A distributed model for liquid-phase heat transfer in fixed beds

Abstract

Although the representation of gas-phase heat transfer by distributed models is now established, corresponding examinations of distributed models for liquid-phase heat transfer have not been reported. In this work liquid flowing through fixed beds of particles was heated at the wall of the bed and the temperature distribution was measured at the end of the bed by an array of thermocouples. The experimental temperature distribution was compared with the predicted temperature distribution for two models of heat transfer in the fixed bed. In the first model heat transfer was assumed to take place by radial and axial thermal dispersion and axial convection with a thermal resistance at the wall taken to represent changes in porosity and conductivity near the wall. In the second model the same model for heat transfer was taken to hold in the bulk region, but a variation in thermal properties was considered to extend over a fraction of a particle diameter from the wall. For heat transfer to small particles and to particles of high thermal conductivity both models represented the experimental data equally well within the range of Reynolds number from 5 to 1000. However, for large particles of low thermal conductivity the two-region model gave a significantly better representation of the experimental measurements.