Working Principle of a Thermal Conductivity Meter

A thermal conductivity meter based on the guarded hot plate method typically employs a dual-specimen measurement configuration with a guarded hot plate assembly comprising a heating unit and a cooling unit. The heating unit is divided into a central metering section and a surrounding guard section separated by a gap, and the assembly is equipped with thermal insulation. The heating unit uses a dual hot-surface heater and a symmetrically arranged cold plate. The spacing of the movable cold plate is set according to the specimen thickness. Two identical specimens are placed vertically between two parallel plates maintained at constant but different temperatures, creating a steady one-dimensional heat flow through the central metering area of the specimen. In steady state, the instrument measures the constant heat flow Q passing through the metering section, the metering area A, and the temperature difference ΔT between the hot and cold faces of the specimen. From these, the thermal resistance R of the specimen is calculated. Knowing the specimen thickness, the thermal conductivity λ can then be accurately determined.