Session: 11-10-01 Single/ Two-Phase Heat Transfer in Active and Passive Systems

Paper Number: 68157

Start Time: Tuesday, 07:20 PM

68157 - Drying of a Fully Saturated Porous Medium With Excess Water Layers - A Numerical Study 

Porous media drying can be very energy inefficient. For example, in the pulp and paper industry, paper drying consumes almost one-third of the total energy used in papermaking. Novel drying technologies can decrease the energy used for drying and lessen the manufacturing processes’ carbon footprint. To assess such technologies, designers can rely on numerical models to predict the de-wetting of porous media. During papermaking, dry paper and water mixture is fully saturated and contains additional “excess water” before the pressing section of a paper machine. Also, during paper coating, the paper surface becomes saturated, and excess moisture can be present near these saturated surfaces.

A theoretical model for simulating the drying of fully saturated porous media with excess water is developed by considering the mass and heat transport during drying. A theoretical model by Asensio and Seyed-Yagoobi [1] developed for paper drying in a paper machine for an unsaturated paper (saturation, s<1) is used as a starting point when developing the current model. The porous medium is assumed to be sandwiched between two excess water layers (bottom and top). The thickness of each water layer is calculated based on local temperature and total moisture content. The numerical model is transient, one-dimensional in space and ignores gravitational acceleration. This paper demonstrates the governing equations, boundary conditions, and results when the saturated porous medium with water layers is heated from one (bottom) side. Continuity and energy equations along with a set of boundary conditions are solved numerically with finite difference methods via MATLAB. Water vapor and liquid water fluxes are estimated with Fick’s and Darcy’s Laws, respectively. Moisture and temperature profiles are estimated in the thickness direction of the porous medium as it dries. Results show that initial drying is due to the drying of the top water layer and is rapid. Then, the bottom water layer’s moisture penetrates the porous medium as porous media becomes slightly unsaturated due to evaporation at its top surface. When the bottom water layer is dried up, the porous media starts losing its moisture more significantly than in the previous stages, as expected.

 

Keywords: moist porous media, heat and mass transfer, excess water, fully saturated, drying, dewatering, water removal, bottom heated, water layers

 

[1] M. C. Asensio and J. Seyed-Yagoobi, "Simulation of Paper-Drying Systems with Incorporation of an Experimental Drum/Paper Thermal Contact Conductance Relationship," ASME. J. Energy Resour. Technol., vol. 115, no. 4, pp. 291-300, December 1993.

Presenting Author: Munevver E. Asar Worcester Polytechnic Institute

Authors:

Munevver E. Asar Worcester Polytechnic Institute
Jamal S. Yagoobi Worcester Polytechnic Institute