Visualization of Heat Transfer Characteristics of 1EHT and Smooth Surface Tubes

Abstract

Abstract High efficiency heat transfer tubes play a major role in industrial applications due to its benefits in recovering more energy, smaller footprint and lower operational costs. Given the importance of enhanced heat transfer tubes, an experimental investigation was carried out to compare the performance of the Vipertex 1EHT tube with an equivalent smooth tube using Particle Image Velocimetry (PIV). For the experimental setup a Dantec Dynamics PIV system was considered, and both tubes used had an outer diameter of 19.05 mm and inner diameter of 17.09 mm. Heat transfer experiments were conducted at 100% of the heater power capacity, i.e. 750 W, and observations were made in terms of boiling visualization, particle velocity vector field, and seeding particle velocity. The results obtained from the visualization showed higher density of bubble formation on the surface of 1EHT tube compared to the smooth tube, as well as a more frequent formation of bubbles. Moreover, the high-speed camera films recorded for comparison between smooth and enhanced tubes, showed that the dimples provided nucleation sites. Additionally, the average particle velocity for the 1EHT tube was 0.300 m.s−1 and for the smooth tube it was only 0.230 m.s−1, as a result of the higher heat transfer of the enhanced tube. These results suggest that the 1EHT tube performs better in boiling heat transfer application, which can be attributed to the enhanced heat transfer area produced by the series of dimples/protrusions and petals distributed over its surface.