Impact of Bowl Shapes on Smoking Quality

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halfy

Starting to Get Obsessed
Mar 6, 2014
245
6
What makes a pipe smoke great? This question mark has been haunting me for quite a few years ever since I became a pipe smoker starting with Stanwell, Peterson, Castello and Dunhill pipes, through late days with mostly high end pipes made by just a handful of carvers in the world. I have tried most of the available pipe brands and carvers' pipes. All of them may smoke good or sometimes not, or on the other hand occasionally good but mostly not. Indeed, there are thousands of smoking habits (e. g. tobacco choice, packing method, puffing pace, to name a few) and theories as it comes to pipes. But we can still list a few things in common that we expect from a good pipe, for instance: stay lit, taste good, easy draw, burns cool, no gurgles, and so on. I truly admire the high-end pipe makers not just for the beautiful outlook of their pipes; they do surpass the other ones in every aspects in terms of smoking quality by far. What's the secret hidden in their workrooms?
As a former physicist I could not resist the temptation of trying to understand the mechanism behind this "mysterious" topic. I once tried to code something aerodynamic to simulate the airflow in pipes. However as I went deeper into technical details I found it so labor intensive. It was like doing a ph. D. so I had to give up the simulation idea. Then I tried to make other approaches but could not find a way into it, until recently I threw away everything but the very basic and general facts in gas and fluid dynamics. So here comes this small article addressing these facts, how they apply to the airflow in pipes and finally the role bowl shape plays in the smoking quality of a pipe.
Let's start with something familiar. The picture below depicts something known to most of us. This diagram roughly shows the temperature distribution in a smoldering pipe. Anyway we would not partition the bowl into the burning, combustion and the condensation zones here. We just say that the temperature is not constant in the whole chamber. Now it is time to talk about the two facts that play essential roles in pipe engineering. They are both directly related to the temperature of the smoke.
640.jpeg

Fact one, for the same gas, the higher the temperature, the higher the viscosity is. Or in simple words, hotter gas is more difficult to flow. The figure below shows the viscosity of air versus temperature at standard atmosphere. As we may see that at 600 ℃ which is the typical temperature of the hottest part in the chamber, the viscosity is significantly higher than the stem end and by the chamber wall. You may want to prove this by puffing into a smoldering pipe. In most cases the smoke would rise from a region close to the wall, or even a smoke ring by coincidence. Please be noted that gas is on the contrary to liquid (hotter liquid flows easier).
640-2.jpeg

Fact two, hot air contains more moisture. And at standard atmosphere the amount of moisture air can carry drops more than half as the temperature drops by 20℃.
640-3.jpeg

And immediately we may realize that the shape/size of the bowl and the specific spot the airway connects to it may determine the airflow in the chamber and the quality of smoke that being drawn into the airway. That is shown in the figure below.
640-4-600x300.jpg

Two extreme cases are shown in the diagrams: a narrow bottom V-shaped bowl (left panel) and a flat bottom square bowl (right panel). Since airflow is always easier through cooler tobacco, the air drawn into the chamber would prefer to go through the cooler part, which is, the space surrounds the ember. In the first case, the ember is tightly confined by the wall thus less cooler space is available. The air flow through the ember is stronger than the latter case. The airflow is shown in the figure by black arrows with the size in correspondence with the flow intensity. This would result in the promotion of combustion and a hotter smoke. Particularly, as the tobacco burned over half way, this effect would be overwhelming as there is very little space surrounding the ember. The smoke may get hot and harsh. All the rich flavors to be released at cooler burning conditions would be gone.
While for the latter case, there is ample space surrounding the ember. Therefore the air would tend to skirt the central hot spot and flows easily along the wall and the coolest bottom edge of the chamber, as shown by the hollow arrows (So no worries about uneven burning here. I have experienced quite a few badly designed V-bowl pipes burning uneven, but never a wide bottom had such problem. The air flows by nature laws, not gut guess.) As a result the ember is less pushed downward by the airflow and the burning would be slower and cooler, and the smoke enters the airway would of course be cooler too, but maybe less flavorful due to very little airflow through the combustion.
And we may go a bit further along the smoke temperature line if we take the two facts mentioned above into consideration. Obviously the smoke in the first case is hotter (and the bowl engineering may push the ember even bigger). So, a hotter smoke, more difficult airflow, more moisture it carries ... Well, a compatible wider airway might be desired here. The reason is two-fold: easier airflow for the higher viscosity and more briar surface absorption for the moisture. As for the latter case, the cooler and drier smoke, a smaller drill size would be enough. The only attention needed here is the bowl size; it shall remain small to maintain a good smoke intensity. If you see a late Jørn Micke pipe, you will know what I am talking about.
An ideal pipe design would be individually quite different, but in general it should be something between the two. The airflow into the ember and the surroundings are well balanced. And the smoke drawn out should be as cool as possible. Remember, the bowl shape and the airway position constitute the selecting philosophy that determines the qualities of the smoke we draw into the airway. Then the airway engineering shall be compatible with the provided smoke. My personal taste is always strongly against the V-bowl engineering. I like the bowl to be small but wide enough at the bottom. In his book Rick Newcombe wrote about a criterion of telling if a pipe would smoke good or not. It was called the "four square test". Inserting a pipe cleaner with white/blue (or white/red) bars from the stem end. If at least four squares of the pipe cleaner can be seen in the tobacco chamber the pipe would probably smoke great. I think this is another version of "ample space at the bottom". And besides this, I would add another advice - do not drill the airway right into the bottom center of the bowl, make it further away in the corner to collect cooler smoke. Well, this is my two cents on some tiny aspects in the engineering department. Happy puffs!

 
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Chasing Embers

Captain of the Black Frigate
Nov 12, 2014
43,256
108,360
Indeed interesting, but for all the engineering, how can a $10 cob smoke as good, if not better, than a $700 artisan?

 
Good stuff, and great diagrams, but there are so many variables left out of the equation; such as, tightness of the pack, the cut or pressing of the tobacco, dryness of the tobacco, the rate of puff, strength of the puff, size of draft hole, and quite a few other things that may have impact on the burn rate inside the chamber. You've made a great argument for cylindrical chambers being the better burner, but the reality of what I find is that I get a cooler and more flavorful smoke from a tapered cone-shaped chamber. Most of my collection are deep cones, with some wide cones being best for tasting.
In fact, I find that many of my pipes that started off as cylinders ended up caking themself into cone-shapes. So, this led me to believe that cones were the natural burn pattern of tobaccos (or at least, the tobaccos that I chose to put into them). Or, maybe the cake forms more quickly in the lower third of the chamber, causing this phenomena for me... only in the pipes that I don't ream with a paper towel after each smoke.
But, something to think about and take into consideration. I am pretty sure that you are dead on, concerning where the draft meets the chamber. My pipes that are drilled dead center at the lowest point in the chamber are not my most pleasant smokers. Thanks for posting.

 

halfy

Starting to Get Obsessed
Mar 6, 2014
245
6
Embers,
This is just my two cent addressing a few of the vast range of factors may affect smoking quality. The materials of cob and briar are quite different, and particularly for cobs they have flat bottom (if the space beneath is packed with tobacco or ash) and the air way enters side ways.
Cosmic,
Would you smoke to the last bit of tobacco? Cone bowls do get a good (rich, intense) taste for the first 1/3 or 1/2 of a smoke. But as the tobacco goes to the last 1/3, I found flatter bowls offer less harsh smoke and more change (in the good way) in taste, and usually the the farewell smoke may develop into something wonderful ("like a dream" ---RSN's words), and I value this small part of smoke way more important than its trivial preceding. Therefore my bottomline criteria of a good smoker is, the very last bit of a smoke should be still addictive...So far my favorite shape is something close to the Dublin shape, but the bottom shall be gently flatter than usual.

 
Jun 27, 2016
1,273
117
Do you think that the arrows on the opposite side of the draught hole could be a little longer or shorter than the ones directly in front of it, but still longer than through the ember? Sometimes it seems that the flow might be a little different between those sides. :puffpipe:

 
Once again, variables. The whole reason I have a passion for tall conical bowls is because of the way it stoves the tobacco as the smoke progresses downward. It "cooks" the tobacco, so for Virginias this leads to a sweeter more flavorful last 1/3rd. But, if I were smoking a latakia blend or aromatic, maybe I wouldn't like this so much.

 

jpmcwjr

Moderator
Staff member
May 12, 2015
24,570
27,078
Carmel Valley, CA
Very interesting and thanks for posting.
My experience indicates that below a certain threshold, the temperature of the smoke doesn't matter. Sorta like coffee: if, say, 100º is the perfect temperature for drinking, 105º or 95º will still be all right. But much higher it will scald you, or much lower and it won't taste right. So, if you're smoking tobacco with good packing, drawing and ignition, and it goes in at the right moisture level, the temp of the smoke coming out will be fine. In part as it hasn't picked up super heated moisture from the tobacco to any degree; no tongue burn.
Have you the means to measure the temp of the smoke as it exits the button? My experience shows that a churchwarden doesn't cool the smoke much, and a nose warmer doesn't deliver smoke that's way hotter than normal due the length of the stem. It'd be great to have actual data on that.

 
IMO, the actual tool of the pipe only factors into about 15% of the equation, the rest is the skill of the smoker. A great pipe smoker can pull a fantastic experience out of any pipe. A mediocre pipe smoker will blame the pipe or the tobacco.
It's the same in every hobby. Guys comparing ratios, in bike gears, talking about why Cannondale makes a rider so much better at riding. And, they throw their nose up at the idea of a WalMart bike. My favorite thing to see is a group of mountain bikers on expensive snobby graphite frames get smoked on the trail by a $100 WalMart clunker. The tool only gets you so far, and the rest is up to the human element.

 

sablebrush52

The Bard Of Barlings
Jun 15, 2013
19,632
44,858
Southern Oregon
jrs457.wixsite.com
Pretty interesting article. It reminds me of the article on "chamber geometry" that was on Roan's "A Passion for Pipes" site, which went over this same topic using similar methods.
I can see where a good chamber design + clean airway can improve the odds of a full rich smoke. But as has been pointed out, the other factor is the smoker's technique. I get the best flavors when I've got the bowl barely going, the tobacco barely smoldering, and can keep the bowl in that state during the length of my smoke. And that takes a knowledge of proper moisture, proper packing for the cut type, and proper cadence that is so well understood that it take no real effort to maintain the desired state. It's often said that a good smoke is 25% equipment and 75% technique, and that seems reasonable.
Maybe this wide chamber base is a factor in why I find pots so often deliver a superior smoke. I wouldn't trade one of my Barling pots for anything anyone else has.

 
I think that these types of thought provoking articles are great to help smokers understand more about chamber geometry, so that they can better understand how to smoke different types of pipes... maybe. Also, I really enjoy Rick Newcombe's work, but even he backpeddles quite a bit after publication in his ideas of better pipes and even the notion of quality.

 

warren

Lifer
Sep 13, 2013
11,700
16,209
Foothills of the Chugach Range, AK
halfy: Thanks. Interesting it was.
I'm always fascinated by those who wish to quantify all aspects of the pipe and it's enjoyment. I'm more aligned with the members who think it's the smoker, more so than the tool, when it comes to enjoying a bowl. I'm also one who tries to keep the experience as simple as possible, stuff well, light and enjoy. Those who dissect the experience, whether the pipe, the blends, the psychology, etc. are oft times too pedantic but, ever interesting. It is the curious who find the new and better, I readily acknowledge.
I learn much, reading about pipes for blends, the different leaves and how they interact for flavor and burn rates, the widely varying methods of keeping pipes in good smoking condition, the engineering of the tool, etc. The one point which is constantly driven home is; smoking a pipe is an extremely personal experience, techniques vary as does what constitutes a satisfying/great smoking experience.

 
May 4, 2015
3,210
16
Interesting read.
Though, as stated above by many more eloquently than I'd ever be able to, I won't be convinced all the other variables don't have many times more to do with a decent smoke than how a pipe is engineered or the chamber is shaped.
I'd put tobacco moisture, firmness of packing, lighting, cadence and burning temperature, tamping and relighting well above the diagrams in terms of importance to this task.

 

halfy

Starting to Get Obsessed
Mar 6, 2014
245
6
I agree with you guys about the smoking technique over pipe qualities... In most case as long as the pipe was not so poorly made, I would by gut feelings knew how to pack and get a great smoke out of that. But a well engineered (or say, properly customized to one’s own habits) pipe will always make everything easy and smooth. I like the Newcombe book but don’t agree with him in particular aspects, such as, the open draw theory. To my experiences an open draw is more error tolerant (easier for both carver and smoker) but not that flavorful...
Well, this article is not intended to make any conclusion that specific bowl shape is more favorable over the others. It just depicts some of the physical scenarios of what’s going on in the chamber ...
And yeah, the arrows close to different wall sides shall vary a bit in size ……

 

Chasing Embers

Captain of the Black Frigate
Nov 12, 2014
43,256
108,360
To my experiences an open draw is more error tolerant (easier for both carver and smoker) but not that flavorful...
This can be fixed by packing the tobacco tighter.

 
May 8, 2017
1,593
1,627
Sugar Grove, IL, USA
Interesting thread. This question of the effect of chamber shape is one which I plan to explore for myself.
I generally have poor luck with conical (v-shaped) chambers because they tend to gurgle. I heard Jeff Gracik say in an interview with Brian Levine that he thought conical chambers shouldn't exist and that's why his J Alan spoon bits don't come in that shape. I think I agree, but am still hoping to find the right cut/packing combo for these since I have several beautiful pipes with conical chambers.

 
Funny how each of us can sense something so differently. I prefer the V-shaped chamber, emphatically. For a delicately flavored Virginia, it is the only way that I can pull the full range of nuances from the tobacco. I have a wide range of degrees of slopes in the V, some being a deep but gentle slop into the bowl, and my Becker scoop, which has a wide but shallow V. The Becker I use for sampling the flavors of my own crops and it is the first pipe I use with any new straight Virginia. For me, none of these gurgle. The only pipes that I can push to gurgle in my herd are the bent stemmed pipes, the more the bend, the faster it can be made to gurgle.
I do however, keep a range of different chamber shapes, so that I can pull different flavors and nuances from the same tobacco; some wide, some thin, some sharply V'd, some cylindrical. Learning how different pipes want to be smoked and how the same blend smoked through different bowls is what fascinates me about the hobby. And, if it were true that all pipes will give the exact same flavors from the same blend were inherently true at all, I'd get bored with all of this and just do something different.

 
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