Visualization and measurement of periodic reverse flow and boiling fluctuations in a microchannel evaporator of an air-conditioning system

Hanfei Tuo, Pega Hrnjak

Research output: Contribution to journalArticlepeer-review

Abstract

This paper presents a simultaneous visualization and measurement on periodic reverse flow and boiling fluctuations of R-134a in a parallel flow microchannel evaporator used for air-conditioning systems. The visualization study shows that the microchannel repeats the transient flow patterns with two stages: liquid rewetting stage, and transient annular evaporating/dewetting stage. Correspondingly, five transient flow patterns are identified along the microchannel: bubbly flow, elongated bubble, liquid lump flow, annular flow, and mist/dryout flow. The reverse flow is observed to begin with the elongated bubble flow at the upstream channel and continue until the transient annular film evaporating/dewetting stage, indicating that the existing immeasurable high pressure within the elongated bubble or at a certain location in the annular flow exceeds the channel inlet and exit pressures. The period of the pressure drop fluctuation and flow pattern alternation are almost identical with that of the reverse flow, and it decreases from 1.49 s to 1.13 s when the average heat flux increases from 14.1 kW/m2 to 18.3 kW/m2. The decrease in oscillation period is mainly due to the shortened time interval for the annular film evaporating/dewetting stage.

Original languageEnglish (US)
Pages (from-to)639-652
Number of pages14
JournalInternational Journal of Heat and Mass Transfer
Volume71
DOIs
StatePublished - Apr 1 2014

Keywords

  • Air-conditioning system
  • Flow visualization
  • Microchannel evaporator
  • Periodic reverse flow
  • R-134a two-phase flow

ASJC Scopus subject areas

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

Fingerprint Dive into the research topics of 'Visualization and measurement of periodic reverse flow and boiling fluctuations in a microchannel evaporator of an air-conditioning system'. Together they form a unique fingerprint.

Cite this