Heat and mass transfer in water‐laden sandstone: Convective heating

Abstract

A theoretical model was developed to predict the heat and mass transfer phenomena in porous materials. A water-filled sandstone was heated in a convective oven and its water loss rates and temperature profiles were compared with theoretical results. In addition to local temperatures, moisture content, gas densities and pressure, this model also predicts the fluid flow pattern in the heated sample.Heat and mass transfer in porous media occurs in many contemporary engineering applications, for instance, enhancing oil recovery, preparation of solid catalysts, and food processing. A familiar example in chemical engineering is drying which is normally confined to mild heating conditions. Classical explanations of interior drying phenomena are largely based on temperature history and drying-rate curves. Recently, Harmathy (1969) and Huang et al. (1979) predicted temperature, moisture content, and pressure profiles in the pendular state by different theoretical approaches, but these are not sufficient to explain the dynamic phenomena occurring in heated materials. To describe the dynamic phenomena quantitatively, we modify Whitaker's (1977) derivations and apply the new model to a sandstone subjected to mild heating conditions. CONCLUSIONS AND SIGNIFICANCEThe predicted phenomena are shown in Figures 15-17. Temperatures in the poroFs medium steadily increase with time. Moisture profiles are smooth and there is no sharp front dividing dry region and wet region in this case. Water vapor densities steadily increase with time. Except for the initial perturbation caused by air equilibration, air densities steadily decrease with time. Internal gas pressure declines at the beginning and then recovers to nearly atmospheric pressure. Although there exist transient flow patterns initially, during most of the heating period water vapor condenses along its path as it flows toward the centerline of the sample; air moves in the same direction, but at smaller flux. Liquid water, however, migrates toward the surface with a flux 2 to 3 orders of magnitude larger than vapor flux.The results obtained in this work help in understanding the pore-level heat and mass transfer phenomena. The model has potential applications in several engineering areas.

Porous media approaches to studying simultaneous heat and mass transfer in food processes. II: Property data and representative results

“…In heating of a high moisture food (Fig. 8a), the pressures stay close to atmospheric, although it can be slightly below atmospheric, as reported by Wei, Davis, Davis, and Gordon (1985). The pressure profiles for the low moisture potato are shown in Fig.…”

Effect of Post‐Precipitation Treatment on the Pore‐Structure Stability of Sol‐Gel‐Derived Lanthanum Zirconate

“…Therefore, in the case of the WWMD sample, the flux of vapor is always toward the surface. 22,23 This flux can result in a smaller pore volume and BET surface area and a lower temperature of crystallization for the WWOD sample.…”

Porous media approaches to studying simultaneous heat and mass transfer in food processes. I: Problem formulations

“…(37). A large value of C would force the system to be close to equilibrium, i.e., (34)) has been developed also in other materials processing context, such as sandstone or a generic porous media (Wei, Davis, Davis, & Gordon, 1985), wood (Turner & Mujumdar, 1996) and concrete (Constant, Moyne, & Perre, 1996). Other researchers have developed heat and mass transfer equations for porous media starting from conservation equations and mechanistic flux models (Chen & Pei, 1989;Ilic & Turner, 1989;Nasrallah & Perre, 1988;Stanish, Schajer, & Kayihan, 1986).…”