Kukulka D., Yan H., Smith R., Li W., 2017, Condensation and Evaporation Characteristics of Flows Inside Three Dimensional Vipertex Enhanced Heat Transfer Tubes
, Chemical Engineering Transactions, 61, 1777-1782.
Results are presented here from an experimental investigation of condensation and evaporation heat transfer that compares the performance of three dimensional (3-D) enhanced heat transfer tubes to the performance of a smooth surface tube. The equivalent outer diameter of all the tubes was 12.7 mm with an inner diameter of 11.5 mm. Both the inner and outer surfaces of the 3-D tubes are enhanced by a primary enhancement and a background pattern made up by an array of dimples. Experimental runs were performed using R410A as the working fluid, over the quality range of 0.2 – 0.9. The test apparatus included a horizontal, straight test section with an active length heated by water circulated in a surrounding annulus. Constant heat flux was maintained and refrigerant quality varied.
For evaporation, the heat transfer coefficient ratio of the 3-D tubes (comparing the heat transfer coefficient of the enhanced tube to that of a smooth tube) is in the range of 1.1 – 1.80 for a mass flux rate that ranges from 80 to 180 kg/m2s. For condensation, the heat transfer coefficient ratio range is 1.1 - 1.75 for mass flux that ranges from 80 to 260 kg/m2 s. Frictional pressure drop values for the enhanced tubes show some variation. Heat transfer enhancement on the inner surface of the 3-D tubes increases the surface area and interfacial turbulence; producing flow separation, secondary flows and a higher heat flux from the wall to the working fluid. 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 designs. These processes are ideal candidates for a redesign that could achieve improved process performance. These three dimensional enhanced tubes recover more energy and provide an opportunity to advance the design of many heat transfer products.
