Combined Guarded-Hot-Plate and Heat Flow Meter Method for absolute thermal conductivity tests excluding thermal contact resistance

A Combined Guarded Hot Plate and Heat Flow Meter Method was developed and tested for absolute thermal conductivity tests of moderate thermal conductivity (up to similar to 10 W/mK) materials. A thin flat guarded heater of known area is placed between two flat-parallel samples of the same material and of different thicknesses. The stack is clamped between two isothermal plates each having a heat flow meter. Heat flux across each of the two samples is inversely proportional to its total thermal resistance - sum of sample's thermal resistance (thickness divided by thermal conductivity) and its two surface contact resistances, which are assumed to be equal for the two samples. After reaching thermal equilibrium the measured amount of electric power of the heater's central part, it's and plates' temperatures, samples' thicknesses and both heat flow meters' readings are used to calculate the material's absolute thermal conductivity excluding the thermal contact resistance. Measurements without taking into account the thermal contact resistance would cause very large errors (as much as hundreds percent in some cases). This combination of the two traditional steady-state methods provides significantly increased accuracy of the absolute thermal conductivity measurements of many very important materials such as ceramics, glasses, plastics, rocks, polymers, composites, fireproof materials, etc. Both theoretical aspects of the combined method and its experimental check using some reference materials (Pyrex, Pyroceram, Vespe (R) 1) are presented.