Effect of channel geometry on flow reversal in microchannel evaporators

Huize Li, Pega Hrnjak

Research output: Contribution to journalArticlepeer-review


Boiling instability and periodic flow reversal are commonly seen in microchannel heat exchangers, but have been studied in air conditioning systems only recently. The amount and frequency of reverse flow largely depends on the geometry of the channels. This paper presents results obtained in a R134a automotive air conditioning system operated under flash gas bypass mode with venting of reversed vapor (to provide better control of the flow). Results for multiple microchannel evaporators with different channel diameters and lengths are presented. The mass flow rate and frequency of reversed vapor are measured for each geometry. Meanwhile, a mechanistic model is developed to simulate the bubble dynamics inside of a single microchannel tube. This model is validated against experimental data and employed to explain the effect of channel length and diameter on flow reversal. Both experimental and simulation results show that larger channel diameter and longer channel length result in less flow reversal with a lower frequency.

Original languageEnglish (US)
Pages (from-to)1-10
Number of pages10
JournalInternational Journal of Heat and Mass Transfer
StatePublished - 2017


  • Flow reversal
  • Microchannel heat exchanger
  • Model of bubble dynamics

ASJC Scopus subject areas

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


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