Experimental investigation on influence of pre-wetting on wetted area and system performance for liquid desiccant air-conditioning system

Currently, the liquid desiccant air conditioning system has been regarded as an environmental-friendly and energy-saving alternative. To improve the performance of liquid desiccant system, the wetted area of desiccant is a key parameter. However, the insufficient wetting has been observed in many previous studies. By making it hydrophilic, the pre-wetting of working surface is supposed to be a simple way to increase the wetted area. But the research of this area is very limited. In this paper, we experimentally investigated the detail impacts of pre-wetting condition on the wetted area and system performance, with a single channel liquid desiccant system. The film area was recorded by a thermal camera. It could be found that the moisture removal rates in the pre-wetting conditions were significantly higher than those in the dry ones, which mainly due to the enhancement of wetted area. When the surface was pre-wetted, the film area increased about 30-60% than the dry conditions. Not only the initial width of falling film was obvious improved for 1-2 times, the film contraction was also effectively restrained during the pre-wetting conditions. The main reason of different wetted area is that when the surface was completely pre-wetted, there were many small liquid desiccant droplets above the surface, which significantly reduce the contact angle of liquid desiccant. Therefore, to improve the wetted area, reduce the contact angle of liquid desiccant is an effective way. Besides the pre-wetting of working surface, many manufacture processes, such as coating and surface treatment, could also be applied to benefit the performance of liquid desiccant system.