Comparison of condensation and evaporation heat transfer on the outside of smooth and enhanced 1EHT tubes

Abstract

Results are presented here from an experimental investigation that evaluated the outside condensation and evaporation heat transfer that took place on a 12.7mm (0.5in.) OD horizontal copper tube. Evaporation conditions include a mass flux that ranged from 10 to 40kg/m2s; with an inlet quality of 0.1 (±0.05); outlet quality of 0.8 (±0.05); and a nominal evaporation temperature of 279K. Condensation conditions considered here include mass flux values that varied from 5 to 50kg/m2s; at a saturation temperature of 318K; with an inlet quality of 0.8 (±0.05); and outlet quality of 0.1 (±0.05). For enhanced tubes, there are limited heat transfer predicting procedures available (within the degree of confidence necessary to perform analysis) since any work that has been done is limited to specific geometry and operating conditions that have been based upon tests from which the predicting procedures have been derived. Therefore, in this study, smooth tubes were compared to the newly developed Vipertex™ 1EHT enhanced surface tube. Average evaporation heat transfer coefficients for R22 and R410A on the 1EHT tube are in the range of one to four times greater than those of a smooth tube. Condensation heat transfer performance on the outside of a 1EHT tube is less than a smooth tube due to the pattern/drainage characteristics of that model of tube for the flow conditions considered.Three dimensional enhanced surfaces can be incorporated on the surface of tubes in order to enhance heat transfer performance. Under many conditions, enhanced surface tubes can recover more energy and provide the opportunity to advance the design of many heat transfer products. Enhanced heat transfer tubes are widely used in a variety of industries in order to reduce cost and create applications that use a smaller footprint. Vipertex 1EHT tubes are a new type of enhanced heat transfer tube that uses multiple enhancement patterns; a primary pattern made up of dimples/protrusions with a secondary pattern that is an array of petals. Since this design is unique and unlike other tubes it is important to investigate the heat transfer characteristics of this novel enhanced heat transfer tube and compare it to other tubes.