A simple method, based on hydraulic analogies, is proposed for achieving good heat transfer with reasonable pressure drop in multiple tube overfeed evaporators. Simply forms for estimating the circulating number and the evaporator pressure drop are offered for both R717 and R22 refrigerants. References for calculating the capacity for vapour return lines are cited. A method of optimising the size of risers in overfeed return lines is reviewed. The conditions that produce hydraulic shock or liquid hammer in refrigerant liquid lines are discussed with sample calculations. Precautions to be taken in the control of hot gas defrosting of low-temperature evaporators, so as to reduce the stresses caused by liquid slugging and thermodynamic shock, are outlined. When the potential for hazardous shocks from hot gas defrosting cannot be positively eliminated, the use of ductile piping materials is recommended.

KEYWORDS: deicing, pipes, heat flow, pressure drop, refrigerants, evaporators, R22, calculating, capacity, sizing, designing, safety, failure.