摘要:

High temperature drying of softwood is used because it provides much faster drying rate than is possible at lower temperatures. However, the occurrence of some drying defects limits its use where the quality is critical. In order to understand the drying phenomena and to describe the drying processes, numcrous mathematical models have been developed in the past two decades.The diffusion model is the earliest attempt to describe wood drying processes and is relatively simple in form, so it is often used for stress analysis. However.further substantial work is still required before it is possible to apply the stress model to kiln control.Recently. transpon-based mathematical models have been receiving attention in modelling studies. This review discusses one of these models, a physiological-transport-based model, which has been further applied to the drying of mixed sap/heartwood boards and the drying of a kiln-wide stack. The mixed boards with a thin heanwood layer parallel to the flat surface are considered to have added difficulty in drying. In the analysis of the timber stack drying, a kiln-wide model is proposed in which the above physiological-transpon-based model is used to generate the characteristic drying curves. Airflow reversal is essential in kiln

ISSN:0737-3937    

DOI:10.1080/07373939508917045

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Vacuum drying, j,e drying under absolute gas pressure of about 10⊃ Pa. is an efficient means of reducing the process period and of producing good quality wood. We will examine here continuous vacuum drying where the plank surfaces are kept at a constant temperature, which remains above the boiling point, and moisture flowing to the surface is extracted from the kiln.

ISSN:0737-3937    

DOI:10.1080/07373939508917046

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Drying experiments with single, porous spheres wetted with mixtures of 2- propanol and water were performed using superheated steam, air, or steam-air mixtures as drying agent. Both the drying rate and the moisture composition were determined experimentally for different temperatures and compositions of the drying agent and for different initial compositions of the moisture.It is shown that evaporation of 2-propanol is enhanced by using superheated steam as drying agent instead of air due to steam condensing on the sample. While the overall drying rate increases with rising steam temperature, the evaporation rate of 2-propanol is hardly affected. When drying samples containing mixtures of 2- propanol and water, internal boiling can occur depending on the vapor–liquid equilibrium. Vapor generated inside the sample may cause mechanical dewatering of the sample which greatly increases the drying rate.

ISSN:0737-3937    

DOI:10.1080/07373939508917047

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Layer crystallization in laminar falling films has been studied for freeze concentration applications. A binary mixture of water and sucrose has been tested in order to compare with literature results from suspension crystallizers. The concentration of sucrose in ice, which is a measure for loss of solute. were from 0.4 to 26.5% for bulk concenwlions of sucrose of 5 to 40%. respectively. The time averaged ice growth rates varied from 3. l0-7 l0 3-10-6 m/s. The results are related to expressions for maximum ice growth rate developed from the gradient criteria. Also an expression for maximum ice growth rate from irreversible thermodvnamics is oresented. Althoueh the exwrimental results show that one–step layercrystallization has amuch lower separation effect than suspension crystallizers with washcolumns, multistep layer crystallization could provide an economical favourable freeze concentration process. A multistep process that combines freeze concentration and reverse osmosis is proposed. A case study shows that it is possibleto reduce the investment costs to less than half of existing processes, for dewatering capacity of 700kg per hour. The energy consumption is also reduced.

ISSN:0737-3937    

DOI:10.1080/07373939508917048

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An experimental study has been carried out on the characteristics of binary adsorption isotherms of water and volatile flavor for typical materials used in a box of a tobacco product or cigarettes. Ethyl acetate chosen as a model for water–soluble volatile flavor. Binary adsorption isotherms for the tobacco, papers, filters, and activated carbons were measured with a flow–type multi–component adsorption system under the canstant conditions of temperature a t 303 K and vapor pressure of water a t 2.5 kPain the vapor pressure range of ethyl acetate from 0 to 4.2 kPa. A linear equation was applied to express the binary adsorption isotherms for the tobacco, papers and filters, while a Dubinin–Astakhov equation was applied for the activated carbons. The binary adsorption was characterized into three groups, depending on the selectivity as well as the mechanism of adsorption; i.e.(l) for tobacco and papers, water was adsorbed much greater rather than ethyl acetate, (2) for filters, ethyl acetate was adsorbed on the surface as great as water, (3) for activated carbons, ethyl acetate was adsorbed much greater onto their micropores rather than water. The results showed that ethyl

ISSN:0737-3937    

DOI:10.1080/07373939508917049

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A fluid bed dryer simulator was developed under Excel 5 wlth Visual Basic for Applications environment The simulator iS based on a mathematical model describing heat and mass transfer in the dryer. The total model incorporates empirical models for the Drying Constant and the Residence Time. These empirical models are crucial in the total model efficiency. Thus a procedure for updating the parameters of the empirical models is provided. This procedure constitutes the ‘learnhg’ property of the simulator. Two databases are Supplied. The first contains laboratory drying data and it is used for tuning the Drying Constant empirical model. The second contains industrial drying data from the real operation of the dryer, and it is used for tuning the Residence Time empirical model. The experience from the industrial application of the simulator proved that the simulator is a powerful tool for flexible operation of an industrial dryer. This paper is presents the total mathematical model of the dryer, the learning concept, and the databases, including useful information concerning the drying kinetics of bentonite. A simulator outline is presented and typical capabilities and uses are briefly described. A case study for flexible operation of an industrial dryer is discussed.

ISSN:0737-3937    

DOI:10.1080/07373939508917050

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We are interested in the simulation of heat and mass transfer processes accompanying the drying of a deformable agricultural product. We have used an implicit method with classical finite differences to resolve the set of equations. The identification of the diffusion coefficient within a thin carrot layer is carried by trial and error on two analytical forms. These two forms take into account moisture content, temperature and shrinkage of the product.

ISSN:0737-3937    

DOI:10.1080/07373939508917051

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An analysis of convective drying of natural rubber in granule form. Exploitation of the mathematical model developed from analysis of internal transfers requires determination of the ‘drying rate’ and the ‘energy exchange coefficient’ between the material and the drying air. This was performed using a portable laboratory drier at the production site, avoiding the problem of changes in the material during transport. Analysis of the drying kinetics of material in thin layers led to modelling the drying rate at the temperatures, rates and relative humidity values encountered in industrial driers. The energy exchange coefficient was found by measurement of air and granule temperatures. Thick layer trials showed the suitability of the model for simulation of changes in moisture content and temperature of air and granules in a granular environment. The study as a whole led to the development of a computer program for simulating a zone drier. This software can be used to optimise the management of an industrial natural rubber drying installation.

ISSN:0737-3937    

DOI:10.1080/07373939508917052

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

he performance of a laboratory scale jet spouted bed (JSB) for drying rice flour slurry was studied. The bed consisted of ceramic balls (5028 mm diameter) and the rice flour slurry was sprayed onto the moving particle surface near the inlet part. All the experiments were carried out at the jet spouting regime. This regime has high bed void fraction and violent movement and collision of bed particles. As a result, the dried product layer is attrited from particle surface as a fine powder and entrained from the bed by the spouting air. The experimental result were presented to show the effects of static bed height, inlet air flow rate and temperature, and feed concentration and flow rate on the outlet air temperature, thernal efficiency, and mean particle size and moisture content of the product. Asimple mathematical model, which is based on the conservation of mass and energy equations, was developed. Predicted results agreed well with those obtained from the experiment.

ISSN:0737-3937    

DOI:10.1080/07373939508917053

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Solvent sorption and drying performance of engineering polymeric blends of ethylene–propylene random copolymer and isotactic polypropylene in the presence of aromatic liquid: has been studied in the temperature interval 25–70°C. The drying of the polymer is studied from the desorption and redesorption experiments. The present results indicate that the rate of solvent migration and the drying phenomenon is controlled by internal mass transfer of solvent molecules within the polymer matrix. A technique is developed to study the sorption (S) –desorption (D) – resorption (RS)–redesorption (RD) i.e., S–D–RS–RD of the polymer sheets. The S–D–RS–RD experiments are a convenient measure of knowing the continuous weight loss of the polymer during long–term solvent exposure.

ISSN:0737-3937    

DOI:10.1080/07373939508917054

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor