Barrel coolers

VanMan said:
I saw a guy using this on the range yesterday. It is a little noisy, but not bad. He says it does a great job, but I see it uses CR123 batteries that could end up being expensive. Maybe not too bad if you get rechargeable CR123 batteries.

https://magnetospeed.com/products-riflekuhl
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I have this one and used quite a bit. Used the Duracell Lithium battery. Over 2 summers on the one battery.
 
PGW Steve said:
This is a case of overthinking the issue. Moving a smallish volume of air down the bore that has a small surface area, is counter intuitive. Move a larger volume of air over the larger surface area of the exterior of the barrel.
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Steve, it appears to me that this is not that obvious:

  • Inner channel surface to external surface ratio is about x3.5 maybe x4 depending on caliber and contour.
  • However inner channel surface is going to used 100% in case you are blowing through, but you cannot possibly blow over external surface using 100%. In fact with a single fan you will blow from one direction and a wide stream and a small part of it will contract and run over a smaller portion of total outside barrel surface.
  • Blowing through inner channel will force air to contact with the hottest steel, while outside surface will always be cooler on a short timeframe. Inner flow against hotter surface will absorb more energy per air volume than outside flow over cooler steel.
  • If you have a carbon wrapped barrel, outside surface is in fact insulated while inner channel will always be air to steel contact.

Did you do any tests on inner vs outside air cooling by any chance?
 
One thing you also need to consider is that external cooling is a 3D solution whereas the bore cooling is 2D. External cooling may only be exposed to the exterior 50%, but there will be some degree of convection of heat increasing that number. Thermal dynamics again, where heat will migrate internally in the barrel, which moves very quickly. Grid something on a bench grinder 2" away from your hand and it gets hot, fast where you hold it, depending on mass.

The 3D affect of a large volume of ambient air hitting the barrel creating a large temperature differential, and extraction of heat. The 2D situation in the barrel, where the air entering is heated up quickly, and as it travels the barrel will be ambient to the bore at some point, and can't carry away as much heat, not so much the surface area, but the volume of air.

External cooling, say the air hits the barrel at 20*C and is 25*C when it leaves the surface. Internal cooling, lets say the barrel surface is 120*C, air entering is 20*C and by the time it has moved down half of the barrel, it's at 50*C. The lower volume of air, which is now hotter, doesn't have the shear temperature differential to extract heat as efficiently.

There's a lot more at play than area here, there's volume of air. How many CFM are internal air pumps? I know there is a lot of air from a fan that doesn't hit the barrel, but the massive amount of air hitting at ambient. The Dewalt fan I use is 650 CFM, and having it angled and hitting the whole surface leads to a lot of heat extraction.

Edit to add, earlier someone posted an air pump from amazon of 450 L/min, that works out to about 15 CFM.
 
PGW Steve said:
One thing you also need to consider is that external cooling is a 3D solution whereas the bore cooling is 2D. External cooling may only be exposed to the exterior 50%, but there will be some degree of convection of heat increasing that number. Thermal dynamics again, where heat will migrate internally in the barrel, which moves very quickly. Grid something on a bench grinder 2" away from your hand and it gets hot, fast where you hold it, depending on mass.

The 3D affect of a large volume of ambient air hitting the barrel creating a large temperature differential, and extraction of heat. The 2D situation in the barrel, where the air entering is heated up quickly, and as it travels the barrel will be ambient to the bore at some point, and can't carry away as much heat, not so much the surface area, but the volume of air.

External cooling, say the air hits the barrel at 20*C and is 25*C when it leaves the surface. Internal cooling, lets say the barrel surface is 120*C, air entering is 20*C and by the time it has moved down half of the barrel, it's at 50*C. The lower volume of air, which is now hotter, doesn't have the shear temperature differential to extract heat as efficiently.

There's a lot more at play than area here, there's volume of air. How many CFM are internal air pumps? I know there is a lot of air from a fan that doesn't hit the barrel, but the massive amount of air hitting at ambient. The Dewalt fan I use is 650 CFM, and having it angled and hitting the whole surface leads to a lot of heat extraction.

Edit to add, earlier someone posted an air pump from amazon of 450 L/min, that works out to about 15 CFM.
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Convection is completely irrelevant, a fan will blow air with significantly more force to overcome any convection slightly warm air might have. Convection flow for air touching outer surface will only be relevant in a still air.

Second, speed of air through the barrel is again completely irrelevant to the question we are trying to evaluate. Energy taken from barrel by passing air is air mass * delta T. There is more energy taken out from the system with N air leaving at 50 degrees than 3 * N air leaving at 25 with ambient at 20. Ambient temp of air is the same in both cases, inside and outside because you are pulling ambient air outside the system so I fail to see any 3D vs 2D you were talking about.

As I said before - this is not such an obvious situation to solve it just by looking at it. It needs numbers.
 
Well, I still haven't used the one I bought from A, but I plan to used it blowing on the muzzle so it will BOTH go down the bore AND Across the outside of the barrel. And maybe put an Ice Cube in front of it too 😄
 
Havent gotten around to my planned testing yet.

Got all the gear ready (fan with tube for internal and fan for external, multimeter with temp probe for internal temps and IR gun for external temps).

Will update when I do.
 
I did some testing but will need to revisit.

I will need to "Red Green" something for a better internal measurement as I wasn't happy with how consistent it was.

What I did notice was that the external fan was much less obnoxious / less noisy than the internal fan (which is why I am curious as to how noisy the blowers being discussed in this thread are). The external fan is *much* easier to use too.

Will report again when I do my "Take Two".
 
owlowl said:
Convection is completely irrelevant, a fan will blow air with significantly more force to overcome any convection slightly warm air might have. Convection flow for air touching outer surface will only be relevant in a still air.

Second, speed of air through the barrel is again completely irrelevant to the question we are trying to evaluate. Energy taken from barrel by passing air is air mass * delta T. There is more energy taken out from the system with N air leaving at 50 degrees than 3 * N air leaving at 25 with ambient at 20. Ambient temp of air is the same in both cases, inside and outside because you are pulling ambient air outside the system so I fail to see any 3D vs 2D you were talking about.

As I said before - this is not such an obvious situation to solve it just by looking at it. It needs numbers.
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Hmmm - Using forced convection (fan) inside the barrel or outside the barrel will increase the heat transfer coefficient over free convection (no fan).

1) Pushing increasing amounts of air through the bore will always increase the rate of heat transfer as you are increasing the heat transfer coefficient, and increasing the temperature difference between air and barrel.
2) Free convection on the barrel surface has a much lower heat transfer coefficient, and is dependent upon geometry and orientation of the surface. Where the barrel sits inside the stock, heat transfer will be marginal, possibly resulting in temperature gradients within the barrel and slight warping. Using a fan offers the same risk.
3) A fella can easily exploit the "stack effect" by orienting the rifle with the muzzle pointing up and the bolt open. This will draw cool air into the breech. As it heats, bouyancy will cause the air to rise through the bore. This results in a "natural convection" system, with a good heat transfer coefficient, approaching forced convection.

I use method 3) - its quite effective. If I wanted to speed things up, I would opt for option 1)
 
I Dont Care About You said:
If you have a 3D printer, this one is easy to make and uses a cheap USB fan

https://www.thingiverse.com/thing:5351868

large_display_20220412_223813.jpg


The fan is $15 on Amazon

https://www.amazon.ca/Wathai-Turbine-Centrifugal-Blower-Cooling/dp/B07Z7PVJH8/ref=sr_1_4?crid=DDY78CIVULCA&dib=eyJ2IjoiMSJ9.xBtv1YCcdqrr5DN-XjQ2UiUaI7wsgGka9xD18kAI39JX23AhdTVjoRDMlKaOT0UImBWfySq4HbSU2cCpTh8U5nxJuV9rR2fi83s2nJsM8OsIDiq6nMR5rKiLBAQqXXBPJdsq4kdmjPK8wzWrQcddCbet0BUXCvtoJS2o4mD3KCOAMBNMn1zFtg0gfIn8tpMY-GpaWIp_KxH9Y5qnvqrz8Qlhkq_WHf7K898ZhGcWd9qDkezC5vAuu6m3WWCC0t0P5PcvHAyDL7fPQCPna1RWsy2rxCxJz8TC9Xh0I_QCTvI.c3SMHZNjQ7C10snlnCw1M21VzBBqjMa3obAs3O9jjFs&dib_tag=se&keywords=75mm+x+30mm+USB+cooler+fan&qid=1756051176&sprefix=75mm+x+30mm+usb+cooler+fan,aps,661&sr=8-4&th=1
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Thanks for sharing that! Great idea.
 
cosmic said:
Hmmm - Using forced convection (fan) inside the barrel or outside the barrel will increase the heat transfer coefficient over free convection (no fan).

1) Pushing increasing amounts of air through the bore will always increase the rate of heat transfer as you are increasing the heat transfer coefficient, and increasing the temperature difference between air and barrel.
2) Free convection on the barrel surface has a much lower heat transfer coefficient, and is dependent upon geometry and orientation of the surface. Where the barrel sits inside the stock, heat transfer will be marginal, possibly resulting in temperature gradients within the barrel and slight warping. Using a fan offers the same risk.
3) A fella can easily exploit the "stack effect" by orienting the rifle with the muzzle pointing up and the bolt open. This will draw cool air into the breech. As it heats, bouyancy will cause the air to rise through the bore. This results in a "natural convection" system, with a good heat transfer coefficient, approaching forced convection.

I use method 3) - its quite effective. If I wanted to speed things up, I would opt for option 1)
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1) Temperature difference between air and barrel has nothing to do with an amount of air pushed through. Ambient air temp is the only temperature you will have unless you are doing air compression/decompression cycle.

2) Expecting outside fans or external air flow to wrap a barrel is... very curious, considering how pathetic air cooling is.

3) Stack effect draws such a miniscule mass of air through the barrel that it is a pure placebo. Differences in a barrel outer finish has way more effect that any chimney draft you can possibly get.
 
Owl - Heat transfer is governed by the Log Mean Temperature Difference (LMTD), which considers both inlet and outlet air temperatures. Increasing the air flow inside the barrel reduces the outlet air temp, thus improving the LMTD, and heat transfer.

The stack effect works for me - it cuts the cooling time in half compared to leaving the rifle at rest on the bench.
 
I shot a "club" PRS match yesterday and someone had a barrel fan stuck in their chamber. Until I saw it I thought some type of car alarm was going off. I know guys were firing rifles nearby but I found it annoying. I'll probably buy one.
 
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