MEMS Seminar: Efficient Energy- Conversion Systems: The Critical Role of Phase-Change Thermo Fluid Phenomena

In the context of the need for a higher efficiency of thermo-mechanical energy conversion systems, some thermodynamic cycles face a renewed interest. Among others, the Organic Rankine Cycle (ORC) can be a valuable option to recover waste heat energy from internal-combustion engines, while absorption chillers are now spreading and adsorption chillers are at an early stage of commercialization in a number of countries.
The aim of the present seminar is to highlight the critical role of one field of mechanical engineering / thermal science in the development of such energy-conversion technologies, namely phase-change thermofluidics. For instance, in ORCs, the thermodynamic conditions that the working fluid meets in the evaporator (evaporating temperature of 100°C and more, i.e. high reduced temperature) are fairly different from standards relevant to refrigeration or air-conditioning systems, for which a certain degree of knowledge has been reached owing to past efforts of research. Regarding the improvement of sorption chillers in which water is the refrigerant (e.g. in LiBr sorption chillers), the most crucial component is the evaporator for which a higher compacity is to be sought. However, the design of compact evaporators is constrained by the vaporization of the refrigerant under a very low pressure (i.e. close to triple point) which has not been widely studied in the past.