Heat pumps can, among other things, heat as well as cool living spaces and are also more climate-friendly when operated with renewable energies such as photovoltaics, compared to, for example, gas heating systems. Against the background of climate change, heat pumps offer technological and ecological advantages. Currently, however, the energy efficiency of heat pumps cannot yet be fully optimized. This is mainly due to the fact that the behavior of the typical oil-refrigerant mixtures in the compressor of a heat pump is thus far not fully understood thermodynamically.
The scientists of the new research unit 5595 “Oil-refrigerant multiphase flows in gaps with moving boundaries – Novel microscopic and macroscopic approaches for experiment, modeling and simulation” (short: “Archimedes”), funded with around four million euros by the German Research Foundation (DFG), want to change that now. The result should, among other things, be a new calculation model for designing compressors, which in turn can significantly improve the energy efficiency of heat pumps and refrigeration machines. The spokesperson of the new DFG research unit is Professor Markus Richter, head of the Professorship of Technical Thermodynamics at Chemnitz University of Technology, with around 1.1 million euros of the total funding allocated to it.
“I am very pleased about the establishment of the DFG research unit ‘Archimedes’ under the leadership of Chemnitz University of Technology – and thus the second research unit at the Faculty of Mechanical Engineering. I congratulate Professor Richter and all other participants on this great success for the Faculty of Mechanical Engineering and our entire university. I would also like to express my heartfelt thanks to all those involved for their outstanding commitment. Without a doubt, the research unit will significantly contribute to strengthening the profile of our university as well as its external appeal”, says the rector of Chemnitz University of Technology, Professor Gerd Strohmeier.
“The behavior of a mixture of lubricating oil and refrigerant – such as the natural refrigerants propane or CO2 – in the compressor of a heat pump or refrigeration machine is a particular challenge for thermo- and fluid dynamics. Factors such as pressure and temperature change the thermophysical behavior and thus the flow behavior, which ultimately has an influence on the heating or cooling performance. For oil-refrigerant mixtures, we will precisely determine the thermophysical properties for the first time in this fundamental research project and, based on this, develop simple applicable equations of state as well as models for viscosity and thermal conductivity. This is an important building block to optimize heat pumps”, explains Professor Markus Richter.
“To develop a comparatively simple calculation model for the flow behavior of oil-refrigerant mixtures in gaps of compressors, we need precise information about how these fluid mixtures behave thermodynamically. The actual gap flow is then examined in a generic experiment of a rotating contour in a cylindrical glass housing. Here, we characterize the flow behavior on a macroscopic level with laser-optical methods and on a microscopic level with high-resolution numerical simulations”, adds co-spokesperson Professor Andreas Brümmer, head of the Chair of Fluidics at TU Dortmund.
The research work is scheduled to begin in the first quarter of 2024. In addition to Chemnitz University of Technology and TU Dortmund, TU Dresden, Friedrich-Alexander-Universität Erlangen-Nürnberg, Karlsruhe Institute of Technology, Ruhr University Bochum, and RWTH Aachen University are involved in the research unit “Archimedes”.