The computer program described in this paper is capable of simulating the behavior of any thermosiphon loop of the form. This program was developed as part of a larger study sponsored by ASHRAE under RP-140 "Development of Performance Criteria for Two-Phase Thermosiphon Loops.". Two additional papers, written as a result of this study, supplement this paper by describing the results of both experimental and computer simulation studies into the operating characteristics of thermosiphon loops.

This paper outlines the operational steps carried out by the program as it simulates, incrementally, the state of the working fluid flowing around the loop. Some of the problems encountered are discussed along with their solutions. A comparison of the simulated and experimental data is also provided to check the validity of the simulated results.