摘要:

Fluidized bed and rotary dryers are two popular types of dryers utilized in almost every area of dryine. In this study, both dryers are analysed regarding their design and operational performance, so that they could be compared in a straightforward way. The mathematical models describing the convective drying process were evaluated for both types of dryers. Design procedures aiming at the determination of optimum sizing and operational characteristics for each type involved were carried out by appropriately optimizing the total annual cost of each structure for a given production capacity. Both dryer types were compared explicitely by evaluating optimum configurations for a wide range of production capacity values. Once the dryer sizing parameters are defined, its operational performance can be evaluated by comparing the optimum operational cost versus production capacity for predefined optimum designed structures. Rotary dryers turn out to be rather expensive compared to fluidized bed dryers, regarding design. On operational grounds, however, it is the other way around, due to the understandably favored heat transfer achieved in rotarv dryers. Characteristic examples covering a wide range of materials - from food products to inorganic minerals -are included in order to demonstrate the performance of each process as well as the effectiveness of the proposed approach.

ISSN:0737-3937    

DOI:10.1080/07373939708917260

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The value of dried lumber to the kiln operator is to a large extent dependent on the final moisture content distribution of the batch. This variation in moisture content arises from the intrinsic heterogeneity of wood and the stochastic nature of the timber drying process. Theoretical analyses of wood drying have hitherto relied upon deterministic models and have limited practical applicability. A methodology is proposed herein whereby the inherent probabilistic dynamics of batch drying can be modelled efliciently using Markov chains. The discretization of the variables of moisture and time that is necessary for this approach is discussed. By simulating the drying process with the model, the progressive transformation of the batch moisture distribution throughout the drying cycle can be studied. Output from the model is compared with experimental drying results to test its validity. There are

ISSN:0737-3937    

DOI:10.1080/07373939708917261

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A mathematical model was constructed and solved in order to describe quantitatively the dynamic behavior of the primary and secondary drying stages of the freeze-drying of pharmaceuticals in trays. The theoretical results were compared with the experimental data of the freeze-drying of skim milk, and the agreement between the experimental data and the theoretical results is good. Detailed model calculations have indicated that the contribution of the removal of hound (unfrozen) water to the total mass flux of the water removed during primary drying, is not significant. For this reason, it was found that one could not

ISSN:0737-3937    

DOI:10.1080/07373939708917262

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Simultaneous heat and mass transfer, during drying of moist capillary porous media, is modeled through different lumped-differential formulations, obtained from spatial integration of the original set of Luikov's equations for temperature and moisture potential. Besides the classical lumped system analysis, improved formulations are proposed, of same mathematicai simplicity, based on approximate evaluations of both temperature and moisture gradients within the medium. The relative merits of such improved zero-dimensional formulations are established, through critical comparisons against analytical solutions for the full partial diflerential system, over a wide range of the governing parameters.

ISSN:0737-3937    

DOI:10.1080/07373939708917263

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Fluidized bed dryers are often used to extract water from granular materials. When the drying process is mainly limited by the resistance against water transport inside the particle the drying behaviour is said to be diffusion-limited. In the literature there are several models that predict this drying process with very diverging results. In this study a model is set up to arrive at a better prediction for this drying process. The heat and mass transfer in the granular material and the drying air is described. The resulting equations are solved numerically. The model must be extended to incorporate the heatcapacity of the dryer.

ISSN:0737-3937    

DOI:10.1080/07373939708917264

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We present a dryer model for simulating the drying of hygroscopic-porous food products in a tunnel dryer. The model employs an improved receding-front formulation by taking into consideration the material volumetric shrinkage and the variation of the heat and mass transfer coefficient during drying. Predicted results show close agreement when compared with experimental data. We report a parametric analysis using the dryer model to study the drying transient and the need to cascade the drying process so as to maximise the drying potential of the air stream.

ISSN:0737-3937    

DOI:10.1080/07373939708917265

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Tortilla pieces were prepared from nixtamalized masa flour, and dried under impinging hot air. The effect of different drying conditions on the drying rate, texture, shrinkage profile and microstructure was analyzed. The results indicated that drying rate was mostly affected by the air temperature; texture was crispier at higher air temperatures: shrinkage of the piece was higher at lower convective heat transfer coeffieient; and microstructure looked smoother at higher air temperature.

ISSN:0737-3937    

DOI:10.1080/07373939708917266

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

We describe a pilot-scale drying plant comprising a closed-circuit, hot-air convection chamber with a heat pump. In this plant, food and forest products can be drled with lower energy consumption and over a wider range of air, speeds, temperatures and relative humidities than in conventional driers. Also the dryinq conditions can be controlled independently of external conditions. Under several different sets of drying conditions, we determined the kinetics of dryinq of grapes that had been variously pretreated. The effects of drying conditions and the pretreatment on the drying time and the appearance of the dried product were evaluated. The drying kinetics can be described by a diffusion model.

ISSN:0737-3937    

DOI:10.1080/07373939708917267

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Sun drying experiments were performed to compare drying of cassava chips in sheet-metal trays with drying on mesh wire trays: In the sheet-metal trays, there was air flow across the top of the bed chips, while the mesh wire trays permitted air to flow through the bed. Drying rate was faster and more uniform in the trays with through-flow air circulation. Higher temperatures were reached by chips in the sheet-metal trays than those in the mesh wire trays because of contact heating, but the drying rate was lower because of the reduced air flow.

ISSN:0737-3937    

DOI:10.1080/07373939708917268

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

In some parts of the world, e. g. China, maize reaches a grain dryer at low temperatures, frequently in the range of -10°C to -20°C. The effect of a low grain temperature, and an equally low ambient temperature, was determined, partially by experimentation and partially by simulation. The percentage of moisture Frozen in maize depends on the grain moisture content and temperature. The low grain and ambient temperatures surprisingly have only a small effect on dryer capacity; however. the influence on the energy consumption is large.

ISSN:0737-3937    

DOI:10.1080/07373939708917269

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor