Division of Information Technology, Engineering and the Environment
School of Advanced Manufacturing and Mechanical Engineering
School of Advanced Manufacturing and Mechanical Engineering
Thesis Abstract
A desiccant evaporative cooling system is a potential alternative to environment-benign conventional vapour compression chillers. It works on an open heat-driven cycle consisting of a combination of a dehumidifier; sensible heat exchanger and evaporative water spay coolers. In this environment-friendly system, dehumidification of air is done at first using a desiccant wheel to very low humidity levels so that evaporative cooling can be employed effectively to reduce the temperature of air.
Desiccant wheel is the heart of the heat-driven cooling system and it uses a solid desiccant for dehumidification. Its matrix consists of multiple channels in the direction of axis of rotation of the wheel. The desiccant material is coated, impregnated or formed in a place on the supporting rotor structure. Proper design of the wheel is very important for the successful operation of the system and theoretical modelling is effective tool in predicting the performance and design optimisation. So in this project, transport phenomenon in the desiccant wheel is studied, model equations are derived and two theoretical models are developed. The first one considers only gas side resistances of heat and mass transfer, whereas the other includes both solid side and gas side resistances. Both models show good agreement with published experimental results. A parametric study of different operational and design parameters is conducted to determine the best performance parameters for a selected climatic condition.
A main disadvantage of the system is the excessive heating of the supply air during dehumidification. To overcome this, two innovative designs for desiccant wheel are developed, namely desiccant wheel with additional cooing streams, non-adiabatic desiccant wheel. Numerical models of both designs are developed. A representative channel of non-adiabatic desiccant wheel is designed and fabricated and conducted the experiments to validate the model. For both new designs, a parametric study is conducted to determine the best operating and design parameters. Finally, the performances of these designs are compared with convectional system and conclusions are drawn.
