Experimental Comparison of the Evaporation and Condensation Heat Transfer Coefficients on the Outside of Enhanced Surface Tubes with Different Outer Diameters

Abstract

An experimental investigation was performed, and results are presented here for an evaporation and condensation heat transfer study that took place using enhanced heat transfer (1EHT) tubes of different outside diameters. Results were compared to the performance of a smooth surface copper tube. The equivalent outer diameter of the horizontal copper tubes considered were 12.7 mm (0.5 in) and 19.05 mm (0.75 in). The test apparatus included a straight horizontal test section with an active length heated by water. Constant heat flux was maintained and refrigerant quality varied.
Experimental runs were performed using R410A and R134a as the working ?uids. Experimental condensation results are presented for a fixed inlet/outlet vapor quality and fixed saturation temperature, while mass flux varied; producing a heat transfer coef?cient increase (compared to smooth tube) in the range 54 to 64 %, with a frictional pressure drop increase for the 1EHT tubes in the range of 8 to 31 %. Unexpected evaporation results were found at higher mass flows; producing a decrease (compared to smooth tubes) of the heat transfer coef?cient for 1EHT tubes in the range of 100 – 220 %; with an increase of frictional pressure drop values for the 1EHT tubes in the range 5 to 17 %.
Enhanced heat transfer tubes are important options to be considered in the design of high efficiency systems. A wide variety of industrial processes involve the transfer of heat energy during phase change and many of those processes employ old technology. These processes are ideal candidates for a redesign that could achieve improved process performance. Vipertex 1EHT enhanced tubes recover more energy and provide an opportunity to advance the design of many heat transfer products.