To investigate the heat transfer from enhanced evaporation surfaces, various structured tubes, particularly with re-entrant cavities, and one smooth reference surface were tested in the pool boiling mode using the hydrocarbon propane as working fluid. The tubes are made of carbon steel ST35.8. As experimental parameters saturation temperatures between 253 K and 293 K and heat fluxes in the range from 2 kW/m2 to 100 kW/m2 are employed. For the visualization of the boiling phenomena and the two-phase flow from the tube surfaces a test rig is employed with a high speed video system. An empirical correlation has been generated to describe the experimental results.
Compared with the smooth reference tube, the structured surfaces with re-entrant cavities show distinct improvements of the heat transfer performance. Particularly for low and medium heat fluxes (q < 40 kW/m2), higher heat transfer coefficients of factors up to 3 were observed.