A simple energy balance to determine heat transfer coefficients from low temperature measurements in a fluidised bed

A bench-scale fluidised bed (105 × 200 mm) was set-up for studying bed-to-gas and wall-to-bed heat transfer. Low temperature (17–200 °C) experiments were conducted at steady state avoiding excessive instrumentation and time. Compressed dry air at ambient temperature entered the bed through a distributor of a 200-mesh brass sieve and fluidised the single charge of alumina particles with a mean diameter of approximately 250 μm. The superficial gas velocity ranged from 0.085 to 0.412 m s− 1. A simple model was developed based on steady state energy balances, i.e. equating the electrical power input separately to the rate of heat transfer from the heater walls to the bed and from the bed to the gas. The bed-to-gas heat transfer coefficient was calculated from the model equations. Inserting this value into the relevant heat transfer equations then extracted the wall-to-bed and bed-to-gas heat transfer coefficients. The agreement between the experimental and predicted values of temperatures validated the model. The latter may be successfully used to design fluidised beds for e.g. drying or combustion.