Research Progress

Analysis of Turbomachinery Losses in sCO2 Brayton Power Blocks:

This study analyzes the contribution of different turbomachinery loss mechanisms to the overall efficiency of a simple recuperated supercritical carbon dioxide (s-CO2) Brayton cycle for output capacities ranging from 100 kW to 1 GW. The optimum turbomachinery specifications suitable for the specified powers are retrieved using a standard design tool that provides information on various turbomachinery losses. The losses are influenced by operating pressures and mass flowrates, which are unknown a priori. An iterative approach is used to arrive at the turbomachinery efficiency and mass flow rate. Earlier studies have shown the dependence of optimal pressures on heat source and sink temperatures alone. This analysis reveals that design-point optimal cycle pressure ratios differ with varying power outputs due to differences in realizable turbomachinery efficiencies. The information on dominant loss mechanisms provides insights on a viable scale of power generation at which s-CO2 Brayton cycles become worthwhile. Poor turbomachinery efficiencies (less than 80%) render the s-CO2 technology commercially unviable at the sub-MW scale. For higher power scales (10 MW and above), axial machines are found to be appropriate, with corresponding turbomachinery efficiencies greater than 85%. The dominant loss mechanisms also help identify issues related to improving turbomachinery efficiencies at the sub-MW power levels, where the cycle efficiencies are not competitive.

Research published in - Seshadri, L., Kumar, P., Nassar, A., and Giri, G. "Analysis of Turbomachinery Losses in sCO₂ Brayton Power Blocks." ASME. J. Energy Resour. Technol. November 2022

(Research snippets):

Vaneless Diffuser Performance in a Super-Critical Carbon Dioxide Centrifugal Compressor with real gas effects

Super-critical Carbon dioxide (s-CO2) flows are neither incompressible nor ideal gas flows. Unlike perfect gases, the enthalpy of s-CO2 near the critical point is a strong function of pressure. Incorporation of these effects is necessary for accurate modeling of flows in centrifugal compressor vaneless diffusers. This study reviews the existing vaneless diffuser modeling technique, and modifications are made to incorporate real gas effects. Like the existing procedure, the proposed formulation does not require multiple iterations for convergence. The results are obtained in a single step using a marching technique. Hence, this model can be incorporated in standard centrifugal compressor design and analysis tools, especially for super-critical carbon dioxide flows, subject to experimental validation.

Research published in Seshadri, L, & Kumar, P. "Vaneless Diffuser Performance in a Super-Critical Carbon Dioxide Centrifugal Compressor with Real Gas Effects." Proceedings of the ASME 2021 Gas Turbine India Conference. ASME 2021 Gas Turbine India Conference. Virtual, online. December 2–3, 2021.

Development of sCO2 test facility at IISc Bangalore

To understand the operational aspects of sCO2 turbomachinery in Brayton cycles, a kW scale test rig is being developed at IISc Bangalore. Major practical issues in the development of kW scale test loop include design and performance of seals, leakage path, windage estimation and bearing thrust management. We have addressed these issues in a conference publication which is expected to be presented in June 2022 at the ASME Turbo Expo 2022 Conference, Rotterdam, The Netherlands

Lakshminarayanan Seshadri, Ashutosh Patel, Vijay Biradar, Pramod Kumar, Pramod Chandra Gopi. "Two Stage Radial Compressor for A Kilowatt Scale Supercritical Carbon Dioxide Power Block: Design Considerations." Proceedings of the ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition, Rotterdam, The Netherlands June 13-18, 2022 (Accepted, Paper no: GT2022-81699)