|
Post by Karl L on Nov 27, 2020 23:56:49 GMT -8
Thanks. Yes, I was also wondering if it was low air flow. But the tube is scaled correctly from Peter's core drawings, I think.
This is a 125mm/5" core. The scaled internal width of the square tube should be 25.2 mm. My tube is 27.2mm internal - i.e. 16% oversized. The Horizonal tube is 2% oversized (It's made from 60x30mm, 3mm wall tube).
The cobra head is 2mm mild steel (~80 thou) - so that's a lot thinner than yours. The vetical square tube is only 1.6mm (1/16") - but that's not disintegrating so fast.
I wonder if the horizonal tube sometimes gets so hot that the air expansion restricts the flow rate? I once had a fire so hot that nearly the whole length of the horizonal tube was glowing red when I looked down it! But that doesn't happen with smaller loads of lighter wood, which is what I've been mostly using.
|
|
|
Post by Karl L on Nov 27, 2020 10:20:27 GMT -8
The onset of colder weather means I've been using my new DSR2 heater every day for around three weeks. I've noticed that the small mild steel deflector plate -- the 'cobra head' on top of the vertical square tube -- has largely disintegrated.
I was expecting the floor channel to last a bit longer - around 1 year at least.
Is there something I am doing that might be making it disintegrate faster than normal? Some of the burns have gone into 'thermal runaway', before I figured out the kind of fuel load that would avoid that.
Thanks for any thoughts.
|
|
|
Post by Karl L on Oct 17, 2020 0:13:35 GMT -8
One thing to suggest Max is right is the Coanda effect.
I think that if you widen the exit side of the port then the Coanda effect will cause the 'jet' of gasses to widen, because will 'stick' to the port walls. If you narrow the port exit then the opposite might occur.
I am guessing that the wider jet won't form the rams horn vortices so well as a narrow jet.
|
|
|
Post by Karl L on Oct 6, 2020 4:54:36 GMT -8
a 2:1 mix with arlite for casting the oven roof slab. Do you mean 2 sand, 1 clay powder, and use this mortar to bond arlite aggregate, making a kind of concrete?
|
|
|
Post by Karl L on Oct 5, 2020 13:18:42 GMT -8
"Also, it seems that everyone is more keen on clay/sand mortar rather than (quite expensive) refractory mortar due to its ability to be modified" not just it's ability to be modified .IMO it's a better material , more suitable as it isn't as rigid as refractory mortar & i think copes with the thermal shock better.Iv'e had some cracking in my firebox on the refractory bricks but the sand/clay mortar is intact. I've often wondered how to make the sand/clay mortar. How do you get the sand and clay to mix?
|
|
|
Post by Karl L on Sept 26, 2020 13:51:21 GMT -8
I noticed the sides of the core box (2mm mild steel, 570 x 550mm) were bulging ~10mm, because of differential heating of the centre of the panels compared to the rim. (I thought this wouldn't be a problem, but clearly it was.) One long piece of Superwool board, in the top box, was broken by the bulge (because it bulged inwards). Here's a photo of the slits: drive.google.com/file/d/1CDvk0gzGVhH3rfIhCmQl4r4LX8t3ezuaKarl, do you think welding a piece of steel like 5x25mm flat horizontaliy on a 2mm steel sheet would it prevent from bending? I'm not sure if I want to build a steel box just to cut clits on it I guess it might work - I'm not sure. The calculations for bulging are complex, and in the end it's just down to trying it and seeing, I think. The slits worked very well for me, in the end. If I was going to do it again I guess I might try building a frame out of 25 x 25 x 3mm steel angle and fitting 100mm-wide strips of sheet into the frame to form the sides, tack welded at one end only.
|
|
|
Post by Karl L on Sept 6, 2020 23:14:42 GMT -8
|
|
|
Post by Karl L on Jul 6, 2020 22:29:33 GMT -8
Many, but not all, of the batch box designs I've seen on this forum have sloping floors, like a V-shaped valley.
What is the purpose of this shape on the floor?
Is it necessary in a smaller system?
Mine is 125mm riser size, with a 177mm-wide firebox. It seems to be working OK without it, but maybe it would be better with it?
(I think remember reading about this a long time ago, but I can't find the post now.)
|
|
|
Post by Karl L on Jul 2, 2020 10:01:41 GMT -8
In my opinion there is insulation :-) -- Skamolex and Superwool board are both sold on the basis of being insulators. I tought those in firebox (not heat riser) are just firebricks. No, in the firebox, currently, it's Skamolex. There is the option to swap out any skamolex 'brick' and replace it with a firebrick. I cut all the skamolex 'bricks' to the exact size of a split firebrick, so it would be easy to replace them, if it seems necessary.
|
|
|
Post by Karl L on Jul 1, 2020 12:10:41 GMT -8
thanks Karl fro the pices. I see now there's no insulation between firebricks and metal, that's why it bended badly. In my opinion there is insulation :-) -- Skamolex and Superwool board are both sold on the basis of being insulators. But there's not enough insulation to prevent the large, thin sheets from buckling. The size of the sheets compared to their thickness is critical: When I cut slits into the sheets the heating of the steel was the same, but there was no buckling.
|
|
|
Post by Karl L on Jun 30, 2020 12:53:14 GMT -8
can you adjust primary and sekondary air individualy? I don't intend to have separate adjustments. I want it to be very simple to operate: Open or Closed. But it is possible to change the primary air CSA, as a 'build option'. The primary air flow restriction is not shown in the photos: I use some very thin Aluminium sheet, inside the 'door frame' (which I call the cowl), to create the same CSA as Peter's door frame. I may also experiment with directing the primary air flow: direct it onto the door glass (to pre-heat the primary air), or away from the door glass. (In a previous stove I could adjust the primary and secondary air independently. I used this during the charcoal phase to restrict the secondary air to a small flow. This reduces the amount of 'ballast' air flowing, but also keeps the steel floor tube cool. I was trying to collect as much heat as possible from the charcoal. I don't know how effective this was.) superwool in the back of fire box look a bit fragile Yes, I mention that in a prevous post. I don't think it will be a problem because the vertical steel tube will protect it a lot. But if it is a problem it's very easy to change it.
|
|
|
Post by Karl L on Jun 29, 2020 3:45:31 GMT -8
|
|
|
Post by Karl L on Jun 29, 2020 2:05:12 GMT -8
I'll try to post some more photos, but first, to clarify:
I'm only using one 25mm layer between the hot side and the 2mm steel sheet, except in the heat riser, where I am using 2 x 25mm layers.
In the fire box this is 25mm Skamolex (i.e. compressed Vermiculite board) blocks, cut to the exact size of a firebrick split. This is so I can selectivly replace Skamolex with firebrick if I need to decrease the insulation value and increase the thermal mass (based on Peter's observations a few months ago). My thought is that I don't have to replace all the Skamolex blocks, but just some of them, to allow fine adjustment. Currently it seems to be burning just fine with the Skamolex.
In the heat riser and top box, I am using Superwool HT board.
The firebox ceiling/topbox floor, and the firebox/heat riser port wall are Superwool board. This is very fragile, but the ceiling doesn't get too much contact with firewood, and the port wall is quite well protected by the foor channel's vertical tube. If these prove to be too fragile I can replace them with firebrick, or perhaps insulating firebrick. Hopefully the loss of insulation value won't matter too much because both sides are hot (even if not the same temperature).
CFB bending The bending was mostly very small, but in the ~550mm long piece it was around 2-3mm. I can't post photos of this because I've already cut it into two.
|
|
|
Post by Karl L on Jun 27, 2020 9:20:23 GMT -8
After the first burn I pulled the core box out of the bell while it was still quite hot. I noticed the sides of the core box (2mm mild steel, 570 x 550mm) were bulging ~10mm, because of differential heating of the centre of the panels compared to the rim. (I thought this wouldn't be a problem, but clearly it was.) One long piece of Superwool board, in the top box, was broken by the bulge (because it bulged inwards). After some thought I decided to cut some vertical slits into the box, to eliminate the bulging. This seems to have worked perfectly - no bulging at all this time, and the burn seemed fine. The core box seemed to remain strong and rigid enough, even with the slits. I also cut the unbroken long piece of Superwool board (~550mm) into two lengths, as there was some differential bending in them. I chose to place the cut at the Stumbling Block, so it could hold the pieces in place. Here's a photo of the slits: drive.google.com/file/d/1CDvk0gzGVhH3rfIhCmQl4r4LX8t3ezua
|
|
|
Post by Karl L on Jun 26, 2020 23:23:42 GMT -8
I use Sketchup 17, but there is an annoying problem with it:
I have my monitor set up to turn off after some minutes, but when this happens Sketchup 17 'locks up', uses 100% of the CPU, and has to be closed to escape from this.
Does anyone have a solution to this? (other than changing my monitor and sleep settings.)
Thanks!
|
|