摘要:

A complete simulation model has been developed for an industrial rotary dryer to account for the heat and mass exchange between the solids and the gas. This simulator is mainly composed of three models: solids transportation model, furnace model, and gas model. The solids transportation model is the modified Cholette-Cloutier model It consists of a series of interactive reservoirs which are subdivided into an active and a dead compartments to account for the characteristic extended tail of the residence time distribution (RTD) curves observed in industrial dryers.

ISSN:0737-3937    

DOI:10.1080/07373930008917741

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The solid particle movement in a rotary drum plays an important role in drying processes. The solid distribution in the drum affects the amount of contact surface between the solid and the gas. The retention time of solids influences the time particles can stay in contact with the gas in order to transfer heat and mass. Any heat and mass transfer model for a solid particle dryer must be able to predict solid flowrate and solid hold-up. There have been several reports in the literature regarding the modelling aspects of solid transport in dryers. If the model is developed for model-based control, it must be simple and yet represent dynamics of the system accurately. This paper addresses solid motion modelling and the effects of different variables involved in solid transport phenomena. Sugar drying process is the case study in this work. A steady state semi-empirical model was modified to predict solid hold-up and flowrate in rotary dryers. This model was incorporated into a heat and mass transfer model ;o predict solid moisture and temperature for inferential and model-based control purposes. Results of several experiments that have been used to investigate dynamics of the system in terms of solid motion and to validate the model are also presented. The approach advocated in this paper is directly applicable to the transport of other solids in rotary drum equipment and can thus be regarded as a generalized model.

ISSN:0737-3937    

DOI:10.1080/07373930008917742

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Thermal stress and hydro stress within a single com kernel during drying are analysed with the mechanics of elasticity and material. The mathematical model of the stress within a single com kernel during drying is given. A finite element method is developed in details to simulate the maximum principal stress and shear stress within a single com at 75°C and 50°C drying air temperatures. The locations of the predicted maximum stresses are described and stress fields at different drying time are obtained. The result shows that the predicted locations of the maximum stresses agree with published materials on stress-crack or burst of com kernels.

ISSN:0737-3937    

DOI:10.1080/07373930008917743

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Pieces of banana, guava and potato were dried in a two-stage heat pump dryer capable of precise control of air humidity with predetermined cyclic variations of air temperature entering the drying chamber. The air temperature variations tested were : a cosine, a reversed cosine and three different square wave profiles with peak-to-valley variations from 20°C to 40°C. The cycle time was about 60 minutes with drying time of approximately 300 minutes. The drying samples were placed on trays in a thin layer. With appropriate choice of temperature-time variation, it is possible to reduce the overall color change while maintaining high drying rates.

ISSN:0737-3937    

DOI:10.1080/07373930008917744

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Color and sorption characteristics of osmotically treated and air dried apple and banana were studied during air drying at 70°C. The color parameters: Lightness (L), Redness (a) and Yellowness (b) were studied, using a Hunter Lab chromatometer. A first order kinetic model was fitted to the experimental data adequately for color parameters, while sorption data for treated and air dried products were fitted to the GAB model. Untreated fruits showed an extensive browning which was monitored by a significant drop of the lightness (L) and an increase of redness (a) and yellowness (b). Osmotically pretreated samples did not brown as much as the untreated samples and the lightness L decreased only slightly while a, b increased slightly. Osmotic pretreatment resulted in a shift in sorption isotherm for both fruits. Osmotic dehydration prevented color damages and decreased the sorption capacity of dehydrated products.

ISSN:0737-3937    

DOI:10.1080/07373930008917745

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The rheological behavior of osmotically dehydrated apple and banana was examined under uniaxial compression and relaxation tests of cylindrical specimens. Compression and relaxation tests were performed, following air drying of osmotically pre-treated samples, at various moisture contents ranging from 0.1 to 1.5 kg/kg dry basis. The maximum stress and the corresponding strain were correlated to the moisture content using simple mathematical equations. It was shown that both parameters increase as water was removed and their values are significantly higher than the corresponding values for untreated air dried samples. The effect of moisture content on compressive behavior of osmotically dried materials was introduced through its effect on the four model parameters: the maximum stress (σmax) the maximum strain (ϵmax), the elastic parameter (E) and the viscoelastic exponent (p). The stress relaxation data of osmotically treated samples were modeled using a two-term Maxwell model. It was shown that osmotic pre-treatment increased the remaining force and it decreased the relaxation time of dehydrated samples. The osmotic dehydration and therefore the sugar gain tend to increase the viscous nature of fruits and decrease their elasticity for both materials, causing plasticity of the structure.

ISSN:0737-3937    

DOI:10.1080/07373930008917746

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Spray drying of jameed - a dried fermented dairy product, is investigated. The study covers the effects of the operating variables upon the physical and chemical characteristics of the dried product. The investigated variables were: feed total solids, feed flow rate, inlet air temperature, air flow rate and atomizer pressure. The product characteristics measured were: total solids, bulk density, average particle size, wettability, dipersibility, color, ash content, salt content, fat content and pH. Best overall results were obtained for a feed total solids of 17%, feed flow rate of 36.5 ml/min, inlet air temperature of 100 /C, air flow rate of 632 cm3/s, and atomizer pressure of 1.5 bar.

ISSN:0737-3937    

DOI:10.1080/07373930008917747

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The moisture sorption isotherms of dried vegetable wastes (based on green leaves and fruits) from wholesale market were determined at 25, 40, 60 and 90°C by the static gravimetric method. Experimental data were fit by using several mathematical models. The G.A.B. and the Halsey model gave the minimum mean square error. G.A.B. parameters were related with temperature by Arrhenius expressions.

ISSN:0737-3937    

DOI:10.1080/07373930008917748

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The thin-layer drying behaviour of vegetable wastes (as a mix of lettuce and cauliflower leaves) from wholesale market for a temperature range of 50-150°C was determined. Drying of this material was found to take part only in the falling-rate period. The experimental data were fitted to the simple exponential model and the Page model. Both models have good prediction capability, Effective diffusion coefficient varied from 6.03*10-9to 3.15*10-8m3/s with an activation energy of diffusion of 19.82 kJ/mol. The temperature dependence of the effective diffusion coefficient was expressed by an Arrhenius-type relationship.

ISSN:0737-3937    

DOI:10.1080/07373930008917749

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Fourier's second law was solved using convective boundary conditions without considering the shrinkage of the solid. The solutions for a finite and an infinite slab were compared to determine the dimensions for a slab to be considered as infinite. The solutions obtained for Bi = 0.1 and Bi = 100 correspond to heat and mass transfer-controlled processes, respectively, during drying. The results show that the finite slab cannot be considered as infinite, even for R2/R1> 20. The relative error obtained when the finite slab was assumed to be infinite was not significant for small Fourier numbers, but it increased as the Fourier number increased; errors were also higher for higher Biot numbers. When the numerical solution of a drying model was obtained for finite and infinite slabs, significant differences in drying kinetics and temperature evolution were observed.

ISSN:0737-3937    

DOI:10.1080/07373930008917750

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor