The Effect of Particle Size on Radiative Heat Transfer in High Temperature Fluidized Beds

摘要

The effect of particle size on the radiative component of heat transfer in high temperature fluidized beds is examined. One radiometer probe is used to measure both the total and radiative components of heat flux. Two sizes of silica sand particles are tested at bed temperatures of 200 to 750C. The radiation heat flux, percentage of total heat flux due to radiation, total heat transfer coefficient, radiative heat transfer coefficient, and bed emissivity are the parameters considered. The radiative heat flux does not vary with particle size, and the values obtained agree with those of previous studies. The percentage of total heat transfer due to radiation is found to be significant for bed temperatures greater than 400C and increases with increasing particle size. At 750C, the radiative component is 20% of the total heat flux for small particles and 30% for the larger particles. The smaller particles have a larger total heat transfer coefficient than the large particles at all bed temperatures. When the fluidizing velocity is increased, the total heat transfer coefficient decreases for both particle sizes. The radiative heat transfer coefficient has the same values for both particle types at all bed temperatures. The emissivity of the bed is larger for the large particles at all temperatures but always remains less than one.