Falling film evaporation on enhanced tubes, part 2: Prediction methods and visualization

For falling film evaporation, the most important thermal design parameters that need to be predicted are the onset of dryout, after which a severe degradation in the evaporator performance is found, and the local heat transfer performance in fully wet and partially dry conditions. Presently, based on the new data and previous data presented in Part 1, new methods for prediction of (i) the nucleate pool boiling heat transfer coefficient, (ii) the onset of dryout and (iii), the bundle heat transfer performance for the enhanced boiling tubes tested at the LTCM laboratory have been developed. These methods minimize the amount of empirical constants required, resulting in only one tube-specific parameter for all three conditions for each enhanced tube. The results from the visualization studies performed are presented and discussed.

► New prediction methods for pool boiling and falling film.
► Same empirical constants for all refrigerants.
► Only one empirical constant per tube.
► In-bundle visualization showed liquid pumping effect into pores.