Heat transfer on wedged membrane fin water wall tubes of CFB boilers

Abstract

Experiment was performed in a cold model circulating fluidized bed (CFB) riser to investigate bed to wall heat transfer on wedged membrane fin of membrane water wall tubes. Sand having an average diameter of 315μm was used as bed material. The membrane tube had diameter and pitch of 25.4 mm and 50 mm respectively. The bases of isosceles triangular wedges having an average of base to height ratio of 0.54 mm were attached to the fin at spacing of 400mm, 500mm and 600mm. It was found that the heat transfer of the wedged membrane fin and the conventional membrane fin increased as suspension density increased. The wedges had an effect on the heat transfer. When compared with the conventional membrane tube, the wedged membrane tube had higher heat transfer coefficient. The effect decreased as the spacing increased. The results could be used to design CFB boilers in order have the smaller size or modify the existing boilers in order to have more capacity.