Abstract: R410a is known as one of the substitutes of R22. Studying the pressure drop of R410a during condensing process is important for designing high efficient condensation heat transfer equipments using R410a as refrigerant. Test rig for condensation heat transfer in micro-scale is established and condensation heat transfer coefficients of R22 and R410a in stainless round tube with the inner diameter of 0.941 mm are measured at a saturate temperature of 40 ℃, with mass flux varying from 200-1 000 kg/(m2•s), over the quality 0.2-0.8. The effects of mass flux and vapor quality were analyzed and present experiment data were compared with SHAH (1979) correlation and AKERS(1959) correlation which are based on experiment data from conventional tubes and widely used. The experimental and analytical results showed that condensation heat transfer coefficients increased with mass flux and vapor quality and obviously faster in high vapor quality region, which indicated that vapor shear force played more important role. The two correlations both can’t predict present experiment data accurately especially in high vapor quality region with the biggest error of 60%. Condensation heat transfer coefficients of R410a are lower than that of R22 at low mass flux and vapor quality but nearly equivalent at intermediate or more higher mass flux.

Key words: Condensation heat transfer, Convective heat transfer, Micro-tube