Library Subscription: Guest

ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Effects of Tube Diameter on Internal Flow Patterns and Heat Transport Performance of Parallel-Tube Heat Transport Device

Get access (open in a dialog) DOI: 10.1615/IHTC15.hpp.009208
pages 3851-3865

Abstract

Parallel-Tube Heat Transport Device (PT-HTD) shows high heat-transport efficiency because of spontaneous internal flow convecting both sensible and latent heats. PT-HTD consists of multiple tubes and two headers in which working fluid evaporates and condenses. In our previous study, the effects of tube diameter, tube number, operating orientation, working fluid, and volumetric filling ratio on heat transport rate had been clarified. However, the relation between two-phase internal flow pattern and heat transport performance had not been quantitatively clarified yet. In this study, simultaneous measurement of heat transport rate and internal flow pattern was performed for three different working fluids (water, ethanol, and FC-72) and for two different inner tube-diameters (2.4 and 4.4 mm). The internal flow patterns were captured by using a high-speed camera, and temporally and spatially changing flow patterns were identified by laterally averaged brightness and twodimensional power spectrum of flow-pattern images. Gas-liquid interfacial velocity was also calculated by the image analysis. The results clearly showed the change of internal flow patterns depending on the working fluids, tube inner diameter, and heat transport rate. One of the important factors affecting the internal flow in PT-HTD was the normalized tube-diameter which was determined by the Laplace length, and the most complicated flow occurred for the lowest surface tension case of FC-72 in this study. At higher heat transport rate, flow characteristic frequency was shifted to lower value for all the three working fluids, and the intermittent and longinterval variation of flow pattern was observed for FC-72 and ????2.4mm case.