## Vacuum assembly of engines.

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Zynerji
42
Joined: Wed Jan 27, 2016 3:14 pm

### Re: Vacuum assembly of engines.

Rodak wrote:
Sun Jan 14, 2018 5:01 pm
Zynerji, there's force and there's work. Now you're doing work.
Isn't that what I've said all along? That the work necessary to move a piston that is acting upon a vacuum is stronger than the atmospheric effect on the vacuum? And the deeper the vacuum, and smaller the chamber containing the vacuum, the more work required to pull it apart?

I mean, if you compress a syringe to its maximum closure, then seal the needle, you would have to compromise the seal to pull it apart, or draw a vacuum. This should be far more difficult if you hooked the needle to a high vacuum source.

Just_a_fan
377
Joined: Sun Jan 31, 2010 7:37 pm

### Re: Vacuum assembly of engines.

The negative exponent is just telling you that the decimal point is moving to the left. 10^-6mbar is a low pressure. 10^-22mbar is a very low pressure. The lowest pressure you can get is 0mbar.

Sat on the beach, the air pressure is 14.7psi. On the top of Mount Everest, the air pressure is about 5psi (the same pressure used in the Apollo capsules, by the way, although that had a much higher % of oxygen to counter the low pressure). In orbit around Earth, air pressure is about 1.4^-7psi. We would consider being in orbit as being a vacuum but it isn't a true vacuum. Intergalactic air pressure (the space between galaxies) is about 1.4^-16psi. Note, this still isn't a pure vacuum because that would be exactly 0psi.

In your engine voids, you might be able to achieve a very low pressure and by increasing the volume of the space you would reduce the pressure further, yes, but you can never get less than zero psi. So the biggest pressure difference you get is 14.7psi. That's it, no more.
Turbo says "Dumpster sounds so much more classy. It's the diamond of the cesspools."

Zynerji
42
Joined: Wed Jan 27, 2016 3:14 pm

### Re: Vacuum assembly of engines.

Just_a_fan wrote:
Sun Jan 14, 2018 7:03 pm
The negative exponent is just telling you that the decimal point is moving to the left. 10^-6mbar is a low pressure. 10^-22mbar is a very low pressure. The lowest pressure you can get is 0mbar.

Sat on the beach, the air pressure is 14.7psi. On the top of Mount Everest, the air pressure is about 5psi (the same pressure used in the Apollo capsules, by the way, although that had a much higher % of oxygen to counter the low pressure). In orbit around Earth, air pressure is about 1.4^-7psi. We would consider being in orbit as being a vacuum but it isn't a true vacuum. Intergalactic air pressure (the space between galaxies) is about 1.4^-16psi. Note, this still isn't a pure vacuum because that would be exactly 0psi.

In your engine voids, you might be able to achieve a very low pressure and by increasing the volume of the space you would reduce the pressure further, yes, but you can never get less than zero psi. So the biggest pressure difference you get is 14.7psi. That's it, no more.
I understand that part. Can you address the syringe math I quoted earlier? To me, it seems like the resistance to pulling It apart would be infinite, as it would be trying to approach 0psi. It would immediately put this to rest for me if you could be so kind as to show the math with some real numbers.

Rodak
5
Joined: Wed Oct 04, 2017 2:02 am

### Re: Vacuum assembly of engines.

Zynerji, the clamping force from a bolt or, in your case, air pressure, is not work. Moving the piston in a syringe is work, you are reducing the density of the trapped gas (and, in fact, reducing the temperature; T2 = (T1)(P2)/P1). Torr is simply a measure of gas density, not a measure of 'vacuum force'.

Zynerji
42
Joined: Wed Jan 27, 2016 3:14 pm

### Re: Vacuum assembly of engines.

Rodak wrote:
Sun Jan 14, 2018 7:50 pm
Zynerji, the clamping force from a bolt or, in your case, air pressure, is not work. Moving the piston in a syringe is work, you are reducing the density of the trapped gas (and, in fact, reducing the temperature; T2 = (T1)(P2)/P1). Torr is simply a measure of gas density, not a measure of 'vacuum force'.
Is there a difference between clamping force, and resistance to movement?

Just_a_fan
377
Joined: Sun Jan 31, 2010 7:37 pm

### Re: Vacuum assembly of engines.

Zynerji wrote:
Sun Jan 14, 2018 7:19 pm

I understand that part. Can you address the syringe math I quoted earlier? To me, it seems like the resistance to pulling It apart would be infinite, as it would be trying to approach 0psi. It would immediately put this to rest for me if you could be so kind as to show the math with some real numbers.
The syringe example you quoted is talking about work done. You do work by pulling on the plunger. The distance you pull gives the work done. The speed you pull the plunger gives the power required. In all cases you exert a force only sufficient to overcome atmospheric pressure. The thread you quoted from goes on to discuss this further.

There is nothing special about 0psi. The only important thing is the pressure on the other side. When you pull back on the piston in front of an evacuated volume, you are actually pushing against atmospheric pressure. The vacuum doesn't pull the plunger in, atmospheric pressure pushes against it in an attempt to fill the vacuum and thus equalise the pressure. Thus the force required to pull the plunger out is atmospheric pressure times plunger cross sectional area.

If you can't grasp this basic idea then there's nothing left to be said.
Turbo says "Dumpster sounds so much more classy. It's the diamond of the cesspools."

marmer
25
Joined: Fri Apr 21, 2017 5:48 am

### Re: Vacuum assembly of engines.

You would be better off putting the engine you design to use vacuum sealed instead of traditional methods inside a larger sealed box that you then over pressure to get the force to make your engine work better than using traditional methods.

However i suspect the size and weight and heat dissipation of such a device would be useless in a F1 environment.

bigblue
20
Joined: Wed Oct 01, 2014 11:18 am

### Re: Vacuum assembly of engines.

You have a bolt with some size head on the outside, and a space underneath it which you're going to make more and more like a perfect vacuum. This means you're reducing the amount of air in the space.

If you remove no air, there's a bunch of air molecules whizzing around bashing your bolt head from underneath, and from the outside.

If you take half the air out, there are less air molecules bashing your bolt from underneath, but the same as before from the outside. It is harder to pull the bolt out than before as this 'outside' air keeps bumping into your bolt head, keeping it pushed in like before, but you have less help from inside.

If you remove all the air from the space underneath the bolt, now it's harder again as you have the same outside air bashing the bolt, and no help from underneath.

If you make the space underneath bigger and have no air in it at all, you still have no help from air bashing into the underneath of your bolt. Whatever shape or size of hole you make, it makes no difference - no air means nothing bashing into the underside. Meanwhile, outside the same 'outside' air is bashing into the bolt head. So it stays pushed in to the same degree (i.e. air pressure times how big the bolt head is), with nothing helping you pull the bolt out from underneath.

Zynerji
42
Joined: Wed Jan 27, 2016 3:14 pm

### Re: Vacuum assembly of engines.

I completely get the point of the outside air pressure pushing in instead of a vacuum sucking in. I still don't see how you can pull a piston out of a hole without filling the space it leaves behind with something. It just seems like it would hydraulically lock in place, as you would be constructing a space, filled with absolutely nothing.

dans79
149
Joined: Sun Mar 03, 2013 6:33 pm
Location: USA

### Re: Vacuum assembly of engines.

All you have to do, is pull with more force than the atmosphere is pushing in.

Zynerji
42
Joined: Wed Jan 27, 2016 3:14 pm

### Re: Vacuum assembly of engines.

dans79 wrote:
Mon Jan 15, 2018 12:07 am
All you have to do, is pull with more force than the atmosphere is pushing in.
What fills the space that creates?

W = dP*V

dP is the pressure difference
V is the volume of the air container

This tells me that the 14.7psi would behave multiplicative with the volume of the the chamber, so it would seem that it would get harder to pull the stud out the larger the empty volume that you create.

dans79
149
Joined: Sun Mar 03, 2013 6:33 pm
Location: USA

### Re: Vacuum assembly of engines.

Read this, and keep in mind that work and force aren't the same thing.

https://van.physics.illinois.edu/qa/listing.php?id=2508

Zynerji
42
Joined: Wed Jan 27, 2016 3:14 pm

### Re: Vacuum assembly of engines.

dans79 wrote:
Mon Jan 15, 2018 2:05 am
Read this, and keep in mind that work and force aren't the same thing.

https://van.physics.illinois.edu/qa/listing.php?id=2508
Thank you, that fixed it.

It was the fact that the vacuum condition already existed that threw my connection off.

I do appreciate everyone's patience!

PlatinumZealot
331
Joined: Thu Jun 12, 2008 2:45 am

### Re: Vacuum assembly of engines.

Zynerji wrote:
Fri Jan 12, 2018 3:15 pm
Just thinking here a bit. What are the thoughts on using lapped "studs" that are assembled in a vacuum instead of bolts? Just having a small (3mm) stud milled on the face of the head with a matching reamed seat milled into the block, and in a deep Torr vacuum, slid together (sealing the negative pressure in the pocket) and then letting the chamber repressurize to atmo.

No hardware = less weight
No rebuilds/sealed engines = no a field access needed
Can also be used to eliminate gaskets by using a tongue and groove approach instead of studs.

Vacuum is cheap. Does anyone have a thought on this?
Would be weaker than steel studs!
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