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Post by coastalrocketeer on Jan 10, 2018 7:37:21 GMT -8
The original full title of this post is:
optimizing heat transfer in stove design through modification of stratification levels up or down in bells and other heat transfer chambers through the induction or dissipation of kinetic energy within the gas flow, via the optimized design of gas passage and mass collection structures, and other means
But for SOME reason the system says that was too long... LOL it couldn't POSSIBLY be because "I'm a bit wordy"...
This is a placeholder first post for posts I will be moving from another thread to not clutter it with the unrelated to that thread portions of this topic that are welcome to be discussed in this thread.
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Post by pinhead on Jan 10, 2018 8:14:10 GMT -8
I read your comment in the other thread so I know where you're going with this. In my last rocket stove, I allowed the barrel to feed directly into the bell beneath it (surrounding the core of the stove). Since I used an 8-inch stove pipe (with an inch of ceramic-fiber blanket inside) as a riser, there is plenty of room between the walls of the barrel and the riser to allow for a reduction in velocity. Velocity is further reduced by gradually widening the entrance into the body of the bell, much like an upside-down funnel. The reduction in stream velocity should serve to promote stratification of the gasses, thus allowing for maximum heat extraction by pulling only the coolest gasses out of the bottom of the bell into the chimney. The configuration of my stove is highly effective, as the chimney temperature drops substantially when I close the bypass (to around local ambient, i.e. temperature of the skin of the bell at that level). Unfortunately the difficult part, IMO, will be measuring the stream velocity which is a major determining factor with regards to stratification. I expect the velocity could be calculated, but that's over my head. I imagine computer modeling could come in handy.
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Post by Deleted on Jan 10, 2018 9:10:36 GMT -8
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Post by coastalrocketeer on Jan 10, 2018 9:33:46 GMT -8
pinhead... It's not central to your post, but I'm not sure if you're aware, that I've named that "ceramic fiber cut to fit and be self supporting inside a larger stove pipe" riser design of yours "Pinhead's 5-minute Riser" It is SUCH a great idea... I just got a roll of 1"x48"x25' for $200 delivered, so $2 a square foot. Meaning I should be able to make 11 6" CSA risers 48" long for $10 cost of blanket each. Or some lesser amoujt of a combination of 6" and larger risers. Not as cheap as scrounged from an old ceramic range or other appliance, but makes the cost of a rider very reasonable if you need 11 of them ;-). (I'm hoping to build stoves for some of my poorer friends who either don't stay warm, or expend a huge effort feeding standard "High efficiency" wood heating appliances, after I build one or two successful systemsp for myself. If there is a thread that discusses and desribes that, relevant posts ought to be copied into a new post named with my "cute" name for it, or some other suitable one to your liking.
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Post by coastalrocketeer on Jan 10, 2018 9:41:03 GMT -8
Rather than the complexity of working by mathematical formulas (which certainly DO have their applications, and I wish I was more proficient at working with...)
I do think that you can also design it by innate understanding, if you can map the relationships of gas flow and how gasses flow around and through immovable objects.
In Increasing velocity of a gas stream, you cannot ever exceed the maximum velocity of a system CSA entrance feeding into the bell (at whatever rate your stove is currently sucking/blowing it through... That's the max without restricting flow at higher flow/hotter fire/more rockety periods of the burn.
Gas flow and stream velocity in these systems is a dynamic variable throughout the burn cycle, and so a measurement you take at one point in time or space, will not necessarily be helpful at another point in the same burn, but the laws of gas flow will apply throughout.
If we understand, follow, and work within their limits and design in harmony with their demands and desires.
You CAN, however use the size and shape of the chamber there, and things like tangential feeding, to induce a vortex/spiral and thereby reduce or modify vertical stratification.
Just the way that a dyson vaccum cleaner uses a vortex to make tiny dust particles that normally float in the slightest breeze fall into the dust cup and not clog up the HEPA filter, we could possibly use a vortex within a bell, to increase mixing and even-ness of temperature in the upper part of a bell, but still send only the heaviest, coldest gasses out the exit... And counter intuitively, that exit could possibly even be placed at or near the TOP of the bell, though performance would be better at "slower" points in the burn cycle where the vortex effect is weaker or not induced at all, to have the exit at the bottom.
Or one could use designed structures to provide low flow restriction impediments to horizontal gas flow, by repeatedly "forcing" a change in direction of the gas flow horizontally, in a way that provides PLENTY of excess effective CSA for free gas flow, over system size, and enough space for some additional stratification between sets of direction changing obstacles as lateral velocity decreases, meaning gasses enter the "main stratification chamber" already partially or fully stratified, and at low velocity.
Even a simple single vertical flat baffle can perform this task, if the spaces gas can flow around it are suitably placed and of sufficient effective CSA above system CSA.
(I am positive that some of these ideas are solid and correct interpretations of what will happen with gas flow, and others are not, and that I will have to do experimentation to prove or disprove these ideas, and welcome anyone to reinforce or shoot holes in my notions based on their own logical interpretations, research, related knowledge and experience! Thanks for playing along!)
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Post by pinhead on Jan 10, 2018 10:44:27 GMT -8
pinhead... It's not central to your post, but I'm not sure if you're aware, that I've named that "ceramic fiber cut to fit and be self supporting inside a larger stove pipe" riser design of yours "Pinhead's 5-minute Riser" It is SUCH a great idea... I just got a roll of 1"x48"x25' for $200 delivered, so $2 a square foot. Meaning I should be able to make 11 6" CSA risers 48" long for $10 cost of blanket each. Or some lesser amoujt of a combination of 6" and larger risers. Not as cheap as scrounged from an old ceramic range or other appliance, but makes the cost of a rider very reasonable if you need 11 of them ;-). (I'm hoping to build stoves for some of my poorer friends who either don't stay warm, or expend a huge effort feeding standard "High efficiency" wood heating appliances, after I build one or two successful systemsp for myself. If there is a thread that discusses and desribes that, relevant posts ought to be copied into a new post named with my "cute" name for it, or some other suitable one to your liking. Here's the thread/post where I initially introduced the CF Riser. donkey32.proboards.com/post/23282/threadUnfortunately I'm not linguistically artistic enough to make up a catchy name.
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Post by pinhead on Jan 10, 2018 11:29:01 GMT -8
Rather than the complexity of working by mathematical formulas (which certainly DO have their applications, and I wish I was more proficient at working with...) I do think that you can also design it by innate understanding, if you can map the relationships of gas flow and how gasses flow around and through immovable objects. In Increasing velocity of a gas stream, you cannot ever exceed the maximum velocity of a system CSA entrance feeding into the bell (at whatever rate your stove is currently sucking/blowing it through... That's the max without restricting flow at higher flow/hotter fire/more rockety periods of the burn. In the name of scientific accuracy, I'd note one caveat: it depends on density (and therefore temperature). The gasses will be relatively more dense once they leave the primary heat exchanger when compared to the flow from the riser. In other words, x m/s in the riser won't necessarily correspond directly to x m/s through the same CSA in the bell. Unfortunately my understanding of gas densities with respect to temperature under slightly lower than atmospheric pressure is limited to theory with no numbers attached. Gas flow and stream velocity in these systems is a dynamic variable throughout the burn cycle, and so a measurement you take at one point in time or space, will not necessarily be helpful at another point in the same burn, but the laws of gas flow will apply throughout. If we understand, follow, and work within their limits and design in harmony with their demands and desires. You CAN, however use the size and shape of the chamber there, and things like tangential feeding, to induce a vortex/spiral and thereby reduce or modify vertical stratification. Just the way that a dyson vaccum cleaner uses a vortex to make tiny dust particles that normally float in the slightest breeze fall into the dust cup and not clog up the HEPA filter, we could possibly use a vortex within a bell, to increase mixing and even-ness of temperature in the upper part of a bell, but still send only the heaviest, coldest gasses out the exit... And counter intuitively, that exit could possibly even be placed at or near the TOP of the bell, though performance would be better at "slower" points in the burn cycle where the vortex effect is weaker or not induced at all, to have the exit at the bottom. Just remember the energy that causes the additional motion will necessarily have to come from somewhere, and will likely be drawn from the available kinetic energy (chimney draft). Or one could use designed structures to provide low flow restriction impediments to horizontal gas flow, by repeatedly "forcing" a change in direction of the gas flow horizontally, in a way that provides PLENTY of excess effective CSA for free gas flow, over system size, and enough space for some additional stratification between sets of direction changing obstacles as lateral velocity decreases, meaning gasses enter the "main stratification chamber" already partially or fully stratified, and at low velocity. Even a simple single vertical flat baffle can perform this task, if the spaces gas can flow around it are suitably placed and of sufficient effective CSA above system CSA. (I am positive that some of these ideas are solid and correct interpretations of what will happen with gas flow, and others are not, and that I will have to do experimentation to prove or disprove these ideas, and welcome anyone to reinforce or shoot holes in my notions based on their own logical interpretations, research, related knowledge and experience! Thanks for playing along!) I like this idea more than vortex-induced motion mostly because it can be used in a low-velocity environment, stealing less energy from the chimney flow. The first picture that came into my head is a series of stalactites and stalagmites made of whatever high-mass material is available.
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Post by smokeout on Jan 10, 2018 13:20:26 GMT -8
I read your comment in the other thread so I know where you're going with this. In my last rocket stove, I allowed the barrel to feed directly into the bell beneath it (surrounding the core of the stove). Since I used an 8-inch stove pipe (with an inch of ceramic-fiber blanket inside) as a riser, there is plenty of room between the walls of the barrel and the riser to allow for a reduction in velocity. Velocity is further reduced by gradually widening the entrance into the body of the bell, much like an upside-down funnel. The reduction in stream velocity should serve to promote stratification of the gasses, thus allowing for maximum heat extraction by pulling only the coolest gasses out of the bottom of the bell into the chimney. The configuration of my stove is highly effective, as the chimney temperature drops substantially when I close the bypass (to around local ambient, i.e. temperature of the skin of the bell at that level). Unfortunately the difficult part, IMO, will be measuring the stream velocity which is a major determining factor with regards to stratification. I expect the velocity could be calculated, but that's over my head. I imagine computer modeling could come in handy. When when I pulled my heat exchanger , I noticed different colors from gas stratification around the outside of the riser pipe. docs.google.com/document/d/11VfeBAOqdEaxfPeQ7PIyoSju6si-bXLFxG-rYNXl9Vw
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Post by coastalrocketeer on Jan 10, 2018 14:17:17 GMT -8
Or one could use designed structures to provide low flow restriction impediments to horizontal gas flow, by repeatedly "forcing" a change in direction of the gas flow horizontally, in a way that provides PLENTY of excess effective CSA for free gas flow, over system size, and enough space for some additional stratification between sets of direction changing obstacles as lateral velocity decreases, meaning gasses enter the "main stratification chamber" already partially or fully stratified, and at low velocity. Even a simple single vertical flat baffle can perform this task, if the spaces gas can flow around it are suitably placed and of sufficient effective CSA above system CSA. I like this idea more than vortex-induced motion mostly because it can be used in a low-velocity environment, stealing less energy from the chimney flow. The first picture that came into my head is a series of stalactites and stalagmites made of whatever high-mass material is available. My understanding is that they have to be arranged such that the gasses are blocked from "forward travel" by the next row of "obstructions" after each previous one, which indicates that there would be higher performing configurations based on the placement of each lateral row of "columns" in relation to one another and the path the gas "desires" to flow through based on existing vectored kinetic energy. An aside of other laws of gasses I've come up with for people to reinforce or repeal based on their own knowledge and experience, or simple math and logical scientific deduction: Heat translates to kinetic energy in a gas, but only RANDOM vectored, and not the DIRECTIONAL type of kinetic energy imparted to the gas by flow within a furnace. Heat carries MUCH MORE (non directional) energy in a hot stream of gasses in a furnace than is embodied by the kinetic energy of gas flow in the low mass, low viscosity liquid that gasses actually are. Bouyancy imparts VERTICAL vectors of kinetic energy to a gas when different temperatures exist, whether the gas has existing directional kinetic energy or not, as long as the gas is surrounded by materials it can lose heat to, or gain heat from. Highly insulative, and/or low mass materials like more gas of differing temperature, or highly insulative refractories, will not absorb or release as much heat to or from a gas as dense conductive ones, and therefore will not as strongly affect temperature and bouyancy, of gasses they conduct or radiate heat to, or absorb heat from. There they are launched out into the great big world... Support 'em with logic, reason, and personal experience, or shoot-em down! No offense will be taken and your thoughtful input will be appreciated. (Need to find all the gas flow laws I've made up to place in one post where people can play "logical shooting gallery" and help me figure out what I know and where I'm wrong, so feel free to help if you are so inspired! The post doesn't exist, so if you find stuff I or anyone else have posted that's applicable, start a thread called "gas flow dynamics discussion" and throw it in, after creating a first post that says "introduction place holder"
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Post by coastalrocketeer on Jan 11, 2018 3:34:05 GMT -8
The more directional kinetic energy a gas stream has, the less bouyancy and temperature change play a role in choosing it's path, proportionally
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Post by coastalrocketeer on Jan 11, 2018 3:39:43 GMT -8
Delta-T, relative, or differential of temperature between gasses in a stream, themselves, and the other materials those gasses come in contact with...
Ie: a 1000F gas stream will lose more heat to a 300F brick than to the same brick already at 600F
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Post by coastalrocketeer on Jan 11, 2018 3:53:52 GMT -8
Characteristics of the current state of both the stream of hot gasses and the materials it comes in contact with, determine heat transfer, and are inter-related.
Delta-T: relative temperature differential
Heat capacity and conductivity of the materials in contact for conduction.
Thermal coupling of the two entities transferring the heat
The method of heat transfer and absorptivity of the receiving material to that form of heat. These are radiative and conductive.
Convection is not a method of heat transfer without the allowance for movement in the vertical plane. ie: gasses can be sucked into the system down low, and exit up high, in a system that provides a net heating effect to the gasses. When your system provides a net cooling effect, the gasses would want to flow downward, which would dictate placing your chimney exit below your intake.
It is a natural result of buoyancy due to volume changes based on temperature differentials in gasses at entry and exit, and imparts ONLY vertically vectored kinetic energy, meaning it is capable only of pushing heat up, and pulling cold down.
This can be used to create horizontal vectored kinetic energy in the gasses as long as their desire to go up or down based on heat gain or loss, is allowed for in the design.
Please suggest anything related that should, or anything included that shouldn't be, or ways that ideas ought be grouped and categorized in these ramblings and musings on the things that gasses in our stoves are naturally wont to do, or inhibited from.
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Post by coastalrocketeer on Jan 11, 2018 6:26:14 GMT -8
Can this one be true? If so, I believe it is KEY to the ability I posit, that one can use structure within bells and gas passage areas to manipulate gas flow velocity in the lateral plane to increase overall heat extraction into a given amount of mass, or concentrate heat extraction to specific areas of that mass, and understanding what we could want to do with it, and how we can work WITH the nature of gas flows in non-equilibrium thermodynamic combustion and gas flow dependent, heat extraction systems, that our heaters, essentially are:
A gas stream, or PART of it, can be stripped of LATERAL velocity by structures, without impeding overall gas flow through the system.
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Post by coastalrocketeer on Jan 11, 2018 6:42:57 GMT -8
In the name of scientific accuracy, I'd note one caveat: it depends on density (and therefore temperature). The gasses will be relatively more dense once they leave the primary heat exchanger when compared to the flow from the riser. In other words, x m/s in the riser won't necessarily correspond directly to x m/s through the same CSA in the bell. Unfortunately my understanding of gas densities with respect to temperature under slightly lower than atmospheric pressure is limited to theory with no numbers attached. Charles's law says that gas volume/density(opposites) is in a direct linear proportion to absolute temperature, dropping to zero volume at 0 degrees Kelvin/-273F The things that might not be linear could effect flow chaotically, that I can think of off the top of my head are the friction between gas molecules and between the gas and passage surfaces in the low CSA areas of the system. These would change proportionally with temperature, density, and velocity, but may not be linear relationships, like gas volume and temp, or might, I'll have to research, or anyone else is welcome to have beat me to it and report what they know, or find out in this thread. Heat transfer occurs with friction between gas molecules and surfaces, and time for contact, with a linear dependence on temperature differential between the materials, and also affected by conductivity, absorptivity/reflectivity of infra-red, and the specific heat capacity of those materials. For a gas that changes volume with temperature, specific heat capacity is constant with mass, and varies with volume... but this friction happens at the molecular level, and does not necessarily cause restriction of the rate of flow by volume or mass in a system. CSA limits that based on the driving pressure differential between intake and exhaust, and Overall, what I'm talking about developing an innate understanding the rules and wonts of manipulating and working with the flow of a gas stream, that transcends in most situations, even needing to know or calculate exact values like "what temperature is the gas at right now in it's passage through the system" or "what is the volumetric density or rate of flow in meters per second" through this part of the system based on the current heat and gas volume output of the core in the present state/stage of the burn cycle" Those things have their place, but mostly in measuring performance parameters, selecting suitable materials for regions of different temperature ranges, and insulative values, and confirming/proving things to the number preoccupied doubters(not meaning you), that can be directly observed and felt, such as "my butt (and house) was consistently warmer through this entire winter on 1/10th the wood" We may not be able to exactly quantify numerically exactly how many more btu's of heat energy the efficient rocket is providing us, but basic common sense tells us that there is a LARGE efficiency increase, in spite of some people's misunderstanding of what "EPA combustion efficiency ratings" quantify, that level them thinking my "79% efficient" box stove only leaves room for a 21% increase in efficiency. Rather than exact measurable numbers and what we can infer from them, this is more about "What can we come to understand intuitively, about what the gas will want and not want to do at any point in the system. And how can we use that set of understandings, to intelligently design gas flow within our systems to work to extract the desired amount of heat (all of it, please?!?) in the desired areas, without restricting gas flow, and/or inhibiting stable operation at any state of heat input, gas flow volume, or flow velocity, anywhere within the dynamic range of the burn cycle,
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Post by coastalrocketeer on Jan 11, 2018 7:09:02 GMT -8
As temperature goes up, density goes down, along with surface friction, and specific heat capacity by volume, while volume (opposite of density) increases, along with flow velocity through any fixed CSA.
All flow through the system is driven by differentials between intake and exhaust, through bouyancy, and directly tied to the height of these connections to the sea of gas around us.
Bouyancy is inherently related to temperature and volume, which according to Charles's Law have a direct linear relationship where as temperature of a gas increases, volume increases in direct proportion.
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