Karl, so long as you have adequate draft the fire should build up regardless of how insulating its surroundings are. That looks like a pretty long burn tunnel, so adding a heat riser 2x its length or more and carefully sealing it to the riser base should take care of things.
Post by Karl playing with geopolymers on Jan 3, 2018 18:08:23 GMT -8
No. The pressure in the riser needs to be lower than in the feed and at the outside. A stable system requires an high chimney or a thermal buffer. It is pretty simple to calculate with the gas laws. Temperatures must be given as absolute temperatures in Kelvin.
For connected vertical tubes the outside air exerts more pressure at the opening of the shorter. To double the volume of a gas with 273.15 K the temperature must be raised by 273.15, to triple it by 2*273.15.
I hope this is understandable enough.
If the riser has double the high of the feed and the feed has 900 K how much is required in the riser ?
Just want to add some experience with highly insulated, short riser, j-tube priming. Even with paper and dry pine kindling it is hard to get my 4" j-tube to burn in the right direction. What I've taken to doing is to fully saturate 5 or 6 charcoal briquets with BBQ lighting fluid in a paint can. There should be enough fluid put into the can that after shaking the briquets in the can for one minute there is still some fluid that is unabsorbed by the briquets, hence "fully saturated". I then stack these briquets in the bottom of the feed tube and put in some oak splits about 14mm in dia. to half fill the feed tube. I then light the briquets and there is quite a flame coming out of the feed tube, but a strong puff of air blown down the feed tube will change the direction of the flame to the riser where is will remain because of the draft effect with this hot flame in the burn chamber. It works every time. The briquets will burn at a high rate for about three minutes and by then the oak is lit, the draft established, and heavier splits added. My riser is only 2.5 times the feed tube height.
Interesting... I'm always learning something in this forum...
I've been building 4.5" J-systems lately with fire brick splits in the feed and burn tunnels, then CFB risers. So i am not speaking from the same experience. Usually to light any J system i twist a sheet of news paper to about 10" long and light the end, move it around til it has fully caught then stick the lit end way into the burn tunnel. Once i see or feel the draft begin to draw up the riser i pull the twist back til flames are showing in the feed tube and add a bunch of scrunched up paper. Only once this wad of tinder has fully caught do i add kindling. May or may not help in this situation...
And leaves me wondering when the buoyancy of hot gasses trumps the relative atmospheric pressures ??
Since by far, most of the heat is reflected the extreme insulation of the small core makes it practically impossible to get the short riser hot enough to sustain draft. At the start the rather soft wood I have got does not deliver enough heat energy to get it going.
Trying to get a j-tube to work with a riser that's marginally higher than the feed and a relatively long tunnel is doomed to fail. Also, it might be that the material isn't as insulative and/or dry as one thinks.
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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?
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mannytheseacow: michaelegan: download AutoCAD student version for free... import .SKP
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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?
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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
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