Guarded Parallel-Plate Instrument for the Determination of the Thermal Conductivity of Gases, Liquids, Solids, and Heterogeneous Systems

•New guarded parallel-plate instrument for determination of thermal conductivity.•Further improvements to guard system in the upper hot part and to peripheral parts.•Typical expanded uncertainties between 2 and 3% with reduced measurement times.•Agreement of measurement results with reference data for gases, liquids, and solids.•Successful application to water-based nanofluids with metal oxide nanoparticles.