| Title |
The Condensation Heat Transfer Characteristics of R-22 and R-407C Inside Small Diameter Tube-in-Tube Heat Exchangers |
| Authors |
Kwang-Il Choi ; Jong-Taek Oh |
| DOI |
https://doi.org/10.6110/KJACR.2021.33.2.080 |
| Keywords |
응축열전달계수; 압력강하; 미세관; 관-관 열교환기 Condensation heat transfer coefficient; Pressure drop; Small diameter tube; Tube-in-tube heat exchanger |
| Abstract |
This paper focuses on the results of an experimental study of condensation heat transfer coefficients with the refrigerants R-22 and R-407C, and looks at the pressure gradient and heat transfer coefficients of horizontal tube-in-tube heat exchangers with the use of small tubes with inner diameters of 4 mm, 3 mm and 2 mm, in a 16.91 mm tube and length of 3,000 mm. Experiments were performed at an inlet saturation temperature of 35 to 45℃ and mass flux ranges from 200 to 600 kg/m2s. The use of an inner tube with a diameter of 4.0 mm resulted in a pressure gradient that was 2.5 times higher than that of an inner tube with a diameter of 8.0mm. In tube-in-tube HEX, the pressure gradients of R-22 measured higher than those of R-407C. The condensation heat transfer coefficients increase with an increase in mass flux, but they decrease with an increase in saturation temperature. Condensation heat transfer coefficients of R-407C were a little higher than those of R-22, and the condensation heat transfer coefficients of double tube HEX were about 40% higher than those of tube-in-tube HEX. The experimental results of this study were also compared with five existing correlations. New condensation heat transfer correlations were developed, and successfully predicted the experimental results with mean deviations of 10.6% and 10.1%, and average deviations are -0.92% and -0.31%, for R-22 and R-407C, respectively. |