Post by lawry on Sept 25, 2016 8:40:40 GMT -8
Hi Everyone
I thought I should do a separate post for thermal conductivity tests of the geopolymer bricks we have been experimenting with, together with @karl and firewatcher recently.
This how I went about it:
I had to calibrate the IR thermometer first. I have a kitchen thermometer so I checked ambient temp which was 24oC. I then used the IR one to check black painted steel with the emissivity at 0.94 it also read 24oC. I then adjusted down the emissivity for firebrick to about 0.7 it also read 24oC. For the Fly Ash bricks emissivity of 0.94 was also sufficient to 24oC
using a normal duty firebrick properties i.e.
density - 2257.5 kg/m3 and conductivity (k) - 1.13 W/m/oC
I used the heat transfer formula to calculate the Watts produced by a propane burner. I ran the burner for 3 minutes.
In order to get the watts we need the temperatures flame side and opposite side. I use millimetres
Q = k.A.(T1 - T2)/d
T1 - 1078oC, T2 - 195.9oC
A (cross sectional area the heat is going through) - 0.088 x 0.114
d (thickness) - 0.025
Q = 2.02 W (I divided all the calcs with the 3 minutes - I realised that it wouldn't make any difference if left out either)
I then did the burner test on all my bricks recording the temps. My bricks all have an A of 0.09*0.09 and thickness of 0.025
here a the temps I measured:
after substituting the 2.02W in the formula I obtained the above k values for my bricks.
The results seem consistent with what "we" expect of bricks. I really hoped that the conductive brick would have more conductivity... I cast another conductive yesterday and it has both silicon carbide and aluminium oxide, I will test it once it cures.
What is your take on the method? Any comments
I thought I should do a separate post for thermal conductivity tests of the geopolymer bricks we have been experimenting with, together with @karl and firewatcher recently.
This how I went about it:
I had to calibrate the IR thermometer first. I have a kitchen thermometer so I checked ambient temp which was 24oC. I then used the IR one to check black painted steel with the emissivity at 0.94 it also read 24oC. I then adjusted down the emissivity for firebrick to about 0.7 it also read 24oC. For the Fly Ash bricks emissivity of 0.94 was also sufficient to 24oC
using a normal duty firebrick properties i.e.
density - 2257.5 kg/m3 and conductivity (k) - 1.13 W/m/oC
I used the heat transfer formula to calculate the Watts produced by a propane burner. I ran the burner for 3 minutes.
In order to get the watts we need the temperatures flame side and opposite side. I use millimetres
Q = k.A.(T1 - T2)/d
T1 - 1078oC, T2 - 195.9oC
A (cross sectional area the heat is going through) - 0.088 x 0.114
d (thickness) - 0.025
Q = 2.02 W (I divided all the calcs with the 3 minutes - I realised that it wouldn't make any difference if left out either)
I then did the burner test on all my bricks recording the temps. My bricks all have an A of 0.09*0.09 and thickness of 0.025
here a the temps I measured:
Normal Firebrick | Fly Ash (FA) Brick | FA Insulative (Perlite) | FA Conductive (Silicon Carbide) | |
T1 | 1078 | 931 | 930.1 | 877 |
T2 | 195.6 | 146 | 103.3 | 186 |
ΔT | 882.4 | 785 | 826.8 | 691 |
D | 2257.5 | 2059 | 1367.9 | 1758.02 |
k | 1.13 (listed) | 1.429 | 1.357 | 1.624 |
after substituting the 2.02W in the formula I obtained the above k values for my bricks.
The results seem consistent with what "we" expect of bricks. I really hoped that the conductive brick would have more conductivity... I cast another conductive yesterday and it has both silicon carbide and aluminium oxide, I will test it once it cures.
What is your take on the method? Any comments