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Proof Carbon Barrel Cooling
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<blockquote data-quote="Zymurgist" data-source="post: 1692187" data-attributes="member: 73422"><p>I posting about barrel thermals on another thread. This is what goes on in Carbon Fiber (CF) barrels:</p><p></p><p>Heat always transfers from hot to cold through a process physicists call entropy. The heat originates from the hot bore and transfers to the cooler external surface of a steel barrel. </p><p></p><p>Steel (and other metals) conduct heat through the free electrons present in the iron atoms. As the steel heats up these electrons increasingly vibrate and collide with nearby electrons. These nearby electrons increase their vibrations which excite more electrons and so on.</p><p></p><p>A material's ability to conduct heat can be measured, steel is around 50 watts per metre-kelvin. High carbon content carbon fiber, from one end of the fiber to the other, is 500W/mK. Wow! That's great! Tens times more heat conduction than steel. But alas, there's more to this. </p><p></p><p>Looking at the one manufacturers CF barrels, they are laid up with the fiber running from muzzle to breach and back again but that is not the path the heat takes. In order to take advantage of the superior performance of CF you would have to lay up the CF with the fibers running from the steel bore core to the surface. </p><p></p><p>So what is the thermal coefficient going across the weave and resin of a CF barrel? I found data that says it's anywhere from less than 1W/mK to 5W/mk. The latter is for a resin that has metal powder mixed in it to improve thermal performance. So, CF across the weave is not a very good conductor of heat and that is why the CF barrel stays hot.</p><p></p><p>Would I use a CF barrel in a hunting rifle? Yes, if it produces the accuracy I want. Would i use one in a high capacity auto loader? Probably not a good idea.</p><p></p><p><strong>Comment: So the CF in this case is more of an insulator, trapping the heat in the steel barrel ?</strong></p><p></p><p>Yes, CF acts like an insulator compared to steel. It does trap heat in the barrel as it doesn't allow it to dissipate into the atmosphere as efficiently as steel does. Styrofoam has around 0.03W/mK thermal coefficient. I'd call styrofoam an insulator.</p><p></p><p>A CF barrel has less Thermal Mass than an all steel barrel and this causes it to have less Specific Heat Capacity than the steel barrel. As a result of that and the fact the heat cannot escape as quickly, the temperature of the CF bore core will rise higher and faster than the bore of an all steel barrel given the same loading and tempo of fire.</p><p></p><p>Some people on this website have suggested having a fan blow on the barrel to help cool it. I think it would be more effective to blow cooling air through the bore. Water would be a much more efficient bore coolant but I'd be very hesitant to use it as it could cause thermal shock to the barrel and damage it. Depending on how hot the barrel is you might even get scalded by the steam.</p><p></p><p><strong>Comment: This may come as a surprise but there are many guys, even well decorated BR shooters that cool their barrels with water while out prairie dog shooting. I have never done it but I have seen it work, push a patch thru then back to shooting, very accurately.</strong></p><p></p><p>That is a great idea. Water has a very high heat of vaporization and even a little bit of it will remove a lot of heat when it turns into steam.</p></blockquote><p></p>
[QUOTE="Zymurgist, post: 1692187, member: 73422"] I posting about barrel thermals on another thread. This is what goes on in Carbon Fiber (CF) barrels: Heat always transfers from hot to cold through a process physicists call entropy. The heat originates from the hot bore and transfers to the cooler external surface of a steel barrel. Steel (and other metals) conduct heat through the free electrons present in the iron atoms. As the steel heats up these electrons increasingly vibrate and collide with nearby electrons. These nearby electrons increase their vibrations which excite more electrons and so on. A material's ability to conduct heat can be measured, steel is around 50 watts per metre-kelvin. High carbon content carbon fiber, from one end of the fiber to the other, is 500W/mK. Wow! That's great! Tens times more heat conduction than steel. But alas, there's more to this. Looking at the one manufacturers CF barrels, they are laid up with the fiber running from muzzle to breach and back again but that is not the path the heat takes. In order to take advantage of the superior performance of CF you would have to lay up the CF with the fibers running from the steel bore core to the surface. So what is the thermal coefficient going across the weave and resin of a CF barrel? I found data that says it's anywhere from less than 1W/mK to 5W/mk. The latter is for a resin that has metal powder mixed in it to improve thermal performance. So, CF across the weave is not a very good conductor of heat and that is why the CF barrel stays hot. Would I use a CF barrel in a hunting rifle? Yes, if it produces the accuracy I want. Would i use one in a high capacity auto loader? Probably not a good idea. [B]Comment: So the CF in this case is more of an insulator, trapping the heat in the steel barrel ?[/B] Yes, CF acts like an insulator compared to steel. It does trap heat in the barrel as it doesn't allow it to dissipate into the atmosphere as efficiently as steel does. Styrofoam has around 0.03W/mK thermal coefficient. I'd call styrofoam an insulator. A CF barrel has less Thermal Mass than an all steel barrel and this causes it to have less Specific Heat Capacity than the steel barrel. As a result of that and the fact the heat cannot escape as quickly, the temperature of the CF bore core will rise higher and faster than the bore of an all steel barrel given the same loading and tempo of fire. Some people on this website have suggested having a fan blow on the barrel to help cool it. I think it would be more effective to blow cooling air through the bore. Water would be a much more efficient bore coolant but I'd be very hesitant to use it as it could cause thermal shock to the barrel and damage it. Depending on how hot the barrel is you might even get scalded by the steam. [B]Comment: This may come as a surprise but there are many guys, even well decorated BR shooters that cool their barrels with water while out prairie dog shooting. I have never done it but I have seen it work, push a patch thru then back to shooting, very accurately.[/B] That is a great idea. Water has a very high heat of vaporization and even a little bit of it will remove a lot of heat when it turns into steam. [/QUOTE]
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