Ivestigation On Flow Boiling Heat Transfer Characteristics Of R290 And R404A In Horizontal Microfin Tube

In recent years, due to the phase-out of HCFCs in refrigeration and air conditioning industry, refrigerants which do little harm to enviroment are being developed and their thermodynamic characteristics are being studied deeply. Because research on substitutions for R22 shows that the heat transfer abilities of its substitutions are less than that of R22, microfin tubes are applied to augment in-tube evaporation and condensation heat transfer.The objective of this dissertation is to conduct on theorical analysis and calculation upon flow boiling heat transfer inside horizontal smooth and microfin tube of R290 and R404A, which are newly environmental replacements of R22. And the major parts of the dissertation are as follows:1. Some different empirical formulations on predicting the in-tube boiling heat transfer coefficients are examined.2. Based on the experimental data collected, the formulations which can predict accurately in-tube boiling heat transfer coefficients of R290 and R404A are seleted. Shah correlation can predict precisely heat transfer coefficients of R290 and R404A in horizontal smooth tube. Koyama correlation which is modified can predict precisely heat transfer coefficients of R290 inside horizontal microfin tube. Thome correlation has good precison in calculating heat transfer coefficients of R404A inside horizontal microfin tube.3. The analyses on different empirical formulations of in-tube boiling heat transfer coefficients indicate that R404A can be treated as pure refrigerant during calculating its the in-tube boiling heat transfer coefficients.4. The effects of geometrical parameters of microfin tubes on the in-tube boiling heat transfer coefficients is analyzed. In addition, the principles on intensifying heat transfer in microfin tube is also analyzed.5. Lockhart & Martinelli pressure drop correlation is studied, and at the same time, based on theexperimental data collected, the accuracy of this formulation is examined.6. The evaluating method on intensifying heat transfer performance in microfin tube is provided, and by this method the performance of R290 and R404A is investigated.