Investigation On In-tube Condensation Heat Transfer And Pressure Drop For R290 And R404A

Owing to the negative influence of CFCs and HCFCs refrigerants on environment, seeking refrigerants which do little harm to envrironment are very important and practical. It is necessary to study thermodynamic characteristics of new replacement for R290 and R404A, the most promising substitutes for R22, a great deal of work is still in need to put them into practice.On the basis of literature survy on the in-tube condensation of refrigerant and refrigerant oil-mixtures, the condensation heat transfer and pressure drop of R290 and R404A are studied in horizontal microfin tube and smooth tube. The heat transfer characteristics of the oil-mixtures are also predicted. The following research has been carried out.1. Some different empirical formulations are analysied for predicting the in-tube condensation heat transfer coefficients.2. Based on the experimental data collected, the formulations are selected which can predict accurately in-tube condensation heat transfer coefficients for R290 and R404A. Shah correlation can predict precisely heat transfer coefficients of R404A in smooth tube;Cavallini —Zecchin correlation can predict precisely heat transfer coefficients of R290 in smooth tube.3. The analysis on different empirical formulations of in-tube condensation heat transfer coefficients indicate that R404A can be treated as pure refrigrant when calculating it's in-tube condensation heat transfer coefficients.4. The empirical formulations for oil-mixtures are adopted to predict the condensation heat transfer coefficients of R290 with oil and R404A with oil in smooth and microfin tubes. The condensation heat transfer coefficient increases with the increase of mass flux;the condensation heat transfer coeffifient decreases with the increase of oil concerntration.5. Lockhart & Martinelli and Kaushink—Azer pressure drop correlations for smooth tubes are studied. Kaushink—Azer pressure drop correlation can predict precisely friction pressure drop of R404A in microfin tube,while modified correlation can predict precisely pressure drop of R290 in microfin tube.