Determination of effective diffusivities and convective coefficients of CO2 in gypsum plasters by dynamic single pellet experiments

Abstract

This paper presents the effective diffusion and convective coefficients obtained for construction gypsum, perlite, and machine plaster pellets by using a dynamic single pellet moment technique at various temperature, and at different pressure drops. The experimental studies were performed by isobaric and non-isobaric conditions across between the upper and lower surfaces of the pellets. The experimental moment values obtained from the experiments carried out were used to calculate desired coefficients such as the effective diffusivity, tortuosity factor, D parameter, and Darcy coefficient. The experimental results for CO2 diffusion in the pellets with porous at isobaric conditions showed that the effective diffusivity values for all gypsum plasters increase with increasing both pellet porosity and the temperature. It was observed that the tortuosity factor depends on macro porosity of the pellets used. The results indicated that the diffusion mechanism for all gypsum plasters is the transient regime diffusion. The effective diffusivity values decreased with increasing the pressure drop. In the range of pressure drop studied, both diffusive (at low pressure drops) and viscous (at high pressure drops) flows for CO2 diffusion in construction gypsum and perlite plasters were dominant. But, the diffusion flow type which is important for machine plaster was only the viscous flow at all pressure drops. Finally, the Darcy coefficients of the gypsum plaster pellets were calculated. It was observed that the results were in agreement with the literature results obtained for porous solids similar to porous gypsum plaster pellets used in this study. (C) 2016 Elsevier Ltd. All rights reserved.