This paper describes recent advances in simulation of zero flow conditions based on work with Daimler using the Air Conditioning Library from Modelon. The Air Conditioning Library is based on the open standard modelling language Modelica. Simulating refrigerant loops at (near) zero flow for large vapor compression cycles is challenging, due to the fast dynamics in the model under those conditions that drastically reduce the step size of the solver. Findings on solver selection and pressure drop correlations are presented. An approach to improve zero flow simulation based on a systematic analysis of heat transfer coefficients is suggested and demonstrated to increase simulation robustness under (near) zero flow conditions.

Engineering, and Modelon. Supervisors were Marcus Thern at the university and Pieter Dermont at AbstractAs the demand for decreased use of energy increases, new ways of using energy sources are investigated. One of these ways is to be able to use low temperature heat sources, which can be done with a rankine or organic rankine cycle. In a rankine cycle there is a working fluid which is pressurized, evaporated, expanded and then condensed again, and the energy release during the expansion can drive a generator which generates electricity.The aims of this master thesis were to model a rankine cycle, parameterise it according to data received from a company, implement control strategies and gain knowledge about its behaviour.The external company provided 11 data sets from their rankine cycle test bench, and they were not all coherent; some had a mass flow that was too low, it required the turbine to have a mechanical efficiency that was above 100 %.A new model of a pump was built, but otherwise models that already existed were used. The components were then parameterised to the different data sets and the simulations gave results that matched the data. For the data sets that were coherent, the simulations gave results that matched the data better. A power point tracking diagram done by the external company was also recreated.Control strategies that controlled the super heating, torque of turbine and working fluid charge in cycle were implemented. A tank before the pump was also added in order to prevent vapour to enter the pump. These control strategies as well as simulation results have created a base for knowledge about rankine cycles as well as organic rankine cycles. The results can be used by Modelon as a base for further investigation as well as for other projects.