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

In the present study, a new version of a guarded parallel-plate instrument (GPPI) for the absolute determination of the thermal conductivity under steady-state conditions is presented. It is based on an existing concept of an automated instrument and includes several modifications with the aim of further improving the achievable accuracy and experimental uncertainty while reducing the measurement time. These modifications mainly include improvements to the guard system in the upper hot part, which lead to a further suppression of parasitic heat fluxes, and the integration of flow circulation systems for the active temperature control in the periphery of the instrument. By using relatively large values for the temperature difference between the heating and cooling plates and for the sample thickness, expanded ( k = 2) measurement uncertainties between (2 and 3)% could typically be achieved for the thermal conductivity. For mean temperatures from (283 to 358) K and atmospheric pressure, the measurement results agree well with reference data for liquid water, toluene, and ethylene glycol as well as air, polytetrafluorethylene (PTFE), and stainless steel 316. In addition, the applicability of the new GPPI for the determination of the effective thermal conductivity of heterogeneous systems was demonstrated using water-based nanofluids containing dispersed silicon dioxide, titanium dioxide, or copper oxide nanoparticles.(c) 2023 Elsevier Ltd. All rights reserved.