Cosmic, sorry, I thought I had more or less indicated the answers to your question(s) in the engineering thread.
The goal for the pipe maker is probably two-fold. First we want a pleasant smoking experience - gurgle free and a pipe that tends to smoke to the bottom, this kind of thing. Second, we want the flavor to be excellent - this is sort of obvious, but I can make a pipe utterly gurgle free and also utterly flavorless by filtering EVERYTHING out of the air - smoke, oils, water, tar, all of it! But then we would have a pipe (or rather a contraption) that did not allow us to taste anything at all.
Perhaps both of these points are the same - let me render it another way. A good pipe gets everything from the bowl to the button - it should be delivering the stuff we taste (which are these big floppy molecules, oils and esters mostly) onto our tongue. (This by the way is why if you smoke hot, you taste nothing - you literally burn up the "flavor" into CO2 and H20. If you ask a physical chemist (or even an engineer, but I have B.SC. and not a P.Eng, I hate engineers, they're all into approximations and charts n stuff) how to get all the bits in a hot gas from one place to another and not have them fall out or stick to something (not have them condense), the answer you'll receive is "laminar flow". Laminar as opposed to turbulent. This is a big deal in the giant oil pipelines, for example, where if the flow is in any way conducive to things sticking to the sides, they will, and the flow will get worse, and more stuff will stick to the sides....). We're talking about a gas and not sludgy oil, but the principles are mostly the same, with one major difference - the Joule-Thompson effect is not at play in liquids, can be in gases.
In the Joule-Thompson effect, we see gas pushed through an aperture have a fairly significant temperature drop (which would cause condensation). But to make it significant, you have to have a pretty small aperture and a pretty high pressure. So if you drilled the stem small enough, I guess you could make it even worse for yourself, but it would have to be a pinhole. I DID run these calculations 10 years back.
Back to laminar flow then. We have a fairly hot system (400-600F) but it's not a high pressure one - you are drawing air out of the pipe at just barely any differential over standard pressure (unless you suck VERY hard on your pipe indeed). You can model this (the link is now dead but there was a site where you could just tweak a pipe, a venturi tube essentially, in shape and size and watch the modelling, create eddies etc). But the simply and obvious answer is that you want to make the tube pretty smooth and pretty uniform. A friend of mine, uttering one of the deep truths of pipe smoking, once remarked with casual grace "Oh, if you're interested in seeing where your pipe ISN'T working, simply open it up and clean it - anywhere that you have black deposits is a condensation area." (And it's this kind of empiricism, this kind of experience-tied-to-thought that I'll suggest over-rides calculation here). Understand that we are drilling a hole around 1/8" and we can't make it square, we can't give it rifling, or fins... there's only so much we can control.
A smooth, uniform airway so as not to cause turbulent flow. How big? How shaped?
An airway with an 11/64" bore is capable at any given pressure of carrying almost double the smoke of an airway at 1/8". If you didn't restrict it at the bit, you could measure the Knudsen flow etc but we DO restrict at the bit so there's a bit more complicated of a system - the pressure in the airway in the stummel is higher than the pressure exerted at the stem because the gas is moving faster through the stem than through the airway (Bernoulli). There is no single equation where you can just sit down and plug numbers in and generate something useful here - there's a lot going on - change of shape of the tube, change of temperature of a cooling gas.
So as I said in a previous post in the other thread, one idea is to build a pipe with an airway that is essentially tapered (large at the bowl and small at the button) such that the pressure in the pipe, the interaction of smoke with tube-wall is less as it travels further (and cools off). The other big idea is to just make the thing a constant volume and bring all the smoke at the same speed and just carefully change its shape, as it were, from round to rectangular.
Both work, both work great. As do "reverse" calabashes, as do bongs really.
My answer isn't that I have an equation that tells me how to build pipes. My answer is that principles of engineering (fluid flow modelling, thermodynamics) and physics lead us to try certain ideas out as pipe makers. A real quick modelling problem for example: Assume an imperfect tenon length, ie, a tiny gap. Is the flow better if I bevel the tenon at 45 degrees of if I round off the inside of the tenon? You can look at stuff like this if you have fluid dynamics modelling software handy. Sorry but that's engineering stuff. Do all pipe makers do it (or need to)? Hell no. Because again, we can knock a lot of this stuff together and make it work really well with just a few iterations in the field.
Making great smokers, time in and out, isn't just drilling a couple holes. It really isn't.
The goal for the pipe maker is probably two-fold. First we want a pleasant smoking experience - gurgle free and a pipe that tends to smoke to the bottom, this kind of thing. Second, we want the flavor to be excellent - this is sort of obvious, but I can make a pipe utterly gurgle free and also utterly flavorless by filtering EVERYTHING out of the air - smoke, oils, water, tar, all of it! But then we would have a pipe (or rather a contraption) that did not allow us to taste anything at all.
Perhaps both of these points are the same - let me render it another way. A good pipe gets everything from the bowl to the button - it should be delivering the stuff we taste (which are these big floppy molecules, oils and esters mostly) onto our tongue. (This by the way is why if you smoke hot, you taste nothing - you literally burn up the "flavor" into CO2 and H20. If you ask a physical chemist (or even an engineer, but I have B.SC. and not a P.Eng, I hate engineers, they're all into approximations and charts n stuff) how to get all the bits in a hot gas from one place to another and not have them fall out or stick to something (not have them condense), the answer you'll receive is "laminar flow". Laminar as opposed to turbulent. This is a big deal in the giant oil pipelines, for example, where if the flow is in any way conducive to things sticking to the sides, they will, and the flow will get worse, and more stuff will stick to the sides....). We're talking about a gas and not sludgy oil, but the principles are mostly the same, with one major difference - the Joule-Thompson effect is not at play in liquids, can be in gases.
In the Joule-Thompson effect, we see gas pushed through an aperture have a fairly significant temperature drop (which would cause condensation). But to make it significant, you have to have a pretty small aperture and a pretty high pressure. So if you drilled the stem small enough, I guess you could make it even worse for yourself, but it would have to be a pinhole. I DID run these calculations 10 years back.
Back to laminar flow then. We have a fairly hot system (400-600F) but it's not a high pressure one - you are drawing air out of the pipe at just barely any differential over standard pressure (unless you suck VERY hard on your pipe indeed). You can model this (the link is now dead but there was a site where you could just tweak a pipe, a venturi tube essentially, in shape and size and watch the modelling, create eddies etc). But the simply and obvious answer is that you want to make the tube pretty smooth and pretty uniform. A friend of mine, uttering one of the deep truths of pipe smoking, once remarked with casual grace "Oh, if you're interested in seeing where your pipe ISN'T working, simply open it up and clean it - anywhere that you have black deposits is a condensation area." (And it's this kind of empiricism, this kind of experience-tied-to-thought that I'll suggest over-rides calculation here). Understand that we are drilling a hole around 1/8" and we can't make it square, we can't give it rifling, or fins... there's only so much we can control.
A smooth, uniform airway so as not to cause turbulent flow. How big? How shaped?
An airway with an 11/64" bore is capable at any given pressure of carrying almost double the smoke of an airway at 1/8". If you didn't restrict it at the bit, you could measure the Knudsen flow etc but we DO restrict at the bit so there's a bit more complicated of a system - the pressure in the airway in the stummel is higher than the pressure exerted at the stem because the gas is moving faster through the stem than through the airway (Bernoulli). There is no single equation where you can just sit down and plug numbers in and generate something useful here - there's a lot going on - change of shape of the tube, change of temperature of a cooling gas.
So as I said in a previous post in the other thread, one idea is to build a pipe with an airway that is essentially tapered (large at the bowl and small at the button) such that the pressure in the pipe, the interaction of smoke with tube-wall is less as it travels further (and cools off). The other big idea is to just make the thing a constant volume and bring all the smoke at the same speed and just carefully change its shape, as it were, from round to rectangular.
Both work, both work great. As do "reverse" calabashes, as do bongs really.
My answer isn't that I have an equation that tells me how to build pipes. My answer is that principles of engineering (fluid flow modelling, thermodynamics) and physics lead us to try certain ideas out as pipe makers. A real quick modelling problem for example: Assume an imperfect tenon length, ie, a tiny gap. Is the flow better if I bevel the tenon at 45 degrees of if I round off the inside of the tenon? You can look at stuff like this if you have fluid dynamics modelling software handy. Sorry but that's engineering stuff. Do all pipe makers do it (or need to)? Hell no. Because again, we can knock a lot of this stuff together and make it work really well with just a few iterations in the field.
Making great smokers, time in and out, isn't just drilling a couple holes. It really isn't.
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