starts off small at first
Join Date: Apr 2006 Location: Bean Town, U.S.A. | Quote:
Originally Posted by Cannon Fodder I know this is an old thread and my physics is weak but if a 12 gram is kept warm will it get more shots? Maybe make a jacket out of something like those reusable gel hand warmers, like I say I don't really know what I'm talking about - please don't flame ;-) | There are just too many variables involved to really asses any individual shot count.
Re reading through some of the hypothesis made here by various members doesn't even begin to establish a constant figure.
Here's a couple good examples.. Quote:
Originally Posted by Leafy If this was hpa and there was no phase change this would be easy. Give me another week or two in thermodynamics and I should be able to calculate an answer. Or just ask CockerPunk, he should know the math by now. Quote:
Originally Posted by splattttttt Don't forget to add and list all the variables Leafy.
You know, i.e. spring tension weight/ hammer weights/ volume capacities from gun to gun starting from the asa to dump chamber including transfer port sizes, valve size, power tube and bolt dimensions... Anything less would prove inconceivable.
Oh, and then there's paint cal., and barrel to ball match, ambient temps and elevation changes, night time vs. day time lol. Is it really worth it? Quote:
Originally Posted by Leafy Jack all that stuff doesn't matter when you're trying to find the theoretical max. All that matters is the amount of energy in the 12 gram and the amount of energy it takes to accelerate a paintball to 300 fps (or 90 m/s because that makes the calculations easier). I just don't know how to deal with the phase change that is taking place. | | | Sometimes you have to ask your self that! Than the physics end of it... Quote:
Originally Posted by mcnuggets I'm probably wrong but just to take a stab at it.
If friction is excluded and there is a perfect seal between paintball and barrel the maximum amount of energy will be imparted to the paintball when the CO2 pressure reaches atmospheric pressure. So the maximum number of shots is limited by, at least, how many times 12g of CO2 expanded out to atmospheric pressure can fill the volume in a given barrel. In other words:
Approximate # of shots = V of 12g of CO2 at 1 atm / V of barrel
Using the ideal gas formula to figure out the volume of 12g of CO2 at:
T=294.111K(70F)
P=100kPA (1atm)
n=12g (1mol CO2/44.010 g [from wikipedia])=0.272665mol
R=8.314472L kPa K^−1 mol^−1
V=6.667689L
So if we expand out 12g of CO2 it can fill ~6.6L.
A 14in barrel has a volume of 0.083317L. So a 12g CO2 can fill that barrel a little more than 80 times. Quote:
Originally Posted by 3022 mcnuggets, that was really nice math/phys exercise. But because you calculate with the volume of the air in the barrel, in your calculation, longer barrels are less efficient. So when we will take the 6" barrel of PGP, there will be more than double shoots than from your 14" barrel? Around 160 shoots per powerlet? That is evidently "little" unrealistic mathematic and the result is so likewise "little" doubtful.
It will be at least necessarily calculate with the volume of barrel in the optimal efficient barrel length, or better calculate with optimal amount of CO2 what will be consumed per shot, under optimal conditions, in this optimal barrel. So basically, Leafy statement is imho closer.
But that leads me rather to calculation with amount of CO2 what you need to accelerate paintball to required muzzle velocity (what is supposed to be usable) by most efficient CA pump setup - that is imho the best combination of theory and empiric.
Imho the best CA pumps using ~0,2g CO2 per shoot with muzzle velocity between 260-300 fps (that is more than 1500 shoots per 12oz or 500 per 4oz). And from this, you can expect 60 shoots per powerlet (12g CO2 in powerlet / 0,2g per shoot = 60 shoots per powerlet) under ideal conditions.
...but few years later, Punisher, with his nelson style pump "Avenger" was able get 62 shoots above 240 fps per powerlet and Palmer has claimed many years before, that he can get up to 56 shoots above 250 fps with his tunned PGP-like sheridan markers. And imho, the theoretical amout of shoots from one powerlet should be larger than that, what has been already practically archived :-).
Years before, I was able get 67 consistent shoots with muzzle velocity around 200 fps from my, only light modified ZGP-94 (lightened hammer, custom valve body) - it was marker build for indoors. Today, Im thinking that the consistency is one of biggest problems of SC efficiency tunning. So, theoretically, if it was possible have 67 consistent shoots, then when it will be perhaps possible raise the velocity in this marker enough (trought improvement in the airflow, sealing and reduction of unintended expansion after valve), it will be perhaps possible get 67 shoots per powerlet on muzzle velocity what is usable even in regular play (~250 fps).
My current record is 30-35 shoots above 250 fps from P68SC (half of them above 270 fps) and ~40 shoots above 240 fps (80% of them are above 250 fps) from PGP. That all in 20-30°C temperature and with ~3 seconds between shoots. In game, where I have typically alot lower rate of fire, I can commonly get above 55 usable shoots with such like markers. Additional tunning of such like markers I consider like really cost counterproductive, but taking performance tunning like separate sport, I think that one day I will be able get more than ~45 shoots above 250 fps like russc with his regged Sniper or 1996XJ with his VSC Phantom.
By the way, pump with solenoid will be imho not more efficient than mechanical pump. You will have here only a lot easier work with finding of the optimal dwell setting, because solenoid can be better controlled than springs. | | Then finally... Keep in mind this is how it all relates to physics. Meaning... how it all relates to on paper.
Bust since you asked? Quote:
Originally Posted by stevedh Ok folks, here's my crack at this...
First start with the energy needed to get a paintball to 300 fps (91 m/s), assuming a mass of 3.2e-3 g and ignoring friction in the barrel***.
KE=0.5*3.2e-3*91^2=13.2 J
This is the magic number, the energy we need to get from our CO2 expansion in the barrel to get the desired velocity.
To relate work with energy, we need the first law of thermodynamics, dU=dQ-dW. Let's assume we have an adiabatic process in which temperature is constant (which would more or less be the case in an idealized slow firing situation), in which case dQ=0.
So we have dU=-dW. dW in turn is given by dW=PdV or W=Pi*Vi-Pf*Vf=U which needs to be 13.2 J when we're all said and done here.
Going with mcnugget's 14" barrel, Vf=0.08 L, Pf=1 atm=101 kPa. Now consider the initial pressure, Pi. Let's say that an unregulated CO2 tank gives you, say, 800 psi (5.4e4 kPa) at the front of the valve and that this is the pressure that is being used to accelerate your paintball down the barrel. So now to adjust velocity we're adjusting the volume of said gas being released by the valve (think about how your IVG works).
So 13.2 J=0.08L*101 kPa-Vi*5.4e4 kPa, Vi=9.4e-5 L, or about 1/10 cm^3. Compare this to the size of the valves in your marker; it's less, but comparable, exactly as it should be.
Next, we want the amount (in moles) of CO2 that is required for this combination of pressure, volume and temperature. As Leafy pointed out, there is a phase change here which has the potential to give us many headaches, but we can approach a result using some assumptions. Let the CO2 be at room temperature and be constant (I know, if you shoot fast your CO2 tank or powerlet gets cold, but it CAN be liquid at room temperature under elevated pressures, which is clearly what we have in a powerlet).
Given PV=nRT, and, thanks to mcnuggets and Wikipedia, CO2 is 44 g/mol, n=5.1 J/(8.314*300)=0.002 moles, so since one 12 gram canister gives about 0.3 moles of CO2, the total number of shots should be 0.3/0.002 = 150.
This is about twice what has been observed in a practical situation, i.e. 3022’s markers, which is to be expected because it is a highly idealized case (we lack friction, temperature and phase changes, and inefficient seals around the paintball (the biggest offender) and in the valve assemblies, etc). The other thing that this doesn’t consider is the pressure change in the powerlet, and how that relates to the pi term above. But I’m an electrical engineer, not a mechanical engineer and haven't had thermo in about 7 years, so give me a break!
So I think its fair to say that something in the 150 shot regime is reasonable, but hardly achievable in real life. It is much more useful to look at other people's setups to see what they have been able to get in the real world. But any anecdotes regarding number of shots for a 12 gram must be considered scientifically, including standard deviations between 12'es and critically, the outside air temperature, as this effects "T" in all these equations quite appreciably. It would be really cool if someone could set up an experiment, not using a paintball gun, but something much simpler, to try and get the absolute maximum out of a 12'e.
Cheers!
PS: another comment I saw on here that I think should be discussed is the effect of barrel length on efficiency. I share 3022's view that there is definitely an optimal length as far as efficiency goes, and it has everything to do with your valve/pressure settings. I'm tired of seeing people talk about how longer barrels are so much more accurate or efficient than short ones, there's just no reason that should be true! |
__________________ "Democracy is the worst form of government except for all the others which have been tried." Winston Churchill THE-SHOOTIST Anyone chubbin' like me for this? mailmanmike Since Monday! That's more than 4 hours though, so according to those cialis ads I should see my doctor. tlane77 I think for a non-chemical chubby it's 6 hours before its time to see a doctor. So you should be good for another couple hours. splattttttt I wasn't goin to google "chubbin" because I assumed it had to do with fat. The lard type, not the fun stuff. But what ever feelings Jeff's experiencing, then they must be of the fun like stuff... tlane77 He's got a woody for your woods. splattttttt land |