Bubble coalescence and break-up in confined oscillating two-phase flows under microgravity conditions

Andrzej I. Nowak, Luca Pietrasanta, Cezary Czajkowski, Marco Marengo, Sławomir Pietrowicz

Research output: Contribution to journalArticlepeer-review

Abstract

Passive two-phase heat transfer systems, such as pulsating heat pipes, are a promising thermal management solution for the rapidly growing space sector. The strong coupling between thermal and hydraulic phenomena complicated the development of reliable off-the-shelf components. This was due to the difficulties in establishing and maintaining the desired slug-plug flow pattern in a wider region sufficiently far from the annular flow, which can lead to evaporator dry-out. In this work, inertial effects on the flow pattern are investigated under adiabatic conditions to define what limits the operability range of a device. The fluid motion characteristics of pulsating heat pipes have been mechanically induced to observe conditions that lead to the break-up or coalescence of bubbles. The authors were granted access to the ESA drop tower microgravity platform to explore surface tension dominant flows and higher hydraulic diameters compared to the ground capillary diameters. A range of fluids (FC-72 and ethanol) and diameters (2.5 mm to 8 mm) has been explored, along with combinations of oscillating fluid flow, analysing high-speed images and estimating velocity and acceleration. Both the Reynolds number, in combination with the modified Bond number, have been investigated, plotting the operating points on a flow map, showing a very clear limit between break-up and coalescence when the velocity and acceleration signs are considered. This new conceptual flow map can be used to further improve existing modelling tools for pulsating heat pipes operating under reduced gravity. Furthermore, images demonstrating the break-up and coalescence may be aid to CFD scientists in verifying their results.

Original languageEnglish
Article number122905
JournalInternational Journal of Heat and Mass Transfer
Volume192
DOIs
Publication statusPublished - 14 Apr 2022

Bibliographical note

Funding Information:
The work was also partially supported by internal research funds from the Department of Thermodynamics and Renewable Energy Sources of the Wrocław University of Science and Technology, Poland, No. 8211104160 (MPK 9090750000).

Funding Information:
This work was supported by the European Space Agency [CORA grant], the EPSRC UK HyHP (EP/P013112/1) research project.

Funding Information:
This work was supported by the European Space Agency [CORA grant], the EPSRC UK HyHP (EP/P013112/1) research project. The work was also partially supported by internal research funds from the Department of Thermodynamics and Renewable Energy Sources of the Wroc?aw University of Science and Technology, Poland, No. 8211104160 (MPK 9090750000). The operation of the present experiments was supported by the Center of Applied Space Technology and Microgravity (ZARM) in Bremen, Germany. We would especially like to thank the team from the Bremen Drop Tower.

Funding Information:
The operation of the present experiments was supported by the Center of Applied Space Technology and Microgravity (ZARM) in Bremen, Germany. We would especially like to thank the team from the Bremen Drop Tower.

Publisher Copyright:
© 2022 Elsevier Ltd

Keywords

  • Break-up
  • Coalescence
  • Flow pattern
  • Microgravity
  • Two-phase flow

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