An experimental investigation on the influence of condenser bypass area for the transient and steady-state heat-transfer performance of heat pipes

Fundamentally, an effective method for improving the performance of transient and steady-state heat transfer is reducing the flow resistance at the phase-change interface based on the counter flow of vapor and liquid within a typical heat pipe. The flow resistance at such an interface is proportional to the volume flow rates of liquid and vapor. Therefore, the flow resistance at the interface can be reduced by limiting the mass flow rate of vapor or liquid. In this study, experiments were performed on a liquid bypass to improve the steady-state thermal performance of heat pipes. A separate bypass tube allowed some liquid to be subcooled in the condenser to bypass the evaporator without passing through the heat pipe. Three liquid-bypass ports were designed and fabricated in a condenser to experimentally investigate the influence of the bypass port area on the thermal performance of the heat pipe under steady-state operation. An on/off valve was attached to each bypass tube port in the condenser to control the bypass flow rate. The results showed that the thermal resistance, an evaluation index of the performance of steady-state heat transfer, generally decreased with an increase in the bypass port area of the condenser. The thermal resistance of a heat pipe with a horizontal tilt angle and one at an inclination angle of 50 degrees decreased by up to 25.5% and 51.6%, respectively.