Operating Characteristics Analysis Of Vapor-liquid Phase Transition In Oscillating Heat Pipes

In the 90 s of last century, Akachi invented a special type of heat pipe, named oscillating heat pipe. Oscillating heat pipes are usually referred to as heat superconductors because of its remarkable heat transfer efficiency that is considerably higher than any metal. That's what draw researchers' attention to studying oscillating heat pipes. So far, however, most researchers are still focus on the observation of phenomenon in oscillating heat pipes and there is still no complete theoretical knowledge about operation mechanism and flow characteristics on oscillating heat pipe. Therefore, this thesis tries to find an answer by numerical simulation study.Oscillating heat pipe research belongs to the typical type of gas-liquid two phase flow. The key of this kind research is to capture the gas-liquid interface accurately. This paper attempts to capture the interface by VOF method, use the theory of phase transition to compute the mass and heat transfer between gas and liquid, choose continuous surface force(CSF) model to calculate surface tension, adopt Kistler's dynamic contact angle model to calculate dynamic contact angle in tube. Based on these, a two-dimensional mathematical model for accurately describing oscillating heat pipe gas-liquid phase change is established. The later numerical simulation about closed oscillating heat pipe's operation is done on the Fluent platform. According to the simulation results, the oscillating heat pipe simulation process is divided into two stages: one is initialization, the other one is heating operation. Aiming at the particularity of oscillating heat pipe initialization, we explain the heat pipe initialization process in detail, and analyzed the three kinds of vacuum degree's effection on initialization.After initialization,heat loading is applied on oscillating heat pipes' evaporation zone. According to the simulation results, we study the bubble's growth, movement and distribution, analyze the relationship between the heat transfer and the bubble motion characteristics, focus on the liquid flow situation in the working medium, analyze the importance of dynamic contact angle model for simulation in this paper.Finally we emphatically choose bubble/plug as the research object, analyze the bubble motion characteristics, working medium flow characteristics and the oscillating characteristics of oscillating heat pipe. Further understanding about the operational mechanism of oscillating heat pipe is getted through the analysis of the running characteristics of oscillating heat pipe.