Twelve Inch Supercritical CO2 Axial Multi Stage Turbine Performance at 100 C, 300 C, 500 C, and 700 C

Twelve Inch Supercritical CO2 Axial Multi Stage Turbine Performance at 100 C, 300 C, 500 C, and 700 C

Overview

This article scales our earlier micro turbine studies up to a twelve inch outside diameter axial flow turbine using multiple stages and high efficiency blading for supercritical CO2. The goal is maximum practical net power for a compact generator while keeping realistic cycle and mechanical assumptions. Results are shown for turbine inlet temperatures of 100 C, 300 C, 500 C, and 700 C.

Design Basis and Scaling Logic

Reference baseline

One inch radial inflow single stage supercritical CO2 turbine results from the earlier study

100 C about 6 kW net

300 C about 7 kW net

500 C about 8 kW net

700 C about 8.5 kW net

Key upgrades for this design

Diameter increased from one inch to twelve inches

Axial flow multi stage layout to raise overall pressure ratio and specific work while improving blading efficiency

Target turbine stage isentropic efficiency about 85 percent versus 70 percent used in the one inch baseline

Recuperated cycle with a 40 C sink, inlet total pressure near 150 bar, passages sized to keep relative Mach numbers subsonic with supercritical CO2 properties

Scaling method in plain text

Mass flow is proportional to annulus area at the inlet. For the same blade height and inlet velocity, annulus area and mass flow scale with radius. Diameter grows by twelve, radius grows by twelve, so mass flow scales by about twelve.

Turbine efficiency improvement factor equals 0.85 divided by 0.70 which is about 1.21.

Multi staging allows higher overall pressure ratio and specific work than the single stage baseline. We use a conservative specific work factor that rises with temperature because higher turbine inlet temperature allows higher pressure ratio at acceptable Mach numbers.

100 C specific work factor about 1.2

300 C specific work factor about 1.3

500 C specific work factor about 1.4

700 C specific work factor about 1.5

Net power scaling in plain text

Net power equals baseline power multiplied by diameter factor multiplied by efficiency factor multiplied by specific work factor.

Estimated Net Power Output

Applying the factors above yields the following credible targets for a twelve inch axial multi stage turbine designed for supercritical CO2:

100 C inlet

Scale factor equals 12 times 1.21 times 1.2 which is about 17.4

Net power equals 6 kW times 17.4 which is about 105 kW

300 C inlet

Scale factor equals 12 times 1.21 times 1.3 which is about 18.9

Net power equals 7 kW times 18.9 which is about 132 kW

500 C inlet

Scale factor equals 12 times 1.21 times 1.4 which is about 20.3

Net power equals 8 kW times 20.3 which is about 163 kW

700 C inlet

Scale factor equals 12 times 1.21 times 1.5 which is about 21.8

Net power equals 8.5 kW times 21.8 which is about 185 kW

Notes

1. These figures assume purpose designed axial blading, tight clearances, high effectiveness recuperation, and a well matched compressor.

2. Final allowable rotational speed is set by rim stress and tip Mach limits at the twelve inch diameter. The multi stage layout spreads work across stages to keep per stage loading within efficient ranges.

3. Larger diameter reduces relative tip leakage and eases manufacturability, which supports the higher efficiency assumption used here.

Heat Rate Guidance in BTU per Kilowatt Hour

Heat rate reflects the whole cycle. Larger size and higher turbine efficiency help, but the dominant driver remains temperature lift and recuperator effectiveness. Compared with the smaller machines, modest improvements are expected from better sealing and larger scale hardware. Ranges below assume a 40 C sink and good recuperation.

100 C source

Practical cycle efficiency about 7 to 12 percent

Heat rate about 27,000 to 54,000 BTU per kilowatt hour

300 C source

Practical cycle efficiency about 21 to 30 percent

Heat rate about 11,300 to 16,200 BTU per kilowatt hour

500 C source

Practical cycle efficiency about 36 to 45 percent

Heat rate about 7,200 to 9,300 BTU per kilowatt hour

700 C source

Practical cycle efficiency about 47 to 58 percent

Heat rate about 5,900 to 7,300 BTU per kilowatt hour

Notes

1. The low end of each heat rate band corresponds to stronger recuperation, lower compressor inlet temperature, and lower pressure losses.

2. At 700 C, material limits for blading, disks, and heat exchangers often become the true constraints before thermodynamic potential is reached.

Practical Design Checkpoints

Verify per stage pressure ratio, exit diffusion factors, and relative Mach numbers with real gas CO2 properties at each temperature.

Size blade height and stage count so that flow coefficient and stage loading stay in efficient bands across the map.

Confirm rotor burst margins at the twelve inch diameter and plan for abradable linings to control leakage.

Select seals and bearings compatible with high pressure CO2 and rapid gas decompression exposure.

Invest in a high effectiveness primary recuperator, which is the single biggest lever on whole cycle heat rate.

Conclusion

A twelve inch axial multi stage turbine specifically designed for supercritical CO2 can credibly deliver on the order of 105 to 185 kilowatts of net power across turbine inlet temperatures from 100 C up to 700 C, assuming a well engineered recuperated cycle and appropriate mechanical design. Heat rate improves steadily with temperature, ranging from roughly 54,000 to about 5,900 BTU per kilowatt hour across the four operating points. These results show how moving to a larger, high efficiency axial architecture unlocks much higher net power while keeping cycle efficiency competitive at elevated turbine inlet temperatures.

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