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Post by satamax on Aug 28, 2014 6:06:24 GMT -8
For the mass? For an eight incher batch. Flat'ish Bell bed, bout 70cm about 1.5 sqm. 3.25m isa. And a Barrel of 3.11m isa. I can get bout 1.1 metric ton on the bed. i can put some more around the Barrel. I would like to have 24 to 48 hour autonomy. Whatcha'r sayin people?
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Post by Deleted on Aug 28, 2014 6:38:25 GMT -8
With dense bricks and an average temperature of 200°C =
1 kJ/kg K * 1000kg *200K = 200000 kJ = ~ 55 kWh.
For an average temperature of 400°C ~ 110 kWh.
Now look up how much energy will be emitted by a given surface material and surface area.
The highest specific heat of common mineral materials is provided by rammed earth ~ 1.26 kJ/kg K.
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Post by satamax on Aug 28, 2014 10:39:53 GMT -8
Karl, sorry but i don't fully understand. What is K? Kelvins? You know i'm a bit daft.
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Post by ericvw on Aug 28, 2014 14:06:52 GMT -8
Lotsa weight! Satamax I believe the K is Kelvin, been a long time since I've dealt with it myself! 24-48 hours, huh? So you're looking to radiate heat for that long? Is this by any chance for that place you posted? Did you end up successfully acquiring it? Let's thank Karl for all but dangling the final answer before our daft noses!!!  Satamax will you post a solution when you get it calculated? Bear up for that weight if it's not on slab... Eric VW |
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Post by satamax on Aug 28, 2014 22:02:52 GMT -8
Hi Eric. Still in the process of buying it. Blady banker is asking for more documents. Next he'll ask for the colour of my undies! Don't worry about the weight, i know how to deal with this. An 8"x8" pine post can whistand 13 metric tons. And i plan on using 4 |
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Post by satamax on Aug 28, 2014 22:18:12 GMT -8
Well, i have bricks. I don't plan to heat the bench at more than 60 or 80C° average. That gives me 7.333kwh for that 1.1 ton figure. I need more like 7.900. But i haven't acounted for the weight of the stove itself. Just the bell for the moment. Karl, that K constant, it's kelvins of temp diferential? Differential with the outside temp? With the absolute zero? With the inside temp? |
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Post by Deleted on Aug 29, 2014 1:22:20 GMT -8
K = Kelvin. in SI units (Système international d’unités, International System of Units)
Used in scientific formulas for a long time.
At German schools since more than 45 years.
I and all the other kids have hated to relearn
all formulas with new standard units.
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Post by Deleted on Aug 29, 2014 4:25:09 GMT -8
BTW Thermochemical heat storage can store huge amounts of energy. Eg. About 388 kWh/m³ by 89°C reactions temperature, About 777 kWh/m³ by 122°C reactions temperature, Water only about 60 kWh/m³. Can store heat for years. If the energy is released it can be used to heat and cool at once. A Critical Review of Thermochemical Energy Storage Systems benthamopen.com/torej/articles/V004/42TOREJ.pdf |
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Post by dpottier on Aug 30, 2014 7:35:26 GMT -8
The highest specific heat of common mineral materials is provided by rammed earth ~ 1.26 kJ/kg K. Hi Karl I am just in the middle of reviewing a paper (about 200 pages) on the use of high density concrete developed specifically for Thermal Energy Storage (TES) systems for electric power generation. They worked with temperatures as high as 600C and even submerged the concrete in molten salt (1085°F (585°C) for 500 hours and looked at the strength and at micro-fissures. I think these new high density concretes might work well as the heat sink for the RMH. From the paper: The silicon carbide sounds interesting and the sandblasting grade runs about $60USD for a 25lb can. David |
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Post by Deleted on Aug 30, 2014 8:25:43 GMT -8
The silicon carbide sounds interesting and the sandblasting grade runs about $60USD for a 25lb can. 350 W/(m·K) is impressibe, but high Thermal Energy Storage in small volumes goes hand in hand with low conductivity. Silicon carbide is therfore only interesting, if the energy storage needs fast charge/discharge cycles and very huge volume and mass do not play a big role. |
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Post by dpottier on Aug 30, 2014 17:28:04 GMT -8
350 W/(m·K) is impressibe, but high Thermal Energy Storage in small volumes goes hand in hand with low conductivity. Silicon carbide is therfore only interesting, if the energy storage needs fast charge/discharge cycles and very huge volume and mass do not play a big role. When building a multi-million dollar solar thermal power station the expense of a few tons of silicon carbide is a peanut and a great place for an engineer to get a research grant to test the materials. I have finished reading the research paper. 25 concrete mixes were tested. Once I digest the table results I will ask permission to post the formula for the mix that gave the best results for both heat storage and cost per cu/ft. One of the issues with using concrete in high temperatures is spalling or possibly exploding. This research found a cost effective solution to this issue. |
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Post by Deleted on Aug 31, 2014 4:27:01 GMT -8
Mixtures for a thermal power station are useless for rocket stoves,
due to far to different requirements.
For rocket stoves they occupy too much volume, are to heavy
and will release the heat to fast, due to high conductivity and more surface.
For example dense bricks and corundum:
The difference of density is much lower than the difference of specific heat,
therefore to store the same amount of heat corundum will need more volume and more mass
and finally release the heat much faster.
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Post by dpottier on Sept 13, 2014 17:31:52 GMT -8
For rocket stoves they occupy too much volume, are to heavy and will release the heat to fast, due to high conductivity and more surface. Karl In the geographic area I am in (Mongolia) there is barely 30cm of top soil and not something that gets used for anything but food production in the few places it exists. We have sand, LOTS of sand (Gobi Desert). We also have sandstone and in one province some volcanics but that area is protected. Sand being the most common raw material with cement being readily available. I have read that using just sand is a better insulator than heat sink. This is the reason I am looking towards concrete as a possible heat sink. Average temperatures from September to April are -20C and get get down to -50C. Space to heat is just 7 meters in diameter.  Multiply this smoke from a small wood fire by 150,000 and change the fuel to coal and/or wood mixed and this is what the night air looks like in a city of 1.3 million. (Note: We had our first snow on 09-13. The air in the city now reeks of the smell of coal smoke, wood smoke and burning rubber and plastics.  Based on available raw materials what would be your best guess as a suitable heat sink? David |
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Post by dpottier on Sept 13, 2014 18:50:56 GMT -8
RMH Thermal Energy Storage (TES) Bench. Colours to show various brick sizes and their locations in the system  Cement Board (fire protection) + Aerogel insulation Do NOT do this with ordinary concrete!! It will explode. It requires a special mix of high density concrete.TES material will withstand temperatures of 600c The 8x8x16 inch TES blocks slide over each other with heating and cooling cycle so fracturing is not an issue TES base block 8"x8"x16" 0.5925926 cubic feet or 0.0219 cubic yards or 0.0168 cubic meters. If pre-mixed concrete*, it is 88 lbs or 40 kgs. TES Base 15 blocks (3 rows of 5) = 1333 lbs or 604 kg TES Top Blocks 8"x6"x16" 0.444 cubic feet or 0.0165 cubic yards or 0.0126 cubic meters. If pre-mixed concrete*, it is 67 lbs or 30 kgs. TES Top 10 blocks (2 rows of 5 or 10 blocks) = 670 lbs or 303 kg TES Pipe Blocks 0.296 cubic feet or 0.011 cubic yards or 0.00839 cubic meters. If pre-mixed concrete*, it is 44 lbs or 20 kgs. TES Pipe 10 blocks (2 rows of 5 or 10 blocks) = 440 lbs or 200 kg Total weight = 2443 lbs or 1108 kg Total volume 84x25.6x16 = 19.9 cu ft Compacted Soil - Total weight at 126 lbs/cu.ft = 2499 lb or 1133.5 kg Cob weighs 95 pounds per cubic foot. Total weight = 1890.5 lb or 857.5 kg Specific heat of water = 1.00 Specific heat of COBB 0.21 Specific heat of the best performing mixtures was 0.25, approximately 1.16 Btu/ft.h.oF (2 W/mK) In addition to just storing the heat I think we also need to make better use of how we use the heat and I don't think radiant heating is the best method.  Destratification Destratification concept for a RMH bench. In this case a bookshelf against the wall but it could also be ducted behind the wall. Drawing the air from the left side of the bench at floor level, then across the heated bricks, exiting on the right side at ceiling level. This system introduces a thermostat into the heating system. The use of Aerogel as insulation helps to hold the heat for a much longer period of time. The recommended "best" room temperature is 20C (68F) and with no cold spots (barring drafts) because of destratification, the room will feel much warmer than 20C.  You will need a fan with flow rate of around 100+ cu. ft/min for a 1000 square foot area (10,000 cubic feet). David |
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Post by Deleted on Sept 14, 2014 1:26:56 GMT -8
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