Finite element analysis of coupled heat and moisture transport in cylindrical porous media and coal logs.

摘要

The purpose of this study is to determine the transient temperature and moisture distributions within finite porous solid cylinders during heating, cooling, and drying. This study includes a literature review, experiments, and a computer model for finite element analyses (FEA). The partial differential equations by Luikov are used to simulate the coupling of heat and mass transfer phenomena, including Soret effect and evaporation. Their solution required input of heat and mass transfer coefficients. These coefficients were obtained from drying experiments by the psychrometry method. The results were correlated in terms of dimensionless numbers: Nu{dollar}rmsb{lcub}h{rcub}=0.059 Resp{lcub}0.65{rcub} Gusp{lcub}-0.44{rcub}{dollar} and Nu{dollar}rmsb{lcub}m{rcub}=0.049 Resp{lcub}0.67{rcub} Gusp{lcub}-0.44{rcub}{dollar}; where Gu is Gukhman number which is defined as {dollar}rm(Tsb{lcub}infty{rcub}{dollar}-T{dollar}rmsb{lcub}w{rcub})/Tsb{lcub}infty{rcub}.{dollar} An extensible FEA framework approach was developed to numerically solve the Luikov equations. The framework. includes a set of object-oriented programs. The extensible FEA framework was demonstrated by a set of examples. The examples extend from steady state to transient problems (Poisson to heat conduction equations), and from the scalar to vector problems (heat conduction to Luikov equations). The specific examples are four application cases related to the heating, cooling and drying of porous solid cylinders with constant transport properties. Two cases simulate coal log heating and cooling during their compaction. The other two cases simulate coal log drying in ambient air. In these FEA simulations, coal logs are modeled as a two-dimensional axially symmetric cylinder. These simulations provide new quantitative predictions of detailed temperature and moisture distributions in finite porous cylinders. The Soret effect, evaporation and geometry cause the temporal temperature and moisture distributions to be nonlinear and dependent on the length-to-diameter ratio. The average temperature and moisture values provide information useful for the design of heating, cooling, and drying systems in coal log manufacture.