Dynamic coupling of phase-heat and mass transfer in porous media and conjugate fluid/porous domains

• Published in: International journal of heat and mass transfer Vol. 106; pp. 1270 - 1286
• Main Authors: Elhalwagy, Mahmoud Mohamed, Straatman, Anthony Gerald
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.03.2017; Elsevier BV
• Subjects: Biot number; Computational fluid dynamics (CFD); Conjugate domains; Constituents; Coupling; Dehydration; Drying; Dynamic coupling; Fluid mechanics; Heat exchange; Heat transfer; Mass transfer; Moisture; Phase ratio; Porous materials; Porous media; Vaporization; Porous media; Dynamic coupling; Heat transfer; Mass transfer; Computational fluid dynamics (CFD); Conjugate domains
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2016.10.108

•Phase dynamic coupling of heat/mass transfer developed in porous media and conjugate domains.•Apportioning the vaporization energy on the phases using the ratio of the heat/mass resistances.•A phase ratio concept developed for implicit mass transfer coupling at macroscopic interfaces.•Validation of interstitial coupling by comparison to a coal particles drying experiment.•Validation of conjugate coupling comparing to drying of apple slice and mineral plaster. A dynamically varying technique for phase heat and mass transfer in porous media and fluid/porous domains has been developed and incorporated into a conjugate finite volume CFD framework. The local interstitial phase mass exchange within porous zones is estimated by comparison of the resistances to moisture transport within the solid and void constituents of the porous material; the higher resistance expression being used as rate-determining. Based on the mass transfer expression, a local estimate of the Biot number is used to physically apportion the withdrawal of vaporization energy from the solid and fluid constituents of the porous medium. A similar approach is used for coupling of the clear fluid and porous CFD cells at the clear fluid/porous interface. A phase ratio concept is introduced at these interfaces to be able to couple the different phases in heat and mass transfer. The model is generic, involving details that allow application to a wide range of cases and is one of the least empirically-adjusted models. The microscopic coupling approach has been validated for Coal packed bed drying. Results show good agreement with experimental data in terms of the matching trends and the small margins for temporal moisture and temperature variation. The macroscopic coupling technique has been tested using the cases of drying of an apple slice and the dehydration of mineral plaster. Investigating the two cases showed a clear difference in behavior as the apple slice case is material-side-resistance dominant – i.e. diffusively dominant – and the plaster case is air-side-resistance dominant – i.e. convectively dominant. The results are physically reasonable and compare well to available experiments and reported results from the literature. The comparisons indicate the capability of the present approach to model the dynamic coupling accurately in a computationally time-efficient manner.