Visualization of Oscillating Heat Pipes

Abstract

As described in previous chapters, fluid flow and heat transfer in an oscillating heat pipe is very complex. To better understand thermally excited oscillating flow, a number of visualization methods have been used to study fluid flow of liquid plugs and vapor bubbles in OHPs. Three typical visualization methods include visible imaging technique, neutron and proton radiographs (Ph.D. dissertation, Missouri). Visible imaging technique is the most widely used but is limited due to the fact that the OHP tubes needed for this method must be made of transparent material only such as glass or OHPs covered with transparent materials. Neutron radiography is used to visualize the movements of liquid plugs and vapor bubbles in an OHP made of metallic materials such as copper and aluminum. With neutron imaging, images of liquid plugs and vapor bubbles can be seen through metallic walls. Proton radiography is also used to image the movement of liquid plugs and vapor bubbles of OHPs and can successfully visualize both liquid and vapor motions. In this chapter, these three visualization methods, which have been used to study oscillating flows in OHPs, will be presented including their observation results of oscillating motions in OHPs.