Heat transfer and flow characteristics of thermally induced two-phase oscillating flow in micro tubes

Abstract

Thermally induced two-phase oscillation in a capillary tube is known to effectively transport large amount of heat. However, the oscillating flow is very complicated, because acceleration, deceleration, evaporation and condensation take place simultaneously. In this study, heat transfer and flow characteristics of the thermally induced oscillating flow in a straight micro tube were experimentally investigated. The experimental setup was composed of heating, cooling, and moving sections. Circular and square tubes were compared to investigate the effects of the channel geometry. In addition, the circular tubes with roughed inner surfaces were tested to investigate the effect of roughness. Furthermore, different types of the moving section were compared. PF-5060 (C6F14) was used for a working fluid. The oscillating motion was detected by the pressure change in the test section and the displacement of the moving section. Effective thermal conductivities representing thermal performance were compared against the heat flux defined by the channel cross-sectional areas. The circular tube showed better performance than the square tube. The circular tubes with roughed inner surface showed better performance than the circular tube with no surface treatment. From the visualization, it is considered that the amount of wetted area affects the thermal performance.

Keywords

• two phase flow
• oscillating heat pipe
• effective thermal conductivity
• frequency
• wetted area