UC Irvine

ABSTRACT OF THE THESIS

Thermal management is important for many engineering systems such as PEM fuel cells, batteries, electrochemical supercapacitors, solar energy, and heat engines. Heat transfer, such as dissipation and cooling, is a major subject in thermal management. Among all the modern technologies of heat dissipation and cooling, heat pipes (HP) have received a growing attention because of their great potential in high thermal and heat transfer performance. The Oscillating Heat Pipe (OHP), a passive HP device originally developed in 1990, is a promising technology involves complex and dynamic two-phase flow and heat transfer. It is regarded as one of the most efficient HPs with two outstanding features: 1.) no external power for operation and 2.) no wick structure build in the capillary tube. In this study, a testing OHP with 150mm x 100mm x 4mm is developed to investigate OHP performance under various conditions. 2 mm thick mini channels are used with 7 turns on the evaporator section. Water and 91% ethanol are used as the working fluid and the filling ratio are tested from 30% to the maximum approachable ratio to investigate the thermal performance. Horizontal and vertical orientations are also studied for its influence on the thermal performance. Various temperatures at the evaporator and condenser sides are applied, along with comparison against literature results. Basic theoretical analysis is performed to assist the experimental study. We find: 1) that water tends to have better heat transfer performance compare to ethanol when operate at low heat transfer rate; and 2) the orientation of the OHP shows little influence on the start-up of the heat transfer system but strongly affects the thermal performance of the system. The vertical orientation has a significant low thermal resistance compared to the horizontal orientation in the testing.