Six Inch Supercritical CO2 Micro Turbine Performance at 100 C, 300 C, 500 C, and 700 C

Six Inch Supercritical CO2 Micro Turbine Performance at 100 C, 300 C, 500 C, and 700 C

Overview

Scaling a purpose designed supercritical CO2 micro turbine from small diameters up to a six inch outside diameter increases inlet annulus area and mass flow in proportion to radius when blade height and throughflow velocity are held constant. With similar stage loading and efficiency, shaft power scales approximately linearly with radius. This article provides first pass net power estimates for a six inch radial inflow sCO2 turbine meant to drive a compact generator, and it includes cycle heat rate guidance for context.

Design Basis and Scaling Notes

Turbine outside diameter: 152.4 mm (six inches)

Inlet radius: 76.2 mm

Inlet blade height: about 0.5 mm (kept the same as the smaller studies for clean scaling)

Inlet annulus area equals 2 times pi times radius times height. Holding height and inlet velocity constant, mass flow and power scale with radius.

Inlet total pressure: about 150 bar

Representative turbine isentropic efficiency: about 70 percent for a carefully designed stage

Whole cycle allowances for leakage, pressure losses, generator, and controls are included in the quoted net figures

Heat sink: about 40 C

Reference scaling: the one inch study yielded about 6, 7, 8, and 8.5 kW net at 100 C, 300 C, 500 C, and 700 C respectively. A six inch rotor has six times the radius of the one inch case, so first order power scales by about six when blade height and inlet velocity are unchanged.

Estimated Net Power Output

100 C inlet: about 36 kilowatts net

300 C inlet: about 42 kilowatts net

500 C inlet: about 48 kilowatts net

700 C inlet: about 51 kilowatts net

Notes

1. These values assume passages, volute, and diffuser are purpose designed for sCO2 with tight clearances and good surface finish.

2. Final allowable speed is set by rim stress and tip Mach limits; those constraints are respected by carrying over the same throughflow velocities used in the smaller studies.

3. Larger diameter reduces relative leakage and eases manufacturability, which can yield modest real world gains beyond simple linear scaling. The estimates above stay conservative.

Heat Rate Guidance in BTU per Kilowatt Hour

Heat rate is primarily governed by temperature lift and overall cycle design, not rotor diameter. Ranges below match compact recuperated sCO2 systems with a 40 C sink.

100 C source

Practical cycle efficiency about 6 to 12 percent

Heat rate about 28,500 to 57,000 BTU per kilowatt hour

300 C source

Practical cycle efficiency about 20 to 30 percent

Heat rate about 11,400 to 17,100 BTU per kilowatt hour

500 C source

Practical cycle efficiency about 35 to 45 percent

Heat rate about 7,600 to 9,750 BTU per kilowatt hour

700 C source

Practical cycle efficiency about 45 to 55 percent

Heat rate about 6,200 to 7,600 BTU per kilowatt hour

Notes

1. Higher recuperator effectiveness and lower cooler outlet temperature push heat rate toward the low end of each range.

2. At higher inlet temperatures, mechanical integrity and materials become the limiting factors before thermodynamic potential is exhausted.

Key Takeaways

Moving from one inch to six inches increases net power by roughly six times when blade height, inlet velocity, and stage loading are held constant.

Heat rate depends on temperature lift and cycle quality; it does not materially change with rotor size in first order estimates.

Best efficiencies and lowest heat rates occur at higher turbine inlet temperatures. Practical ceilings on power density are set by tip speed, rotor stress, sealing, bearings, and recuperator effectiveness.

Conclusion

A purpose designed six inch supercritical CO2 radial inflow turbine can credibly deliver about 36 to 51 kilowatts of net power across turbine inlet temperatures from 100 C to 700 C, provided the cycle includes an effective recuperator and the mechanical design meets stress and sealing requirements. Heat rates span from roughly 57,000 down to about 6,200 BTU per kilowatt hour as temperature increases, reflecting the dominance of thermodynamic temperature lift and cycle effectiveness over simple geometric scaling.

TEL: 1-608-238-6001 Email: greg@infinityturbine.com

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CONTACT TEL: 1-608-238-6001 Email: greg@infinityturbine.com (Standard Web Page) | PDF