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Post by rakettimuurari on Apr 20, 2018 22:49:46 GMT -8
I'd like to share my 2day- project... This started from the idea to prolong the firebox of the existing Skamet 110 sauna- stove with firebricks in order to accommodate longer cordwood. Original stove:  It is a small stove for 5-12M 2 saunas with 115mm cross sectioned pipe. When planning the thing I happened to remember what docbb had here or vortex and serg247 brought up here. After going through most of the Russian forum with translator mentioned in the first link by docbb, I decided to try this double chambered furnace idea in my sauna. I knew that stove was wasting some of its power to warm the sky as I got the secondary burn in the chimney all the way up to damper slits (2m from floor) if opened the damper entirely. So idea of having longer firebox + more controlled secondary burn was tempting. Quick drawing was made for 38 firebricks, adding some 80kg of mass to be heated (not optimal in sauna). New primary chamber has approx. same volume as secondary; around 25 liters. Firebox narrow and high as used in batch rocket to improve burn. Dry laying...  Cutting the port. Went for 80% of CSA which can be tuned with firebricks to be smaller... went instantly with tuning for trusty 70% which worked.  Base ready for the stove. Cast iron slabs are there to give more durability for primary burn chamber ceiling. Super wool was added under them. Door is from the old cooking stove.  Whole set up standing...  Firebrick adjustable "nozzle" in new secondary burn chamber, which is in actual sauna stove.  And what can I say... It works like charm! Sauna heated in same time as before, stones stay hotter and vapour of thrown water is stronger than before + 1/4 to 1/3 less wood is consumed. Top end of the chimney does not give smoke and not even steam - there are only transparent heat vibrations visible -> burns quite clean. Probably I will have to enstrengthen the ceiling of the secondary chamber at some point... |
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Post by Vortex on Apr 21, 2018 4:24:07 GMT -8
Nice work, rakettimuurari!
From the short video it looks like the port is a little wide and the top box a little high. Have you experimented with any different configurations yet?
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Post by rakettimuurari on Apr 21, 2018 5:12:13 GMT -8
Nice work, rakettimuurari! From the short video it looks like the port is a little wide and the top box a little high. Have you experimented with any different configurations yet? Thx vortex, for yourself too  Tonight is another saunanight (sauna frequency somehow got increased ...) and before I saw your post I was actually planning to choke the port to be even bit smaller by just sliding the brick; we'll see how it affects. I have also considered to increase the height of firebrick nozzle/ port depth; now it is around 15cm in total. It would be easier than cutting the bottom of the sauna stove away... I understood in Russian forum that port can actually be deeper without adverse effects? I have understood that they got higher temps by reducing the distance between the port and upper chamber ceiling like you suggested too... although Google translator is very poetic and weird with Russian at times  On the other hand the higher secondary chamber possibly decreases the thermal stress in the chamber ceiling providing longer operating life? Probably the jet will be already enhanced by choking the port but other than that i am cautious as there is now more than enough power + burn is all out smokeless... At first full burn I was sure that stove will melt by the sound of the burn; like jet plane taking off. Do you think the "flamethrower" stream should be even more intense? ..and; have you found the system size - port size ratio from anywhere for Aryanka?? I was not able to find it... so i just tried to figure it out from some venturi- effect references... ***
...if I was older and wiser I would install right at this point a 2,5 cm firebrick plate free floating in to the secondary chamber ceiling, at the place where the flame jet collides... Russian proverb violated by google translator: "It is not very playful piano" |
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Post by Vortex on Apr 21, 2018 9:38:50 GMT -8
The jet above your port looks like it's starting to disperse before it hits the roof, so there's not much double vortex forming. Oh wait, which way around is your port, front to back or side to side - It's difficult to tell from your pictures? I presumed it was front to back, so if it's not then that would explain why it looks too wide to me. The front to back port and the narrow top box works well together to shape and contain the double vortex, but the height of the top box has to be correct as well - too high and the jet disperses before hitting it, too low and there isn't enough room for the gasses to mix properly. I would do as you said and add a free floating slab up against the roof, it'll lower it a bit and help to protect it from the intense heat there. Also it would make it easier to replace later if necessary. I have not been able to find any ratio, other than what Peter came up with from his experiments. proverbs rarely translate well, can be fun to see what comes back after going through a few other languages though  |
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Post by rakettimuurari on Apr 21, 2018 23:04:03 GMT -8
Oh wait, which way around is your port, front to back or side to side - It's difficult to tell from your pictures? I presumed it was front to back, so if it's not then that would explain why it looks too wide to me. Yes, you could say it is side to side - 9 cm wide, 6 cm deep from front to back; this is very close to 70% of CSA as stove's chimney connector pipe is 10 cm/ 4 inch wide inside. I wanted to place the port side to side and little behind as the exits (2) from secondary chamber are in the ceiling in the front, just behind the glass door. That will make the hot gases stay in the chamber just bit longer. Last night I narrowed the port to near 60% CSA and also built the port to reach 6,6 cm higher in the secondary chamber. Jet was visibly weaker and sauna was less efficient. So basically it seems that the first configuration with 70% CSA port happened to be optimal. I still need to try it with the mentioned two modifications applied separately... I think I will end up doing this... just need to figure out the holder system configuration as i don't have welding tools. When the bottom of the stove gives up finally one day, I am planning to make replacement plate between the chambers with refractory mass. Then it is easy to lower the upper chamber and also to try front to back port. |
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serg247
Junior Member
The mountain can not be conquered, it can allow it to ascend...
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Post by serg247 on Apr 22, 2018 0:48:29 GMT -8
rakettimuurari
How and how much air is supplied to the upper chamber?
If you use the furnace Peter, but instead of riser upper chamber, it simplifies the supply of air and mixing, turbulence. Upper chamber only for afterburning and heat recovery.
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Post by rakettimuurari on Apr 22, 2018 22:33:59 GMT -8
rakettimuurari How and how much air is supplied to the upper chamber? If you use the furnace Peter, but instead of riser upper chamber, it simplifies the supply of air and mixing, turbulence. Upper chamber only for afterburning and heat recovery. Hello Serg, There is no secondary air supply at all as I wanted as simple configuration as possible. Also I have understood that those Russian versions neither have it although there was some discussion about it in forums in case the secondary chamber has a door... Originally I was thinking to use the ash box hatch/ intake air of original stove for secondary air but with that it behaved worse. The way it is installed now (ash box sealed) it will burn all the excess air from primary chamber in the secondary I think... so there is no extra air to cool it down. more than that the junction between the stove and primary chamber is not 100% air tight so really small amounts of air is getting inside just below the port. *If you use the furnace Peter, but instead of riser upper chamber, it simplifies the supply of air and mixing, turbulence. Upper chamber only for afterburning and heat recovery.
-can you elaborate what you mean by this? |
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serg247
Junior Member
The mountain can not be conquered, it can allow it to ascend...
Posts: 111
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Post by serg247 on Apr 23, 2018 0:03:15 GMT -8
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Post by Vortex on Apr 23, 2018 4:21:52 GMT -8
Serg, I thought you meant like Peter's Double Shoebox Rocket version, that has the port in the top. Your picture looks like a straight Batch Box Rocket with the port at the rear, which would make the stove like Yasintoda's "Batch cookstove with a small riser". Is that correct? |
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serg247
Junior Member
The mountain can not be conquered, it can allow it to ascend...
Posts: 111
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Post by serg247 on Apr 23, 2018 11:52:43 GMT -8
Absolutely correct. Secondary air supply and turbulence are transferred from the upper chamber with a short riser.
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Post by pigbuttons on Apr 23, 2018 18:45:25 GMT -8
Awesome stove/sauna. A lot of inspiration, and some perspiration, lead to a fine outcome.
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Post by rakettimuurari on Apr 23, 2018 23:18:47 GMT -8
pigbuttons: Thanks! One more actual benefit towards wood savings has also been the fact, that new mass of bricks accumulates so much heat during the heating cycle, that there is absolutely no need to dry the sauna with any other means... like usually we have added few wood blocks to firebox when leaving sauna. Drying is important aspect in keeping the otherwise unheated structure intact from humidity damage in finnish true 4 seasons weather... I also have 160mm Rocket Mass Heater in dressing room for winter.
vortex, serg: Yes, I went back to check the double shoebox again; it is very similar. I just never dared to think exposing the metal stove to rocket temps... Already with this system I am relatively sure something will be soon destroyed by heat, not to mention the scenario where I would implement Peter's system's even better combustion. Secondary air floor channel also adds complexity and vulnerability.
As for now I smoothed an old chimney damper of cast iron (20x30cm) with angle grinder and fixed it on the ceiling of secondary chamber at the point where the flame jet hits making it now 5mm of cast iron + ca. 3mm of steel. I also made some additional sealing around the nozzle so no gas will stream from any other gaps. Secondary air can be still given by just opening the upper chamber door some millimeter if experiment are needed. I was watching Matt's pre-port secondary air videos some time ago and I am interested to experiment how would choking the primary air/ adding more secondary air configuration work. Slowing the burning process but still keeping the secondary chamber hot is interesting option for this sauna stove...
What do you guys see going on in this video? Maybe it demands insulated top chamber to get high enough temps? There seem to be not too much secondary air either...?
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Post by Vortex on Apr 24, 2018 2:53:41 GMT -8
Haven't seen that video before, it looks to me like there's not enough air when the door is closed. You dont have to have the jet of flame hitting directly on the underside of the metal top, you can make it like Madhatter has on his 3 incher: donkey32.proboards.com/thread/2670/3-shoebox-heater |
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serg247
Junior Member
The mountain can not be conquered, it can allow it to ascend...
Posts: 111
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Post by serg247 on Apr 24, 2018 3:46:23 GMT -8
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Post by Vortex on Apr 24, 2018 5:47:23 GMT -8
A few pages on he said (Google Translation):
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