MODELS FOR HEAT TRANSFER CALCULATION DURING FILM CONDENSATION INSIDE HORIZONTAL TUBES

Abstract

The study of heat transfer during condensation in the middle of the pipes is relevant due to the constant need to improve the design of various heat exchangers (condensers of refrigeration and air conditioning systems, reactor safety systems, and power plant heaters). It is important to know the exact values of heat transfer coefficients in the case of condensation when their value is close to the heat transfer from the cooling side. Well-known theoretical, semi-empirical and experimental models and correlations for heat transfer calculation during condensation of working fluids inside smooth horizontal pipes have been described in the article. Selected models are widely used in various scientific publications for heat transfer prediction and construction of various heat exchangers with in-tube condensation. All correlations allow determining the average by tube perimeter, but local by the length of the tube, heat transfer coefficients in the case of annular and intermediate regimes of two-phase flow. All used dependences take into account current modes of phase flow. For choosing the best correlations, a comparison between selected models and experimental values of heat transfer coefficients obtained by different authors for condensation of ten working fluids inside smooth horizontal tubes with internal diameters more than 3 mm have been performed. Experimental values were selected from well-known works, in which heat transfer was studied during condensation of such fluids as fluorocarbons, immersion refrigerants, hydrocarbons and steam in the case of intermediate and annular phase flows with a detailed description of research conditions (geometrical parameters of investigated tubes and regimes parameters of condensation process, such as heat flux, mass velocity, vapour quality, and condensation temperature). Comparison of various models with experimental data of different authors allowed identifying the models that show the best convergence with experiments among all correlations. Recommendations (range of application) for use of models in engineering practice are given.