دانلود رایگان مقاله انگلیسی همبستگی انتقال حرارت مبتنی بر جریان سامان یافته برای R245fa در لوله 3 میلی متری - الزویر 2018

Abstract

241 heat transfer measurements for R254fa were conducted. The heat transfer coefficient was determined for a smooth stainless steel tube with an inner tube diameter of 3 mm. The experiments were conducted for five mass fluxes (100, 300, 500, 700 and 1000 kg/(m2 s)), three heat fluxes (10, 30 and 50 kW/m2 ) and at three saturation temperatures (40
C, 70
C and 125
C). The experiments were used to determine the influence of the saturation temperature, mass flux, heat flux, vapour quality and flow regime on the heat transfer coefficient. At a low saturation temperature, the heat transfer coefficient increases with an increasing mass flux. However, at a high saturation temperature the heat transfer coefficient decreases with an increasing mass flux. Furthermore, the heat transfer coefficient increases with increasing vapour quality at a low saturation temperature. On the contrary, the heat transfer coefficient decreases at higher saturation temperatures. Due to the fact that most heat transfer models found in literature are developed for low saturation temperatures and one flow regime, the heat transfer coefficients predicted by the existing models do not comply very well with the experimental data. Thus, a new heat transfer correlation for R254fa was proposed. The new correlation has a Mean Absolute Error of 11.7% for the experimental data of a tube with an inner tube diameter of 3 mm. Finally, this new correlation was also verified with R245fa datasets of other authors.

Conclusion

This work presented 241 unpublished experimental heat transfer measurements of R245fa in a tube with an inner diameter of 3 mm and discussed the influence of the saturation temperature, mass flux, heat flux and vapour quality on the heat transfer coefficient. The heat transfer coefficient respectively increased and decreased with an increasing mass flux at a low and high saturation temperature. Furthermore, the heat transfer coefficient increased with increasing vapour quality at a low saturation temperature. On the contrary, the heat transfer coefficient decreased at higher saturation temperatures. Hence, the influence of vapour quality and mass flux on the heat transfer coefficient is dependent of the saturation temperature. The combined dataset of this work (241 data points) and Charnay et al. [13] (973 data points) is best predicted by the correlation of Choi et al. [23]. However, the experimental data of the annular flow is overpredicted. A new flow regime dependant correlation for R245fa was proposed. The new correlation is experimentally validated for tubes with an inner diameter of 3 mm, a temperature range of 40–125
C, a mass flux between 100 kg/(m2 s) and 1000 kg/(m2 s) and a heat flux between 10 kW/m2 and 50 kW/m2 . Finally, this new correlation was also verified with R245fa datasets of other authors.