For thermal conductivity measurement of insulating samples (lambda<5 W/mK) in form of plate based on measuring the net heat flux through the sample per unit temperature gradient.

 

Operating principle

Thermal conductivity of any homogeneous materials is  the steady heat flux per unit area, per unit temperature gradient so that thermal conductivity is easily determined from the ratio between the net heat flux through the sample measured in W/m2 over the temperature gradient across the sample measured in K/m.

 

The net Heat flux through the sample to be tested is supplied by the flat electric heater thermally insulated by the thick polystyrene plate shown in the figure. The sample to be tested is placed between the heater and the air cooled bottom sink. Accurate results are obtained if the sample thickness is lower than 1/10 of the lateral dimensions and if temperature gradiant is about 10 K.

 

Advantages

- absolute thermal measurement; reference insulating samples are not needed
- measurement independent on the sample temperature
- the time required to wait for steady net heat flux is short
- accurate measurement 5%
- device available for numerous size samples.