摘要:

The performance of batch and continuous fluidized solids dryers has been modeled, with allowance for diffusional moisture transport in the dense phase particles and for interstitial gas-to-particle mass transfer within the dense phase, as well as for interphase exchange resistance between gas bubbles and the dense phase. Two types of boundary conditions are employed. Variations of the bed temperature and product moisture content in the bed with time are predicted numerically under various batch drying conditions. Exit product moisture contents, bed temperatures and outlet air humidities are also predicted for continuous drying at various mean residence times. The model can be used for homogeneous as well as bubbling fluidized bed drying. It can be used for a wide range of materials, including cereal grains and granular synthetic polymeric materials.

ISSN:0737-3937    

DOI:10.1080/07373939508916940

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Drying behavior of a single suspended droplet of various protein and carbohydrate solutions was investigated experimentally. For small molecular weight carbohydrates such as sucrose and glucose, the constant-rate period was observed, which was followed by the falling rate period characterized as the “regular regime”. During the falling rate period. the drying rate was very low due to a sharp decrease of the water diffusion coefficient with decreasing water concentration No remarkable constant rate periods were observed for large-molecular carbohydrates and proteins. This is because the water diffusion coefficient is low even at high water concentrations. The drying curves or bovine serum albumin, skimmilk and model-food liquid solutions were found to be predicted by a computer simulation with the concentration dependent water diffusion coefficient of maltodextrin of dextrose equivalent =11. The experimental investigations on the ethanol and enzyme retention during drying indicated that the ethanol is lost during the costant-rate period and the enzyme inactivation occurs during the constant-rate period (regular regime).

ISSN:0737-3937    

DOI:10.1080/07373939508916941

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Dynamic and spatially multi-dimensional mathematical models of the primary and secondary drying stages of the freeze-drying of pharmaceutical crystalline and amorphous solutes in vials, are constructed and presented in this work. The models account for the removal of free and bound water and could also provide the geometric shape of the moving interface and its position. It is proved that the temperature of the moving interface can not be constant if the flux of heat flow to the sides of the vial is not zero. It is also proved that the slope of the free surface (moving interface) at the edge of the vial is always curved downward.

ISSN:0737-3937    

DOI:10.1080/07373939508916942

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The development of MlMO control systems for individual conveyor-belt drying chambers was studied for the case of industrial units used for the moisture removal from wet raisins. The process was considered to be a 2×2 open-loop system in which material moisture content and temperature at the exit of the drying chamber were to be controlled. Its dynamic behavior was investigated via digital simulation of the corresponding process mathematical model which involves 6 state variables. The effect of several manipulated and load variables on process outputs was explored by examining the corresponding responces obtained when the input variables were step forced into the non-linear dryer model simulator around the operational point studied. Reliable transfer functions for each interaction module were produced, based on simulated data and process basic constants. The best control configuration was selected bv deriving the RGA values of each one that was based on its frequency information. The propsed scheme, used steam and fresh air flowrates as manipulated variables. This scheme was found to imply insignificant interactions between material moisture content and temperature loops. The suggested pairing was material moisture content controlled by steam flowrate and fresh air flowrate controlling material temperature. Single-loop PI-feedback controllers were installed in each loop and tuned by Ziegler-Nichols techniques. The closed-loop system performance was examined by suitably introdcuing step changes to both set-points as well as to process disturbances. The overall control system performance proved to be quite satisfactory.

ISSN:0737-3937    

DOI:10.1080/07373939508916943

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A finite element formulation and the solution of a set of nonlinear coupled heat and mass transfer equations for a two-phase system with a moving evaporation interface is presented. The interface condition takes into account the moisture transfer balance at the moving boundary. The finite element results were compared with existing results for a single phase system for model validation. In the two-phase system, the movement of evaporation front has an appreciable effect on the temperature and moisture distribution inside the porous medium during drying. The effect of the nondimensional heat of vapourization parameter γ on the evaporation front, temperature and moisture distribution in porous medium was studied. The higher the value of γ, the slower is the movement of the evaporation front. The temperature decreased and the moisture content increased as the nondimensional vapourization parameter γ increased. This model has potential applications in studying the heat and mass transfer characteristics in food and biomaterials.

ISSN:0737-3937    

DOI:10.1080/07373939508916944

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper presents a simulation study of air flow inside dryers. An adaptive finite element methodology for two-dimensional problems was developed. This study is the first application of nadaptive techniques to such tupe of problems. The formultion is generic and can be easily extended to three-dimensional analysis. Several dryer configurations were studied in order to verify the efficiency and accuracy of the proposed methodology. Results agreed well with experimental data and show significant imporvements when compared to the conventional finite elements analysis.

ISSN:0737-3937    

DOI:10.1080/07373939508916945

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new dynamic model of corn drying based on compartmental structure and quality prediction was built up from a thin layer model to industrial scale. From the system analysis to the programming, we focus mainly on numerical resolution of the equations and on the ergonomy of the software.

ISSN:0737-3937    

DOI:10.1080/07373939508916946

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

All the works so far on simulation of grain drying by natural convection of air presents conflicting reslts on the drying time forecast. In this work the models of Hukill, Thompson and Michigan are tested in same type of dryer. Appropriate equations are developed to correct the drying time, starting form the models of Thompson and Hukill. The solution of the equations of michigan model is developed on fintie difference and similarly and some speical technuques are utilized on the Thompson model. 53 test results are utilzed here to validate the simulation model of drying.

ISSN:0737-3937    

DOI:10.1080/07373939508916947

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

One requirement in designing and operating and operating system is to minimize the moisture change in stored grain. Moisture transfer during the aeration process is generally believed to be caused by the partial pressure difference between water in grain and water in air (P3−P4). A mathematical model was developed for rough rice, which predicts the partial pressure difference under various grain and ambient conditions. Observations of moisture change over 10 aeration tests confirmed the good correlation between sorption phenomena and partial pressure differences. Studies indicated that air relative humidity, air temperature, grain temperature and grain moisture are significant factors influencing the partial pressure differences and, thus, affecting

ISSN:0737-3937    

DOI:10.1080/07373939508916948

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Two mathematical models (an equilibrium model and a combined model) were evaluated, which described the moisture and heat transfer in low temperature drying and aeration. The predicted moisture contents from both models were compared with the experimental data. Comparisons indicated that the combined model was more accurate than the equilibrium model. The combined model is based on the idea that the partial pressure difference is the driving force in moisture transfer. A series of simulation was performed using the combined model to evaluate the effect of air temperature, air relative humidity, and the temperature difference between grain and air on the moisture changes in stored rough rice. The simulation results proved the concept of using the partial pressure difference to describe the moisture transfer in stored grain. A minimum of 5.6°C in

ISSN:0737-3937    

DOI:10.1080/07373939508916949

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor