Hydrocarbon condensation in horizontal smooth tubes: Part Ⅱ - Heat transfer coefficient and pressure drop modeling

摘要

In this second part, Part Ⅱ of a two-part study, data reported in Part Ⅰ for condensation of hydrocarbons over a wide range of conditions are used to develop models for pressure drop and heat transfer coefficients. The pressure drop model accounts for the pressure drop occurring in the vapor and liquid phases, and due to phase interactions. The model provides improved predictions over existing correlations at lower frictional pressure drop conditions, such as in larger tube diameters and at higher saturation pressures. The data from Part I of this study are also used to develop a physically consistent condensation heat transfer model for horizontal smooth tubes. This model incorporates a novel method to account for the heat transfer through the upper liquid film that typically forms in horizontal tubes. The approach models the evolution of the liquid film from purely horizontal (annular) flow to a combination of vertical (falling film) and horizontal (annular) flow. Moreover, the evolution with quality is modeled continuously without resorting to interpolation between flow regimes. In doing so, this model accurately reflects the observations from flow visualization studies, and is a departure from the approach typically followed in existing correlations. Both models are developed using a database containing only hydrocarbon data (propane and pentane), but are shown to also accurately predict synthetic refrigerant behavior. Special attention is paid to developing a model that is equally applicable to all of the operating conditions in the database, thus equal weighting is given to high pressure and low pressure conditions, and all mass fluxes and tube diameters. The models predict the frictional pressure drop and heat transfer coefficient for the propane database with average deviations of 3% and -1%, respectively.