颗粒速度，并用条件平均法对测量结果进行了分析，区分了颗粒接触和无颗粒接触。颗粒接触时的局部平均换热系数与颗粒体积分数的关系符合Kunii的大颗粒模型，对于0.42 mm颗粒，在管子下侧表面，对于1 mm颗粒，局部平均换热系数与整个管面上的颗粒体积分数的关系一致。(大颗粒意味着其热时间常数足够长于其在管子表面的停留时间)

The instantaneous heat transfer coefficient, particle volume fraction and particle velocity around a tube in a fluidized bed were simultaneously measured at the same location on the tube surface, using glass beads with average diameter of 0.42 mm and 1.0 mm as a fluidized particle.The heat transfer tube was a phenolic circular cylinder, around which a stainless steel foil with 0.01 mm thickness was stuck to make uniform heat generation on the tube surface. A chromel-constantan thermocouple of 0.012 mm diameter was inserted between the thin foil and the phenolic tube. The instantaneous heat transfer coefficient was estimated from the measured thermocouple temperature, using the inverse heat conduction analysis. This measuring system can respond to a fluctuated heat transfer coefficient with a frequency lower than 40-50 Hz.The particle volume fraction and particle velocity around a tube were measured by the optical fiber probe which was stuck on the tube surface.The measured results were analyzed by the conditional averaging method, distinguishing particle contact from no particle contact. The relationship between the local average heat transfer coefficient and the particle volume fraction during particle contact, on the lower side surface of the tube for the 0.42 mm particle and on all the tube surface for the 1 mm particle, is consistent with the Kunii's large particle model. (The large particle means that its thermal time constant is sufficiently longer than its residence time at the tube surface)