Help With Steam Explanation

I've been lurking here for years, but I seldom post. Learned a lot though. Apparently not enough.

Now I've come before the font of collective wisdom, hat in hand.

I made an offhand remark to SWMBO that I'd like to build a fire piston.

"And that would be...?" "Method of starting fires. Works on compression, sorta like a Diesel."

Blank Stare.

Well, me bein' typically full of refined oats, I proceeds to expound upon the principle. Yep. Uh-huh. So I sez...

"Ya know about the gas laws, right? Ya know, Bernoulli, Boyle, and prob'ly a couple other dead guys? 'Member the part 'bout compressin' gasses gettin' hot and expandin' gasses gettin cold? Like that."

So she sez, "I have a question."

Now, I figger that I can field any technical question posed by a mere female without blinkin'.

"Shoot." "Water." "Huh?" "Water."

Blank Stare.

So she sez, "Water exists as a liquid and a gas, right?" "Yeeesss...Kind of. I think. Not sure that steam is a *gas* exactly, but..." "Well, water is steam in a compressed state, right? And you heat water to make it expand into steam, right? And when steam cools, it condenses back into water. So wouldn't that violate the gas laws?"

Great Big Googly Eyed Blank Stare.

"Uh, well technically, no, but ah, state change uses energy, and thermodynamics and stuff like that there, and uh, yes, violations, no uhhh, kinda, sorta......ahem. Umm."

Blast. And damn if she ain't hidin' a grin up her sleeve.

Any you fellas what has had the benefit of a real education want to chime in with the answer? Heck, I'm not 100% sure I even know what the question is!

I have a sort of vauge idea, but I can't find words to express it.

And she's still hidin' that grin.

TIA

Kenneth James

Reply to
K. James
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gas laws apply to gasses, not liquids. when a substance changes state, you ca't continue to apply the gas laws to them - a liquid is not just a compressed gas, it's a different kind of matter. Water is a liquid. if you heat it, the water absorbs heat and eventually turns to steam (heat of evaporation) - if you extract heat, it turns back to water (condensation), and if you extract even more heat, it becomes ice. so, in a way your wife is right - it does violate the gas laws because the state change makes the substance no longer a gas.

Reply to
william_b_noble

Do a Google search on fire piston, you'll get lot of hits.

Rather than lecture SWMBO, make one to demonstrate.

I've known several "mere females" who'd understand the thermodynamics well enough to design a better fire piston, and a couple who could design and make a working model if they cared to bother.

Good tinder is one secret to success.

Have fun!

Reply to
Don Foreman

I use clothes dryer lint for tender. Works great. Use just a very small amount.

Reply to
Rich

"Rich" wrote in news: snipped-for-privacy@individual.net:

I would add that it is imperative to not have any nylon, or synthetic lint in the mix. Further, I'm pretty sure that the 'tender" used is supposed to be charred as in char cloth used in the flint-steel method of starting a fire.

Reply to
granpaw

Since we're on the subject. Does anyone here have pictures etc. of their fire piston on the web? Thanks Karl

Reply to
Karl Vorwerk

On Sun, 16 Jan 2005 04:35:23 GMT, "K. James" vaguely proposed a theory ......and in reply I say!:

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You have the answer there. Water is not "steam in a compressed state", really. Change of state does require energy. Steam is gas. Actually the steam you can _see_ is condensing already to form water vapour, IIRC.

Gases occur when the molecules get enough energy to break apart from their liquid state and move about independently.

So if you add heat to water fast enough it changes to steam (gas) which takes energy. Leave it to give up heat, and it changes back to water and it gives out energy. Solids and liquids are not quite as dramatic as liquids to gases.

Water _would_ be steam in a compressed state, under enormous pressure, at constant temperature above 212 F. This takes _inout_ of energy, to do the compressing.

Reply to
Old Nick

Bunch of Google hits for sellers of fire pistons. Since they were mentioned here a couple-three days ago, I've been messing around trying to make one. Tip: there's a reason they're made out of stuff like buffalo horn. Mk I was cut off an old broomstick. Air blew right through the wood... Mk II is hard maple with strategically placed epoxy. Still doesn't make fire. At the risk of initiating another "it costs too much" thread, I'd now say the $55 to $95 prices are very reasonable for a fire piston.

The guys with the metal milling toys would have better results, sooner, than woodies like me.

Reply to
Australopithecus scobis

Sure, I can do that.

1) you can't ever win an argument like this with your wife.

2) even if you *do* manage to win, you still loose.

3) tell her she's right, and take her out to dinner as a prize.

Now that that's out of the way, the real answer is that the universal gas law is really called the "ideal" universal gas law.

"Ideal" modifying 'gas' in this case.

The law only works for "ideal gasses" which are gasses that are made up of atoms that DO NOT INTERACT WITH EACH OTHER.

Basically an ideal gas is a collection of tiny particles that obey a particular kinetic energy distribution, based on their temperature.

The hotter the container is, the faster they zoom around inside, and bump into the walls of the container.

The moment they do stuff like condense or stick together to form a liquid, the law no longer works because they're either not an 'ideal' gas, or they're no longer a gas, but rather a liquid. Even if they start to interact a little bit, you need to make a correction for the law.

PV=nkT is the math on this.

P is pressure - how much the gage reads on the container. (absolute)

V is volume of the box

n is the number of atoms of the gas you put inside the box

k is a proportionality constant, 'boltzman's constant' named for him

T is the temperature inside the box, again in absolute units (K)

All things being equal, if V goes down, then T goes up. As LONG as it's an ideal *gas*.

Jim

Reply to
jim rozen

Reply to
Tom Miller

On Sun, 16 Jan 2005 04:35:23 GMT, "K. James" vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

Be nice to hear how our "help" was applied K.

Reply to
Old Nick

There are two theories to arguing with a woman. Neither one works.

But I'm interested in this fire piston thingy. First time I've heard of it. I did my homework, however, and seem to have a good handle on the concept.

I see that most fire pistons are made from wood, horn, bone or plastic. I did not, in my travels on the web, see any made of metal. Is there a reason for that?

-Frank

Reply to
Frank J Warner

I'm guessing it's because the metal would chill the air heated by compression. If it were big enough and compressed fast enough it'd probably work OK. Diesel engines are fire pistons!

Reply to
Don Foreman

Don Foreman wrote in news: snipped-for-privacy@4ax.com:

In a way yes they are, but don't they need a battery to work, as in 'glow plugs'? A fire piston on the other hand uses compression alone to ignite the tender which is for instance a bit of charred cotton cloth, or something of that nature. IMHO it is because these are examples of primitive fire making tools that they aren't normally made out of metal, not that it wouldn't work.

granpaw

Reply to
notreallyme

Yes, but only for starting. Once running the glow plugs are switched off, right?

Jim

Reply to
jim rozen

notreallyme wrote in news:Xns95E6510CD96E0granpawiicenturyteln@216.196.97.142:

Nope. Glow plugs are used as a starting aid in cold weather, but they aren't a requirement for the engine to work.

Reply to
Old Fangled

Actually...not really. A diesel engine ignites the fuel/air mixture purely by compression. Now...most, if not all, of them have glow plugs that are used to help the process get started when the engine temperature is low enough that even the massive compression of the diesel engine is not enough to get the air/fuel mixture up above the ignition temperature. A glow plug, by the by, is really nothing more than a small heating element that sticks into the cylinder and heats up to red-hot for a few moments when the engine is first started. This extra heat is enough to ensure that combustion will start, and, once the engine runs for a few minutes, it will have warmed up enough that the ignition is self-sustaining. Typically, glow plugs are set to run for no more than a minute or so (although their real usefulness ends after the first ignition in the cylinder). It is perfectly possible to start a diesel engine without working glow plugs. As long as the block is warmed a little bit, the engine will fire up. Most large diesel engines come with a 1 kw heater element that screws into the block (typically by the oil filter), and is plugged into 110v to keep things heated up. I am reduced to this myself, as my truck currently has some issues with the glow plug circuitry, and, without the block heater, it just won't fire off below about 35 degrees. Regards Dave Mundt

Reply to
Dave Mundt

On Sun, 23 Jan 2005 06:48:44 GMT, snipped-for-privacy@esper.com (Dave Mundt) vaguely proposed a theory ......and in reply I say!:

remove ns from my header address to reply via email

snip

snip

???

Reply to
Old Nick

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