The Thermal Diffusivity of Glass Sieves: II. Gas-saturated Frits

The thermal diffusivity of gas-saturated glass sieves (frits) of porosities between 20 % and 48 % is presented as measured at room temperature and ambient pressure. The saturants cover a range in thermal diffusivity from 20.63 × 10–6 m2⋅s−1 to 172 × 10–6 m2⋅s−1. The experiments were carried out using a transient hot-bridge instrument of an expanded uncertainty of 5 % to 10 %. It turned out that all measured thermal diffusivities of the gas-saturated frits (1) are smaller than that of the borosilicate glass the frits are made from and (2) are completely different from the thermal diffusivities of the liquid-saturated frits. Both these discrepancies can be attributed to characteristic properties of the matrix and not directly to the saturants. The first divergence results from thermal tortuosity that lengthens the pathway of heat through the matrix, whereas the second arises from dissolved He that enhances the transport of heat through the matrix.

The Thermal Diffusivity of Glass Sieves: I. Liquid Saturated Frits

The thermal diffusivity of evacuated and liquid-saturated borosilicate glass sieves (frits) of porosities between 20 % and 48 % is presented as measured at room temperature. The saturants cover a range in thermal diffusivity from 0.091 mm2·s−1 to 0.143 mm2·s−1. The runs were carried out using a transient hot bridge (THB) measuring instrument of an expanded uncertainty of 5 % to 10 %. The experimental results are successfully fitted to a novel transient parallel-serial (TPSC) conduction model for the time-dependent composite heat transfer in porous media. The TPSC-model is an extension of the steady-state parallel-serial conduction (PSC) model to predict the thermal conductivity. The TPSC model confirms the so-called thermal porosity of the frits under test, a term that has been introduced in a former report on the thermal conductivity of the matrices (Hammerschmidt and Abid, Int J Thermophys 42:40, 2021). The experimental findings on the conductive transport of heat by glass sieves and their accurate mathematical description in the framework of the PSC and TPSC models might effectively support improving the thermal management of electronic devices and lithium-ion batteries.