STUDY OF FLUID MOTIONS AND THERMAL PERFORMANCE OF WATER AND ACETONE OSCILLATING HEAT PIPES USING NEUTRON IMAGING

Quantitative analysis of fluid motion in an oscillating heat pipe (OHP) is essential to better understand fluid flow and heat transfer mechanisms in an OHP. Two copper OHPs filled with water and acetone respectively were investigated by a neutron imaging technique to visualize the fluid motions in the OHP. Temperatures on the OHP surface were measured while neutron images were taken simultaneously. Algorithms to determine the degree of activity and the interface passing count were developed to analyze fluid motions quantitatively from the neutron images. Then, the degree of activity and the interface passing count were compared with temperatures. The results showed that there are patterns of temperature change before and after start-up of the oscillation motions. The acetone OHP showed better thermal performance at a similar heat input, while the water OHP showed better thermal performance at a similar degree of activity. Interfaces in the acetone OHP oscillate more frequently and travel further. Low latent heat at low heat input, low viscosity, and high thermal conductivity are preferred for the working fluid to achieve better thermal performance.