The effect of twisted tape inserts on heat transfer and pressure drop of R1234yf condensation flow: An experimental study

•HTC and pressure drop rises with mass velocity and quality in plain and TTI tubes.•Gravity-dominated regimes (stratified-wavy) are more sensitive to vapor quality.•Shear-dominated regimes (intermittent/annular) are more sensitive to mass velocity;•Tapes increase HTC and pressure drop, the less twist ratio, the more increment.•Twist ratio of 9 has the highest thermal performance, usually less than one. This paper deals with condensation flow inside plain and twisted tape inserted (TTI) tubes with diameter and length of 8.7 mm and 700 mm, respectively. R1234yf, identified as a viable alternative for R134a with low global warning potential (GWP), is examined as the working fluid. The heat transfer coefficient and the pressure drop of the flow are measured in different mass velocities and vapor qualities ranging 160–310 kg m−2 s−1 and 0.12–0.84, respectively. A well-equipped test rig consisting of a test condenser and other necessary equipment is employed to precisely adjust the test conditions. Experimental results for the plain tube are compared with some well-known correlations. As a result, Shah and Souza et al. equations are the most reliable equations to predict the flow heat transfer coefficient and its pressure drop, respectively. Different twisted tape inserts with three twist ratios of 6, 9, and 12 are exploited to study the effect of twisted tape geometry. The results indicate that up to 42% and 235% increment in the heat transfer coefficient and the pressure drop, respectively, is associated with implementing twisted tape inserts. In addition, it was shown that, among some correlations proposed previously in the literature, the experimental heat transfer coefficient and pressure drop in TTI tubes can be predicted by Akhavan Behabadi et al. and Hejazi et al. correlations with reasonable accuracy. According to the results, the twist ratio of 6 gives the highest increase in the heat transfer coefficient, while the ratio of 9 is associated with the highest overall enhancement ratio.