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lbispo

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  1. Good to know, I learned a lot during this exercise and I already have few things to improve on the new design. As K23 bricks, thicker element in order to reduce the power density... Let's see how long this one lasts.
  2. It is easier said than done, kind of hard to work with metals... Any other concerns about the metal being in the middle? The paint already peeled off completely.
  3. I'm not sure if the number are accurate, but if I used the formula correctly, I have put in a graph Q vs Hole size (need to multiply to area in order to find the real number) as you can see below, it is not linear:
  4. Back to the math, as I'm still looking for a solution since the insulation wrap on the outside looks ugly, for comparison reasons, K26 + 2" (50mm) blanket = Q = 544 W I'm now considering drilling hole on the bricks, considering the following: Conductive heat formula -> Q = U A dT Area = 0.413m2 dT = 1000K (or Celsius) K26 thermal conductivity 0.25 W/mK (@400C) Brick is 0.065m (2.5") Air thermal conductivity 0.05 W/mK (@400C) Convection heat transfer 25 W/(m2 K) Will keep the area constant for simplicity K26 (0.25W/mK and 2.5") brick results in Q = 1433 W K23 (0.14W/mK and 3") brick results in Q = 782 W If I replace the brick by air (holes) at a 28%, I get Q = 776 W on my current K26 bricks, which would theoretically match K23 performance. That is kind of 2x 1/2" (12mm) per brick along the longer side. Sounds right? Q (W) Improv Hole fill 1433 0% 0% 1369 4% 2% 1310 9% 3% 1256 12% 5% 1206 16% 6% 1160 19% 8% 1118 22% 9% 1078 25% 11% 1041 27% 12% 1007 30% 14% 975 32% 15% 944 34% 17% 916 36% 18% 889 38% 20% 864 40% 22% 840 41% 23% 818 43% 25% 796 44% 26% 776 46% 28% 757 47% 29% 738 48% 31% 721 50% 32% 704 51% 34% 688 52% 35% 673 53% 37% 659 54% 38% 645 55% 40% 631 56% 42% 618 57% 43% 606 58% 45% 594 59% 46%
  5. Better, Air thermal conductivity at 400C is 0.05W/mK versus K23 which has 0.14W/mK -> accordingly to: https://www.engineeringtoolbox.com/air-properties-viscosity-conductivity-heat-capacity-d_1509.html I guess it can also be calculate as the brick datasheet presents some mechanical number that i have no understanding how to interpret EDIT: it just occurred to me now, differently from double glazed windows, the air inside the brick would be "breathable", otherwise it may expand and explode if too airtight as the air expands... or not? have no idea
  6. That makes sense... I believe the coating is made of Zirconium Silicate-ZrSiO4 (at least this one) radiation heat transfer formula is Q/t = σeAT^4 -> As we can see, the only thin that can change the amount of heat transfer is Area or Surface Emissivity: Ceramic Produces infrared wavelengths in the 2 to 10 μm range (quick google); Concrete, and ceramics, have an emissivity of 0.90 and 0.95 -> https://www.optotherm.com/emiss-table.htm from the following document, ZrSiO4 has an emissivity ranging from 0.35 til 0.74: https://www.matec-conferences.org/articles/matecconf/pdf/2016/45/matecconf_d2me2016_02012.pdf As you mentioned earlier that the big loss at higher temperatures is radiation, if we replace the numbers in the formula considering the following number for simplicity: A = constant; T differece betweem surface and surrounding = constant σ = 5.67 × 10^−8 J/s · m2 · K4 = also constant concrete (brick) e = 0.95 zircon e = 0.74 0.74/0.95 = 19.5% less loss (on the radiation part). This is a quick dirty napkin paper calculation but I'm convinced, and this is the worst case scenario (0.74).
  7. Making holes on IFB was an option that i had not have considered, I was thinking about casting, in order to reduce waste and freight cost (for my personal purpose). The table you shared, is the temperature, for example Super lights... 950C the maximum temperature? Apparently the information is somehow standard, as the table you shared, CB-10 = 0.35W/mK ... pretty close to mine, which is this one btw: https://shop.vitcas.com/insulation-refractory-castable-1300ins.html
  8. I received the datasheet from the castable IFB (that is how they call it) and the thermal conductivity is: 400C/750F -> 0.38W/mK; 600C/1110F -> 0.40W/mK; 800C/1470F -> 0.42W/mK; At this level, I do not see a benefit of making it perforated, unless there's another castable, or brick recipe.
  9. Great insights. From my personal test, I see the relay cycling not very often, thus a SSR would add very few benefit, and it would dissipate an awful amount of heat, meaning that the enclosure will need to be different. @Bill Kielb Is perforated insulation brick a thing ? It it's just an idea? The guy selling bricks in Denmark have a powdered insulating brick version that I could cast a perforated brick and test... I like that idea
  10. This is good information... I have not put it in full power to see what it can do. I was running bisque at 60C/hr.... It was cycling the relay very seldom, therefore I do not believe it would coupe with 175C/hr Yes, the metal drum is inside the blanket, I do not like it, I'm thinking about ways around it... My cat also is planning to have a go with the blanket, that will be a mess and upsetting, so I will need to do something about it. The concrete brick is there. I just bisque fired with ~4/5kg of stuff, here is how it looks: 4 segments, this is the rate measured: 71C/hr, 210C/hr, 127C/hr, 60C/hr
  11. Thanks for the comments... I believe now it starts the dilemma, as it is feasible to improve it, I may as well make it larger ... never ending project
  12. Thanks for the warm welcome. I'm pleased to share that the theory proved to be right. I lousily wrapped the thing with 25mm (1") blanket and fired up to 981degC (1800F), I cranked the temp rate at the beginning but at the end it was 45.7 C/hr. Cones: 012, 06 and 05 1/2 Today I will put some load and bisque with a 12hrs schedule. Have a good weekend
  13. Ops... the blanked is 1" (25mm)... Got confused with the units thing. I probably have enough to do 2x... I can remove the top 3" of the kiln and only fire cup coasters If relevant, my calculations are: (probably not right) Area = 0.413m2 internal temp = 900C external temp = 160C Brick thermal conductivity = 0.31 Loss = 1467btu/h (or W) With 25mm blanket Blanket thermal conductivity is 0.16 @ 800C Loss = 838btu/h (or W) It could be better.
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