Thermal hydraulic characteristic of thermosyphon pressurized with non-condensable gas

Abstract

Thermosyphon or wickless heat pipe has been applied in many fields of industry due to its high thermal conductance and passive working principle. Many studies have been done to elucidate the complex thermal hydraulic phenomena inside thermosyphon. Parameters such as geometry, type of working fluid, inclination angle of operation, confinement and entrainment have been major focal points in discussion related to thermosyphon research. However, in recent experimental studies, it has been reported that adding non-condensable gas along with working fluid during the initial charging of thermosyphon increase its entrainment limitation. This finding is important, considering some previous studies regard the presence of non-condensable gas as a hinderance on thermosyphon's condenser performance. In this study, experiments were conducted on a pressurized thermosyphon charged with water and argon gas as a non-condensable substance. Observations have been made especially on the case where cooling temperature on the outside of the condenser is far below operation temperature inside thermosyphon. It was found that low thermal conductivity of non-condensable gas causes large temperature gradient along the condenser. For this condition, currently available correlations cannot be applied. Therefore, experiments were required to prove this hypothesis, involving varying amounts of non-condensable gas. These amounts were expressed by the initial pressure values, ranging from 13 kPa to 160 kPa. The analysis of heat transfer in the evaporator and the condenser was conducted using correlations available in the literature. It was found that a new model is required to describe thermal-hydraulic phenomena in the condenser. The model is currently being validated with experimental data and good agreement has been achieved.