Research on convection heat transfer character of super critical carbon dioxide flows inside horizontal tube

• Studied heat transfer character of super critical R744 (in horizontal tube).
• Temperature range is from 29 to 55 °C, pressure is 8, 9 and 10 MPa.
• A new empirical correlation has been developed.

This paper mainly studied the heat transfer character of super critical carbon dioxide, also named R744. Super critical carbon dioxide can be used in gas cooler for air conditioning system. Compared with traditional Freon coolant, R744 has higher density and lower viscosity, which is benefit for heat transfer process. So it is important to study heat transfer character for super critical carbon dioxide. The experiment research is taken for the temperature ranging from 29 to 55 °C, while pressure is 8, 9 and 10 MPa. The Reynold number is about 2 × 105. Thermal resistance method is used to measure heat transfer coefficient. The results found that convection heat transfer enhances near the pseudo critical point, in the region far away from pseudo-critical point, heat transfer character is just like ordinary single-phase fluid. The heat transfer coefficient violently changeable region is also the region where thermal property change rapidly. It is also found that heat transfer coefficient gets its max at the region near the pseudo-critical point. In addition, the results obtained in this paper are compared with other researchers’ results.