An experimental and computer simulation investigation has been carried out to determine the operating characteristics of recirculation two phase thermosiphon loops in which both the evaporator and the condenser consist of a bank of tubes running from an inlet to an outlet header, the recirculation is achieved through the use of a separator at the evaporator header outlet which permits the liquid collected to be recirculated directly to the evaporator inlet header.

The experimental loop utilized three tubes in each heat exchanger. Either unit could be used as the evaporator or the condenser. The system was instrumental to permit the measurement of tube surface temperatures, fluid temperatures, fluid flow rates and heat transfer rates. The length of the heat exchanger tubes was fixed, however, nearly all other parameters could be-varied including the tube diameters, the angle of inclination of either heat exchanger independently, the operating temperature difference, the mean temperature of the loop, the elevation of one heat exchanger with respect to the other, the working fluid and the charge in the loop.

The basic computer simulation program developed under ASHRAE project RP 140 was modified and used as the basis of the program for the recirculation loop study. This program was first used to simulate loop operation for the experimental operating conditions. A comparison of the simulated and experimental behaviours showed that the computer program was able to accurately predict the behaviour of such systems. Further simulation studies for other loop configurations were also carried out.

The recirculation two phase, multi tube thermosiphon loop has been found to yield higher loop conductance and to be much less sensitive to operating conditions than a similar non-recirculation loop.