Stochastic Modelling of Grain Moisture Content.in Near-Ambient Drying

ABSTRACT

A stochastic analytical model was developed to describe the mass transfer in a thin layer of grain ventilated with unheated air. As an excitation to the drying system, a stochastic analytical model of variations in ambient air temperature and relative humidity during the drying period, based on a sine function. was used. Mean. carrelation function, variance and the standard deviation were determined for main moisture content treated as a random process. The stochastic models of variations in air temperature and relative humidity were fined to the observed historical data. The standard deviation and m ean of grain moisture content calculated from the developed analytical model were compared to changes in mean and the standard deviation obtained from the numerical deterministic model of mass transfer and hourly weather data from 17 year.     

STOCHASTIC MODELING OF GRAIN TEMPERATURE IN NEAR-AMBENT DRYING

Stochastic analytical model was developed to describe the heat transfer in a thin layer of grain ventilated with ambient air. As an excitation to the drying system, a stochastic analytical model of ambient air temperature variations during the period of drying, based on a sine function, was used. Mean, correlation function, variance and the standard deviation were determined for air and grain temperature, both treated as random processes. The stochastic model of air temperature variation was fitted to the observed historical data. The effect of the standard deviation of air temperature of the three different climates (Canadian in Winnipeg, Polish in Poman and English in Weddington) on the standard deviation of grain temperature is shown.     

Modelling and Simulation of Momentum, Heat, and Mass Transfer in a Deep-Bed Grain Dryer

This article concerns the modelling and simulation of a deep-bed grain dryer in a large diameter-column. Two-dimensional (2D) models of deep-bed grain dryers were built by considering simultaneously momentum, heat, and mass transfer in the drying phase together with coupled heat and mass balance in the grain phase. The dynamic equations are solved numerically by using finite difference method. The momentum equations are applied to simulate pressure drop and velocity field of the drying air across the bed. The mass and heat balance in the two phases determine the profile of temperature and moisture content in both phases. Further, drying rate curves for various temperature of inlet drying gas together with moisture content of grain were simulated. The simulated profiles are in close agreement with experimental data.     

Coupled Heat and Mass Transfer in a Solar Grain Dryer

This paper presents the analysis of a coupled heat and mass transfer process in a fixed-bed solar grain dryer. Measurements of moisture concentration and air humidity along with temperature measurements were carried out in a solar grain dryer located in Port Harcourt, Nigeria, at the latitude of 4.858°N and longitude of 8.372°E. The process was also modelled, mathematically, by a set of partial differential equations that were coupled within the grain and through the grain boundary with the hot drying air. A finite difference scheme was used to obtain the moisture concentration and air humidity, and temperature fields within the grain and drying air. There was good agreement between the theoretical and experimental results at specified Biot and Posnov numbers, and varying Fourier number. The effects of time, space, and key model parameters such as the Biot and Posnov numbers and the initial conditions of the grains and drying air were simulated and discussed. The results from this study can be used to specify the design parameters for solar grain dryers.     

Prediction of Moisture Content Evolution in a Grain Batch Dryer Based on On–line Temperature Measurements

ABSTRACT

The time evolution of the moisture content in a grain batch fluidized bed dryer is estimated by means of an on–line non–linear estimator (Marquardt–Levenberg algorithm). The inputs to the estimation algorithm are on–line temperature measurements and the output is the surface moisture content. The surface moisture content is used for predicting the grain moisture content through the solution of a single ordinary differential equation that combines the moisture and energy balances over the dryer. In this way the drying curves are obtained through incorporating in a very simple model easily obtainable physical information of the process.     

Biosorption of the Reactive Blue 5G Dye in a Fixed Bed Column Packed with Orange Bagasse: Experimental and Mathematical Modelling

The removal of reactive dye in a fixed bed column packed with orange bagasse was modelled using a model that considers the effects of axial dispersion, external and internal mass transfer limitations, and the equilibrium in the liquid-solid interface. The equilibrium and kinetic parameters were obtained through fit the model to the experimental data. In the parameters identification procedure the PSO optimization method was used. The mathematical model showed good performance when describing the dye adsorption process. Furthermore, orange bagasse is an attractive and cost-effective alternative as an adsorbent to remove reactive blue 5G dye from wastewaters.     

Mathematical Modeling the Drying of Poplar Wood Particles in a Closed-Loop Triple Pass Rotary Dryer

Closed-loop drying systems are an attractive alternative to conventional drying systems because they provide a wide range of potential advantages. Consequently, type of drying process is attracting increased interest. Rotary drying of wood particles can be assumed as an incorporated process involving fluid–solid interactions and simultaneous heat and mass transfer within and between the particles. Understanding these mechanisms during rotary drying processes may result in determination of the optimum drying parameters and improved dryer design. In this study, due to the complexity and nonlinearity of the momentum, heat, and mass transfer equations, a computerized mathematical model of a closed-loop triple-pass concurrent rotary dryer was developed to simulate the drying behavior of poplar wood particles within the dryer drums. Wood particle moisture content and temperature, drying air temperature, and drying air humidity ratio along the drums lengths can be simulated using this model. The model presented in this work has been shown to successfully predict the steady-state behavior of a concurrent rotary dryer and can be used to analyze the effects of various drying process parameters on the performance of the closed-loop triple-pass rotary dryer to determine the optimum drying parameters. The model was also used to simulate the performance of industrial closed-loop rotary dryers under various operating conditions.     

The Drying of Sludge in a Cyclone Dryer Using Computational Fluid Dynamics

A control volume-based technique implemented in FLUENT (ANSYS Inc., Canonsburg, PA) computational fluid dynamics (CFD) package was applied along with the kinetic theory of granular flow (KTGF) to simulate the flow pattern and heat and mass transfer processes for sludge material in a large-scale cyclone dryer. The drying characteristics of sludge at the dryer inlet were obtained from a previous study on the drying of sludge in a large-scale pneumatic dryer. User-defined subroutines were added to extend FLUENT's capability to account for mixture properties and to simulate the constant and falling rate drying periods. The convective heat and mass transfer coefficients were modeled using published correlations for Nusselt and Sherwood numbers. Sensitivity analysis was conducted to determine the effect of gas-phase velocity and temperature on the final product outcome. Numerical predictions for the multiphase flow hydrodynamics showed a highly diluted region in the dryer core and a higher concentration of particles close to the wall region, an indication of nonuniform distribution of particles at a cross-sectional area. The numerical predictions for the hydrodynamic profiles qualitatively depicted the flow behavior natural to these designs. The work demonstrated the successful application of CFD in the design stage of a combined pneumatic-cyclone dryer model.     

Cross-Flow Drying of Wheat. A Simulation Program with a Diffusion-Based Deep-Bed Model and a Kinetic Equation for Viability Loss Estimations.

ABSTRACT

A mathematical model of heat and mass transfer for fixed beds was developed according to the modern theory of process simulation and standard laws of thermodynamics and transport phenomena. The mass transfer grain-air was predicted with simplified diffusional expressions together with an equation for the static equilibrium moisture content. Four differential equations were obtained for a grain layer and they were integrated along the bed depth and time with second and a fourth-order methods, respectively. The model was validated by comparing drying time predictions with experimental values, being the average error of 6%. The model was extended into a program for continuous cross-flow drying-cooling     

Mathematical Modeling of a Continuous Vibrating Fluidized Bed Dryer for Grain

A mathematical model for the drying of grain in a continuous vibrating fluidized bed dryer was developed. Simple equipment and material models were applied to describe the process. In the plug-flow equipment model, a thin layer of particles moving forward and well mixed in the direction of the gas flow was examined. Mass and heat transfer within a single wet particle was described by effective transport coefficients. Assuming constant effective mass transport coefficient and thermal conductivity, analytical solutions of the mass and energy balances were obtained. The variation in both transport coefficients along the dryer was taken into account by a stepwise application of the analytical solution in space intervals with averaged coefficients from previous locations in the dryer. Calculation results were in fairly good agreement with experimental data from the literature. However, the results depend strongly on relationships used to determine the heat and mass transfer coefficients; because the results from correlations found in the literature vary considerably, the correlations should be adapted to the specific equipment in order to obtain reliable results.     

A Parametric Study of Spray Drying of a Solution in a Pulsating High-Temperature Turbulent Flow

Spray drying of a concentrated common salt (NaCl) solution carried out in the intense oscillating high-temperature turbulent flow field generated in the tailpipe of a pulse combustor was simulated. Simulation of such transport process problems is especially crucial since the environmental conditions are too hostile for detailed and reliable measurements. The momentum, heat, and mass transfer processes between the gas and droplet phases during drying were simulated using a computational fluid dynamic solver. The simulated profiles of flow field, temperature, and humidity of gaseous phase, and particle trajectories in a drying chamber are presented and discussed. The effects of gas temperature, pulse frequency and amplitude, and gas mass flow rate on the transient flow patterns, droplet trajectories, and overall dryer performance were investigated. Different turbulence models were also tested. Simulation results show that the flow field and droplet drying conditions vary widely during a single pulsating period. Very short drying times and very high drying rate characterize pulse combustion spray drying. Thus, pulse combustion drying can be applied to drying of fine droplets of highly heat-sensitive materials although the jet temperature initially is extremely high.     

A Parametric Study of Spray Drying of a Solution in a Pulsating High-Temperature Turbulent Flow

Spray drying of a concentrated common salt (NaCl) solution carried out in the intense oscillating high-temperature turbulent flow field generated in the tailpipe of a pulse combustor was simulated. Simulation of such transport process problems is especially crucial since the environmental conditions are too hostile for detailed and reliable measurements. The momentum, heat, and mass transfer processes between the gas and droplet phases during drying were simulated using a computational fluid dynamic solver. The simulated profiles of flow field, temperature, and humidity of gaseous phase, and particle trajectories in a drying chamber are presented and discussed. The effects of gas temperature, pulse frequency and amplitude, and gas mass flow rate on the transient flow patterns, droplet trajectories, and overall dryer performance were investigated. Different turbulence models were also tested. Simulation results show that the flow field and droplet drying conditions vary widely during a single pulsating period. Very short drying times and very high drying rate characterize pulse combustion spray drying. Thus, pulse combustion drying can be applied to drying of fine droplets of highly heat-sensitive materials although the jet temperature initially is extremely high.     

煤块回水过程传质特性的实验研究

本文对干燥煤块的回水现象进行了实验研究。验证了回水过程具有三个特征阶段，并分析了环境因素，煤块粒径，初始含水率及干燥方式等因素对回水过程的影响。     

Modeling of Diffusion in Capillary Porous Materials During the Drying Process

This paper presents a model of heterogenous diffusion in capillary porous materials during the process of drying. The governing heat and mass transfer equations have been established using the liquid as well as vapor flow. Two models have been presented. Model 1 does not consider the heat conduction while the model 2 has been established by considering the conduction. The developed models and the numerical solutions of the resulting differential equations can take into account the moisture and temperature dependent thermophysical properties of the product. All equations have been established in spherical coordinates but the programme written for the purpose of calculations can be used for other geometries also. Numerical calculations have been performed for gas concrete and tiles using model 1, while model 2 has been used for gas concrete only because of the lack of data for thermophysical properties of the tile. For gas concrete it was seen that conduction has only marginal effect on the drying process and the numerical predictions of the drying process were reasonably accurate.     

SO3掺杂对高镁熟料中方镁石含量,C3S晶粒尺寸及晶型的影响

随着水泥行业的快速发展,高品质石灰石成为日趋紧缺的资源,合理有效地利用高镁质石灰石原料煅烧水泥熟料又被赋予更加重要的资源综合利用的意义.本文借助化学分析、岩相分析、胶砂试验研究、XRD等检测方法等,探讨了不同掺量的SO3对高镁熟料中方镁石含量、C3S晶粒尺寸及晶型的影响.结果表明:适当的SO3掺加量能够有效减少高镁熟料中方镁石含量,有利于高镁熟料中氧化镁的固溶,促进C3S晶粒尺寸的增大,稳定熟料中M1型C3S,提高熟料的力学性能,在SO3掺量为1％时,得到的熟料力学性能最好,为高镁石灰石今后在水泥行业的利用提供一定理论和实验依据.     

Analysis of the Disintegration of Distiller's Spent Grain Compacts as Affected by Drying in Superheated Steam

Breaking and disintegrating of biomass compacts while they are being dried in superheated steam (SS) is a common problem observed during the initial stage of SS drying. The present work investigated the moisture and temperature changes, volume and density variation, crushing resistance, and tensile strength of single cylindrical compacts produced from wet distiller's spent grain (WDG) under SS drying conditions. The wet compacts were dried in SS at 110, 130, and 150°C with SS velocities of 0.9, 1.1, and 1.4 m/s. For a specific temperature and velocity, the compacts were exposed to SS for time periods of 5, 120, 300, and 600 s and the changes in physical properties were analyzed. An increase in a percentage increase in volume by 78–130% and a decrease in density by 51–61% were observed as a result of drying the compact in SS. The results obtained from the study were compared with hot-air dried compacts for 600 s, indicating that SS drying had a substantial role in stimulating the relaxation of stresses stored in the compacts as compared with a convection hot-air drying process.     

A Novel Method of Measuring Moisture Content Distribution in Timber During Drying Using CT Scanning and Image Processing Techniques

A new method for the nondestructive measurement of moisture content (MC) distribution in timber during drying was developed using X-ray computed tomography (CT) scanning and image processing techniques. The deformed cross section in the CT images due to shrinkage was corrected with the image registration, and the shrinkage was measured by digital image correlation analysis. The pixel-wise MC distributions during drying were measured and visualized successfully. The total timber MC estimated from the MC values of each pixel were strongly correlated with those measured by calculation without geometrical transformation of CT images. The coefficient of determination (R ²) and the standard error of prediction (SEP) were 0.99 and 0.18%, respectively, within the MC range of 19.2–47.3%. In addition, the measured shrinkage distribution during drying was in accordance with the diamonding deformation observed. The results suggest that CT scanning combined with image processing techniques is an effective tool for nondestructive assessment of MC distribution during drying.     

Mass Transfer in the Celery Slice: Effects of Temperature, Moisture Content, and Density on Water Diffusivity

Statistical tests were applied to determine the effects of temperature, moisture content, density, and porosity of material on the effective moisture diffusion coefficient during convective drying of root celery. In biological materials with colloidal capillary-porous structure (like root celery), which shrink considerably during drying and show high heterogeneity, the effective water diffusion coefficient depends not only on material temperature and moisture content, but also on its density. It was found that statistical tests can be applied to predict which independent variables should describe the water diffusivity in colloidal capillary-porous materials. A mathematical model of the effective water diffusion coefficient in root celery was formulated as Arhenius-type equation with moisture content of the raw material, its temperature and density as independent variables.