This has been recently published in Applied Thermal Engineering:
https://www.sciencedirect.com/science/article/abs/pii/S1359431115000915
Comparison of Tubeside Condensation and Evaporation Characteristics of Smooth and Enhanced Heat Transfer 1EHT Tubes
David J. Kukulka, Rick Smith, Wei Li
Results are presented here from an experimental investigation that was performed to evaluate the inside condensation and evaporation heat transfer of R410A, R22 and R32 that took place in a 12.7 mm (0.5 in) O.D. horizontal copper tube at low mass fluxes. Tubes considered in this evaluation consisted of a smooth tube (inner diameter 11.43 mm) and a newly developed enhanced surface Vipertex® 1EHT tube. Heat transfer enhancement is an important factor in obtaining energy efficiency improvements in a variety of heat transfer applications. Utilization of enhanced heat transfer tubes is often utilized in the development of high performance air conditioning and refrigeration systems. Vipertex® has designed and produced these surfaces through three dimensional material surface modifications which produces flow optimized, enhanced heat transfer tubes that increase heat transfer. Heat transfer enhancement plays an important role in improving energy efficiencies and developing high performance thermal systems. This study details the evaluation of the in-tube evaporation and condensation that takes place in these tubes over a wide range of conditions.
The test apparatus utilized included a straight horizontal test section with an active length heated by water circulated in the surrounding annulus. Constant heat flux was maintained and refrigerant quality varied. In-tube evaporation measurements of R22, R32 and R410A are reported for evaporation at 10 OC with mass flow rates in the range of 15 to 40 kg/h. Single phase measurements are reported for mass flow rates from 15 kg/h to 80 kg/h. Condensation tests were conducted at a saturation temperature of 47OC, with an inlet quality of 0.8 and an outlet quality of 0.1. In a comparison to smooth tubes, the average heat transfer coefficients for the Vipertex® 1EHT tube exceeded those of a smooth tube. Average evaporation and condensation heat transfer coefficients for R22, R32 and R410A in the 1EHT tube are approximately two times greater than those of a smooth tube.
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. Many of those processes employ old technology; this makes those processes ideal candidates for a redesign using enhanced surfaces that would produce improved process performance. Vipertex® 1EHT enhanced tubes recover more energy and provide an opportunity to advance the design of many heat transfer products.