Microfin tube is one of the most popular enhancements for in-tube boiling and condensation of refrigerants. The reason for its popularity is the larger heat transfer enhancement relative to the slightly increased pressure drop. Because of its outstanding performance

it has strongly attracted the attention of a large number of investigators

and numerous papers have been published on microfin tubes [1～3] .However

almost all microfin tubes studied by those investigators were single helix (2-D) microfin geometry. A new 3-D microfin tube was first developed by Du and Xin

et al . (1995). Their 3-D microfin tube is seamless. Xin and Wang had studied the in-tube condensation heat transfer performance of the 3-D microfin tube with R-11 and steam. In 1996

Chamra and Webb et al . presented another 3-D microfin tube

which were manufactured by using high frequency welding method. They reported the condensation performance with refrigerant R22. The experimental data of the two 3-D microfin tubes in their papers demonstrated higher heat transfer performances as compared with 2-D micro-fin tubes. However

no one reported the refrigerant R134a condensation performance in 3-D microfin tube. The purpose of this paper focuses on the condensation performance for refrigerant R134a in a new 3-D micro -fin tube. The experiments are carried out at different inlet pressure: 0.51-0.77 MPa ( temperature: 18 - 30 ℃)

the mass flux is between 125 and 285 kg/m 2·s

and the vapor quality

x

is from 1.00 to 0.14. The data are compared with those of smooth tube

which are calculated with Shahs correlation. The ratio of enhancement for condensation is 1.7-3 (at x =0.6) in the experimental range of the mass flux noted above. The average ratio of enhancement is 2.2. The effects of mass flux and quality are also reported.