Modeling of the heat-transfer process in a differential scanning calorimeter

✍ Scribed by B. Sen

• Publisher: American Institute of Chemical Engineers
• Year: 1992
• Tongue: English
• Weight: 546 KB
• Volume: 38
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690380312

✦ Synopsis

Abstract

The model developed predicts a priori potential errors associated with the energy trace recorded by an isoperibol differential power scanning calorimeter in the measurement of heat of adsorption of H~2~ on Pt and Pd catalysts. The uptake of H~2~ by the catalyst sample was approximated by a diffusion‐limited quasi‐steady‐state moving boundary model. This approximation is valid only if the parameter [(adsorption capacity of cat. sample)/(inlet conc. of H~2~)] is extremely large (∼ 24). The effect of flow rate, amount of H~2~ adsorbed, sink temperature, and the thermal conductivity of the adsorbate mixture was examined. Model predictions indicate that the error in the energy trace recorded by the DSC is appreciable: if a large difference exists between the thermal conductivity of the inert carrier, Ar (K = 0.017 J/m·K·s), and the adsorbate, H~2~ (k = 0.174 J/m·K·s); if the heat sink temperature is much lower (∼ 90 K) than the measurement temperature. However, these errors can be eliminated by matching the thermal conductivity of the inert carrier and adsorbate, such as He (k = 0.143 J/m·K·s) and H~2~ (k = 0.174 J/m·K·s). The results agree well with the experimental observations of Vannice et al. (1987) on high‐purity Pt and Pd powder and supported Pt catalysts, if the H~2~ uptake by the catalyst sample in the calorimeter is small (⩽2 μmol).