Thermodynamic Analysis of the Dryout Limit of Oscillating Heat Pipes

Florian Schwarz,Alexander Lodermeyer,Alexander Hensler,Stefan Becker,Vladimir Danov

doi:10.3390/en13236346

Florian Schwarz, Alexander Lodermeyer + Show 3 more

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https://doi.org/10.3390/en13236346

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Journal: Energies	Publication Date: Dec 1, 2020
Citations: 7	License type: CC BY 4.0

Affiliation: University of Erlangen-Nuremberg, Siemens (Germany)

Abstract

The operating limits of oscillating heat pipes (OHP) are crucial for the optimal design of cooling systems. In particular, the dryout limit is a key factor in optimizing the functionality of an OHP. As shown in previous studies, experimental approaches to determine the dryout limit lead to contradictory results. This work proposes a compact theory to predict a dryout threshold that unifies the experimental and analytical data. The theory is based on the influence of vapor quality on the flow pattern. When the vapor quality exceeds a certain limit (x = 0.006), the flow pattern changes from slug flow to annular flow and the heat transfer decreases abruptly. The results indicate a uniform threshold value, which has been validated experimentally and by the literature. With that approach, it becomes possible to design an OHP with an optimized filling ratio and, hence, substantially improve its cooling abilities.

Highlights

The trend to miniaturize electronic components leads to an increased power density and to new requirements of thermal management
A theory to determine the dryout threshold for oscillating heat pipes (OHP) was derived through a thermodynamic consideration
The filling ratio at charging temperature is different from the filling ratio at operating temperature

Summary

Introduction

The trend to miniaturize electronic components leads to an increased power density and to new requirements of thermal management. In the field of power electronics, cooling plays a key role. The power density dissipation of semiconductors is about. Modern wide bandgap semiconductors such as SiC or GaN will raise the heat flux density above 1000 W/cm2 [1,2]. These large heat fluxes are exceptionally well handled by two-phase cooling systems. An established two-phase cooling system is the conventional heat pipe. They are considered to be state of the art in electronic devices and are available in different designs and shapes [3]

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