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Post by Vortex on Oct 13, 2019 8:56:33 GMT -8
Very nice. But is there still room for the cat to sleep on? The hearth shelf is the same size as on the old stove so there would be, but unfortunately Pussycat died a few years ago, she was 21. |
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Post by Vortex on Oct 17, 2019 10:04:56 GMT -8
I got the new chimney cowl on a few days ago and have had a chance to test it out now. It has less resistance than my old original cowl, but more than the 8" stainless umbrella cowl I used while I was waiting for the new one to arrive.  While doing the yearly clean-out of the stove I made a couple of improvements. I upgraded the insulation around the afterburner, and moved the top shelf back from 3" to 3-3/4". This coupled with the lowered resistance of the 8" umbrella cowl had a surprising effect on the burn. I could close the damper much earlier without any stalling, but more surprising was a higher temperature in the afterburner which badly burned the glass in a single firing, and a drop in the exhaust temp of 10 degrees to around 70*C. With the new cowl I'm still getting the same lowered exhaust temps, closing the damper is a bit later but still a lot earlier than it was. Haven't noticed any increase in etching of the glass yet. The steel sheet on the front of the stove has always bowed out a bit when hot, which caused the door to drag on the hearth. It got worse after I cut the hole for the afterburner chamber as the steel then had less strength. I came up with the idea of putting a threaded bar right through the stove from front to back, like the tie rods and anchor plates used on old buildings. It worked perfectly.   I've found a supplier of 1200 *C High Temperature Resistant Fused Silica Glass Sheet, for roughly the same price I've been paying for the Robax, so I'm going to give it a try. |
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Post by cork on Oct 17, 2019 10:39:13 GMT -8
I would have thought if the temperature in the afterburner was higher then the exhaust temperature would be higher!
After sleeping on it I understand what is happening (probably).
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Post by Jura on Oct 17, 2019 23:40:15 GMT -8
I'd love to know what kind of magic keeps those 2-parts of the ceiling in horizontal position. (ie. without settling down in the middle front) They are shored up on their back, left and right side and do not seem to be so tightly packed. btw. I have recently given a hand in constructing such a cookstove  Does it resemble anything to you :-) ? |
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Post by Vortex on Oct 18, 2019 6:44:12 GMT -8
Hi Rafał, The front of my firebox roof is supported by the door frame. Is that the Vortex stove you were building for the bevy? I would have thought if the temperature in the afterburner was higher then the exhaust temperature would be higher! After sleeping on it I understand what is happening (probably). I'd love to know what your theory is James, I can't think of any way to explain it. I'll get the thermometer probes re-installed into the afterburner, put the umbrella cowl back on and re-run it and see what temps it's getting to. It burns the glass badly but I can polish it out in about 15 minutes with a felt pad on the orbital sander and a mix of T-Cut and red iron oxide powder. |
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Post by Jura on Oct 18, 2019 12:39:17 GMT -8
Hi Rafał, The front of my firebox roof is supported by the door frame. Goshshsh.. I could have figured it out by myself. It must have obviously been too early for my logic to take up such a demanding task ;-) Is that the Vortex stove you were building for the bevy? No, that's not the one. I joined an action of a Polish Masonry Association to give a hand with constructing a combined system of a heating stove, cooking range and a pizza oven for a person in need. To my surprise the cook stove firebox could have been ranked as a vortex one (no tertiary air, much poorer insulation, single cast iron switchback). As to the real vortex core based cook stove: it is almost finished, but someone who tried to pull out metal rods from the ceiling cast broke two of them. it was some month ago. (we didn't have any willow stick at hand while casting the firebox ceiling so we used old welding electrode rods wrapped with a paper tape) I went ballistic and left the place. (we are not much in a hurry as the buffer tank and all installation needs to be filled up with water before we can lit a fire in the vortex firebox (as the heat exchanger is placed right at the path fumes exiting from the single switch back chamber, and there is no way to deflect them) I'll be there next week so will try to shoot some photos. |
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Post by Vortex on Oct 19, 2019 2:28:18 GMT -8
I pulled the short downward willow sticks out of mine but the long ones that came out the end of the throat I left to burn out. Takes a lot of work to cast one of them right so I understand your frustration. Would love to see any pics you have of those stoves.
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Post by cork on Oct 19, 2019 6:20:55 GMT -8
Hi Trev,
I'm afraid my theory was flawed but grasping at straws, maybe the higher flow rate moved the hottest part of the burn down the afterburner chamber damaging your glass and also maybe the gases are not completely burnt off before they hit the cooling steel, resulting in lower exhaust temps. This may of course be way off the mark as I have no experience but felt I had to make some kind of reply. James.
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Post by Jura on Oct 19, 2019 15:00:34 GMT -8
Would love to see any pics you have of those stoves. So far I can share the pics from the PMA workshop/gathering. I'm PMing you a link to a google photos gallery. As to vortex cook stove: Believe it or not but in the bevy of four non of us had a smartphone. (My was stolen in UA, One Friends got broken, another two do not use mobiles at all) So the only photo I have for the time being is the below one. Dry stacked (shot by a visiting neighbor)  |
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Post by Vortex on Oct 20, 2019 9:59:37 GMT -8
Thanks for the link Rafał, Hi Trev, I'm afraid my theory was flawed but grasping at straws, maybe the higher flow rate moved the hottest part of the burn down the afterburner chamber damaging your glass and also maybe the gases are not completely burnt off before they hit the cooling steel, resulting in lower exhaust temps. This may of course be way off the mark as I have no experience but felt I had to make some kind of reply. James. The glass getting burnt could well be the increased gas flow driving the stove to higher temps and pushing the heat farther down the afterburner. I haven't had a chance to set it up and re-run it with the umbrella cowl yet, but I have a theory about why the chimney temp is lower. The slightly larger top gap exit from the afterburner and less restrictive cowl both lower the resistance to gas flow. That allows me to close the bypass damper much earlier without it stalling. (I'm now closing it when the chimney temp reaches 120*C, whereas before I had to wait to 200*C.) So now the top of the stove and chimney are not getting heated up so much by the initial blast. Before the top of the stove got really hot, and that heat gradually leaked away into the chimney through the rest of the burn keeping the exhaust temperature higher. Now most of that heat is going into the main mass. |
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Post by cork on Oct 22, 2019 9:41:05 GMT -8
Would it be worthwhile running the stove on bypass to 200*C ,closing it and checking exit temperature near end of burn?
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Post by Vortex on Oct 23, 2019 8:57:31 GMT -8
Ran it today with the temperature probe re-installed into the afterburner and everything else as close as I can remember it to that previous run. I didn't get the excessive heat in the afterburner like before, it was in normal range (went up to 844*C / 1551*F) no burnt glass, but the exhaust temps are still running lower.
I closed the bypass when chimney temp 120*C, it dropped slowly over about 5 mins to 60*C, stayed there for 15 minutes then very slowly started rising and reached 78*C for a few mins at the peak of the burn, then quickly dropped back to 60*C in the coaling phase. I'll keep trying slight variations and see if I can hopefully hit the sweet spot again.
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Post by Vortex on Oct 24, 2019 5:21:49 GMT -8
Would it be worthwhile running the stove on bypass to 200*C ,closing it and checking exit temperature near end of burn? Took your advice James, ran it to 200*C before closing the bypass today, the temp dropped slowly and never went below 70*C. Seems my theory that it's heat in the bypass, manifold and chimney from that startup blast that's keeping the temp up through the rest of the burn is at least partly correct. Afterburner temp peaked at 845*C, so no progress there. |
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Post by cork on Oct 24, 2019 11:02:27 GMT -8
Another contributory factor may be that in your yearly clean out you probably removed the fly ash from the underside of the hot plate. Still inclined to think the temperature, turbulence,time equilibrium has been upset. Also how important is your draft regulator as my build is very tight in an inglenook and it would be much easier without it? Hoping living in a less exposed area it will be ok.
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Post by Vortex on Oct 25, 2019 8:40:49 GMT -8
I doubt you'd really need the draft regulator where you are, you could always add one later if necessary.
The underside of the hotplate gets hot whether the bypass is open or not, and they get scraped every year as part of the annual clean-out, it's never made a difference to the chimney temp before. The top of the internal chimney, manifold and lower external chimney get heated up fast when the bypass is open, that seems to be what was collecting the heat and keeping the chimney temps up, now it's getting closed earlier it's not happening as much.
the afterburner glass has often got a little smoke tint at startup which clears quite quickly, but since changing to the low resistance cowl and larger afterburner top-gap, I've noticed the tint returning again sometimes around the peak of the burn, then clearing again. I experimented with giving it more or less air, and found closing the tertiary air before the peak of the burn stopped it from happening. Seems that with less resistance to flow the air openings can be smaller as it can draw it through faster.
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