Abstract
The paper presents the influence of selected components parameters on the performance of supercritical carbon dioxide power unit. For this analysis mathematical model of supercritical recompression Brayton cycle was created. The analysis took into consideration changes in the net cycle power and efficiency for different compressor inlet temperatures. The results were obtained for a fixed minimum pressure of 7.4 MPa and fixed recompression split ratio. The studies conducted in this paper included also consideration of sensitivity of the cycle efficiency to a change in recuperators heat transfer area. In order to determine how each recuperator influences the cycle performance, an analysis of efficiency dependence on the recuperators area was made. Another parameters that were investigated are to a change in turbine and compressors isentropic efficiency and their influence on the cycle efficiency. In the reference cycle, isentropic efficiencies were set up as 88% for both the main and recompression compressor, and 90% for the turbine. Since isentropic efficiency is a sort of measure of broadly defined quality of a turbine or compressor, including airfoil shape, sealing, etc., it may be a significant cost factor that should be considered during cycle design. Therefore, a sensitivity analysis of cycle efficiency to both compressors and turbine isentropic efficiencies was conducted.
Highlights
In the 1960s, Feher [1] studied various gases’ properties for a purpose of finding the most suitable one for a supercritical thermodynamic cycle
The analysis proved that CO2 supercritical cycle offers several desirable features as high thermal efficiency, low volume to power ratio and no blade corrosion and cavitation
The results obtained when recompression ratio was dynamically optimized for each temperature level indicate that the cycle efficiency rises along with decreasing compressor inlet temperature above and under the critical point as well
Summary
In the 1960s, Feher [1] studied various gases’ properties for a purpose of finding the most suitable one for a supercritical thermodynamic cycle. Carbon dioxide was proposed as a working fluid due to several reasons. CO2 thermodynamic and transport properties are well known, cycle analysis is based on reasonably firm data. Carbon dioxide is abundant, non-toxic and has relatively low cost. The analysis proved that CO2 supercritical cycle offers several desirable features as high thermal efficiency (the investigated cycle reached a thermal efficiency of 55% under ideal conditions), low volume to power ratio and no blade corrosion and cavitation. The pre-compression Brayton cycle is one of the ways to increase the generation within the cycle and reduce the pinch-point problem.
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