Numerical investigations on flow boiling heat transfer of ammonia water binary solution (NH3/H2O) in a horizontal microchannel

Ren Yang, Yi Wang, Yongliang Li

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Abstract

The flow boiling heat transfer characteristics of NH3/H2O mixture in a 2D single horizontal microchannel (0.4 mm width × 6 mm length) were investigated by Computational Fluid Dynamics (CFD) method. The multiphase VOF model and modified phase change Lee method were adopted to address the non-isothermal phase change process of the flowing zeotropic NH3/H2O mixture, while the variations of the binary mixture thermophysical properties were also taken into account. The effects of mass flux (46~552 kg/(m2∙K)), inlet NH3 concentration (0-35% by mole) and heating wall temperature (20.5~70 C) on the overall and local flow boiling heat transfer performance have been comparatively evaluated under constant heating wall temperatures. According to the numerical results, the heat dissipation rate of NH3/H2O mixture flow boiling could reach up to 1.41 MW/m2 at a mass flux of 552 kg/(m2∙s), which was 2.05 times of water single-phase flow cooling under a same constant heating wall temperature of 50 C. It was also revealed that, for NH3/H2O mixture flow boiling in the microchannel, there was a threshold of inlet NH3 concentration to maintain a certain level of heat dissipation rate at a given mass flow rate and further increasing the inlet NH3 concentration would no longer benefit the heat dissipation process. Furthermore, there were no local dry-outs found throughout the whole microchannel length under all the simulation conditions in this study, which could be attributed to the unique flow boiling behaviors of zeotropic NH3/H2O mixture. Therefore, it should be noticed that NH3/H2O mixture, under certain conditions, could be a good alternative coolant for preventing local dry-outs and maintaining a certain functional temperature of electronic components.

Original languageEnglish
Article number121091
Number of pages13
JournalInternational Journal of Heat and Mass Transfer
Volume171
Issue number121091
Early online date19 Feb 2021
DOIs
Publication statusPublished - Jun 2021

Bibliographical note

Funding Information: The authors would like to acknowledge the financial support of the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom (Grant Nos. EP/N000714/1 and EP/N021142/1).

Keywords

  • flow boiling heat transfer
  • microchannel
  • zeotropic NH3/H2O mixture
  • numerical simulation

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes

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