摘要:

Highfrequency drying of a porous ceramic has been studied experimentally. The influence of electrode voltage, electrode distance, electric conductivity of the moisture and geometry of the product on the drying rate was investigated. There exists an optimal conductivity for maximum power dissipation and the geometry of the product has a focusing effect on the electric field. A theoretical discussion concludes, that the eddy current free quasi-stationary field is the type of field commonly present in highfrequency drying. With this type of field and the fact, that the complex permittivity of the product changes during drying, the experimental observations can be understood. From theory and experiment, conclusions are drawn in respect to a typical drying curve at highfrequency drying.

ISSN:0737-3937    

DOI:10.1080/07373939608917161

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The prediction of a hydrodynamic model for the isothermal transport of liquid in partially saturated porous media is compared with experimentally obtained values of water transport in clay. The transport obeys the diffusion equation, The diffusion coefficient is described as a function of porosity, permeability and pore size distribution. The comparison indicates that the model needs some refinement.

ISSN:0737-3937    

DOI:10.1080/07373939608917162

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Moisture diffusivity is the most crucial property in drying calculations. Literature data are scarce due to the variation of both experimental measurement techniques and methods of analysis. The effect of using different methods of analysis on the same experimental drying data is examined in this work. Detailed and simplified mathematical models, incorporating moisture diffusivity as model parameter, are applied. It is proved, that significant differences in the calculated values of moisture diffusivity result when different models are used, and probably these differences explain the variation in literature data. Thus, the adoption of a standardised methodology will be of great importance in moisture diffusivity evaluation.

ISSN:0737-3937    

DOI:10.1080/07373939608917163

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In this study, seedcoat cracking during heated air drying was investigated in five varieties of Minnesota grown soybeans. Effects of initial moisture contents, drying temperatures and time on cracking levels were evaluated. Digital image analysis (DIA) was employed to measure initial sizes and shapes of soybeans in order to evaluate the influence of physical properties of mature seeds on cracking frequency.

ISSN:0737-3937    

DOI:10.1080/07373939608917164

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

MRI techniques were developed and employed for non-destructive and noninvasive study of seedcoat cracking in low moisture soybean kernels during heated air drying. Proton density image and transient moisture distribution profile of a single soybean kernel can be obtained using MRI. These MRI techniques proved to be particularly useful for the continuous observation of initiation and propagation of seedcoat cracking during the entire period of drying process without interruption.

ISSN:0737-3937    

DOI:10.1080/07373939608917165

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

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

ISSN:0737-3937    

DOI:10.1080/07373939608917166

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A complete model for the drying of coated webs. as implemented in the spreadsheet DRYWEB for Lotus and for Excel, is described. The model predicts the temperatures and solvent levels throughout the length of the dryer. The initial transient as the coated web approaches the equilibrium temperature in the consiant rate period is calculated. The coating is divided into slices for a finite difference calculation of solvent diffusion to the surface, using a simple free volume model of diffusion. The semi-empirical constants needed can be found from one or two trial runs. The possible use of infra-red heating in addition to convection heating is included in both the constant and falling rates. The calculation of infra-red energy is discussed. The model assumes that the temperature is uniform from the top of the coating to the bottom of the base, and that assumption is justified.

ISSN:0737-3937    

DOI:10.1080/07373939608917167

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A mathematical model of a tunnel dryer for the dehydration of grapes is presented and applied to the determination of optimal operating conditions of the dryer. The dryer is of semi-batch structure, operating with trucks and trays. The cycle period is determined by meeting appropriate quality specifications for the final product. The nominal conditions were evaluated bv suitably minimizing. the total fuel demand, expressed as fuel consumption to production capacity, under some constraints regarding the production rate of the dryer and the maximum permissible air temperature. An nominal air humidity value was evaluated suggesting a minimum cycle period value for the production capacity and fuel demand. The nominal conditions required operation of the dryer on the maximum permissible air temperature. The optimum operation was evaluated by maximizing the total profit resulting from the operation of the dryer. The optimization variables were temperature and humidity of the drying air stream. A charteristic case study of industrial grape was included to illustrate the effectiveness of the proposed approach.

ISSN:0737-3937    

DOI:10.1080/07373939608917168

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A mathematical model for simulation of softwood drying also in temperatures exceeding the boiling point of water is presented. The equations are formulated in a conservative form based on the classical volume averaging technique with an addition of a pressure-driven moisture flux in the boundary condition. Numerical results using the control volume method are presented to show that this term missing in existing simulation models may account far the calculated build up of moisture at the very surface of a wood board. The possibility of neglecting the air- phase in the calculation of total gaseous pressure is investigated by means of an example. It shows that the effect of air pressure is only of very litde importance in the case of transversal flow in moderate tempertures.

ISSN:0737-3937    

DOI:10.1080/07373939608917169

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The physical properties of air and superheated steam were analysed in a range of temperature applied in paper and paperboard drying processes. On the basis of tests carried out on a pilot stand the values of energy indices for air and steam drying processes are compared. With the drying media temperature as Tm= 300°C, nozzle velocity v= 60m/s and using the Huang and Mujumdar model as well as relationships given by Chance a compartive analysis of the results has been carried out Variation of several indices in the range of temperatures 100-600°C and various nozzle velocities was studied.

ISSN:0737-3937    

DOI:10.1080/07373939608917170

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor