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 un-derstand fluid flow and heat transfer mechanisms in an oscillating heat pipe. Two copper oscillat-ing heat pipes filling with water and acetone respectively were investigated by a neutron imaging technique to visualize the fluid motions in the oscillating heat pipes. Temperatures on the surface of the oscillating heat pipes were measured while neutron images were taken simultaneously. Al-gorithms 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 oscillating heat pipe showed better thermal performance at a similar heat input, while the water oscillating heat pipe showed better thermal performance at a similar degree of activity. Interfaces in the acetone oscillating heat pipe oscillate more frequently and travel further. A virtuous circle is formed between sensible heat transfer and latent heat transfer for better thermal performance. Low latent heat at low heat input, low viscosity and high thermal conductivity are preferred for the working fluid to achieve better thermal performance.