An open-photoacoustic-cell method for thermal characterization of a two-layer system

Abstract

In the present work, we use an open-photoacoustic-cell ͑OPC͒ operating at high frequency to measure thermal properties of two-layer system samples. Photothermal deflection technique is also employed to measure the samples. The effective thermal diffusivity measured using the OPC method is interpreted using the concept of effective thermal resistance for a series two-layer system. The results show the reliability of the photoacoustic method for a complete thermal characterization of the samples. In addition, by varying the sample effective thickness, the thermal diffusivity and conductivity of each layer are precisely determined. The effective thermal diffusivity, thermal conductivity, and specific heat of a porous catalyst layer ͑thickness varying from 13 to 53 m͒ deposited on an aluminum foil ͑53 m in thickness͒ were thus measured and found to be ͑3.7Ϯ 0.3͒ ϫ 10 −3 cm 2 / s, ͑7.5Ϯ 0.7͒ ϫ 10 −3 W / cm K, and ͑1.6Ϯ 0.2͒ J / gK, respectively.

Effective transport properties for polymer electrolyte membrane fuel cells – With a focus on the gas diffusion layer

“…Using the guarded heat method described earlier in Section 2.3.1, Khandelwal and Mench [44], measured the thermal conductivity of a catalyst layer having 0.5 mg cm À2 platinum on carbon to be 0.27 AE 0.05 W/m K. The thermal conductivity of the catalyst layer was also measured by Astrath et al [129] using an openphotoacoustic-cell method. With this technique, a thermal energy, in the form of a laser, is used to excite a probe.…”

Photoacoustic effects in nanocomposite structure ‘porous silicon-liquid’

“…Photoacoustic (PA) techniques have proven to be capable for studying of porous materials [2] and layered structures [3]. This is mainly due to the fact that, in most cases of their practical implementations, they are nondestructive.…”

Open photoacoustic cell for thermal diffusivity measurements of a fast hardening cement used in dental restoring

“…The contribution from the sample bending to the PA signal is calculated by solving the thermoelastic equations, whereas the thermal diffusion contribution is attained by solving the heat conduction differential equation, as described in details in Refs. 12, 18-20. Assuming that all light is absorbed at the sample surface and considering no axial heat flux, the pressure fluctuation in the air chamber of a photoacoustic cell due to thermal diffusion (TD) and thermoelastic (TE) bending of a thermally thick sample, i.e., l s a s ) 1, is expressed in one-dimension by 12,[18][19][20] …”

“…Apart from several different apparatuses for the PA detection, the simplicity and the usefulness of the open-photoacoustic-cell (OPC) make this technique easily applicable to thermal characterization of solid materials such as the measurement of thermal diffusivity and thermal conductivity. [11][12][13][14] Mineral Trioxide Aggregate (MTA) is the most popular material used in dentistry. MTA is composed of a white or gray powder of fine hydrophilic particles consisting of compounds of tricalcium silicate, tricalcium oxide, tricalcium aluminate, and silicate oxide.…”