CHAPTER 21: Applications of Fluids at Supercritical Pressure in the Area of Power Generation – Movements Towards Economically-viable Clean Energy

Developments concerning the role of fluids at supercritical pressure in power generation systems are described. Such fluids change from being liquid-like to gas-like in a rapid but continuous manner with the increasing temperature. This can lead to important effects on flow, turbulence and heat transfer. My first experience of using such fluids was when I and colleagues commenced research on a completely novel experiment using carbon dioxide. The idea was to achieve a fully developed, stably-stratified, turbulent flow and heat transfer condition between two horizontal planes, with the upper one being heated and the lower one cooled in such a way that there was no net heat transfer to the fluid. This experiment provided clear evidence of significantly enhanced turbulent diffusion of heat. Later, experiments with turbulent flow in heated vertical tubes also exhibited striking features, including severe localized deterioration of heat transfer. Physically based ideas are presented, which explain the mechanisms involved. These led to the development of advanced semi-empirical models. The chapter ends with a section on thermal power conversion cycles which use supercritical pressure carbon dioxide. Their application to advanced nuclear reactors designs is discussed and also to solar energy and waste heat recovery. It is anticipated that such cycles will eventually be widely used in efficient power plants that produce ‘clean energy’.