Investigation of Particle and Air Flows in a Mixed-Flow Dryer

Even though the mixed-flow dryer is well established on the commercial market for the drying of grain, maize, and rice, there further potential as well as a need to optimize the dryer apparatus and to improve product quality. Unfavorable designs can cause uneven mass flow and air flow distributions, resulting in locally different drying conditions and, hence, uneven grain drying. The aim of the present article is to evaluate traditional designs of mixed-flow dryers by numerical and experimental investigation of particle and air flows and to discover design deficits. For this purpose, the dryer geometry and different air duct arrangements (horizontal and diagonal) were studied using the discrete element method (DEM) and computational fluid dynamics (CFD). Drying experiments were performed to evaluate the grain moisture and temperature distributions. With regard to particle flow, a typical core flow was detected as in silos with a retarded particle flow at the dryer walls and a fast flow region in the center of the dryer. This was caused by the wall friction effect and the half air ducts fixed at the side walls. With regard to the air flow, dead zones were discovered for the diagonal air duct arrangement. Based on the design deficits identified for the traditional geometry, a new geometry for the mixed-flow dryer that is still under development is discussed.

[1]  Francisco Cardoso,et al.  DEM simulation of wave propagation in granular materials , 2000 .

[2]  M. Gustafsson,et al.  MODELING AND SIMULATION OF CROSSFLOW MOVING BED GRAIN DRYERS , 1998 .

[3]  F. Menter.  Two-equation eddy-viscosity turbulence models for engineering applications , 1994 .

[4]  Jochen Mellmann,et al.  Experiments on Hot-Air Drying of Wheat in a Semi-Technical Mixed-Flow Dryer , 2007 .

[5]  Grant M. Campbell,et al.  Discrete Modeling and Suggested Measurement of Heat Transfer in Gas–Solids Flows , 2003 .

[6]  Dariush Zare,et al.  Simulation and Validation of Microwave-Assisted Fluidized Bed Drying of Soybeans , 2012 .

[7]  F. Bertrand,et al.  DEM-based models for the mixing of granular materials , 2005 .

[8]  J. Vasseur,et al.  Superheated steam dryer: simulations and experiments on product drying , 2002 .

[9]  P. Cundall.  A computer model for simulating progressive, large-scale movements in blocky rock systems , 1971 .

[10]  U. Hoffmann,et al.  Experimental and theoretical investigations of a spray dryer with simultaneous chemical reaction , 2001 .

[11]  J. Straatsma,et al.  Spray drying of food products: 1. Simulation model , 1999 .

[12]  Evangelos Tsotsas,et al.  Particle velocity profiles and residence time distribution in mixed-flow grain dryers , 2011 .

[13]  P. Cundall,et al.  A discrete numerical model for granular assemblies , 1979 .

[14]  Avi Levy,et al.  Modeling of Heat Transfer in Pneumatic Conveyer Using a Combined DEM-CFD Numerical Code , 2010 .

[15]  Arun S. Mujumdar,et al.  A Numerical Study of Heat Transfer Mechanisms in Gas–Solids Flows Through Pipes Using a Coupled CFD and DEM Model , 2003 .

[16]  Da-Wen Sun,et al.  Computational fluid dynamics (CFD) ¿ an effective and efficient design and analysis tool for the food industry: A review , 2006 .

[17]  S. Luding.  Cohesive, frictional powders: contact models for tension , 2008 .

[18]  N. Mohsenin.  Physical properties of plant and animal materials , 1970 .

[19]  F. W. Bakker-Arkema,et al.  Drying and Storage Of Grains and Oilseeds , 1992 .

[20]  Aibing Yu,et al.  Simulated and measured flow of granules in a bladed mixer—a detailed comparison , 2001 .

[21]  Jochen Mellmann,et al.  Solids transport in mixed-flow dryers , 2011 .

[22]  Evangelos Tsotsas,et al.  Modeling of Contact Dryers , 2007 .

[23]  Francis Courtois,et al.  Control Strategies for Corn Mixed-Flow Dryers , 1995 .

[24]  Digvir S. Jayas,et al.  Grain Drying: Theory and Practice , 1998 .

[25]  Stefan Cenkowski,et al.  Airflow patterns in a mixed-flow dryer , 1990 .

[26]  Evangelos Tsotsas,et al.  Mixing of particles in rotary drums: A comparison of discrete element simulations with experimental results and penetration models for thermal processes , 2006 .

[27]  R. Kačianauskas,et al.  Investigation of adequacy of multi-sphere approximation of elliptical particles for DEM simulations , 2010 .

[28]  Jintang Li,et al.  APPLICATION OF THE DISCRETE ELEMENT MODELLING IN AIR DRYING OF PARTICULATE SOLIDS , 2002 .

[29]  Deyong Yang,et al.  Research on Modeling and Simulation of Mixed Flow Grain Dryer , 2007 .

[30]  Francis Courtois.  Computer-Aided Design of Corn Dryers With Quality Prediction , 1995 .

[31]  汤光斌,et al.  Grain drying systems , 2012 .

[32]  Jili Zhang,et al.  Fuzzy Control of Mixed-Flow Grain Dryer , 2003 .

[33]  T. Metzger,et al.  Moisture content and residence time distributions in mixed-flow grain dryers , 2011 .

[34]  F. Maio,et al.  Comparison of contact-force models for the simulation of collisions in DEM-based granular flow codes , 2004 .

[35]  T. Metzger,et al.  Residence Time Distribution in Mixed-Flow Grain Dryers , 2011 .

[36]  D. M. Bruce,et al.  Two-Dimensional Simulation Model of Steady-state Mixed-flow Grain Drying. Part 1: The Model , 1998 .

[37]  D. M. Bruce.  Simulation of multiple-bed concurrent-, counter-, and mixed-flow grain driers , 1984 .

[38]  Thanit Swasdisevi,et al.  Investigation of Temperature Distribution and Heat Transfer in Fluidized Bed Using a Combined CFD-DEM Model , 2011 .