Abstract

Centrifugal compressor is one of the key components in the Super-critical carbon dioxide (SCO2) Brayton cycle process, its performance prediction under variable operating conditions are concerned a lot with consideration of the unique of SCO2 properties. At the same time, the general techniques, including numerical simulation, test, and theoretical analysis with the loss models, are applied to evaluate the compressor performance. In addition with numerical analysis on the performance of the compressor, the flow loss models from air compressor were studied and extended the application to the SCO2 compressors, including incidence loss, blade loading loss, passage flow loss, tip clearance loss, mixing loss, disk friction loss, vaneless diffuser loss. All of these models were investigated to get the performance of a SCO2 compressor. The CO2 quality was got from the multipurpose NIST REFPROP 9.0 (NiST) which is based on Span and Wagner equation of state. The quality was added in the numerical simulation process. Besides, the passage flow loss factor has been modified to get more accurate theoretical performance prediction method for SCO2 compressor. The predicted performance map was compared to the numerical results, and the comparison results proved that, the combination of the loss models provided the similar results as those from the numerical simulation. For the SCO2 centrifugal compressor, the passage flow loss covers the most part among all the compressor flow losses. The value of the passage flow loss factor applied in the theoretical performance prediction method ranges between 0.008∼0.025, which is higher than that for air. Finally, the performance evaluation by improved loss models at different compression starting points were compared with that by the numerical results, it was found that, closer to the critical point would make the passage flow loss increase a lot, which may even exceed its rational range and the produced loss would be beyond expectation. This might be the reason for the low efficiency of SCO2 compressor in the practical working conditions.

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