Natural circulation defrosting with propane in horizontal evaporators of large capacity air-to water heat pump

This paper presents natural circulation defrosting for a large capacity horizontally mounted evaporator designed for a propane refrigeration cycle. This defrosting method is based on a two-phase thermosiphon. It is mounted as an additional loop next to a nominal refrigeration circuit to allow switching between the completely different requirements for refrigerant charge either in nominal heat pump operation or in defrosting mode. A fin-and-tube heat exchanger with 5mm round tube with a conventional 32 port nozzle distributor was successfully tested. Considered design criteria, thermal performance and analysis of the defrosting process are presented.