Translation of Heat Transfer Measurements from Laboratory CFBs to the Conditions of CFB-Boilers

Artikel i vetenskaplig tidskrift, 2003

The aim of this work is to find a method for translation of heat transfer data from cold laboratory units to boiler conditions. From a compilation of existing data on heat transfer to walls in hot and cold circulating fluidized beds it is concluded that the results can be translated approximately by compensating for changes in the thermal conductivity of the gas and thermal radiation. A more general methodology is developed by deriving the criteria for thermal similarity. The only criterion that was added to those for fluid-dynamic similarity was the ratio of heat capacity of gas and particles. The thermal scaling is tested by comparing heat transfer measurements in a boiler with measurements in a scaled laboratory model. The results show that the Nusselt numbers were not the same in the boiler and the scaled model, which can be a result of the characteristic length-scale chosen, a too low heat capacity of the scaled particles or a failure to scale the local fluid-dynamics at the wall.