Effect of particle characteristics on particle collision behaviors and heat transfer performance in a down-flow circulating fluidized bed evaporator

Abstract

The effects of particle characteristics on particle collision behaviors and heat transfer are investigated based on standard deviation and kurtosis analysis in a down-flow circulating fluidized bed evaporator. Results show particle addition can enhance heat transfer for all types of particles. The maximum enhancing factor reaches 33.0% within the experimental range by adding polytetrafluoroethylene particles at ε=1.5%, V=5.16 m3/h and q = 8 kW/m2. For different types of particles, with increased amount of added particles, enhancing factor initially increases and then decreases; standard deviation increases but kurtosis decreases. With increased circulation flow rate, standard deviation and enhancing factor tend to increase but kurtosis decrease. With increased heat flux, standard deviation tends to increase but kurtosis and enhancing factor decrease. Density, sedimentation velocity and surface wetting performance obviously influence particle collision and heat transfer performance. High standard deviation and low kurtosis are beneficial to heat transfer.