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Post by fiedia on May 25, 2021 23:15:02 GMT -8
Very impressive.
Could you please give some details or pictures about your air inlet design? Can you reduce indepedantly the primary and floor channel entries?
I would like also to know more about your bell, materials and wall thickness.
Thanks
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Post by ericaus on May 26, 2021 15:47:15 GMT -8
Ericaus. Your water can also come from the fuel, and from the air too. I see the towels, does it drip under the bell? What is your flue temp? I guess, with your huge metal bell, you might have created a big rocket fractional distillation tower. The culprit i guess is bell and flue temps. As long as your bell walls are not over let say 60/70C° You will have condensation. I didn't think of it when you were building it. But with such a big radiating surface, you're cooling may be more than you should. Sorry to say, but you might be in for recurring trouble with that. I don't know how to calculate the dew point. But you might have to calculate it. And your big bell tube is bound to cool back down to ambient every time it's not in use. So condensation at each startup? It might not be the case. You might have to brick the inside, to keep a bit of warmth. Anyway, first things to check. Bottom of the bell temp, and first elbow flue temp. HTH. Thanks Max, Yes it drips from under the bell, with some drips from the flue as well. It seems the exit temperature from the bell is around 130C after the first burn.  I haven't measured the exit temperature from the flue outlet on the roof yet. I don't really have the option of lining the bell with bricks. I can't get access. And I think it would reduce the diameter of the bell to the point that it would restrict the gasses passing down past the riser. I'm thinking if it persists, I'll pump some kind of sealant, maybe a silicon based type into the base flange plate and let it self level so it seals the joint between the flange plate and the barrel. I can then have a drain point fitting with flexible hose going out through the floor. A fairly simple fix I would imagine (hopefully). |
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Post by ericaus on May 26, 2021 16:04:05 GMT -8
Very impressive.
Could you please give some details or pictures about your air inlet design? Can you reduce indepedantly the primary and floor channel entries?
I would like also to know more about your bell, materials and wall thickness.
Thanks
Thanks Fiedia, Here is the configuration of the secondary air inlet. It runs through a channel under the firebrick base. The bottom of the firebox and the underside of the firebrick base form the channel. The sides are also edges of the base firebricks.  This is controlled simultaneously by the stainless steel control disk on the lower door. Here's a better picture.  The bell is made from mild steel 12mm wall seamed pipe with appropriate fittings welded on. The top and bottom flange plates are laser cut from 20mm boiler plate. Can't remember the grade, not that it's important in this application.   |
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Post by ericaus on May 26, 2021 19:47:48 GMT -8
Ericaus. Sorry to say, but you might be in for recurring trouble with that. I don't know how to calculate the dew point. But you might have to calculate it. HTH. You might be on to something here Max. Average humidity here in Melbourne for this time of year is 76 percent, so using this online calculator it doesn't take much cooling to form dew.   |
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Post by peterberg on May 27, 2021 0:47:34 GMT -8
Hmmm... Relative humidity is dependent on air temperature. By raising the temperature the dew point should be going down accordingly. Using the same calculator, filling in the actual exhaust temperature and the desired dew point the outcome is entirely different. For example, exhaust 150 ºC and dew point 100 ºC comes down to 20.85% RH. In order to know the dew point you'll need to measure the exhaust gases' relative humidity and temperature.
Even in the case of one degree difference between exhaust and dew point temperature, the relative humidity is below 100% and dew won't be formed.
Surprisingly, also for me, I didn't expect those values to be so close together.
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Post by fiedia on May 27, 2021 23:09:01 GMT -8
ericaus 76% HR in Melbourne means that at the ambiant temperature (let's say between 20 and 25 °C), air contains 76 % of the water it can absorb before dew. Dew will start at 100% HR. The hotter is the air, the more water it can absorb. So, the water coming from the outside air in your stove will never condense since it is hotter inside than outside your bell. But inside your stove,there are other sources of water: - your concrete HR which still has some water in it, it won't last more than few burns - wood combustion creates water, one can not avoid this - remaining water in the wood, I still have some water dripping from the oven door when burning insufficiently dryed wood. This additional water is absorbed by the hot air coming from the combustion. But it will condensate if the air is in contact with a cold surface : flues, doors and your cold steel bell.
Water + temperature does absolutely no good to steel. I do not know how long it may take to corrode completely your thick steel walls but keep in mind that the higher the temperature, the faster is the corrosion. So if condensation persist with well dryed wood, you would better give some thermal inertia to your bell (bricks, clay, concrete...) or some light insulation (the latter will not prevent condensation at the start as pointed out by Satamax). It can be done from outside.
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Post by ericaus on May 28, 2021 1:11:54 GMT -8
Hmmm... Relative humidity is dependent on air temperature. By raising the temperature the dew point should be going down accordingly. Using the same calculator, filling in the actual exhaust temperature and the desired dew point the outcome is entirely different. For example, exhaust 150 ºC and dew point 100 ºC comes down to 20.85% RH. In order to know the dew point you'll need to measure the exhaust gases' relative humidity and temperature. Even in the case of one degree difference between exhaust and dew point temperature, the relative humidity is below 100% and dew won't be formed. Surprisingly, also for me, I didn't expect those values to be so close together. Thanks Peter, Yes I have no way to take those measurements unfortunately. I'm convinced now that it's not the refractory dry out. I consistently get around a litre per burn. I think I'm just going to have to live with it and seal the base. I've put a barbed fitting in the lower flange inspection plate, so I can either have a container under it or feed a hose through the floor.  The other problem is that water drips from all the flue connections as well, so that means other catchment systems will have to be implemented. I have some ideas, but unfortunately it's all just extra work. I've yet to check the pH of the water, but that's on the list. |
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Post by ericaus on May 28, 2021 1:24:36 GMT -8
ericaus 76% HR in Melbourne means that at the ambiant temperature (let's say between 20 and 25 °C), air contains 76 % of the water it can absorb before dew. Dew will start at 100% HR. The hotter is the air, the more water it can absorb. So, the water coming from the outside air in your stove will never condense since it is hotter inside than outside your bell. But inside your stove,there are other sources of water: - your concrete HR which still has some water in it, it won't last more than few burns - wood combustion creates water, one can not avoid this - remaining water in the wood, I still have some water dripping from the oven door when burning insufficiently dryed wood. This additional water is absorbed by the hot air coming from the combustion. But it will condensate if the air is in contact with a cold surface : flues, doors and your cold steel bell.
Water + temperature does absolutely no good to steel. I do not know how long it may take to corrode completely your thick steel walls but keep in mind that the higher the temperature, the faster is the corrosion. So if condensation persist with well dryed wood, you would better give some thermal inertia to your bell (bricks, clay, concrete...) or some light insulation (the latter will not prevent condensation at the start as pointed out by Satamax). It can be done from outside. Thanks for all that info Fiedia, looks like I'm stuck with it somehow. As mentioned earlier, I'll seal around the circumference of the barrel where it connects to the lower flange plate and I'll paint the top of the flange plate with heat proof paint to protect it from corrosion. I'm hoping that the water running down the internal walls of the bell won't really present any corrosion issues. It's 12mm wall thickness, so it should see me out. Haha. The design of the unit doesn't really lend itself to having any added insulation, either internally, or externally. I think I'll just have to live with it. |
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Post by fiedia on May 28, 2021 5:56:34 GMT -8
I had some water dripping from my flue during several days. I think it came mainly from all the water stored in the bricks inside the stove (I put them in water before building). Let's hope that your water problem will disappear after few burns.
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Post by ericaus on May 30, 2021 0:54:16 GMT -8
I had some water dripping from my flue during several days. I think it came mainly from all the water stored in the bricks inside the stove (I put them in water before building). Let's hope that your water problem will disappear after few burns. Thanks Fiedia, but it's here to stay. I'm sure now. I'm getting busy making up a catchment system for the overhead flue connections that are leaking water as well. I'll post some pictures when I'm done. |
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Post by satamax on Jun 2, 2021 1:13:28 GMT -8
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Post by ericaus on Jun 4, 2021 2:10:42 GMT -8
Yes they are nice units Max. I'd like to mount one on top of the barrel, but it's above head height so I'd need a mirror to read it. |
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Post by satamax on Jun 4, 2021 2:58:45 GMT -8
Eric, the second one has a capillary of 150cm or 200cm between the dial and the probe. But the important spot to measure, is in the flow of gases, in the chimney stack, just after exiting the stove.
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Post by ericaus on Jun 7, 2021 0:13:13 GMT -8
Eric, the second one has a capillary of 150cm or 200cm between the dial and the probe. But the important spot to measure, is in the flow of gases, in the chimney stack, just after exiting the stove. Thanks Max, yes I should install one in the outlet. I currently have two of the probe type mounted in the system. The top one is about 500mm down from the top of the barrel, mounted on the barrel with the probe in the gas flow from the outlet of the riser. This seems to sit at around 150C. The other one is located at the bottom close to the outlet valve. This one tends to sit on 100C - 120C. There an image of this one above. I still haven't been able to measure the gas temperature where it exhausts out of the top of the flue. I think it would be pretty cool, given the fact that I can hold my hand against the flue surface 3 metres lower than the outlet. I don't know what the threshold temperature is for touching a surface with the hand and staying in contact, but I'm guessing it would be under 50C. |
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Post by fiedia on Jun 8, 2021 0:13:23 GMT -8
I mesure 400°C min 30cm above the HR. Your 150°C seem quite low.
You put your hand on the flue. Is the pipe insulated with mineral wool between two stainless skins? In that case, the outer skin stays usually cold. In case it is not insulated, it is a source of condensates.
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