The Helical Oscillating Heat Pipe: Flow Pattern Behaviour Study

Y Sriudom,T Chompookham,S Rittidech

doi:10.1155/2014/194374

Abstract

This research aims to study the effect of evaporator temperature, pitch distance, and working fluid on the internal flow pattern and the heat transfer characteristics of the helical oscillating heat pipe. A Pyrex tube with an inner diameter of 2.4 mm was used to study the flow pattern in the evaporator section. The pitch distance varied at 1, 1.5, and 2 cm. Water and R-123 were used as working fluid with a filling ratio of 80% by total volume. In the evaporator section, the water temperature varied at 60, 75, and 90°C to supply heat to the heat pipe. In the condenser section, air with a temperature of 25°C was used as heat sink. From the results, it was found that 4 internal flow patterns, bubble flow, slug flow, annular flow, and stratified wavy flow, were observed in the evaporator section for both working fluids. The heat transfer rate decreased when the pitch distance was increased from 1 to 2 cm. The maximum heat flux was 2,132.6 and 1,773.4 W/m2 for the working fluid of R-123 and water, respectively. Both occurred at a pitch distance of 1 cm and an evaporator temperature of 90°C.

Highlights

The pulsating or oscillating heat pipe (OHP) is a type of high-performance heat pipe
The bubble flow was formed as the small vapor bubbles at the bottom coil of evaporator section when the heat was applied to a long liquid slug
From the research on the effect of evaporator temperature, pitch distance, and working fluid on the internal flow patterns and the heat transfer rate of the helical oscillating heat pipe (HOHP), it was found that when water and R-123 were used as working fluid, there were 4 internal flow patterns

Summary

Introduction

The pulsating or oscillating heat pipe (OHP) is a type of high-performance heat pipe. The heat transfer characteristics of the OHP significantly depend on the internal flow pattern because each flow pattern shows different heat transfer capability This is related to many variables such as tube inner diameter, tube length, inclination angle, evaporator temperature, and working fluid. Charoensawan and Terdtoon, for example, studied the horizontal CLOHP performance at normal operating conditions with the varied inner diameters, evaporator lengths, and number of turns. Bhuwakietkumjohn et al studied the top heat mode CLOHP with check valve (THMCLOHP/CV) performance They found that the THMCLOHP/CV performance increased when the evaporator section length was decreased. The best performance occurred when the number of check valves was 2 sets; and the maximum heat flux occurred when the working fluid was R-123 at the inner diameter of 2 mm [6].

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