A numerical investigation on how to efficiently utilise carbon dioxide in convection-based energy systems

Owing to the environmentally benign nature and the special property variation at supercritical pressure, greenhouse gas carbon dioxide is regarded as the best retrofit to meet the future demand on long-term environmental-friendly working fluids. However, how to efficiently utilise carbon dioxide to reduce energy consumption and mitigate global warming is still an unsolved problem. In this paper, the natural convection heat transfer of carbon dioxide under supercritical pressure condition in a small cavity is studied for the first time. The potential of carbon dioxide as working fluid is quantitatively estimated in terms of enhancing heat transfer and reducing the cost of heat exchangers. It is found that the operating conditions including the temperature, temperature difference and pressure all have significant effects on heat transfer rate due to the special property variations of the CO2 fluid. Furthermore, a heat transfer correlation is proposed for the first time to quantitatively describe the natural convection heat transfer of CO2 at supercritical pressure in a small cavity.