Experimental study on heat transfer of supercritical carbon dioxide in a long silica-based porous-media tube

The heat transfer phenomena of supercritical carbon dioxide were experimentally investigated in a vertical tube containing silica-based porous media. The experiment was conducted at various levels of static pressure, flow rates, and initial wall temperatures as well as with silica sand of porous media in a long test section to study the heat transfer characteristics of supercritical carbon dioxide (CO2). The results indicated that the average heat transfer coefficient and outlet temperature at an initial wall temperature of 150 A degrees C were higher and lower than that of 200 A degrees C. The heat transfer performance was significantly influenced by flow rate of supercritical CO2. The porous media was provided large heat exchange surface between particles and CO2 to increase the heat transfer coefficient, especially when small diameter of particles. When the inlet temperature was higher than the pseudocritical temperature, the heat transfer coefficient sharply dropped when x/L ae 0.5, because of the development of a thermal boundary and the decrease of CO2 thermophysical properties of CO2 in a far pseudocritical temperature. When the pseudocritical temperature was higher than the inlet temperature of the fluid, the local heat transfer coefficient was affected by a thermal boundary and thermophysical properties of CO2 in pseudocritical point at a higher initial wall temperature or lower supercritical pressure when x/L ae 0.75; only the thermophysical properties of supercritical CO2 in pseudocritical point played a pivotal role when x/L > 0.75 at a lower initial wall temperature or higher supercritical pressure. In the present study, the supercritical pressure of 10.5 MPa constituted an optimal operating condition for supercritical CO2 a long silica-based porous-media tube because of the high heat transfer performance at 150 and 200 A degrees C.