Ph.d.-forsvar Jesper Graa Andreasen

Numerical evaluation of advanced working fluids for organic Rankine cycle systems

The use of environmentally friendly heat sources for electricity generation as alternatives to fossil fuels requires the implementation of new technology. The low temperature and/or low thermal power capacity of alternative heat sources such as waste heat or geothermal heat discourages the use of conventional steam Rankine cycle power systems. On the other hand, the use of organic Rankine cycle systems is advantageous at these conditions. The selection of the working fluid for the organic Rankine cycle system constitutes an important design decision, which affects the design of the equipment used in the system and the thermodynamic and economic performance of the system.


The evaluation of the thermodynamic performance, for example the efficiency or the net power output, of zeotropic mixtures compared to pure fluids is a main focus point in this PhD Thesis. When using the conventional method of assuming the same minimum temperature difference in the heat exchangers for zeotropic mixtures and pure fluids, the net power output obtained with zeotropic mixtures is estimated to be up to 13.6 % higher compared to pure fluids. However, when an alternative approach of assuming an upper limit for the UA values of the heat exchangers is used the increase in the net power output is up to 2.56 % higher for zeotropic mixture compared to pure fluids. These results indicate that the combined use of the conventional and the alternative method can result in better identification of promising working fluids at an early stage in the working fluid selection.


In the technoeconomic comparison, the mixture R1234yf/i-butane reaches the highest net present value for an organic Rankine cycle system using geothermal heat. The net present value of the mixture is 43.1 million €, which is 2.1 million € higher compared to R1234yf and 9.6 million € higher compared to i-butane. This result indicates that the implementation of zeotropic mixtures as working fluids in organic Rankine cycle systems can be economically feasible.


man 30 sep 19
13:00 - 17:00


DTU Mekanik


DTU Lyngby Campus, Bygning 421, Auditorium 002