الفهرس 
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Abstract
Energy and environment are two hot topics worldwide today. Air conditioning has accounted for 1/3 of the total energy used by the whole society. The design of HVAC systems for thermal comfort requires increasing attention. Ventilation air accounts for 20-40% of the cooling load for HVAC industry. In hot and humid regions where latent load from fresh air is as heavy as 50% of the cooling load. Reducing this part of energy is very crucial for the reduction of energy consumption of the whole HVAC system.
Desiccants, in both liquid and solid forms, are a subset of sorbents that have a high affinity to water molecules. Liquid desiccants absorb water molecules, while solid desiccants adsorb water molecules and hold them on their vast surfaces (specific surface areas are typically hundreds of m2/g).
Desiccant cooling and air dehumidification systems are good alternative for air conditioning. In these systems, fresh air is dehumidified and then sensibly and evaporatively cooled before being sent to the space to be conditioned. These systems work without conventional refrigerants, such as fluorocarbons. Moreover, they can use a low temperature heat source such as(waste heat or solar heat) to regenerate the applied desiccant. Therefore, intensive efforts have been conducted to improve the performance of these systems. In humid air climate countries -like the almost dwelling zones in Egypt in summer- dehumidifying air by desiccants is one of the promising techniques in case of high latent load.
Pseudo steady state model is developed to analyze transient coupled heat and mass transfer as it occurs in adiabatic adsorption of water vapor by solid desiccants (activated alumina and silica gel) in a hollow cylindrical packed bed.
The experimental test rig, which is designed and installed in cooperation with El-Delta for fertilizers and chemical industries in Talkha, El-mansoura, Egypt, contains blower, air heater, desiccant packed bed, heat exchanger, humidifier and vapor compression air conditioner. The system is equipped with the necessary measuring instruments.
The performance of the desiccant unit when coupled with a vapor compression air conditioning unit in a hybrid system is investigated.
In the theoretical part of this study, prediction of air exit conditions from the bed is carried out based on the model of Barlow for the analysis of adsorption process and desiccant cooling system. Acceptable agreement is found between the theoretical and experimental results.
Alumina is superior when compared with silica gel from the point of view of air dehumidification. But silica gel can be regenerated using air of temperature of 77 °C. On the other hand, regeneration air process of activated alumina needs more heat load.
Bed cooling at the end of regeneration process is almost essential to improve the system performance. In case of natural cooling, it is found that longer cooling period results in an increase in the adsorption rate during the adsorption mode of operation. However, forced convection cooling of the bed may preferable to minimize the bed cooling period.
Economical study is performed to evaluate compare the proposed desiccant system with a vapor compression with cooling capacity of 4 kW. It has been found that a significant saving in the operation cost of 0.278 L.E. for every 1h running of the proposed system compared with the vapor compression system.