About the Beale number

[Aviator168]

Have been studying the Beale number for the past week. The number is basically derived from past stirling engines. The problem is the more about I know how they got this number, the more I became suspicious its correctness and usefulness. For example. Those stirling engines, they based on to come up with the number, all have heating tubes and internal heating surface is at most the same and generally far smaller than external heating surface. Another example is that they assume heat transfers from outside of the tubes. Well, I just happen to know a stirling built by a friend of mine has the heat transferred from inside the tube. This allows the tubes to have very thin walls even when the engine is pressurized. So, what is your opinion about the Beale number? Should we still use it as a guide to estimate the output power of our designs?

Edit. If I use the Beale formula to calculate the number for Andy Ross' pressurized stirling engine, I came up with a number in the range of 0.25 to 0.5 (since I don't know what the rpm of the engine is) which is much much high than the maximum of 0.15.

[Ian S C]

How can you heat a Stirling Engine from inside, it's an externally heated engine?
Ian S C

[Aviator168]

You run the heating tube inside the engine with a lot of fins. Fuel is burned inside the tube similar this.
https://www.youtube.com/watch?v=zn4YVYdp8lE

[vamoose]

That's an interesting approach. Turning things inside out could make for a very compact burner and heat exchange system..
Nice..

[Aviator168]

Yes. But the design also calls for high temperature alloys with high thermal conductivity.