CHARACTERISTIC FEATURES OF HEAT-TRANSFER IN CIRCULATING FLUIDIZED-BED BOILERS

The characteristic features of heat transfer in circulating fluidized bed boilers are described. First, the conditions for heat transfer are listed. Then, examples of measurements from the research boiler at Chalmers University of Technology are presented, including thermal and fluid-dynamic boundary layers as well as heat transfer coefficients measured with a heat flow meter and with thermocouples mounted on the tube walls of the boiler. Differences in heat transfer efficiency of the fins and of the tubes of a membrane tube wall are shown. Finally, heat transfer mechanisms are briefly discussed, and the influence of the macroscopic flow pattern caused by exit, secondary air, etc. is indicated.