Influence of oil on R-410A two-phase frictional pressure drop in a small U-type wavy tube

I. Y. Chen*, C. L. Won, Chi-Chuan Wang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Scopus citations


This study presents single-phase and two-phase pressure drop data with oil concentration C = 0, 1, 3 and 5% in a copper wavy tube having an inner diameter of 3.25 mm and a curvature radius of 6.35 mm. The ratio of frictional factor between U-bend in wavy tube and straight tube (fC/fS) is about 1.5 to 2.5 for Re = 2500 ∼ 25000. The effect of secondary flow is very crucial in the U-bend that it increases the pressure drop considerably. However, the effect of oil concentration on friction factor is negligible provided the properties are based on mixture. The ratio between two-phase pressure gradients of U-bend and straight tube is about 3. This ratio is increased with oil concentration and vapor quality. The oil effect on two-phase pressure drop is especially pronounced at high vapor quality because the effective oil concentration in liquid mixture is increased with vapor quality. The frictional two-phase multiplier for straight tube can be fairly correlated by using the Chisholm correlation. A modified two-phase friction factor based on the Geary correlation is also utilized to predict the frictional two-phase pressure gradient in U-bend. The predictions give a good agreement to the present oil-refrigerant data with a mean deviation of 12.92%.

Original languageEnglish
Pages (from-to)797-808
Number of pages12
JournalInternational Communications in Heat and Mass Transfer
Issue number6
StatePublished - 1 May 2005


  • Frictional pressure drop
  • Oil and refrigerant
  • Two-phase flow
  • U-type wavy tube

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