Study on heat transfer characteristics of supercritical CO2/propane mixtures in vertical tube

The performance optimization of the Brayton cycle could be achieved by further investigation of supercritical CO2/propane mixtures. In this paper, the heat transfer characteristics of supercritical CO2/propane mixtures in a vertical tube are numerically analyzed. The addition of propane could reduce or even eliminate heat transfer deterioration. Compared to CO2, the wall temperature peak of CO2/propane mixtures (alpha = 7 %) could be reduced by 45.5 K. After the pseudo-critical temperature, the effect of heat flux on the wall temperature of CO2 is more significant than that of mixture. Further, new critical heat flux criterion and Nu correlations are proposed for supercritical CO2/propane mixtures. The correlations could accurately reproduce the trend of Nu and capture the onset of heat transfer deterioration in the upward flow. At Re = 40168-84765 and Pr = 1.2-5.4, the maximum prediction deviation of the new correlations is +/- 14 %. Approximately 98.4 % of the prediction deviations are within +/- 10 %.

Automated summary

This paper investigates the heat transfer characteristics of supercritical CO2/propane mixtures in a vertical tube and proposes new correlations to accurately predict the heat transfer trend. It is found that the addition of propane can reduce heat transfer deterioration and the proposed correlations have a maximum prediction deviation of +/- 14%.