Date of Award

1993

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor

Vic Cundy

Abstract

A comprehensive heat transfer model is developed which describes heat transfer phenomena in rotary desorbers. This model predicts the temperatures of the solids bed and gases in the desorber and the rate of water evaporation from the solids. Emphasis is placed on describing the heat transfer process between the rotating wall of a desorber and the adjacent bed of solids. A heat-balance integral method is used to model heat conduction from the wall to adjacent wet bed particles. This solution includes the effects of water evaporation near the wall and a thermal contact resistance between the wall and the first layer of particles. The model allows for water evaporation before the bulk bed temperature reaches the saturation temperature of the water. Radiative and convective heat transfer to the solids are coupled with the wall-to-bed heat transfer rate to find the total heat transfer rate to the solids. Energy balances are performed on an axial zone of the desorber and are used to find the resulting change in solids and gas temperatures across the zone, thereby predicting axial temperature profiles. Experiments are performed on a batch-type, pilot-scale desorber. A bed temperature probe is used to determine the transient temperature of the bed at several radial and axial locations. In these experiments, the particle size, the rotation rate, and the initial moisture content of the solids are varied. It is found that particles heated by the rotating wall are not completely mixed with the remainder of the bed, reducing wall-to-bed heat transfer. Evaporation rates are inferred from measured velocities at the exit of the desorber. Mass balances are performed on the water, with good results. A significant amount of water is found to evaporate before the bulk bed temperature reaches the water saturation temperature. The measured bed temperatures and evaporation rates compare favorably to predictions of the model. The important features of the experimental data, including the bulk bed temperature profiles and water evaporation before the bed temperature reaches the water saturation temperature, are predicted.

Pages

284

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