Question Stem Engineers

[Moonlite37]

Would a steam engine operate better at high atmospheric pressure, or low atmospheric?

 

[JCinKY]

(quoted from post at 10:08:33 07/22/19) Would a steam engine operate better at high atmospheric pressure, or low atmospheric?

If by better you mean efficient, then lower atmospheric pressure.

Water boiling at a lower temperature, less coal/wood you would have to burn.

Water boils at 212 degrees at sea level with 14.1 psi of atmospheric pressure.

Water boils on Everest at 160 degrees and 4.9 psi of atmospheric pressure.

 

[Janicholson]

The lower the atmospheric pressure, the greater differential between the internal actual pressure in PSI (not gauge adjusted) the greater the effective pressure on the piston/s. However it also changes the safety margin because the boiler construction is designed and rated foe differential pressure between inside and outside of the boiler walls. Jim

 

[Moonlite37]

so would the same engine operate equally well with the same gauge pressure?

 

[David G]

Higher outside pressure will allow higher absolute pressure in the boiler, thus more energy in the steam.

 

[Janicholson]

Good question. Most pressure gauges used by us common people (and not research scientists) are adjusted so they read Zero pressure when sitting on the bench disconnected. (or on a line with no pressure in it, like a oxygen gauge on a Oxy/acetylene torch with it blead out to be put away) This means that the gauge is compensating for the atmospheric pressure of 14.7 PSI to show Zero. That gauge, put into a vacuum chamber, would try to move CCW below the zero. Jim

 

[Janicholson]

If the entire setup is under the same over pressure, and up to the point that the water is superheated (which then becomes indistinguishable from liquid. Jim

 

[Pete in Holland MI]

Interesting question. Thinking about the pressure gauge, a standard bourdon tube gauge relies on a force inside of the bourdon tube trying to straighten it out. It relies on a pressure differential between the system it is attached to, and the outside air.

If the pressure gauge and the entire closed loop system is put into a pressure tank and raised to 100 psi in the pressure tank, and the closed loop system the gauge is attached to is open to the pressure in the tank, there would be no movement of the gauge. If you seal that closed loop system and add pressure, or draw it away, then yes, the gauge would move. Consequently, if at 100 psi pressure tank pressure, then the closed loop system to the gauge is sealed, reducing/elevating the tank pressure will cause a pressure differential between the closed loop system and the tank, which will yield movement to the gauge needle.

 

[Steve@Advance]

Theoretically the steam would exert more force because of the lower atmospheric pressure, provided it was an open system, as in exhausting to atmosphere. But I suspect it would be minimal compared to the forces being exerted.

But, I'm not sure what effect the lack of oxygen to the boiler fire would play. That is why the steam exhausts through the boiler stack, to cause air to be drawn into the fire box, sort of a reverse turbo charger.

But would that provide enough draft to overcome the lack of oxygen?

One thing for sure, if there was a way to make it more efficient, they did it! Especially toward the end of the steam age. I've stood and studied the plumbing on static displays, some of that stuff is mind boggling!

 

[David G]

You sure of that?

Steam pressure gauges are in PSIG, steam tables are in PSIA.

There is more energy in the higher PSIA steam.

 

[jeffcat]

Boy oh Boy. This is a good one. Checked several dynamic sites and boiler groups, and TRAINS magazine site. General opinion is steam engine will maitain its efficiency at low or high. When the atmosphere is too thin for good complete combustion, that is when they start to loose. Diesels are a whole different kettle of fish. Yes the higher they go they start to starve. They need turbos just to get up there. In really high railroads like in South AmericA the diesel engines needed to be pushed by the old steam locomotives just to move a few cars. After the design engineering people really put some big equipment on the front of those diesels did they get some performance out of them. Same as WWII with super high altitude fighters and bombers. With out superchargers they were worthless low level escorts. On this subject go on line and do some reading. Lots of yes and no and what if.

 

[Moonlite37]

Looks like I will ever know, and likely do not need to know. I have struggled with the question, "if a tree fell in the woods------"? Next question ,If 10 people smelled a rose, would the tenth person get as much scent as the first one?

 

[Steve@Advance]

David, no I am not sure...

That's what I was referring to as "open system" where the steam is released as a total loss to atmosphere. The force is relative to the pressure differential between inside the cylinder and the outside atmosphere.

I "think" what PSIA is a measurement of is a return system operated under a vacuum, as a closed system where the spent steam is condensed and returned through the system via vacuum.

This is seen more on steam turbines which require more pure and treated water, and ships where fresh water has to be distilled, and cannot be processed fast enough for total loss system.

PSIA is another system of measuring pressure relative to vacuum instead of PSIG which is relative to whatever atmosphere is available.

I think...

 

[Steve@Advance]

"If 10 people smelled a rose, would the tenth person get as much scent as the first one?"

A lot would depend on the life stage of the rose and how much time between people doing the sniffing. Was it just opening, mid life, dying stage? Temperature would also have an effect.

Here's another:

If you could measure the amount of light in a black painted room, no outside light, just a given amount of artificial light requiring x number of watts, then lined the walls and floor with solar cells and loaded them to the max with resistance load outside the room, then measure the light again...

Would the light level be less?

Would it be the same?

If the same isn't that a free ride for the solar power?

Where did it come from?

 

[Sekelbos]

My take is the lower atmospheric pressure will have a minimal effect on the output of a steam engine.Power is generated via piston and steam pressure.Steam pressure is supplied from a pressure vessel which is pressurized to a predetermined pressure. Internal combustion engines (non turbo) have less oxygen and therefore less combustion pressure and therefore a lower horsepower output.Maybe the coal will burn a bit slower with less oxygen so you could need a bit bigger fire?!

 

[Moonlite37]

I think you have discovered the perpetual motion (power) machine

 

[JMOR]

(quoted from post at 03:05:57 07/23/19) I think you have discovered the perpetual motion (power) machine

think we have discovered a whole bunch of people who think they know something, who really don't know Jack S.