With the rising costs of electricity due to increasing demand of electric power, liquid desiccant systems have received significant attention as a way to reduce latent loads on air conditioning systems. In particular, the performance of liquid desiccant systems in humid climates has shown significant reductions in energy consumption. In general, these liquid desiccant systems are composed by an absorber or dehumidifier and a regenerator that utilizes a heat source to reject the water from the diluted liquid desiccant. As the humidity of the air is absorbed at the dehumidifier, the temperature of the liquid desiccant increases due to the addition of heat from the enthalpy of condensation of the water vapor. Thus, many designs of liquid desiccant absorbers include the flow of a cooling fluid that removes heat from the liquid desiccant lowering its temperature.

A different application of liquid desiccant systems corresponds to the localized removal of moisture from the air inside low temperature rooms that contain relatively high levels of humidity such as refrigerated warehouses for the food industry. The purpose is to reduce the formation of ice at the surface of the evaporator. Due to the low temperature of the air inside these rooms, no cooling fluid is necessary for the removal of heat from the liquid desiccant. Thus, the designs of the absorbers differ from the designs used in more conventional applications.

In this thesis, mathematical models of the heat and mass transfer for an adiabatic parallel-plate absorber for which a thin film of liquid desiccant flows down its walls and dehumidifies the air in cross-flow configuration are developed. Numerical results are obtained and the performance of the absorber as a function of several parameters including inlet air temperature and relative humidity, inlet liquid desiccant temperature, mass flow rates of air and liquid desiccant, and liquid desiccant concentration is analyzed. The results are compared with experimental data available for an absorber using calcium chloride as the liquid desiccant. The geometry of the absorber is optimized to improve the dehumidifying performance of the core.

The continuous increase in the demand of energy and the high costs of fuels in many areas in the world are fostering improvements in energy efficiency in many sectors. Defrosting due to ice formation on the surface of cooling coils is a major source of inefficiencies in the refrigerated warehouse sector which, just in California, accounts for 1,800 million kWh of energy consumption per year. Liquid desiccants have been identified as a means of reducing latent loads in air conditioning and refrigeration systems. However, the interaction of liquid desiccant films and humid air is a subject that has not been analyzed in detail. In the past, significant efforts have been made in understanding liquid-film absorption processes in heat and mass exchangers for several flow configurations, using various numerical and experimental techniques. However, studies concerning liquid desiccant films near freezing conditions with coupled momentum, heat and mass transfer using non-isothermal thermo-physical properties are rare in the literature. The purpose of this dissertation is to investigate the effect of heat and mass transfer in the interaction of a liquid desiccant film in contact with a humid air stream. Velocity, temperature, and concentration distributions, as well as, film stability are studied experimentally and numerically. The results show a delay in the formation of the ice on the cooling coil due to the reduction of the dew point temperature of the evaporator inlet air, thus reducing operating costs. Moreover, the results show that an effectiveness of the internal heat exchanger less than 60\% leads to a desorption process which is opposite to the aims of the dehumidification system. The stability analysis of the liquid film is evaluated using the Orr-Sommerfeld equation with methodologies such as the small wavenumber technique and complete orthonormalization method. Most works found in the literature have focused on the particularly simplified cases of absorption with uniform properties, namely, isothermal systems. The techniques used to analyze film stability allow the inclusion of the effects of heat, mass, and temperature dependent properties, which constitutes a major contribution of this work. Stabilizing and de-stabilizing effects of different parameters are discussed in the results.