A REVIEW OF HEAT TRANSFER OF CO2 AT SUPERCRITICAL PRESSURE IN THE CRITICAL AND PSEUDO-CRITICAL REGION

This paper presents a comprehensive analysis of heat-transfer characteristics and correlations for CO2 at supercritical pressure in the critical and pseudo-critical region. Firstly, the thermophysical properties of CO2 are discussed along with their influence on heat-transfer characteristics. This is followed by a review of existing experimental and numerical studies on heat transfer and pressure drop for different channel geometries (smooth tubes, porous tubes, concentric annular passages, micro fin tubes, and helical coils), covering hydraulic diameters from 0.27 to 22.8 mm and bulk temperature from 0 to 120 degrees C and pressure from 74 to 150 bar, as well as factors influencing heat transfer. The review of published works shows that the heat-transfer characteristics are influenced by the geometry configuration and operating conditions, including channel shape and dimension, mass flux, heat flux, bulk temperature and pressure, flow direction, buoyancy, and heating or cooling conditions. Detailed comparisons and analysis of available heat-transfer correlations for CO2 at supercritical pressure are discussed and the review shows that there is lack of universal correlations able to accurately describe local heat transfer and pressure drop for different channel geometries and in particular for the pseudo-critical region. The paper identifies research gaps and proposes research and development needs to fill these gaps to ensure that reliable heat transfer and pressure drop correlations are developed to cover a wider range of operating conditions and applications.