Performance characteristics of thin-multilayer activated alumina bed

- Activated alumina has large mass transfer characteristics in hot very humid zones.
- Activated alumina adsorption rate is doubled as inlet air RH rises from 50% to 80%.
- Long cycle durations reach high COP but with high moisture content of exit air.
- Short cycle durations attain uniform moisture content of exit air but with low COP.
- Activated alumina has better COP and faster dynamic response than silica gel.

This paper reports the experimental mass transfer characteristics of thin-multilayer activated alumina bed that is used in desiccant-cooling systems working in humid and very humid climates, during adsorption and regeneration processes. These characteristics include transient response, adsorption and desorption rates, mass transfer coefficients and latent COP. Effects of dry bulb temperature and humidity of ambient air on single, double or triple-layers bed are experimentally investigated. In addition, effects of cycle duration on latent COP and adsorption process are considered. The experimental results proved that long cycle duration achieves high latent COP but with large moisture content of exit air while short cycle duration accomplishes uniform moisture content of exit air but with lower latent COP. The mass transfer characteristics of activated alumina beds are superior for hot very humid climates (high ambient temperature and relative humidity) with more uniform relative humidity of exit air being achieved by triple-layers bed. The comparison between activated alumina and silica gel, under the same conditions, revealed that activated alumina achieves higher COP, particularly for short cycle duration.