Specific Heat Measurements of Large-Size Samples with the Hot Disk Thermal Constants Analyser

Abstract

The present work presents some results and considerations for testing the specific heat of large-size samples (dimensions up to 250 mm x 250 mm in-plane, and 75 mm in thickness). Recent interest on testing thermal transport properties of anisotropic composite structures, including highly-anisotropic stacked structures such as Li-Ion batteries, or weave structures with graphite- or nanotube fillers, may involve individual layer thicknesses of significant size. To estimate the effective, or total, heat capacity of such a structure may be rather challenging with a test method such as DSC – since it is difficult to prepare a small-volume sample which would represent the averaged heat capacity of the total structure. An experimental method on utilizing Hot Disk sensors have earlier been presented, whereby a high-conducting metal cell containing the sample, of thickness within 5 mm, and maximum diameter of around 20 mm. Two experiments are carried out: One in which a constant heating power is heating this cell – when empty – and the cell is located within an insulated environment (to minimize heat losses from the cell). Another corresponding experiment is performed in which identical experimental conditions (possibly with a higher heating power) – but applied to a cell with an internal sample. Heat losses (from the cell to the surrounding insulation) can be approximately accounted for, allowing the estimation of the heat capacity of the sample inside the cell – by comparing these two experiments. Some example applications are demonstrated and discussed, from testing of anisotropic rock samples, to a full-size Li-Ion battery used for automobiles.