Experimental Study of Axial Grooved Variable Conductance Heat Pipe

Abstract

The thermal performance of a gas-loaded variable conductance heat pipe (VCHP) is investigated. The VCHP consists of a conventional constant-conductance heat pipe and a reservoir: the reservoir is connected to the end of the condenser of the heat pipe. The heat pipe section of the VCHP is an axial grooved aluminum pipe. The working fluid and the non- condensate gas were 20 ml acetone and air, respectively. The heat load was given to the evaporator section, while the condenser section was water-cooled. By keeping the reservoir temperature constant, the temperature of the adiabatic section was kept constant against the change in the heat load to the evaporator, as well as against the change in the temperature of the condenser section. The temperature of the evaporator section could be regulated by adjusting the heat input to the reservoir: The temperature of the evaporator section could also be kept constant against the change in the temperature of the condenser section, and against the change in the heat load to the evaporator section. conducted on the ETS-III and the ETS-V successfully. 3 However, VCHP has not been used in a Japanese satellite since then. This paper investigates the fundamental thermal performance of a VCHP. The heat load to the evaporator section and the temperature of the condenser section were changed to measure the thermal performance of the VCHP. The fundamental operations of the VCHP were demonstrated. The PID control of the heater on the reservoir is employed to control the temperature of evaporator section. It is certain that VCHP is a useful temperature control device which enables the power reduction for temperature control. II. Gas-controlled heat pipe A conventional heat pipe contains a working fluid which is saturated in it. It is composed of three main parts; an evaporator, a condenser and an adiabatic sections. A wick is put on the inner surface of the pipe. During the operation, the working fluid is vaporized by the heat load to the evaporator section. The vapor flows through the adiabatic section to the condenser section, and it condenses there. The capillary force develops in the vapor-liquid interface in the wick. The capillary force pumps the liquid to the evaporator for re-evaporation. A conventional heat pipe realizes high heat transfer performance and has uniform temperature distribution over its surface by the latent heat exchange. VCHP contains a non-condensable gas along with a working fluid. A gas reservoir is connected to the end of the condenser section. During the operation, the vapor of the working fluid sweeps away the non-condensable gas to the reservoir. At one part of the condenser section, the vapor cannot condense there due to the existence of the non- condensable gas. This portion is inactive part of the condenser section. The non-condensable gas represents a diffusion barrier against the flowing vapor. The vapor can condense at the rest part of the condenser section, which is active part of the condenser section. The active condenser area is changed passively according to the variation of the heat load to the evaporator section and to the thermal condition in the condenser section, i.e. the temperature of T