Analysis of supercritical CO2 cooling in macro- and micro channels

A comprehensive analysis of heat transfer and pressure drop experimental data and correlations for supercritical CO2 cooling in macro- and micro-channels is presented in this article. First, the physical and transport properties of CO2 at supercritical conditions are discussed and then their influence on heat transfer and pressure drops. Next, a review of experimental studies on heat transfer and pressure drops of supercritical CO2 cooling is provided and detailed comparisons and analysis relative to the available heat transfer and pressure drop correlations for supercritical CO2 cooling were done where possible. Furthermore, noting the lack of all pertinent experimental details required to use the data published in many of these studies, comments are given on how to reduce and present supercritical CO2 experimental data properly in the future. In addition, the effect of oil on heat transfer and pressure drops for supercritical CO2 is shown to significantly decrease the former and to increase the latter. Comparison of experimental data to a selection of heat transfer correlations shows that the Fang et al. [2001b. Modeling and analysis of gas coolers. ASHRAE Trans. 107 (1), 4–13] correlation gives the closest values to the experimental data but is still not satisfactory. According to the comparison and analysis, it is recommended that further efforts be made to develop good heat transfer methods for supercritical CO2 cooling based on accurate database in the future. To achieve this, more careful experiments should be done over a wide range of test parameters to meet the requirement in practical applications. In addition, four experimental studies show that the Blasius equation works well for CO2 cooling in the near supercritical region. More careful experimental data are still needed to further validate this conclusion because some experimental data are much different from others.