A MODEL COMBINING CONVECTIVE AND RADIATIVE HEAT TRANSFER IN CFB BOILERS

摘要

A mathematical model for description of heat transfer under Circulating Fluidized .Bed (CFB)-conditions is proposed. According to the dominating heat transfer mechanisms (particle convection and particle radiation) the model is based on two modules describing radiative and convective part. The shielding effect of the dense and cool wall layer is included and demonstrated. Due to the variation of particles concentration in the wall layer the radiation behaviour changes between optical thin and optical thick. Therefore three different methodes for calculation of the mean extinction coefficient were used. The generation of a wall layer close to wall and platen heat exchangers in CFB's was investigated in experimental way. In a further step bed to wall heat transfer coefficients were measured and are compared to data from literature.