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Post by Karl L on Feb 13, 2023 0:38:38 GMT -8
One experiment I've been thinking about is to inject secondary air sideways underneath the firebox roof.
This would be through horizontal slots at the top of the fire box side walls, aimed at the port.
The slots would be right at the top so the air hugs the firebox roof via the Coanda effect.
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Post by Karl L on Feb 12, 2023 22:54:24 GMT -8
why are there flames in the air channel, maybe the wood or maybe the increased volume of the afterburner. It looks like the flames in the air channel are gas leaking up between the firebox roof sections, then igniting in the secondary air.
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Post by Karl L on Feb 5, 2023 8:50:43 GMT -8
Trev (or anyone),
Do you have any idea how magnetite bricks might cope with being laid horizontally to form the roof of the top chamber? I was thinking I might put one or two layers in that position, but they will likely get very hot -- glowing red? -- and so undergo extreme thermal cycling hundreds of times over the life of the stove. Especially if I put some insulation over the top of them, as I want the heat they hold to slowly distribute within the stove, not be radiated quickly from the hot spots.
I am not worred about these bricks in the other parts of the stove as they will be in compression. But laid-flat bricks will have to hold up their own weight (as beams) so the material will be in a small amount of tension. I wouldn't want them to fall into the gas path or damage the afterburner if they failed.
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Post by Karl L on Feb 3, 2023 11:23:29 GMT -8
I've seen it fixed with screws and/or something like skamol glue. Biggest piece inside a 100mm (4") vortex is 300x260mm (12x10") - top of firebox - largest piece exposed to high temperatures. Best to not screw them then ? The problems come with long pieces and large temperature differentials. Here's the thread where I found this out the hard way: Vermiculite board cracks in S-Portal testIf the Skomolex has high temperatures on both sides (as does the top of a Vortext firebox) then it will bend a lot less. I tend to build the Skomolex box inside some other material (e.g. steel), and then design the pieces so they hold themselves together like a 3D jigsaw, and then use pins made from 3mm steel fencing wire into drilled holes to lock some peices in place. But Martyn seems to have glue and/or screwed his 4" firebox together, and it seems to be working pretty well.
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Post by Karl L on Feb 3, 2023 7:25:08 GMT -8
Karl, if they have been kept outside then they will probably loose 40% of that once dried out, if fact you will want to get them as dry as possible before using them. Thanks for the tip Martyn, I was thinking the same thing about making sure they were dry before heating them up a lot. But I don't think it's possible for them to lose that much weight. If they were made from 100% water they would weigh 2kg each, so max possible loss would be 25%.
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Post by Karl L on Feb 3, 2023 4:06:38 GMT -8
The heater bricks arrived today, 75 of them, from a reclamation company. They said the bricks were all the same, but they've delivered two different sizes. photosI think I can design around that, and it might be better to design it to cope with slight diffences in available bricks if any need replacing. But I did buy some extra to allow for breakages and replacements. The heavier bricks weigh around 8kg each, the lighter around 7.6kg. So 60 of them in a stove will be ~480kg!
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Post by Karl L on Feb 2, 2023 10:21:27 GMT -8
The threshold is still 30mm high and in the same position. I do plan to try it half an inch farther in from the door some time soon. Hi Trev,
I'm thinking about door and primary air arrangements.
I haven't been able to work out the exact positioning of your threshold relative to the primary air inlet slot.
E.g. is the top of the primary air slot level with the top of the threshold?
How far back from the mesh is the threshold? (It looks like the mesh is tipped 'back', to angle the airflow slightly upwards, so maybe the average distance?)
Thanks, Karl
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Post by Karl L on Jan 29, 2023 8:06:57 GMT -8
... I find after mid burn I can reduce the primary and add the secondary air up through the ash trap, it seems to work as well as adding it through the sides of the port, but with the added bonus of burning up the embers nicely at the end. Thanks Trev. I'm trying to decide whether to include extra thickness between the firebox and the afterburner, in case I later need to put in a secondary air channel to deal with overfueling situations. Does your 'secondary air through the ash trap' method mean that secondary air injected into the port is not needed? I seem to remember you saying that sending air up through the fuel led to overfueling, unless it was very near the end of the burn? Thanks, Karl
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Post by Karl L on Jan 27, 2023 12:33:52 GMT -8
How many fires a day are you presently lighting? It's possible you could light less often with the larger system size. It's also easier to scale down the core of a 125mm system than to try and scale up a whole 115mm system and core. The number of fires depends a lot on how cold it is. On average: 2 fires a day.
But one thing I forgot to mention is that my current stove is a quick conversion from a 125mm DSR2, using the DSR2 firebox. This is narrower and taller than a proper 115mm Vortex firebox. I haven't figured out a way to get a steady and reliable burn with this firebox loaded to the top.
So, using a proper 115mm firebox I think I will be able load in 50% more wood. But I'll think about your comment about it being easier to scale down than up - thanks.
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Post by Karl L on Jan 27, 2023 6:59:18 GMT -8
I quite like the 45 degree 'diagonal fold' shelf idea. It's good you've maintained the same surface area to volume ratio. I would extend the top chamber and shelf back level with the rear of the stove though, that would avoid any more bends while maximizing the use of the space and remove the path of least resistance on the right hand corner. Thanks Trev. I'm not sure I understand you about extending the top chamber back. Do you mean move the back wall of the top chamber towards the back of the stove, and move the diagonal edge of the triangular shelf back too? (I think I understand what you mean by the path of least resistance: that bit where you can look straight down past the triangular shelf and the afterburner shelf, and into the front of the afterburner.) Is it a 125mm or 115mm system size, you seem to have mentioned both? I have a 115mm system here currently, and was planning to build a 125mm system. But now I am wondering if a 125mm will be larger than I really need, just to heat a large-ish room. The 115mm core, being slightly smaller, seems to fit better with the other elements of the design. It's very hard to know, but I guess this new stove will harvest and store more heat than the old one because it has a higher ISA (allowed by a bypass and better flue) and more mass. In which case it may not be necesary to build a 125mm system.
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Post by Karl L on Jan 26, 2023 13:28:52 GMT -8
For various reasons it would be good to locate the flue pipe at the back of the stove. It also needs to be near the centre of the stove (looking from the front). The problem is that it then blocks the Vortex core exit port. I was thinking that one way around this is to make the gases do a 'diagonal fold'. This brings the gases out at the front of the stove, going in the right direction. It also has a similar length for each flow path. The disadvantage is that the flow path has another two 90-degree bends - but the other solutions I can think of also have at least another two 90-degree bends, and the overall system has fewer 90-degree bends than Trev's mass arrangement. Here's a Sketchup of the idea: link (You have to 'hide' the cover over the core to see the diagonal fold.) Are there any reasons this might not work?
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Post by Karl L on Jan 26, 2023 11:37:30 GMT -8
On a different note, was thinking of ordering a vermiculite board for a project later this year, but seeing it crack so easily makes me wonder. The one I could find is rated 1100C max. I've used Vermiculite board a lot, rated at 1100C. One thing to bear in mind is that its coefficient of thermal expansion is similar to steel - i.e. not negligible. So if it's very hot on one face and cold on another it will bend. And if it's a big piece and it's restrained from bending then it will break. I never have a problem with this because I divide large surfaces into smaller pieces and allow them to move a little.
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Post by Karl L on Jan 20, 2023 3:35:42 GMT -8
I forget to say the stove is based on Trev's vortex stove: sketchup
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Post by Karl L on Jan 20, 2023 3:26:40 GMT -8
Best heigth of firebox' ceiling in my case is about 100 cm (3.3'). Just enough while sitting in front of the thing on a lowish stool so I am able to look straight into the firebox. But then, I am certainly not the tallest guy on the block so it depends greatly on your size, I'd say. That last sentence isn't very clear, do you mean the flue comes out of the top of the planned heater? Thanks, Peter. The insulated flue runs through the mass, from the bottom and then out of the top, and then there is a further insulated section rising up from the top of the mass, then a 45 degree bend into an existing uninsulated chimney. I was thinking that the higher I raise the whole stove, the shorter will be the insulated part of the flue.
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Post by Karl L on Jan 20, 2023 1:49:35 GMT -8
My current stove has the firebox roof at about 450mm (18") above floor level.
Given it's necessary to load the firebox nearly to the top, and set a top-lit fire, having it this low makes it hard to use with out straining my neck.
Is there an ideal height for loading a firebox?
I also have to bear in mind that the higher the firebox, the shorter the insulated part of my flue becomes.
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