Experimental investigation of the effects of heat transport pipeline configurations on the performance of a passive phase-change cooling system

The separate-type passive phase-change cooling systems provide considerable flexibility in the placement of the evaporator and condenser. An experimental study of flow characteristics and heat transfer during condensation inside the connecting section, i.e. heat transport pipeline, was conducted. Measurements were made in round tubes with diameters ranging from 20 to 38. mm, lengths from 1 to 6. m, and inclination angles from 0° to 30°. Distilled water was used as the working fluid. The study primarily took into account the effect of various parameters (inner diameter, length and inclination angle) on the performance of a cooling system. Flow visualization showed that at all operating conditions the flow pattern was the droplet flow. Heat transfer coefficient increased with increasing tube length, inner diameter and inclination angle. The system pressure drop also increased with an increase in the tube length while decreased with increasing inclination angle. For a constant heat load, an obvious decrease of evaporator temperature was observed for longer tubes. Moreover, the cooling system needed a certain time (defined as "delayed time", represented the robustness of the system) to reach the steady-state again when the heat load increased. Different tube configurations can result in different "delayed time".