Paradigmnoia

Thanks' for taking the time in answering my questions

As you I am wondering what can be the cause of the differences in temperatures between your measurements and the simulations.

So some thoughts, remarks :

**1. Dimensions**

For the length of the simulated rod I used 5 cm

Don't know if that is correct.

A longer rod would have a higher temperature in the middle

Also I used an heating element over the full length.

Don't know if this true for your rod.

**2. Power balance cross check**

Deviding your rod in for example 5 sections and measuring the temperature of each section we should be able to calculate the total radiated and convective power.

That should about match the the applied power of the heating element

If you find the effort too much then I am prepared to make a spreadsheet with the calculations based on your data.

**3. Thermal conductance**

Maybe the thermal conductance is higher then the values I used.

This will lead to smaller temperatures drops and thus higher temperatures.

Against this is that the thermal conductance is also an important factor in the transient time constant.

And we have seen that in the simulation this about matches your transient profile.

**4. Possibility that Durapot has lower broadband emissivities**

Against this is that Durapot is less dense then Alumina, or it has more pores.

And the pores increase the emissivity

**5. Pyrometer emissivity**

For 735 C I have following my derived curve an Optris in band emissivity of about .93.

Since I believe your Pyrometer works with the 8 to 14 uM band, it covers less of the high emissivity values of the Alumina spectrum.

As a result I expect your Pyrometer should have a value less then .93.

My calculated value for that temperature is .90.

But that would only result in a difference of about 10 degree C on the pyrometer.

That you measured in your calibration a value higher then .90 can indeed be due to the pores increasing the emissvity somewhat compared to dense Alumina.

There is some theory about the heat distribution in round cylinders.

I will see if I can use that for some calculations and see if that will give some answers.