Measuring thermal conductivity is not so easy …

logo_smallMeasuring the thermal conductivity seems to be easy. A stable temperature gradient is generated over a sample and the heat flow through this sample is measured . The thermal conductivity is this heat flow divided by the temperature gradient, section and multiplied with the thickness. But it seems not that easy. A recent  publication  on the website of Aalborg shows that at least measuring the thermal conductivity of cellular glass is not straigthforward. Indeed, in four cases, the declared value of the maufacturers is lower than the measured value. In the case of GLAPOR, I selected and transported the samples myselves, which reduces the risk of wrong sampling to almost zero.

All measurements are done with the Guarded Hot Plate EP500 from  Lambda Meßtechnik.  This is a one sample Guarded Hot Plate, which is described in the standard EN12667, where we find the following setup.

GHPoneplate

Samples can be easiliy loaded in this system and it should be perfect for students to be used. Nevertheless, it is impossible that 4 products from two manufactures are not in line with the published declared value with 10% exceedance. For that reason, we think that misuse or a defect of the equipment is the reason of the high measured thermal conductivities.

 

 

 

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