A parametric study of boiling heat transfer in horizontal tube bundles

摘要

Boiling heat transfer outside a section of a uniformly heated horizontal tube bundle in an upward crossflow was investigated using R-113 as the working fluid. Two in-line tube bundles with pitch-to-diameter ratios of 1.3 and 1.7 were tested. Each tube bundle had five columns and 27 rows. Heat transfer coefficients obtained from 14 instrumented tubes are reported for a variety of flow conditions. The effects of heat flux, mass velocity, pressure and pitch-to-diameter ratio of the heat transfer coefficient were determined.;At high heat fluxes there was no significant variation in the heat transfer coefficient in the tube bundle. However, at low heat fluxes and mass velocities, the heat transfer coefficient increased at positions higher in the tube bundle. As pressure and mass velocity increased so did the heat transfer coefficients. The tube bundle with the larger pitch-to-diameter ratio had higher heat transfer coefficients than the smaller test section at low heat fluxes. However, the differences decreased as heat flux increased. A Chen-type correlation was developed, with an S factor and an F factor being described for tube bundles, for the prediction of local tube-averaged heat transfer coefficients. This correlation correlated the data to within 27.3%. It was concluded that the Chen-type correlation as developed for intube flow is not directly applicable to shellside flow, but the approach is applicable; improvements in the procedures to estimate the S and F factors should result in more accurate predictions. The mechanism governing convective two-phase heat transfer in spray/annular flow in a tube bundle was explored. It was concluded that the mechanism is conduction through a thin liquid film. A model for predicting the liquid film thickness at the minimum flow area of the tube bundle was proposed for the annular/spray flow pattern. The heat transfer coefficient was predicted using a film conduction model and adopting a liquid film waviness correction factor. The absolute average deviation between the predicted and experimental heat transfer coefficients was 19.1%.