Investigation of the convective heat transfer coefficient during condensation in vertical tubes

Condensation heat transfer coefficient is investigated experimentally for smooth and microfin tubes during downflow of R134a in this study. Firstly, condensation inside of the tube was investigated according to Nusselt analysis, then the effect of interfacial shear stress was paid attension. Some information and correlations were given about pressure drop in the literature. Suggested flow regime charts for condensation in vertical tubes was mentioned. Some heat transfer models on smooth vertical tubes in the literature was presented. Researches on condensation inside of the horizontal smooth tubes were examined generally. For that reason summary of researches on condensation inside horizontal microfin tubes was presented as parameters and models. Also void fraction models needed for calculation of heat transfer and pressure drop were summarized as well. Some of pressure drop models in the vertical and horizontal tubes that are in the literature were presented. Besides, some of pressure drop models in the horizontal tubes were summarized. Condensation heat transfer coefficient was researched by using R134a refrigerant for two phase flow. Experiments were done while gas and liquid phases of R134a were flowing downward together. Detailed information about experimental setup and tested tubes was given. List of the equipments was presented. Moreover, information on measurements and evaluation of experiments was given. Parameter range was given in the analyse part of experimental results. Results were studied for the smooth and microfin tube according to Nusselt theory and interfacial shear stress. Apart from this, alteration of film thickness and local convection heat transfer coefficient along the test tube was showed for the smooth and microfin tubes. Methods of experimental uncertainty analysis were explained in the last part. Uncertainty values of mass velocity, vapor quality of inlet test tube, heat flux, convection heat transfer coefficient, friction factor were presented from accuracy of measurement devices and calibration values. Incase of using microfin tube instead of smooth tube condensation heat transfer coefficient was increased between %60-82 and interfacial shear stress between liquid-vapor phases should not be negleted for the accurate solution in Nusselt theorem under the circumstances of the thesis. Information about calibration studies were given as appendix in the thesis. Keywords: Two phase flow, microfin tube, smooth tube, condensation