پديدآورندگان :
bakhshi farzad School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran , Akhavan-Behabadi MohammadAli School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran , Ahmadi Sanaan School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran , Mohammadi Rasool School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran
چكيده فارسي :
In this study, the flow condensation heat transfer of R134a in annulus of the tube-in-tube heat exchangers for low-range mass fluxes has been experimentally investigated. For this purpose, two tube-in-tube heat exchangers with different inner tube surface characteristics are employed. Inner tubes have inner and outer diameters of 16 mm and 18 mm respectively. One of these tubes has a smooth outer surface, and the other one has gradient wettability with strip patterns that include smooth and micro-nano structures. The heat transfer coefficient is calculated during condensation in annulus space between tubes, and results are compared together. The experiments are performed in mass fluxes 43.6, 39.6, 27.75 and 19.82 kg/m2s and vapor quality range of 0.2 to 0.7. Generally, results show that heat exchangers include inner tubes with hybrid wettability surface have higher heat transfer coefficients compared to the heat exchanger with a smooth surface, using this hybrid pattern promotes the heat transfer coefficient to a maximum of 1.24 times. Also, results showed heat transfer coefficients decrease with the increase of temperature difference between saturation temperature of condensing refrigerant and inner tube wall temperature.
