Heat and mass transfer performance comparison between a direct-contact liquid desiccant packed bed and a liquid-to-air membrane energy exchanger for air dehumidification

Abstract

Entrainment of liquid desiccant droplets into the airstream and flow maldistribution are two challenges for liquid desiccant packed beds. Liquid-to-air membrane energy exchangers are novel liquid desiccant exchangers that have the potential to overcome these challenges by using membranes to separate the air and solution flows but have higher heat and moisture transfer resistances. As a new contribution of this study, the heat mass transfer performance of these two exchangers with the same volume and operating condition are compared at two conditions: (1) with the same pressure drop on the air side and (2) with the same total heat/mass transfer area. Results show that liquid-to-air membrane energy exchanger gets up to 13 and 20% higher latent and total effectiveness respectively than the packed bed at the same air pressure drop. Reversely, the packed bed achieves up to 16% higher mass transfer performance than the liquid-to-air membrane energy exchanger with the same heat/mass transfer area. The flow maldistribution and its influences in the packed bed and liquid-to-air membrane energy exchanger are also discussed. Finally, the impact of membrane on the heat mass transfer in the liquid-to-air membrane energy exchanger is evaluated. The membrane accounts for 6∼12% and 26∼43% of the overall heat and mass transfer resistance, respectively, depending on the width of the air channel.