摘要:

A transient one dimensional first principles model is developed for the drying of a porous material (wood is used as an example) that includes both heat and mass transfer. Heat transfer by conduction and convection, mass transfer by binary gas diffusion, pressure-driven bulk flow in the gas and liquid, and diffusion of bound water are included in the analysis. The diffusive mass transfer terms are modeled using a Fickian approach, while the bulk flow is modeled assuming Darcian flow. Depending on the state (pendular or funicular) of the moisture in the wood, appropriate terms are considered in the development of the governing mass equations. The results provide distributions within the material of each moisture phase (vapor, liquid, and bound), temperature, and total pressure. Information regarding the drying rate and evaporation rate is also presented. Average distributions are obtained as a function of time, and compared with experimental data from the literature. It is observed that the total pressure within the material can be considerably above one atmosphere during the drying process.

ISSN:0737-3937    

DOI:10.1080/07373939708917365

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A transient one dimensional first principles model is developed for the drying of a porous material (paper) that includes both heat and mass transfer. All three modes of heat transfer are considered; conduction, convection and radiation. The conduction is assumed to be in one dimension, through the porous material. The convection is assumed to exist only at the surface as a boundary condition. The radiation is assumed to be a volumetric phenomenon, so that the material internally absorbs, emits, and scatters energy. The absorption and scattering coefficients are spectrally dependent. Furthermore, the material is considered to have a non-unity refractive index with diffuse surfaces. In the mass transfer it is assumed that water exists in three phases: bound, free and vapor. The results provide profiles within the material for each moisture phase, temperature, and pressure and the effect of radiation on these distributions.

ISSN:0737-3937    

DOI:10.1080/07373939708917366

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A comprehensive experimental study of the drying of enzymes (E) and gin seng (GS) biomateriaJs provides a basis for mathematical modelling of the drying process with respect to the inactivation kinetics. Temperature of 20 - 120 °C was established for a number of enzymes while removing moisture with no thermal destruction. The kinetic parameters of inactivation were obtained for dry and wet enzymes and gin seng biomatenals. The software for kinetic parameters calculations for drying and inactivation of enzymes and gin seng biomateriaJs was drawn up, tested and verified experimentally. Methods of drying, design of dryers and regimes of drying of pure enzymes and gin seng biomaterials with minimum loss of bioactivity are suggested on the basis of model analysis and experimental data.

ISSN:0737-3937    

DOI:10.1080/07373939708917367

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Microwave vacuum drying kinetics of three fruits (namely, apple, kiwi and pear) were studied by introducing an one-parameter empirical mass transfer model, involving a characteristic parameter (drying constant), as a function of process variables. The model was tested with data produced in a microwave oven equipped with vacuum apparatus, using non-linear regression analysis. The investigation involved a wide range of microwave power and vacuum pressure levels. The parameters of the model considered were found to be greatly affected by the microwave power level while vacuum pressure affected slightly the process.

ISSN:0737-3937    

DOI:10.1080/07373939708917368

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The effect of drying method on bulk density, particle density, specific volume and porosity of banana, apple, carrot and potato at various moisture contents was investigated, using a large set of experimental measurements. Samples were dehydrated with five different drying methods: conventional, vacuum, microwave, freeze and osmotic drying. A simple mathematical model was used In order to correlate the above properties with the material moisture content. Four parameters with physical meaning were incorporated in the model: the enclosed water density pw, the dry solid density ps, the dry solid bulk density pboand the volume shrinkage coefficient β'. The effect of drying method on the examined properties was taken into account through its effect on the corresponding parameters. Only, dry solid bulk density was dependent on both material and drying method. Freeze dried materials developed the highest porosity, whereas the lowest one was obtained using conventional air drying.

ISSN:0737-3937    

DOI:10.1080/07373939708917369

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Closed-form solutions of the non-steady state diffusion equation with constant transport coefficients are presented. The diffusion coefficient is assumed to be finite, but the surface emission coefficient can be either finite or infinite. Mathematical conditions are established for the transport coefficients to be constant. When these conditions are met, the transport coefficients can then be easily evaluated. Diffusion test data can be compared against these conditions to determine whether or not the transport coefficients are constant. Desorption test data of northern red oak indicate that initial moisture content in wood and equilibrium moisture content in the environment are closely related to the constancy of the transport coefficients.

ISSN:0737-3937    

DOI:10.1080/07373939708917370

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Grain drying is a simultaneous heat and moisture transfer problem. The modelling of such a problem is of significance in understanding and controlling the drying process. In the present study, a mathematical model for coupled heat and moisture transfer problem is presented. The model consists of four partial differential equations for mass balance, heat balance, heat transfer and drying rate. A simple finite difference method is used to solve the equations. The method shows good flexibility in choosing time and space steps which enable the simulation of long term grain drying/cooling processes. A deep barley bed is used as an example of grain beds in the current simulation. The results are verified against experimental data taken from literature. The analysis of the effects of operating conditions on the temperature and moisture content within the bed is also carried out

ISSN:0737-3937    

DOI:10.1080/07373939708917371

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0737-3937    

DOI:10.1080/07373939708917372

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A semi-empirical linear equation has been developed to optimise the amount of maltodextrin additive (DE 6) required to successfully spray dry a sugar-rich product on the basis of its composition. Based on spray drying experiments, drying index values for individual sugars (sucrose, glucose, fructose) and citric acid were determined, and using these index values an equation for model mixtures of these components was established. This equation has been tested with two sugar-rich natural products, pineapple juice and honey. The relationship was found to be valid for these products.

ISSN:0737-3937    

DOI:10.1080/07373939708917373

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

This paper presents an application of artificial neural network (ANN) technique to develop a model representing the non-linear drying process. The air heat plant (AHP), an important component in drying process is fabricated and used for building the ANN model. An optimal feed forward neural network topology is identified for the air heating system set-up. The training sets are obtained from experimental data. Back propogation algorithm with momentum factor is used for training. The results show that the back propogation ANN can learn the functional mapping between input and output. The advantages of ANN model developed for AHP is highlighted. The developed model can be used for control purposes.

ISSN:0737-3937    

DOI:10.1080/07373939708917374

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor