I wonder what would be the effect of a proper airstreamed venturi port.
I mean the back of the firebox would be rounded in a shape which would concentrate the flames on the port, then the port sides would be shaped properly for the air to flow as best as it can; and the gasses expansion after that would suck what's on the firebox side.
I won't try, i have no means of testing nor the time. But it would be cool to know.
And may be a longer port, i mean, narrow, venturi shaped, to concentrate all the flames in a little area, insulated like mad.
Technicaly the rapid expansion of gasses after a venturi is what creates the suction effect. like, increasing the flow of compressed air.
I've tried smaller and wider ports as well, results were not as good. So yes, the constant could be 72.36% but the question of why isn't answered.
Tantalizing, don't you think?
Yes, quite. Peter, you know more about this than I do.. Where else in the stove world do we see ratios like this? Is there some corollary to another type of stove? Something well known.. ? Perhaps a connection can be inferred somewhere. ?
@donkey, To my knowledge, nowhere in the stove world is something like this known, sorry. During all these years of digging through stove information I've never come across a constant, let alone this particular one.
@max, Shaping the firebox to optimize the venturi effect could lead to a less usable fire box. Maybe I could try a shaped port, sometime in the years ahead...
Very interesting. Since you seem to be the one who's knowledgable, what radius at the port entrance would you recommend? And what is the hydraulic diameter of a port of say, 240 x 54 mm?
The radius should be as big as feasible. At a given widh the height of the port influences the flow velocity in the port, which depends on the velocity before the port and the CSA ratio of box and port. I think the height of the port will influence the head loss mainly by the flow velocity, which is neglible by a radius to diameter ratio > 0.25. A ratio of 0.4 could be used for safety. 54 mm x 0.25 = 13.5 mm. 54 mm x 0.4 = 21.6 mm. I would recommend a radius of 15-20 mm.
OK, I've recalculated the rectangle of 240 x 54 mm to a circle of 128.45694 mm or 0.1284569 m diameter. Inserting this dia in the Thermal Wizard, flow velocity of 2 meter/sec. and a minimum of 0.03 m for the bellmouth radius, this would result in a Head Loss Coefficient of 0. Anything smaller radius would result in a slight loss.
On the other hand, only counting the sides of the port to be rounded off, this sides combined could be seen as the circumference of a circle with a diameter of 0.1527888 m. Using a radius of 0.04 m, this would result in no loss again.
This Thermal Wizard is maybe not fit for calculating a rectangle duct, I don't know.
Alright, maybe someone who's gearing up for the Woodstove Design Challenge could use this!
Karl, Peter, i was thinking about the airfoil shape you see in some high end carburetors. Tho, not having seen one for a fair while, i can't remember if it's normal a normal airfoil or a reversed one. I have seen a flame in such a venturi, gas flame, which created a horendous amount of suction. The gas jet has to be placed perfectly to create the best suction, it was like a ramjet of some kind but meant for sucking air or throwing flames. Can't remember exactly. Had a light thrust, but it had thrust. If we could implement that effect into a rocket, that would be mad I'm imagining this in the burn tunel of a J tube. I've been searching images for a while. But can't seem to find a rendering of this.
where: Q = stack effect draft (draught in British English) flow rate, m³/s A = flow area, m² C = discharge coefficient (usually taken to be from 0.65 to 0.70) g = gravitational acceleration, 9.81 m/s² h = height or distance, m Ti = average inside temperature, K To = outside air temperature, K
U.S. customary units:
where: Q = stack effect draft flow rate, ft³/s A = area, ft² C = discharge coefficient (usually taken to be from 0.65 to 0.70) g = gravitational acceleration, 32.17 ft/s² h = height or distance, ft Ti = average inside temperature, °R To = outside air temperature, °R
This equation assumes that the resistance to the draft flow is similar to the resistance of flow through an orifice characterized by a discharge coefficient C.
Notice that there IS a constant here AND it's in the "ballpark" of our 72% -- discharge coefficient.
I'm not sure how (or even if) this relates, though it FEELS at least close to the right direction for further inquiry.
In a nozzle or other constriction, the discharge coefficient (also known as coefficient of discharge) is the ratio of the actual discharge to the theoretical discharge, i.e., the ratio of the mass flow rate at the discharge end of the nozzle to that of an ideal nozzle which expands an identical working fluid from the same initial conditions to the same exit pressures.
Where exactly should the port sit in terms of height relative to the batch box? Should the top of the port sit level with the top of the batch box, or bottom of port level with bottom of batch box, or somewhere in between?
TexasGonzo: Sooooo glad I found this site! Its always rewarding to find such a super group of folks! To any and all, feel free to PM me anytime. Thanks for having me!
Mar 11, 2019 18:56:41 GMT -8
jlmtech: GADGET: CONSIDER USING A JET PUMP INSTEAD OF A BLOWER FAN TO INDUCE DRAFT; NO CLOGGING.
Mar 26, 2019 8:19:28 GMT -8
michaelegan: i am unable to open the sketchup files on my mac. I used sketchup a few years back but apparently the company now requires a subscription. does anyone have any advice/instructions on how to use the program or how to view pictures without spending money?
Aug 20, 2019 18:41:48 GMT -8
mannytheseacow: michaelegan: download AutoCAD student version for free... import .SKP
Aug 23, 2019 13:33:44 GMT -8
topbaza: hi everyone, been searching all over net and this is were i need to be i think!!
Sept 28, 2019 6:16:25 GMT -8
anounaki: Hi, why I cant upload photos when I make new tread to this forum?
Feb 28, 2020 2:09:40 GMT -8
ahansen: photos under 1 mb not possible?
Jun 4, 2020 0:09:21 GMT -8
belgiangulch: Photo's are possible. They must be downloaded elsewhere and the image url (adress) is copyied.
Sept 14, 2020 7:26:15 GMT -8
belgiangulch: While creating a thread click on the small picture in the banner above the reply. A box pops up, paste the image url in the box. Pay no attention to the huge list of numbers and such.When you finish and hit reply your post with pictures will come up.
Sept 14, 2020 7:29:27 GMT -8
deadstarsstillburn: Hi there. I was directed this way by folks on the Permies.com website and am hoping I can get some information on how a total newbie can get started designing, siting, building, and not-dying-in-a-horrible-house-fire with a new RMH in a 160-year old home
Oct 21, 2020 6:52:10 GMT -8
deadstarsstillburn: The people over there recommended either a 6" batchbox or an 8" J-tube. I don't know what those are but am going to try to figure that out. What I need is a blueprint that I can scale to fit the need for my house. I have something likne 5000 square feet
Oct 21, 2020 6:53:00 GMT -8
deadstarsstillburn: but I do not need to heat all of it by any means. probably only need to heat half of that, maybe less.
Oct 21, 2020 6:53:15 GMT -8
deadstarsstillburn: moreover, the house has 3 storeys (large attic) so I assume if I get very efficient heating on the ground floor, that will go a long way toward heating the upstairs as well, no?
Oct 21, 2020 6:53:59 GMT -8
BenAlexanderT: Happy new year everybody. I wish you the best
Dec 31, 2020 15:06:14 GMT -8
Solomon: Anybody in Southern Oregon, in Jackson or Josephine counties?
Jan 16, 2021 21:54:43 GMT -8
gnomedome: i realsie this is from 2009
Apr 14, 2021 8:30:44 GMT -8
gnomedome: i realize this is from 2009 id love to see the photos from this ..as im looking to build a sauna soon similar to this .... if anyody sees this post firstname.lastname@example.org..... the photos in this post did not show up
Apr 14, 2021 8:32:00 GMT -8