Thermal conductivity is a principle property of materials with which heat energy is conducted through. Accurate knowledge of a material’s thermal conductivity is essential for predicting heat transfer by conduction.
We use the latest version of the old Lees Disc method – where one hotter plate and one colder plate have the sample placed between them. iso 8301 is for the Heat Flow measurement where we calibrate with PMMA, Vespel, Pyrex or Pyroceram which-ever is closest and we also have a new liquid cell too for very soft materials and liquids. (iso 8302 is the guarded Hot plate method which NPL used to use, and took 3 days to make one sample measurement!)
Samples from 200 micron of coating on Cu or other metal up to 200 mm can be measured on our 6 systems. The Fox 50s for samples up to 25.5mm thick can go from 0 to 250°C. For these rigid samples we need a 45 to 60mm diameter or octagonal sample which can withstand 4 bar Pressure, P. for the more conducting samples we need two different thicknesses where t1 >2 times t2, as otherwise there are large surface resistance errors.
For liquids we need 50 to 100millilitres ideally of sample to be syringed in to the cell. Max T so far run with this set up is 160°C mean, on some oils. (190°C is in theory possible!) The Fox 50 has measured from 0.03W/m.K to 100W/m.K in our lab although the conservative spec says 0.1 to 10 only!
For vacuum panels and foams etc we can run at 0 to 20°C mean T for samples from 10 to 200mm thickness by up to 605mm square – or if door shaped we can run each end separately by leaving one of the apparatus doors open!! This system can either run with 1 bar Pressure to measure the thickness at each corner if rigid – or if compressible we can choose the thickness. Hence for soft foams we can often run at 10 to 50% compression if asked for this.
For samples from 7 to 50mm thick we can test at mean T’s from 0 to 150°C where we use the Fox 200 HT. Samples should be at least 125mm square up to 200mm square (or could be circular!) to completely cover the 75mm square transducers. This apparatuses for foams (the Fox 600, 304, 314, and 200) are check calibrated regularly using IRMM ePS calibration standards which are updated every 5 years. We have measured from 0.003W/m.K up to 0.5W/m.K on these systems.
All these apparatus are manufactured by Lasercomp Inc, who are now part of TA Instruments Inc. For nearly 20 years we were the UK agents and distributors for Lasercomp and sold more than 100 apparatus in Europe for them. Hence we have over 20 years thermal conductivity experience and helped them run thinner and thinner samples by suggesting changes etc.”
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