Design and performance of an internal heat exchange desiccant wheel

A fundamental limitation in the dehumidification performance of adiabatic desiccant wheels occurs due to heating of the air stream to be dried. This results from both the carry-over of heat stored in the wheel and the release of the adsorption heat. Previous authors have identified an isothermal dehumidification process as theoretically superior, though the practicalities of constructing such a wheel have meant that demonstrating the benefit is difficult. Recently experimental data from testing of an internally cooled wheel was published. Here we use this data to calibrate a mathematical heat and mass transfer model of the internally cooled heat exchange desiccant wheel. The model is then used to estimate the performance for selected modifications to the design and materials. The results show that more than a 40% improvement is possible relative to the previously tested cooled wheel. The results have application to the development of desiccant air-conditioners.