摘要:

Fish crackers are semi-prepared starch-based products which must be expanded just prior to consumption. This work aims at the experimental and theoretical study of the thin-layer drying process of fish crackers in a thin disc geometry. The process was carried out in an insulated cabinet dryer and the experimental kinetic drying data were fitted using the analytical solutions resulting from both a drying model governed by the Fick' s second law and a model based on the lumped system, highlighting the adequacy of each of them. Therefore, it was possible to calculate the mass transfer coefficients for seven different blends offish crackers. Also, the effect of the drying time on the bulk density of the puffed product was evaluated for these seven blends. Both the kinetic drying parameters and the optimal bulk density responses were analyzed using the Simplex-Lattice Design over a mixture triangle within a minimal number of experiments.

ISSN:0737-3937    

DOI:10.1080/07373930008917690

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A numerical solution of the diffusion equation to describe solute transport inside ellipsoids, assuming a constant difiusion coefficient and a corrective boundary condition, is presented. The difiusion equation in a prolate spheroidal coordinate system was used for a hidimensional case. The finite volume method was employed to discretize the basic equation, utilizing a uniform grid size. The equation was solved irteratively using the Gauss-Seidel method. The effect of Biot number and the aspect ratio of the body on diffusion rate and concentration during the process is presented. Plots are presented for Biot numbers from 0.05 to infinity and aspect ratios of 1.1, 2.0 and 5.0. To investigate the effect of the aspect ratio, different results changing the aspect ratio for Bi= 1.0 are shown. The results show that the model is consistent and it may be used to solve other cases such as those that include cylinder and sphere geometry, and/ or those with variable diffusion coefficients with small modifications.

ISSN:0737-3937    

DOI:10.1080/07373930008917691

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This work presents a methodology far obtaining heat and mass transfer coefficients for problems involving natural convection along a flat plate. In order to simulate drying conditions, a set of data has been obtained for the temperature range between 20 and 98° C and for various absolute humidities, both of the wall and ambient. It is shown that for drying at temperatures above 80° C, Nusselt and Sherwood numbers change very appreciably with respect to values obtained at smaller temperatures. The simulated results show that even for very low temperature differences, the transient period in natural convection along a flal vertical plate is smaller than 3s.

ISSN:0737-3937    

DOI:10.1080/07373930008917692

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In this work a phenomenological mathematical model that describes the continuous drying process is presented. Heat and mass transfer in gas phase, solid phase and gas-solid interface were taking in account in the model. In addition, the equilibrium and interfaces conditions were evaluated using the product sorption isotherm. Model structure is a system of four couple differential equations in conjunction with five algebraicequations. The results shown that this structure is robust with respect to heat or mass transfer controlled mechanisms. Behaviors predicted were similar with other simulators results and with the behavior reported by chemical engineering texts. The proposed mathematical model is able to use in continuous drying operation design involving heat and mass transfer properties and equilibrium relationships.

ISSN:0737-3937    

DOI:10.1080/07373930008917693

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper describes the use of a computational fluid dynamics code (Star-CD)in the food industry. We assessed the capability of CFD to predict airflow patterns in a modern sausage dryer by comparing numerical results with experimental air velocity data. Qualitative and quantitative comparisons showed that simulated values agreed closely with measurements although some discrepancies appeared for specific flow conditions. Using CFD, it was established that these differences couid be attributed to slow time-variations in the blower airflow rate. These comparisons also revealed errors in measurement.

ISSN:0737-3937    

DOI:10.1080/07373930008917694

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An overall system model for a countercurrent rotary dryer has been developed with the ullimale aim of assessing controller pairings in these dryers. This model is based on heat and mass balances within dryer regions combined with two subsidiary models, one describing the equipment (which determines particle transport and heat transfer)and the other describing the behaviour of the material (the drying kinetics). Six partial differential equations have been set up to evaluate six state variables: solids moisture content, solids temperature, gas humidity, gas temperature, solids holdup and gas holdup as functions of time and rotary dryer length. A control-volume method has been used to reduce the six partial differential equations with respect to time and the length of the rotary dryer to six ordinary differential equations in time.

ISSN:0737-3937    

DOI:10.1080/07373930008917695

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The selection of dryers is an art in which knowledge, experience and science all play important roles. Historically, dryer selection has been made by experts on the basis of their extensive knowledge. However, in recent years, computer-based techniques have been developed, which have the potential of at least partially deskilling this process. Of the various possibilities, fuzzy expert systems, in which the selection qualifiers are represented as linguistic rather than numerical variables, are the most promising. This paper describes the development of a fuzzy system for the selection of batch dryers for food products. It featured a novel modular approach in which independent selection goals for dryer type, atmospheric, vacuum or freeze operation, and single or multiple units were adopted. This made the system particularly flexible and amenable to adaptation. The program starts from a ‘ drying process checklist“ in which the principal process variables are specified, and provides a ranked list of feasible alternative dryers. The algorithm was extensively tested and provided quite plausible results. Four representative case studies are presented and discussed.

ISSN:0737-3937    

DOI:10.1080/07373930008917696

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Design of fluidized bed dryers constitutes a mathematical programming problem involving the evaluation of appropriate structural and operational process variables so that total annual plant cost involved is optimized. The increasing need for dehydrated products of the highest quality, imposes the development of new criteria that, together with cost, determine the design rules for drying processes. Quality of dehydrated products is a complex resultant of properties characterizing the final products, where the most important one is color. Color is determined as a three-parameter resultant, whose values for products undergone drying should deviate from the corresponding ones of natural products, as little as possible. In this case, product quality dryer design is a complex multi-objective optimization problem, involving the color deviation vector as an objective function and as constraints the ones deriving from the process mathematical model. The mathematical model of the dryer was developed and the fundamental color deterioration laws were determined for the drying process. Non-preference multi-criteria optimization methods were used and the Pareto-optimal set of efficient solutions was evaluated. An example covering the drying of sliced potato was included to demonstrate the performance of the design procedure, as well as the effectiveness of the proposed approach.

ISSN:0737-3937    

DOI:10.1080/07373930008917697

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Fuzzy logic provides a means for converting a linguistic control strategy, based on expert knowledge, into an automatic control strategy. Its performance depends on membership function and rule sets. In the traditional Fuzzy Logic Control (FLC) approach, the optimal membership is formed by trial-and-error method. In this paper, Genetic Algorithm (GA) is applied to generate the optimal membership function of FLC. The membership function thus obtained is utilized in the design of the Hybrid Intelligent Control (HIC) scheme. The investigation is carried out for an Air Heat System ( AHS) an important component of drying process. The knowledge of the optimum PID controller designed, is used to develop the traditional FLC scheme. The computational difficulties in finding optimal memebership function of traditional FLC is allieviated using GA in the design of HIC scheme. The qualitative performance indicies are evaluated for the three control strategies, namely, PID, FLC and HIC. The comparison reveals that the HIC schene designed based on the hybridisation of FLC with GA performs better. Moreover, GA is found to be an effective tool for designing the FLC, eliminating the human interface required to generate the membership functions.

ISSN:0737-3937    

DOI:10.1080/07373930008917698

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A model of a well-mixed fluidized-bed dryer within a process flowsheeiing package (SPEEDUP(tm)) has been developed and applied to a parameter sensitivity study, a steady-state controllability analysis and an optimization study. This approach is more general and would be more easily applied to a complex flowsheet than one which relied on stand-alone dryer modelling packages. The simulation has shown that industrial data may be fitted to the mode outputs with sensible values of unknown parameters. For this case study, the parameter sensitivity study has found that the heat loss from the dryer and the critical moisture content of the material have the greatest impact on the dryer operation at the current operating point. An optimization study has demonstrated the dominant effect of the heat loss from the dryer on the current operating cost and the current operating conditions, and substantial cost savings (around 50% ) could be achieved with a well-insulated and airtight dryer, for the specific case studied here.

ISSN:0737-3937    

DOI:10.1080/07373930008917699

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor