A forced convection heat transfer correlation of rarefied gases cross-flowing over a circular cylinder

With the rapid development of aeronautics and astronautics, there is increased interest in understanding the behavior of heat transfer of rarefied gases particularly in the environment outside of the atmospheric layer. Currently, empirical correlations are correlated at standard atmospheric pressure, but this may not be suitable for rarefied gases flow, particularly at Knudsen number (Kn) > 0.1. In this study, the forced convection heat transfer of rarefied gases cross-flowing over a circular cylinder is studied at Reynolds number of 10−3 to 20 and Knudsen number of 10−3 to 3. The experiment is conducted at the velocity of 0.5-20 m/s and the pressure of 100 Pa ∼ 100 kPa. It is found that the heat transfer coefficient in the continuum flow regime mainly depends on the Reynolds number and the effect of the Knudsen number was quite weak. In the regimes of slip flow and transitional flow, the heat transfer coefficient slightly decreased as the Reynolds number decreased. However, the Knudsen number plays a significant role in heat transfer performance in both the slip flow regime and the transitional flow regime. The effects of Reynolds and Knudsen numbers on heat transfer were measured and analyzed. Based on the experimental data, an empirical correlation of the forced convection heat transfer of rarefied gases cross-flowing over a circular cylinder was developed. The correlation coefficient (R) was greater than 0.99, corresponding to a fitting error of less than ±10.5% based on a 95% confidence level. The study provides theoretical guidance for future engineering design of rarefied gases flow and heat transfer.