感温液晶による循環流動層ライザー壁温分布の可視化

Abstract

In order to investigate heat transfer distributions on riser walls of a circulating fluidized bed (CFB) under rolling motion, a series of visualization experiments which utilized thermo-chromic liquid crystal was performed. Superficial velocity and rolling period were varied in the experiments, while amplitude of the rolling motion was fixed at 15deg. One-dimensional unsteady thermal conduction analysis was also carried out to evaluate followability of liquid crystal coloration to changes in riser wall temperature. The following results were obtained: (1) Thermal conduction analysis shows that the response delay time of liquid crystal coloration to the wall temperature stays within several seconds under the present experimental conditions. (2) In bubbling and turbulent fluidization regimes at the upright attitude, a remarkable change in liquid crystal coloration due to the steep gradient of voidage was observed at the bottom of the riser wall. On the other hand, uniform coloration was observed over the entire area at the middle of the riser wall. Time-averaged heat transfer rate of the present experiment agrees well with previous results. (3) When the CFB undergoes rolling motion, liquid crystal coloration changes periodically at the middle part of the riser wall. The change is induced by heat transfer fluctuation due to the periodic change of the downflow.