Heat transfer coefficient evaluation of condensing air-steam mixtures in tubes

The paper summarizes the experiments on steam condensation carried out at the University of Rome "La Sapienza" - DINCE in the COTINCO experimental facility (1999-2001) and in the ITASCO facility (2003), where steam and air-steam condensation tests inside honzontal and inclined tubes were performed, aiming at investigating the physicai phenomena involved in condensation of steam within tubes and to develop models and heat transfer wrrelations for the given conditions. In the COTTNCO facility the condensing tube (22 mm ID) was extemally cooled by water at ambient temperature; the Reynolds number of the inlet mixture ranges between 4300 and 6200, and the tube could be inclined between 0" and 45" with respect to the horizontai. The new test facility (ITASCO - In-Tube Air-Steam COndensation) allows the investigation of three different tubes (12 mm, 20 mm and 27 mm ID), to evaiuate the effects on the heat transfer wefficient of the tube diameter and the type of nonwndensable gas, and with a wider range of the mixture Reynolds number. In the ITASCO facility, tubes are externally fmed and air-cooled. in the paper, a selected data base obtained in the COTINCO tests will be presented, using a correlation of the experimental data in dimensionless form. To correlate the experimental Shenvood number to the steam-air mixture Reynolds number, the analogy behveen heat and mass transfer was used. Finally, a preliminary set of the results obtained with the ITASCO facilitv is mesented and discussed.