An investigation on convective condensation heat transfer of R۱۳۴a outside a tube with hybrid wettability surface

In this study, the flow condensation heat transfer of R۱۳۴a 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 ۱۶ mm and ۱۸ 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 ۴۳.۶, ۳۹.۶, ۲۷.۷۵ and ۱۹.۸۲ kg/m۲s and vapor quality range of ۰.۲ to ۰.۷. 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 ۱.۲۴ 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.

Keywords:

Convective condensation , Heat transfer , Annulus , Hybrid wettability , Experimental.