The essential requirements for comfortable and healthy indoor environments are adequate ventilation and humidity control. In the humidity rich regions of the world to solve the above problems the key solution is the air conditioners based on liquid desiccants technology.
Liquid desiccants are solutions that have a high affinity for water vapor. This property is the key to creating cooling systems that dehumidify air without over-cooling. Liquid desiccants used in the systems commonly are very strong solutions of the ionic salts lithium chloride and calcium chloride.
These ionic salts have the attractive characteristic and have essential zero vapor pressure. Because of such reason, vapors of the desiccant will not appear in the air supplied by the LDAC (liquid decissant air conditioner). This technology can enhance heat transfer by a mechanism that is the inverse of vaporative cooling. When air flows over a surface wetted with water, evaporation from the film of water will lower the temperature of the water-air interface toward the wet-bulb temperature of the air. This wet-bulb temperature is a function of the air’s initial temperature and humidity.
A line of constant enthalpy that passes through the air’s state point intersects the saturation line on a psychrometric chart at approximately the wet-bulb temperature.
A liquid-desiccant air conditioner (LDAC) has three major components: (1) the conditioner, which dries and cools the process air, (2) the regenerator, which heats the weak desiccant to drive off the water that was absorbed in the conditioner, and (3) the interchange heat exchanger, which uses the hot, concentrated desiccant that leaves the regenerator to preheat the cool, weak desiccant that leaves the conditioner. The conditioner is a water-to-air heat exchanger that is constructed from plastic plates. Cooling water flows within the plates and films of liquid desiccant flow down the outer surfaces of the plates. When air flows over a surface that is wetted with a desiccant, the desiccant can either absorb or desorbs water, depending on whether the desiccant’s equilibrium relative humidity is above or below the air’s relative humidity.