摘要:

This paper presents the derivation of a model to predict heat and mass transfer in a system consisting of a turbulently flowing fluid overlying a saturated hygroscopic porous medium. Comparisons with experimental and numerical simulations have been carried out to check the accuracy of components of the model. Finally, a case study using silica gel as a representative hygroscopic porous medium is presented as an application of the model. It is shown that moisture is convected from the warm interior of a bulk of porous medium to the relatively cool periphery. This result has profound practical implications when the hygroscopic medium is stored agricultural produce as the region of high moisture content may become moldy.

ISSN:0737-3937    

DOI:10.1080/07373930008917837

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

This paper deals with the simulation of VOCs concentration dispersion, evaporated from flooring materials, with the purpose of understanding VOCs evaporation and dispersion mechanisms. A test chamber is examined whose flooring material emits a number of VOCs. Given the area specific ventilation rate and considering it as boundary conditions, experimental data for the examined compounds concentration, the dispersion of the VOCs concentrations is examined under steady state and transient conditions. The model developed is used in conjunction with a general - purpose CFD code, PHOENFCS, that can provide detailed information on the flow as well as concentration fields. The results of the above two simulation cases are used as a guide for two other cases, where faster restoration of the air indoor quality was investigated by changing the ventilation rate in the chamber. The simulation results were used as a basis for further analysis for VOC evaporation for other flooring materials; this will allow proper material selection as well as proper ventilation system for a more healthy and comfortable environment in a building.

ISSN:0737-3937    

DOI:10.1080/07373930008917838

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In the present study the sublimation of large solid carbon dioxide particles inside fluidized beds of fine particles is investigated. A model which takes the surface area of the sublimable particles into account is used to describe the sublimation kinetics. Based on this model, the results of different experiments, namely single particle experiments using a precision scale, batch experiments in a laboratory-scale fluidized bed and continuous experiments in a larger circulating fluidized bed are compared. The main focus of the study is to evaluate the influences of the particle size, of the inert bed material, of the bed temperature and of the superficial gas velocity, respectively.

ISSN:0737-3937    

DOI:10.1080/07373930008917839

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Fine and homogeneous powders of Y-Ba-Cu complex oxides are necessary to improve the quality of YBCO bulk high temperature superconductors. The powders which contain BaCO3must be sintered for producing YBCO super-conductors at temperature above 850 °C. Therefore, complex oxide is desired. In order to prepare fine complex oxides powders, suspension was synthesized by simultaneous hydrolization of 2-propanol solution of metal isopropoxides. However, the suspension was not dried by a hot air drying method, because aggregation occurs due to cohesion of particle along with evaporation. Also, the suspension could not be freeze-dried, because the freezing point of 2-propanol is −88.5°C. So, supercritical fluid drying method using supercritical carbon dioxide was applied. The results from these experiments suggest that this method is useful for drying of the suspension prepared by the alkoxide route.

ISSN:0737-3937    

DOI:10.1080/07373930008917840

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Dehydration by Successive Pressure Drops (DDS) is a new unit operation, based on a repetition of compression/decompression cycles. In this work, we present the application of this drying process to baker's yeast. Drying rate, cycle efficiency, cell survival and the activities of four enzymes were evaluated. The effects of two parameters of DDS (PI and Dvp) on drying kinetics and product quality were studied, using the surface responses methodology. The results were also compared to those obtained with freeze-drying. PI had a positive effect on drying rate. Both PI and Dvp had an effect on cycle efficiency, particularly Dvp. Cell survival were much higher than that obtained with freeze-drying, with no significant impact of the parameters. The enzymatic activities were higher or close to the corresponding activities of freeze-dried sample, except the glucose-6-phosphate activity. The effects of PI and Dvp varied according to the enzyme.

ISSN:0737-3937    

DOI:10.1080/07373930008917841

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Using Luikov's heat and mass transfer equations and a finite element formulation, the drying process of an anisotropic biological product (sweet potato) was investigated. The model was used to determine the coefficients of heat and mass transfer, the mass diffusivity normal and parallel to the fibers of sweet potato samples. These parameters were estimated by minimizing the deviation of experimental data and numerical predictions.

ISSN:0737-3937    

DOI:10.1080/07373930008917842

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

It is common knowledge that sample size and drying temperature are two of the most important factors affecting the drying rate and quality of food. However, what is less commonly known are how these two factors interact relative to each other and their effects on the drying behaviour of potato. These effects were evaluated under controlled drying conditions using a thermogravimetric analyser. The least-squares method was used to fit a model to the experimental data and the response variables (slope of the first drying stage, transition moisture content and slope of the second drying stage) were determined systematically. Central composite design was applied for response surface modelling of the factors and regression methodology was used to analyse the results. The results showed that both temperature and sample dimension have significant (P=0.01) effect on drying behaviour of potato. Sample dimension significantly affected the transition moisture content, whilst both temperature and sample dimension significantly affected the slopes of the first and second stage of drying.

ISSN:0737-3937    

DOI:10.1080/07373930008917843

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

An experimental radial-flow, circular bin dryer with a dehumidifier was fabricated and tested for rough rice drying. Results showed that high-moisture paddy could be dried to 14% moisture content (wet basis) over a 24 h drying span at an average drying rate of 0.5%/h. The open-cycle system's specific moisture extraction rate and the dehumidifier's coefficient of performance were within the usual range of values cited for similar conventional systems or equipment. The quality of the dehumidifier-dried and naturally dried paddy was similar with respect to minimum grain Assuring, The system was found to be a technically feasible, more energy-efficient and safer alternative to electrical resistance heating in the conditioning of ambient air for drying under humid tropical conditions.

ISSN:0737-3937    

DOI:10.1080/07373930008917844

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

In a previous study, a unified approach to the calculation of the size and energy consumption of well-mixed fluidized bed dryers was developed. A computer code was written and a parametric study undertaken to determine the effects of the principal operating variables. The results were shown to depend on the form of the drying kinetics. The present paper describes the formulation of an analytical model of a well-mixed fluidized bed dryer, which applies for materials that exhibit linear falling-rate drying. These materials are typified by small hygroscopic particles, which are frequently dried in such equipment. Equations are presented that enable the drying time, specific energy consumption, heater duty and bed area to be calculated. The predictions of these equations agreed well with previously published experimental findings and with the results of computer simulations for a typical solid (ion exchange resin) exhibiting the required drying characteristics.

ISSN:0737-3937    

DOI:10.1080/07373930008917845

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A batch-indirect rotary drier heated with steam was experimentally operated to obtain data of moisture content and temperature versus time for soy meal and fish meal. Operation conditions were as follow: steam pressure (1 to 4 bar), rotation speed (3.7 to 11.6 r.p.m.) and rate of vapor extraction (0.059 to 0.256 m/s).

ISSN:0737-3937    

DOI:10.1080/07373930008917846

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor