Experimental Investigation to Evaluate the Evaporation and Condensation Heat Transfer Coefficients on the Outside of Vipertex Enhanced Performance 1EHT Tubes

Abstract

An experimental investigation was performed, for a wide range of mass flux values and qualities, to evaluate and compare the convective condensation and evaporation on the outside of a smooth tube and the newly developed Vipertex enhanced heat transfer 1EHT tube. Heat transfer enhancement has been an important factor in obtaining energy ef?ciency improvements in many two phase heat transfer applications. Utilization of enhanced heat transfer tubes is an effective method that is often utilized in the development of high performance thermal systems. Vipertex™ enhanced surfaces, have been designed and produced through material surface modifications which result in flow optimized heat transfer tubes that increase heat transfer. Surface enhancement of the 1EHT tube is accomplished by using a more pronounced primary enhancement (dimple characters) that has been produced over a secondary pattern made up of petal arrays. Heat transfer processes that involve phase-change processes are typically efficient modes of heat transfer; however current energy demands and the desire to increase efficiencies of systems have prompted the development of enhanced heat transfer surfaces that are used in processes involving evaporation and condensation. Vipertex™ was able to develop a series of optimized, three dimensional tubes that enhance heat transfer. This study details the condensation and evaporation results on the outer surface of the Vipertex 1EHT tube.
Results are presented here from an experimental investigation of two phase heat transfer that took place on the outside of a 12.7 mm (0.5 in) O.D. horizontal copper tube. Average evaporation heat transfer coefficients for the outside of the Vipertex 1EHT tube are approximately one to four times greater than those of a smooth tube. However for condensation, the heat transfer is approximately 23 % ~ 65 % of the heat transfer coefficient found for the smooth tube. In both cases the pressure drop increases.