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In this paper the salient features of an experimental investigation on heat transfer enhancement by twisted-tape inserts inside a horizontal R-22 condenser are reported. The test condenser has four test sections connected in series, and each test section has an inside diameter of 12.7 mm and length of 950 mm. Three twisted-tape inserts with twist ratios, y, of 14.95, 9.05, and 5.90 were put, one by one, in the entire length of the test condenser. The refrigerant mass velocity G was varied from 210 to 372 kg/s-m2 in four steps. Enhancement in the average heat transfer coefficient h was attained up to 25% for the twisted-tape insert with the twist ratio y of 5.90, as compared to the plain tube flow. It was also found that the twisted-tape inserts are more effective at low vapor mass velocities inside the tubes. An empirical correlation equation was also developed to calculate the heat transfer coefficients. This equation predicts the experimental heat transfer coefficient within an error band of ±30% for a tube with the twisted-tape inserts.

Units: SI

Citation: ASHRAE Transactions, vol. 111, pt. 1, Orlando 2005