adiel
Junior Member
Posts: 119
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Post by adiel on May 23, 2015 10:13:39 GMT -8
Riser sleeves are disposables intended for single use. However in casting they need to withstand liquid metal, in a stove the have only to support their own weight and withstand the heat. sorry i dont understand what you're saying - would you use these serves as risers?
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Deleted
Deleted Member
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Post by Deleted on May 23, 2015 19:56:20 GMT -8
As riser sleeves are intended for one time use nobody knows, which effects thousands of heating cycles may have.
I have had a professional education with respect to heat insulation of buildings and think that the temperature effects of riser sleeves are highly overestimated. The calculations are not overly hard to do.
New developments seem to make risers superfluous anyway.
Let's see: Standard reverse side test for fire protection with a 10mm disc of 20cm diameter. Flame temperature given with obove 1100°C. Air temperature assumed with 20°C Flame side temperature 800°C. Reverse side temperature 400°C. Thermal conductivity 0.3W/m*K
Heat = (Thermal Conductivity / Distance)x Area × Temperature Gradient. Q = (λ / D)x A × ΔT. (0.3W/m*K / 0.01m) x 0.0314 m2 × 400K = 376.8W
For 1" the heat flow would be only 150W, provided this does not increase ΔT.
A bunsen burner is far to weak for a realistic test. From advertisementsfor roofers burner very small 25 Ø Heating capacity: 13,3 kW small 35 Ø Heating capacity: 18.1 kW standard 45 Ø Heating capacity: 44,6 kW
In a stove the flame side temperature will be significantly higher than 800°C, but the gas temperature on the other side will be much higher too, resulting in a significantly lower gradient.
This simple calculation lets look the expectations a bit silly, which some people seem to have. The effects for 0.05W/m*K to 0.3W/m*K as well as the effects of heat capacity will be neglible, even if the surface area is significantly higher as in case of the disc.
morticcios riser sleeves are darn cheap, but some people have spent reportedly a lot of money, which they could have thrown out of the window as well. IMHO
The equation above is from Fourier's law, which has consequences one may not expect.
Standard reverse side test for fire protection again: 0.2W/m*K will increase ΔT to 600°C, which will finally allow a heat flow of 376.8W too. Thus only if a lower thermal conduction can not increase ΔT it will actually result in a lower heat flow.
On the other hand a 600 times increased thermal conductivity will not permit a 600 fold heat flow, as unavoidably this will cause a very much smaller temperature difference.
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morticcio
Full Member
"The problem with internet quotes is that you can't always depend on their accuracy" - Aristotle
Posts: 371
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Post by morticcio on May 25, 2015 1:11:08 GMT -8
Karl, are you saying they are unsuitable for risers full stop or just direct exposure to the flames? At 10mm thick I always intended to use backup insulation.
I'll do more testing - if anything they can be used for the quick fabrication of the prototype riser combinations like Shilo & Adiel are building.
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Post by pyrophile on May 25, 2015 1:53:31 GMT -8
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Deleted
Deleted Member
Posts: 0
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Post by Deleted on May 25, 2015 4:24:31 GMT -8
Fibers have large surfaces and the hot gases may be able to penetrate the sleeves a bit. At high temperatures and low oxigen CO may be able to steal oxigen from the fibers and make them brittle.
Extreme temperatures have been reported for the new cores. There is no way the decomposition end recombination of water could contribute to this.
The explanation is much simpler. The afterburner just cannot throw much heat towards the combustions chamber, (would come back anyway) thus concentrating heat without insulation. Downdraft burners take advantage of this effect too.
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