摘要:

Magnetic resonance imaging (MRI) was used to obtain moisture profiles of a model food gel during drying. A cylinder of gel, 1 cm in diameter, with an initial moisture content of 76% was imaged while drying at room temperature. Moisture profiles were obtained from the imaging data by imaging calibration samples of known moisture content. Signal intensity of the images was found to be highly proportional to solids content. The moisture profiles were compared to profiles predicted by a finite difference solution of Fickian radial diffusion in a cylinder. Actual moisture profiles obtained by MRI were much flatter near the center of the cylinder, with a steeper moisture profile near the edge, compared to the typical parabolic shape of the Fickian model. The Fickian model was found to be an inaccurate predictor of the interior moisture profile of the model food gel, since effective diffusivity was found to not be solely a function of moisture content. The moisture profiles obtained provide for a method to evaluate other mass transfer models, and the methods outlined provide a technique to explore mass transfer within actual food materials during processing.

ISSN:0737-3937    

DOI:10.1080/07373939208916440

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0737-3937    

DOI:10.1080/07373939208916439

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A feedforward-feedback control of a cross-flow dryer is developed based on a simple mass balance on the dryer. The feedforward action is based on a pseudo inlet moisture and adjusts the grain flow to correct for inlet moisture variations. The feedback loop accounts for possible process changes and model inaccuracies. Simulations of a rice dryer show good control of the outlet moisture for variations in the inlet moisture with or without simultaneous disturbances in air flowrate. Effect of the'feedforward algorithm on feedback control is also investigated and the suggested combination of feedforward and feedback controls is tested for variations in the inlet moisture when its measurements are biased.

ISSN:0737-3937    

DOI:10.1080/07373939208916441

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper describes the results of theoretical and experimental studies on the effect of air flow on particle transport through cascading rotary dryers. Two possible models are formulated. In the first, the drag coefficient between the air and the solids is calculated on the assumption that the particles can be regarded as isolated spheres. This approach has been employed widely in the literature to estimate particle residence times in rotary dryers. The results yielded coefficients which were 1–2 orders of magntiude greater than those measured experimentally; this demonstrates the inadequacy of this approach. In the second model, the curtains are treated as flat. two-sided plates and the drag coefficient calculated accordingly. The predictions of this model are in much closer accord with the

ISSN:0737-3937    

DOI:10.1080/07373939208916442

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Extended thin film evaporation with external diffusion resistance is analyzed for the constant rate period of the drying process, in which a polar liquid evaporates from porous bodies made of glass. The extended thin film is defined as the Liquid film in which the disjoining pressure dominates the fluid flar field and works as the driving force replenishing the evaporating Liquid. The results of the analysis shows that due to the existence of the evaporating thin Liquid film, the evaporation fran the extended thin film can compensate the reduction of evaporation rate caused by the increase of the dry spots and keep the drying rate the same as or even greater than that of the completely wetted surface. The external diffusion resistance makes the vapor concentration near the porous solid surface remain constant and therefore keeps

ISSN:0737-3937    

DOI:10.1080/07373939208916443

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

lntermittent heating in a thermal drying is one way to improve energy utilization and to enhance the quality for some products. Using the finite element method and Luikov's theory. the temperature, moisture and stress distributions at different instances of intermittent drying were obtained. Several examples were analyzed using this method. The numerical results are compared with prior experimental and theoretical results. This numerical simulation method could be used to devise an intermittent drying process schedule optimal operation.

ISSN:0737-3937    

DOI:10.1080/07373939208916444

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A drier project necessitates the efficient formulation of the behaviour of product samples. When the temperature gap is great, the drying rate must make explicit the influence of the thnc air parameters : temperature, moisture, velocity. The case of the grape demonsnates that the adimensional expression formulated by Van Meel and Keey. must be completed in order to be adjusted to experiments.

ISSN:0737-3937    

DOI:10.1080/07373939208916445

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Alfalfa juice was extracted from plants during the graving phases of the first and second crops. The alfalfa juice was dried and solute concentrations were measured periodically during the process using freezing point depression (FPD) as an indicator. Solute/solvent weight ratios were calculated from the freezing point depression of fresh unconcentrated 'uice extracted from both firsc and second crops. At the time of harvest, tie FPD was a function of this ratio. The first and second crops behaved distinctively different during the drying process, with the second having a larger soluce concentration and a greater FPD at a given moisture content. The appearance of preci itate during the drying process and the general1 large FPD makes this materiay a questionable product for drying vitg low temperature processes.

ISSN:0737-3937    

DOI:10.1080/07373939208916446

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The local clinoptilolite from Bigadis region in Turkiye, was used for air drying in packed column. The effective diffusion coefficient of water in natural zeolite was found as 5×10−10m2s−1from isothermal uptake measurements. Effects of packing height and airvelocity on breakthrough curves were studied.

ISSN:0737-3937    

DOI:10.1080/07373939208916447

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

An experimental dehydration system comprising two dehydration units, and in which control and data acquisition functions were computerized, was developed. Product mass is continuously monitored using a built-in weighbridge which facilitates drying rate studies. Product temperatures are also monitored on a continuous basis. Control of wet bulb temperature is achieved by varying the rate of recirculation of air, in conjunction with humidification. Dehydration under isothermal conditions as well as programmed temperature control is supported. In the latter mode temperature programming is performed according to change in mass to simulate the typical air temperature profiles encountered in commercial dehydration tunnels during parallel- and counter- flow operations.

ISSN:0737-3937    

DOI:10.1080/07373939208916448

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor