Heat Transport Capability and Fluid Flow Neutron Radiography of Three-Dimensional Oscillating Heat Pipes

An experimental investigation into the parameters affecting heat transport in two three-dimensional oscillating heat pipes (OHP) was implemented. A three-dimensional OHP is one in which the center axis of the circular channels containing the internal working fluid do not lie in the same plane. This novel design allows for more turns in a more compact size. The OHPs in the current investigation is made of copper tubing (3.175 mm OD, 1.65 mm ID) wrapped in a three-dimensional fashion around two copper spreaders that act as the evaporator and condenser. The two OHPs have 10 and 20 turns in both the evaporator and condenser. The 20 Turn OHP was filled to 50% of the total volume with high performance liquid chromatography (HPLC) grade water. Transient and steady state temperature data was recorded at different locations for various parameters. Parameters such as heat input, operating temperature, and filling ratio were varied to determine its effect on overall heat transport. Neutron radiography was simultaneously implemented to create images of the internal working fluid flow at a rate of 30 frames per second (fps). Results show the average temperature drop from the evaporator to condenser decreases at higher heat inputs due to an increase in temperature in the condenser region caused by greater oscillations. These large oscillations were visually observed using neutron radiography. As the operating temperature is increased, the thermal resistance is reduced due to increased fluid flow caused by changes in fluid properties. A decrease in filling ratio tends to create more steady fluid motion; however, the heat transfer performance is reduced.