Investigation of temperature oscillations in a novel loop heat pipe with a vapor-driven jet injector

This paper presents a flow visualization study on the temperature oscillations inside a loop heat pipe in order to gain a better understanding of its heat transfer characteristics. A flat loop heat pipe (FLHP) with a flat evaporator instead of a typical cylindrical evaporator was built using copper as the shell and water as the working fluid. An experimental setup was designed by using the transparent material instead of copper in some parts of the FLHP. The experiment results showed that there were at least three different flow patterns in the vapor line as the heating power increased. The temperatures in different locations of the loop oscillated even when the heating power was kept constant. The largest amplitude of the temperature oscillation in the loop was located at the condenser outlet. It was found that the temperature oscillation at the condenser outlet could be divided into two types, one with smaller amplitudes and the other with larger amplitudes. The smaller amplitude temperature oscillations were always there when the heating power was increased step by step, while the larger amplitude temperature oscillations would disappear initially and show up later. Finally, the location of the vapor/liquid interface inside the condenser varied with the temperature oscillations, resulting in liquid/vapor interface motion in the compensation chamber.

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Steady-State and Transient Performance of a Miniature Loop Heat Pipe

ASME 3rd International Conference on Microchannels and Minichannels, Part B cont’d ◽

10.1115/icmm2005-75122 ◽

2005 ◽

Cited By ~ 8

Author(s):

Yuming Chen ◽

Manfred Groll ◽

Rainer Mertz ◽

Yu. F. Maydanik ◽

S. V. Vershinin

Keyword(s):

Steady State ◽

Heat Pipe ◽

Electronics Cooling ◽

Consumer Electronics ◽

Outer Diameter ◽

Loop Heat Pipe ◽

Operating Characteristics ◽

Evaporator Temperature ◽

Temperature Oscillations ◽

Compensation Chamber

A series of tests have been carried out with a miniature loop heat pipe (mLHP), which has been developed for consumer electronics cooling, for horizontal and four vertical orientations under different sink temperatures. The mLHP has a cylindrical evaporator of 5 mm outer diameter and 29 mm length. The steady-state operating characteristics are similar for different orientations except for the orientation where the evaporator is above the compensation chamber. At an evaporator temperature of 75 °C, an evaporator heat load up to 70 W can be reached with thermal resistance of about 0.2 °C/W. The transient behavior of the mLHP is studied in detail. In general, the mLHP can be started up with very low power input (5 W). Big temperature oscillations in the liquid line were found in many cases, however, the temperature oscillations in the evaporator are minimum. The orientations greatly influence the operating characteristics of the mLHP. At least for the horizontal orientation, the overall performance of the tested mLHP is satisfying.

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