The evaluation of a small capacity shell and tube ammonia evaporator

The use of ammonia as refrigerant is widespread in vapour compression and ammonia/water absorption systems. Ammonia is not actually used in low capacity applications mainly because of the lack of economical available equipment. For this reason, the objective of this study is the numerical and experimental evaluation of a small capacity ammonia shell and tube evaporator with enhanced heat transfer surfaces. An experimental system to evaluate small capacity heat exchangers was developed. A shell and tube evaporator with external low fin tubes was successfully tested. The experimental uncertainty for the evaporator capacity has been estimated within ±5.5%. The experimental results were used to validate a heat exchanger numerical tool that predicts reasonably well the cooling capacity and load outlet temperatures. The methodology presented in this work can be applied to evaluate other refrigerants in similar shell and tube evaporators and to optimize the design of an evaporator for a specific application.