Zhivko
How do you intend to join the fins to the outer casing of the heater? if they are not welded to the case, there will be very little heat transfer.
GeoffV
Big Beta Stirling 1kw, 100degC to 400degC
Re: Big Beta Stirling 1kw, 100degC to 400degC
If I remember your chart correctly, the heat transfer is quite steep if gap is under 0.1mm. I don't think I have much less than 0.1mm since outer shell stainless steel was compressed strongly before welding it. Still I would be glad to here from you - what do you think the value is for 0,05mm gap.Geoff V wrote:Zhivko
How do you intend to join the fins to the outer casing of the heater? if they are not welded to the case, there will be very little heat transfer.
GeoffV
The price difference was 1:8, comparing this method and EDM cost (cca. 8000€
) of cutting slotted exchangers - so this method of assembling was very tempting for me to try.Will see how it goes in any case I am open for suggestions how to fill that gap also... I was thinking of soldering but don't know which solder would withstand such high temperature.
Regards,
zhivko
Re: Big Beta Stirling 1kw, 100degC to 400degC
Zhivko
The chart I published shows heat transfer from a solid to air, not a solid to air to a solid! For heat transfer to take place there must be a temperature difference, so by definition the fins will be cooler than the temperature of the air by conduction alone. There will be some radiant heating of the fins but no longer to the displacer, as it is now shrouded, so I would expect this arrangement to be inferior to the original configuration.
The only technique for joining the fins to the outer casing, that I'm aware of, is furnace brazing with nickel filler, but this would be difficult/impossible with this design, see the work conducted by Andy Ross.
Finally, I am concerned that you have reduced the diameter of the displacer, If so then the displacement ratio will have changed?
I still believe development of your original design would have been the best route, as Peter Lynn has demonstrated.
GeoffV
The chart I published shows heat transfer from a solid to air, not a solid to air to a solid! For heat transfer to take place there must be a temperature difference, so by definition the fins will be cooler than the temperature of the air by conduction alone. There will be some radiant heating of the fins but no longer to the displacer, as it is now shrouded, so I would expect this arrangement to be inferior to the original configuration.
The only technique for joining the fins to the outer casing, that I'm aware of, is furnace brazing with nickel filler, but this would be difficult/impossible with this design, see the work conducted by Andy Ross.
Finally, I am concerned that you have reduced the diameter of the displacer, If so then the displacement ratio will have changed?
I still believe development of your original design would have been the best route, as Peter Lynn has demonstrated.
GeoffV
Re: Big Beta Stirling 1kw, 100degC to 400degC
GeofV
thanks for comment - you are right regarding heat transfer. Maybe I could still improve heat transfer using thermo nickel paste (for example: http://www.tedpella.com/technote_html/1 ... 0%20TN.pdf. Although it's maximum reach is "only" 538 °C - I mean what could go wrong if I go over that temperature?
I think it will be not difficult to apply it with kind of injection needle (it must be 250mm long).
I didn't recalculate new volumes thinking that better heat transfer and added regenerator would automatically benefit efficiency...
I am aware that I constantly doing compromises because of already made parts trying to reuse them as much as possible. Will see what happens.
regards
thanks for comment - you are right regarding heat transfer. Maybe I could still improve heat transfer using thermo nickel paste (for example: http://www.tedpella.com/technote_html/1 ... 0%20TN.pdf. Although it's maximum reach is "only" 538 °C - I mean what could go wrong if I go over that temperature?
I think it will be not difficult to apply it with kind of injection needle (it must be 250mm long).
I didn't recalculate new volumes thinking that better heat transfer and added regenerator would automatically benefit efficiency...
I am aware that I constantly doing compromises because of already made parts trying to reuse them as much as possible. Will see what happens.
regards
Re: Big Beta Stirling 1kw, 100degC to 400degC
Hi everybody,
After brazing stainless steel lamelas and adding ss regenerator into cylinder, there has been quite an improvement in engine operation - although I still didn't measure power output.
Still there is not water cooling added...
Still place for improvement you can hear sound of banging displacer.
I need to add displacer piston ring (bronze PTFE).
Check this video:
Youtube link of Big Beta Stirling Engine
After brazing stainless steel lamelas and adding ss regenerator into cylinder, there has been quite an improvement in engine operation - although I still didn't measure power output.
Still there is not water cooling added...
Still place for improvement you can hear sound of banging displacer.
I need to add displacer piston ring (bronze PTFE).
Check this video:
Youtube link of Big Beta Stirling Engine
Re: Big Beta Stirling 1kw, 100degC to 400degC
zhivko, get the displacer sorted out, then I strongly recommend getting the cooling working well, it's just as important to get rid of the waste heat as it is to get the heat into the motor in the first place. Good cooling should make quite a difference to the power of the motor. Ian S C
Re: Big Beta Stirling 1kw, 100degC to 400degC
Ian, yes cooling would be an issue - but I am not there yet.
Couldn't think any better than placing ceramic bearing near the displacer middle - probably 2 of them. Looks like crank mechanism is swinging displacer and for such long displacer already small angles can cause big friction.
the issues here are:
1. low distance from displacer to cylinder wall
2. don't want to open displacer - don't want the hot air come inside it since it could warm displacer and consequently bottom part that should be cold as possible.
Does anybody have some clever way how to do it?
Thanks in advance
Zhivko
Couldn't think any better than placing ceramic bearing near the displacer middle - probably 2 of them. Looks like crank mechanism is swinging displacer and for such long displacer already small angles can cause big friction.
the issues here are:
1. low distance from displacer to cylinder wall
2. don't want to open displacer - don't want the hot air come inside it since it could warm displacer and consequently bottom part that should be cold as possible.
Does anybody have some clever way how to do it?
Thanks in advance
Zhivko