Experimental measurements of bed-to-tube surface heat transfer coefficient were conducted in a 12 MW_th circulating fluidized bed boiler/gasifier where a vertical U-tube was immersed into the bed. The aim was to study the influence of superficial gas velocity, solid flux of bed material, direction of the tube relative to the circulating particle flow, choice of fluidization gas, bed temperature and to compare the results with predicted values based on heat transfer correlations.

The experiments displayed high heat transfer coefficients of around 550 W/(m²K) with sand and with ilmenite approximately 850 W/(m²K) when operating with air at a superficial gas velocity of 0.25 m/s. Replacing air with steam and recirculated flue gas as fluidization gas increased the heat transfer by more than 40% with both steam and flue gas. Having the U-tube oriented parallel to the circulating particle flow reduced the heat transfer by around 8% compared to a perpendicular orientation.

床到管表面的传热系数的实验测量在12 MW进行了_第循环流化床锅炉/气化器，其中一个垂直U型管浸在该床上。目的是研究表观气体速度，床层材料的固体通量，管相对于循环颗粒流的方向，流化气体的选择，床层温度的影响，并将结果与​​基于传热相关性的预测值进行比较。

实验表明，当空气以0.25 m / s的表观气体速度运行时，沙子和钛铁矿的传热系数约为550 W /（m ² K），约为850 W /（m ² K）。用蒸汽和循环烟气代替空气作为流化气体，蒸汽和烟气的热传递都增加了40％以上。与垂直方向相比，使U型管的方向平行于循环的粒子流方向可使传热减少约8％。