Effects of a countercurrent gas flow on falling-film mode transitions between horizontal tubes

Binglu Ruan, Anthony M. Jacobi, Liansheng Li

Research output: Contribution to journalArticlepeer-review


A liquid film falling between horizontal tubes is known to take the form of droplets, jets or sheets, depending on the liquid flow rate; the form of the flow is the so-called "falling-film mode". Although previously neglected in studies of mode transition, a countercurrent gas flow often exists in falling-film heat exchangers, and its effect on the liquid flow might be important: it could impact the flow regime, lead to local "dryout," and decrease the heat transfer rate. Experiments are conducted to explore the effects of a countercurrent gas flow and liquid feeding length on falling-film mode transitions for a liquid flowing over horizontal tubes. The effects on mode transition are shown to depend on fluid properties and are explained in terms of unsteadiness and film thickness. In general, transition hysteresis is reduced with an increasing gas velocity. A correlation is developed to predict the countercurrent gas flow effects on falling-film mode transitions. The liquid feeding length can affect mode transitions in quiescent surroundings and when a countercurrent gas flow imposed.

Original languageEnglish (US)
Pages (from-to)1216-1225
Number of pages10
JournalExperimental Thermal and Fluid Science
Issue number8
StatePublished - Nov 2009


  • Countercurrent gas flow
  • Falling-film
  • Heat exchangers
  • Horizontal tubes
  • Mode transitions

ASJC Scopus subject areas

  • General Chemical Engineering
  • Nuclear Energy and Engineering
  • Aerospace Engineering
  • Mechanical Engineering
  • Fluid Flow and Transfer Processes


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