Measurements and correlations of frictional single-phase and two-phase pressure drops of R-410A flow in small U-type return bends

Ing Youn Chen*, Chi-Chuan Wang, Shy Yau Lin

*Corresponding author for this work

Research output: Contribution to journalArticle

43 Scopus citations

Abstract

This study presents single-phase and two-phase frictional data for R-410A in four U-type return bends with tube diameter D=3.3 and 5.07 mm and curvature ratio (2R/D) ranged from 3.91 to 8.15, and their frictional performances are investigated. The friction factor fC and two-phase pressure gradient in the return bend considerably increase with the decrease of curvature ratio. For D=5.07 mm and G≥200 kg m-2 s-1, the ratio of (dp/dz)C/(dp/dz)S is relatively independent of the vapor quality x. However, a considerable rise of this ratio is encountered at x<0.5 and G=100 kg m-2s-1. The significant increase of this ratio may be attributed to the change of flow pattern from stratified flow to annular flow. In contrast, for D=3.3 mm and G≥300 kg m-2s-1, the higher pressure gradient ratio at lower x was not observed. The flow pattern at low vapor quality is slug flow and no dramatic change of flow pattern across the return bend is seen. For the single-phase results, existing correlations give fair agreements with the present fC data. For two-phase results, the Geary correlation shows a better agreement with the data. A modified two-phase friction factor based on the Geary correlation is then proposed. The proposed correlation gives a good agreement to the present R-410A data and Geary's R-22 data with a mean deviation of 19.1%.

Original languageEnglish
Pages (from-to)2241-2249
Number of pages9
JournalInternational Journal of Heat and Mass Transfer
Volume47
Issue number10-11
DOIs
StatePublished - 1 Jan 2004

Keywords

  • Friction factor
  • Return bend
  • Two-phase pressure gradient

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