Analysis of the onset of the oscillation motion in a pulsating heat pipe

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Abstract

Increasing interest in the use of plastic foils for flexible electronic applications calls for a more efficient cooling approach suitable for this material. A pulsating heat pipe (PHP) is a promising heat transfer device that could be integrated in these flexible electronics. The working principle of these devices is not yet fully understood. It is an interplay between convective heat transfer, evaporation of liquid at the hot side and condensation of the vapor at the cold side. Several factors can play an important role including pressure differences, frictional forces, inertia forces, and capillary forces. Extended models are needed to fully understand and control heat removal by PHPs. In this work, a 1D mathematical model is developed that describes the main driving forces for the fluid motion. Main focus is on the onset of the oscillating motion. Also an experimental investigation is conducted on the onset of the motion to verify the model. The movement of a liquid slug in a heated capillary tube is captured by a high speed camera. From these pictures the positions and velocities are determined and compared with the 1D mathematical model. The measurements show good agreement with the numerical results. The study is extended to a single loop closed PHP to investigate the effects of length, channel diameter, shear stress and capillary force on oscillatory motion. It is seen that shear stress create damping effect whereas the effect of capillary force can be neglected. The decrease in channel diameter and increase in length is found to result in a reduction of the oscillating frequency. Finally, a PHP with two turns is also investigated. It is shown that in case that the number of slugs is larger than the number of heating sections, some slugs will coalescence such that the number of slugs equals the number of heating sections. It is also shown that a minimum heat input is required for getting a continuous oscillatory motion.
Original languageEnglish
Title of host publicationProceedings of the 3rd European Conference on Microfluidics, 3-5 December 2012, Heidelberg, Germany
EditorsS Colin, GL Morini, JJ Brandner
Place of PublicationParis
PublisherSHF
PagesFLU12-61-1/10
Publication statusPublished - 2012
Event3rd European Conference on Microfluidics (MicroFlu’12) - Heidelberg, Germany
Duration: 3 Dec 20125 Dec 2012
Conference number: 3
http://www.microfluidics2012.eu/

Conference

Conference3rd European Conference on Microfluidics (MicroFlu’12)
Abbreviated titleMicroFlu’12
CountryGermany
CityHeidelberg
Period3/12/125/12/12
Internet address

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