Re: mod II stirling engine report

Discussion on Stirling or "hot air" engines (all types)
ulther
Posts: 5
Joined: Wed Dec 14, 2016 3:41 pm

Re: Re: mod II stirling engine report

Post by ulther » Mon Dec 19, 2016 4:01 am

Aviator168 wrote:
Let's settle on one thing here. We are not talking about toys models. I understand the parasitic drag induced by the connector; but that's a compromise I am willing to make, and why not. It is in direct proportion to heat exchange area. Now a couple of question. Why do you need 150 bar and what rpm and temperatures are you talking about? Have you consider the efficiency losses just moving the air back and forth (regardless of friction losses). For instances, 1 liter of air weights about 1 gram at 1 bar. At 150 bars, it will weight 150 grams. Regardless of rpm, it will take a lot of energy to move 150 grams of working fluid back and forth.
Well at first we are talking about mod II stirling engine that uses 15MPa= approximately 15bar. That is where I got the number.
Now to the part of gas moving back and forth. What do you think causes efficiency losses for fluid moving back and forth?? It's flow friction! You can't talk about it excluding flow friction. It is basically The ONLY factor that causes efficiency losses just by moving fluid back and forth. Friction is determined by various factors: viscosity of the gas (obviously it uses helium not air), surface finish of fluid traveling path, fluid traveling speed and various other small factors (example: small radius at the entrance of each tube/passageway in order to minimize “entrance losses”).
GAS(FLUID) TRAVELING THROUGH NARROW PIPES AT HIGH VELOCITIES SUFFER FROM HIGH FRICTION TO WALLS OF THOSE PIPES.
I am very sorry if I am wrong but you don't seem to understand that gas or any fluid is affected by friction when contacting any surface.

Aviator168
Posts: 308
Joined: Tue Feb 08, 2011 2:29 pm
Location: Brokeville, NY. USA

Re: Re: mod II stirling engine report

Post by Aviator168 » Mon Dec 19, 2016 7:33 am

First. 15MPa is not 15bar. It is more like, 150bar. That was the reason I asked the question to begin with.
The ONLY factor that causes efficiency losses just by moving fluid back and forth.
When you talk about 'efficiency losses', you are also implying that substantial amount of work was created; but the mod II didn't create a lot of power on 15MPa.
GAS(FLUID) TRAVELING THROUGH NARROW PIPES AT HIGH VELOCITIES SUFFER FROM HIGH FRICTION TO WALLS OF THOSE PIPES.
That's only part of it.
{\displaystyle F_{drag}=qA_{s}C_{D}}
https://en.wikipedia.org/wiki/Parasitic_drag
As velocities increase, the dynamic pressure is lower and drag is lower. You also forgot about the friction of between the pistons and the cylinder walls.

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