Thermal Rating and Design of Ammonia Condensers

Abstract

Condensers are used widely in industry in operations like distillation, refrigeration, petroleum industry and air conditioning units. Condensers are also an integral part of refrigeration systems. Ammonia is the most widely used refrigerant in the industry. In a typical vapor-compression cycle of a refrigeration system, the refrigerant vapors are compressed and enter the condenser in a superheated state. It is first de-superheated and then condensed by rejecting heat to an external medium. The refrigerant may leave the condenser as a saturated or a subcooled liquid, depending upon the temperature of the external medium and design of the condenser. For condensation of ammonia, generally three types of condensers are used in the refrigeration industry viz. Water-cooled condensers, Air-cooled condensers and Evaporative Condensers. This thesis has been carried out to analyze and compare the differences in the design of Water-Cooled Condensers, Air-Cooled Condensers and Evaporative Condensers, for the same process system. For analysis purpose, a case of Ammonia Condenser has been taken up. Ammonia-Water system is taken as the first case and Ammonia-Air system as the second case. These condensers have been designed manually as well as in HTRI to do a comparative analysis. While designing a heat exchanger manually, it is very difficult to vary all the parameters simultaneously and see the effect. Manual calculations become more of a trial and error loop. HTRI proves to be efficient and rigorous software for the design and optimization of heat exchangers. It is not time consuming and gives the user full control over the design as well. Water and air are the most widely used cooling medium. But, evaporative condensers are becoming a very attractive option for condensation. So, evaporative condenser has been taken as the third case for design. These condensers combine air-and-water cooling together. These condensers have many advantages over the conventional water and air-cooled condensers. Evaporative condenser consumes about one-third that of the flow circulated between the watercooled condenser and cooling tower. Evaporative condensers reduce the water pumping and chemical treatment requirements and costs associated with water condenser-cooling tower system. Evaporative condensers can also achieve lower condensing temperature than the air cooled and water cooled condensers. It is also a compact system. Due to these reasons, evaporative condensers can be seen as a better option for condensation of ammonia.