摘要:

Models to describe drying pmesses are necessary for engineering design and optimization. Many resenrch studies in the past century have had the objective of developing mathematical models to describe drying processes in porous solids. This review identifies key characteristics of drying models including controlling process resistances, internal mechanisms of moisture movement, and methods of model cufficient determination, model solution, and model validation. Similarities and differences between previous work are noted, and strategies for future drying model development are discussed.

ISSN:0737-3937    

DOI:10.1080/07373939308916801

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In porous materials with pores containing both a gas and a liquid phase each a mixture of several components mass transfer by diffusion may occur simultaneously in both phases. An effective diffusivity is required in order to describe these effects when a homogeneous model is used. Unsteady-state diffusion experiments were performed such that a bed of glass beads partially saturated with glycerol was either loaded by passing wet air or dried by removing water or 2-propanol initially mixed to the glycerol. The effective diffusivity was obtained by applying the equation of unsteady-state diffusion to the observed change of mass. Superposition of the limiting cases of single-phase vapor and liquid diffusion in partially saturated systems yields a simple equation that describes the effective diffusivity as a function of pore saturation and correlates well with the measured values.

ISSN:0737-3937    

DOI:10.1080/07373939308916802

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Drying of corn was studied at high and low humidity condiitions. Drying rate was measured, and test weight (bulk density), solid density, stress cracks, and breakage susceptibility of the dried grain at 15% (w.b.) were measured. Twenty four 350-g samples were dried under eight drying conditions in the 71° –104°C temperature range and 0.8%–80% RH relative humidity range. Each sample was exposed to the drying wnditions by using a semi-closed air flow cycle through a thin-layer of grain. High humidity drying reduced the drying rate by up to 44% and did not increase bulk density or solid density significantly as wmpared with low humidity drying. However, high humidity drying did reduce the multiple stress cracks in the corn kernels by up to 33.0 percentage points, increased the number of kernels with no stress cracks by up to 28.7 percentage points, and reduced Wisconsin and Stein breakage susceptibilities by up to 8.9 and 13.5 percentage poinu, respectively.

ISSN:0737-3937    

DOI:10.1080/07373939308916803

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A finite element method (FEM) with axial symmetry conditions and isoparametric elements has been applied to describe the freeze drying of a certain pharmaceutical contained in vials in industrial like conditions. Several operating strategies vere proved on the basis of considering three different stages during freeze-drying in relation with the modification of heating and product temperature evolutions. The model offers interesting perspectives to find the most adequate combination of operating conditions in order to reduce drying time.

ISSN:0737-3937    

DOI:10.1080/07373939308916804

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Absorption of hydrogen sulfide gas in ammoniacal solution of zinc chloride is accompanied with an instantaneous chemical reaction forming zinc sulfide precipitates. Such reactions are moat suited for operation of spray drying with reaction. A mathematical model for the system which incorporates chemical reaction, heat, mass and momentum transfer has been proposed. It is assumed that the gases and the spray droplets move in co-current plug flow mode end spray is considered monodiaperse for sake of simplicity. The differential equations derived for the modal have been solved as an initial value problem uslng the Runge-Kutta method. The variations of temperature, humidity, droplet diame-ter. moisture content and concentrations of reactants are pra-dieted along the length of the column and compared with exprimental data.

ISSN:0737-3937    

DOI:10.1080/07373939308916805

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Dynamic heat and material balances were developed, and residence time, heat and mass transfer rates were calculated using literature correlations. The model equations were solved numerically using the Speedup simulation package and tested against industrial data.

ISSN:0737-3937    

DOI:10.1080/07373939308916806

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

This work present. a detailed study of heat and mass transport phenomena between a large sublimable object and a gas-solid fluidized bed of either inert or adsorbent fine panicles. Heat (h) and mass (k)transfer coefficients are related to the size and adsorption capacity of the fine particles, as well as to the diameter of the spherical immersed object and to the bed temperature. Convective and conductive components are also identified, and correlations are proposed to predict all of them. The significant differences which appear for the various working conditions may be accounted for considering the particular mechanisms that prevail in every case. A simple "surface renewal" model clearly shows the leading role of the object surface temperature. For adsorbent panicles, a local overheating phenomenon at the exchange surface is demonstrated.

ISSN:0737-3937    

DOI:10.1080/07373939308916807

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Eighteen drying experiments on malting barley variety Jarek with initial moisture content ranging from 8to 29 % (w.b.) and exposure time from 0.5 to 5.0 hours were carried out. Drying chamber was not equipped with a fan. so the barley drying was slow. Temperature in the chamber was set up 40, 50, 60 or 70deg;C.In each experiment 11 samples were prepared: one sample for control germination was not treated and ten samples were removing from the chamber at regular time intervals of 0,5 h. Both air temperature in the chamber and grain temperature were measured during the treatment. After treatment each sample was tested on moisture content and after 3 months on germination. The relation between standard deviation of normally distributed death rate and moisture content and grain temperature was determined. Critical temperature for viability reduction of 1 % and 3 % was correlated with logarithm of moisture content and logarithm of exposure time.

ISSN:0737-3937    

DOI:10.1080/07373939308916808

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

It is shown that in small laboratory rotary dryers and coolers particles fall discontinuously from flights in the regime where a relatively small number of particles fall from flights and that particles fall continuously from flights forming multiple cascading layers in the regime of a relatively large number of falling particles. The correction factor for the gas-to-particle heat transfer coefficient estimated by the Ranz-Marshall equation is about 1 in the former case and takes on values lower than 1 in the latter

ISSN:0737-3937    

DOI:10.1080/07373939308916809

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Rotary-stream fluidized bed drying is the combination of fluidized bed drying and pneumatic drying. Both non-viscous and viscous materials and even sticky paste can be dried successfully with this technique. The material being processed is turned to powder or granular product of controlled homogeneous in one treatment and no further pulverization is necessary. Correlation of Eu vs Re and Nu vs Re were obtained from hydrodynamic experiment and drying experiment respectively.

ISSN:0737-3937    

DOI:10.1080/07373939308916810

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor