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Effeciency from Cold Tanks / Air vs Hot Tanks / Air


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#1 TechPB-Mike

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Posted 24 December 2008 - 03:49 PM

Alright, this is a tough one for Punkworks

In the summer time, when my tanks were hot coming off the air fill station, shooting in 100 degree heat, I was getting MUCH better efficiency out of my guns

For instance -

DM8 in Supergun Show - 10 pods @ 4000psi, 90 degrees outside @ 290fps
DM9 in upcoming show - 7 pods @ 4000psi, 50 degrees outside @ 290fps

Ego 8 in Supergun Show - 14 pods @ 4000psi, 90 degrees outsite @ 290fps
Ego 9 in upcoming show - 8 pods @ 4000psi, 50 degrees outside @ 290fps

My theory is that hot tanks at 4200psi @ 110 degrees will make a more efficient gun than letting it cool to 4000psi @ 90 degrees

There is some wierd shit going on with temperature and efficiency. Here are two tests I propose-

Does cold tanks and/or cold air make the guns less efficient?
Does hot tanks and/or hot air make the guns more efficient?


Because my readings on efficiency are all over the place with this weather

#2 nickydp33

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Posted 24 December 2008 - 03:58 PM

never experienced this yet. but i live in chicago an the weather here is pretty crazy some days.
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#3 hocnic1587

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Posted 24 December 2008 - 04:03 PM

hm... this ir really interesting. I seems like only the temp of the tank and the temp of the air inside the tank would matter. No one cares about the outside air temp cause this doesn't affect anything. Only the tank temp would matter. And the hotter the more shots because as we all hopefully know, gas expands as it gets hotter. As it expands you have more pressure which in turn will equal more shots. I just don't see and science or logic about the temp outside the tank. Any other thoughts? All of this is of course my opinion.
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#4 brycelarson

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Posted 24 December 2008 - 04:59 PM

this is an easy one - we can do it when we do the next round of paint v dry firing efficiency testing. We use a water bath to cool the tank to 70 degrees before each test - in this case we can use a water bath to raise or lower temp and see how many psi a certain number of shots from a particular gun takes.

I'll just need to get one of those little instant read thermometers.

Any preference on what type of gun we use?

Here's my take on it - you were shooting different guns. I know it's simplistic - but maybe the second gun of each set was less efficient than the first gun. The other place may be lube. I dunno how much thicker grease is at 50 than 90 - but that may matter in this case.

#5 hocnic1587

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Posted 24 December 2008 - 05:06 PM

Good point on the lube thing. They probly need to be stripped ad cleaned really good and then lubed and or oiled the same amount. Also with the less efficient gun thing shouldn't you test spool vs. poppet. I wonder how weather affects the two. Is it the same for a spool as it would be the poppet. But then different guns would have to be used and you would have to find the ration of temp to number of balls and all kinds of things. Best thing would to be to try to find a spool gun and poppet that get around the same shots off the same fill. Then test that. I really don't know just throwing in some ideas. Good luck
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#6 Poe

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Posted 24 December 2008 - 05:41 PM

...
My theory is that hot tanks at 4200psi @ 110 degrees will make a more efficient gun than letting it cool to 4000psi @ 90 degrees

There is some wierd shit going on with temperature and efficiency. Here are two tests I propose-

Does cold tanks and/or cold air make the guns less efficient?
Does hot tanks and/or hot air make the guns more efficient?
...


I think a lot of it has to do with the tank and ambient temperature allowing the pressurized air to heat up quicker (cool down slower). Air is a good insulator. In both examples the air in the tank likely started at the same temperature. The only difference was that the pressurized air was able to absorb heat faster on hotter days with a hotter tank.

Each shot will decrease the tank's air temperature thus decreasing pressure. As the tank absorbs heat the air absorbs heat (energy) and the pressure rises. In your efficiency tests there isn't enough time for it to regain much energy between shots. The hotter the tank and/or ambient temperature the slower your pressure will drop resulting in more shots.

If you start with a cold tank the ambient air will expend most of it's energy trying to heat up the tank. When shooting fast, air in the tank will only get colder.

Starting with a tank that's already hot and using it on a hot day will allow the pressurized air to absorb heat faster allowing it to maintain pressure for longer.

Just my thoughts.

#7 Christopher

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Posted 24 December 2008 - 06:17 PM

I would take a very close look at how the lubrication reacts to the heat. I would think that most lubrication would thin out in a hotter temperature, thus giving a much more thin/slick surface. Different lubrications react differently to heat. From what I've seen, the difference in viscosity can sometimes be drastic.

Edited by Christopher, 24 December 2008 - 06:18 PM.


#8 BenM

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Posted 24 December 2008 - 07:47 PM

Hi, I'm pretty new to the TechPB community, I've been lurking in the forums, and i'd like to get more involved now. I'll introduce myself. I'm a mechanical engineering student from Canada. This is by far the most interesting forum for me since i'm a science geek. I've though about this situation and this is my take on what could be happeneing from Mikes observations.

The temperature of the air in the tank drops as the gas expands inside the tank after each shot. As a result the density of the air will increase, and the pressure in the tank will decrease. (Its important to note that the density of the air will increse from the drop in temperature, and will also decrese since the total amount of air in the tank reduces after each shot. The significance of these would need to be evaluated in order to determine the dominating factor.) The temperature drop is relatively quick during Mike's efficiency tests, so Heat transfer through the bottle can probably be neglected(ie. Heat from the environment--> bottle -->Air inside tank).
Since the air at a lower temperature has a higher density, more air per shot will be expelled from the tank. I think this would cover any loss in efficiency as far as the tank is concerned.

As for the marker there are many things to consider but these are what I think will have a significant impact. The increase in viscosity of the lubrication will probably be the major factor that effects efficiency. Since viscosity like many other properties are dependant on temperature. Another thing to consider is thermal expansion or contraction of the components of the gun as cooler air passes by. Obviously it would depend on the material of each part, but some parts will contract more that others which could change tollerances, thus more air could be wasted by leaking past seals etc.

Another thing to consider is the intitial temperature of the air before it is even compressed into the tank. Obviously the temperature increases during the compression process but there is a 40 degree difference in the inititial temperatures.

Anyways just thought I'd contribute.

Ben

#9 swift

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Posted 24 December 2008 - 08:53 PM

im no scientist but think about it, when its hot the air has more volume and is moving around much more. Also once it is being shot throughout the gun, it may not get as cold as the air that has already cooled creating in a small way more more volume and supporting the theory of better efficiency at these higher temperatures.....

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#10 BenM

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Posted 24 December 2008 - 11:10 PM

im no scientist but think about it, when its hot the air has more volume and is moving around much more. Also once it is being shot throughout the gun, it may not get as cold as the air that has already cooled creating in a small way more more volume and supporting the theory of better efficiency at these higher temperatures.....

swift


True, hot air has more volume then cold air when considering a constant mass, and constant pressure. However, when you are using a set pressure of 4Ksi at different temperatures you no longer have a constant mass, and the quantity of air in the tank is different. In fact you should have less air in the tank at higher temperatures.

#11 cockerpunk

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Posted 25 December 2008 - 01:17 AM

what happening there is that the energy in the ambient air (as heat) is flowing into the tank (as a Qin term) faster due to the larger gradient.

we'll for sure take a look at this this weekend when we do another round of efficiency testing.
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#12 BenM

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Posted 25 December 2008 - 02:44 AM

Yeah that's sorta what i was implying in my last paragraph but i see i sorta of contradicted myself. I guess that's what you get after some wine on christmas eve. Its quite a complicated situation with fluid properties constantly changing, But I guess that's where you guys come in to make some correlations backed by empirical evidence, Good luck! I'll be watching for this one. :)

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#13 hocnic1587

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Posted 25 December 2008 - 02:59 AM

commenting on what swift had, and correct me if i am wrong, but i don't think that hot air has more volume in this situation. This would be because we have a tank such as a 68 cubic inch tank. That is the volume. What really matters is the density of the air ocuppying that space. I think that is the dumb version of what the science guy was saying. Remember i not 100 percent on this so corect me if i am wrong and i probly am. haha. complicated stuff.
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#14 Voudim

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Posted 25 December 2008 - 07:34 AM

prob because like any plasma,gases expand. when heat is apply atoms are not as stressed or stressed on not sure,I think my science teacher told me about this a while ago...
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