Is the mm5 coffee cup Stirling engine completely airtight?

[stuffandthings]

It's in the title. I need to increase an engine's pressure by increasing ambient pressure for a science project, and I obviously can't do that if the engine's completely airtight.

[Ian S C]

I doubt if you can effectively pressurise an LTD type motor, it may be possible to maintain pressure at atmospheric, or little better by using a valve system, but these motors have very little power, and any power increase would be marginal. Ian S C

[stuffandthings]

I had to eventually change the project. Thanks for all of your help.

Instead, I will be increasing the temperature of the hot and cold ends of the engine by an equal amount while maintaining a constant temperature difference, which should decrease efficiency.

Will placing an ltd-engine on dry ice or a skillet (not above 100 degrees Celcius) potentially harm the engine?

[Ian S C]

to run the motor normally, place it on a coffee cup of boiling water, the direction it runs is its normal direction of rotation. Put it on a container of dry ice, it will rotate in the other direction, the top (cold end), becomes the hot end, you might get it to run sitting on some ice blocks. To speed it up a bit, sit it on the boiling water, and put the ice blocks on the cold end, or you might be able to use the dry ice, this will increase the temperature differential. Ian S C

[stuffandthings]

If I were to increase the temperature of both ends of a Stirling engine by an equal amount (keeping a constant temperature difference), would the efficiency decrease?

[vamoose]

Yep, that's correct...

Here is a handy calculator for us lazy people who 'carnot' be bothered crunching the numbers

http://hyperphysics.phy-astr.gsu.edu/hb ... arnot.html



(remember to use the correct conversion widows depending on your needs e.g.- K, °C, °F )

For example using a Delta T of 50°C

@ 100°C hot side > 50°C cold side... max carnot efficiency is 13.399%

@ 150°C hot side > 100°C cold side... max carnot efficiency is 11.816%

[stuffandthings]

Thanks. I knew about the law, I was just asking to know if it translated to real-life performance.

[vamoose]

Ah, i see..

I would say yes, if the temp increase was significant enough.
An easy tell would be to see the rpm increase...

It would be very nice to see if the rpm increased by the same amount as the theoretical efficiency difference, although it may not for different reasons, but its worth a try!

for example using the previouse numbers i posted

13.4/11.8 = 1.13

so, if the higher window delta T rpm was around 100rpm, and the lower window delt T was around 113rpm, (or equivalent ratios) then it would be representative of the mathematical relationship of the related temperature conversion efficiencies, (plus or minus ∞ )

vamoose

[stuffandthings]

Thanks.
Is there any real-life scenario in which both ends of a Stirling engine would increase by an equal temperature?