Modeling the kinetics of drying of viscose fibre

The dependences for describing the kinetics of drying of viscose fibre in restriction of external and internal diffusion with consideration of the period of heating the material are examined. The kinetic dependences are compared with the experimental data for different viscose fibre drying modes and types (convection and microwave with exhaust of vapors). It was confirmed that microwave drying significantly enhances moisture removal. The experimental data on viscose fibre drying kinetics were generalized with a modified quasistationary method. These dependences describe the periods of constant and diminishing drying rates and the heating period with accuracy sufficient for practical calculations. It was shown how to determine the fibre moisture content in any drying zone with the proposed equations. __________ Translated from Khimicheskie Volokna, No. 6, pp. 54–57, November–December, 2006.     

A Generalized Dimensionless Model for Deep Bed Drying of Paddy

A generalized dimensionless model of paddy drying was developed from a validated partial differential equation (PDE) drying model using the dimensional analysis of Buckingham theorem. This generalized dimensionless model considered all drying parameters in an equation to predict the grain moisture content during the drying process. Statistical parameters, namely, coefficient of determination (R ²), chi-square (χ²), mean relative deviation (MRD), and root mean square error (RMSE), were used as criteria to compare the dimensionless model with a validated PDE model. Based on these calculated parameters, it was concluded that the generalized dimensionless model fitted reasonably well with data from the PDE model and good agreement was found between the generalized dimensionless model and experimental drying data.     

Intensification of thermooxidation of polyacrylonitrile fibres

It was found that in thermooxidation of PAN fibres in air by the conductive (contact) method, the density of 1.38–1.40 g/cm³, required for subsequent high-temperature treatment, is attained in 30–60 min. The chemical composition and equilibrium sorption of the PAN fibre oxidized by convective tempering do not differ significantly from the fibre fabricated in industrial conditions in convective tempering. All-Russian Scientific-Research Institute of Polymer Fibres, Mytishchi. Translated fromKhimicheskie Volokna. No. 6, pp. 22–24, November–December, 1999.     

Mechanical characteristics of nap-raised nonwoven materials

In processing the experimental data, an equation was obtained that can be used for predicting the change in the nap height of materials undergoing heat treatment and with a known bicomponent fibre content under the effect of mechanical loads. The optimum duration of heat treatment of nap-raised materials is 1–2 min and the temperature is 175°C. __________ Translated from Khimicheskie Volokna, No. 1, pp. 43–45, January–February, 2007.     

Thermophysical and Tribological Properties of Composite Materials Reinforced with Polyoxadiazole Fibres

The effect of the technology for manufacture of a composite material on the coefficient of linear thermal expansion is examined. The low- and high-temperature extrema of the dilatometric curve are found. The effect of physicochemical transformations both in the phenol—formaldehyde binder and in the Arselon reinforcing fibre is demonstrated. The important decrease in the friction coefficient of polymer composite materials with respect to steel in reinforcement with polyoxadiazole fibre in comparison to cotton fibre is demonstrated. __________ Translated from Khimicheskie Volokna, No. 3, pp. 50–53, May–June, 2005.     

Convective mass transfer in the system poly-m-phenylene isophthalamide solution—precipitator

The conditions of the appearance of convective currents in solutions of PmPIPA on contact with different precipitators were investigated. The dependence of the structure and properties of fibres, flat, and fibre membranes in fibre-film polymer binders on the development of convective currents in solutions of a polymer was demonstrated. Translated from Khimicheskie Volokna, No. 3, pp. 19–21, May–June, 1998.     

OPTIMUM OPERATING CONDITIONS IN DRYING FOODSTUFFS WITH SUPERHEATED STEAM

It is inferred from experimental data that in drying foodstuffs with superheated steam, the initial drying rate has a direct effect on the rate at which the overall drying takes place. That is, the faster the initial drying rate, the shorter the overall drying time. This criterion is very convenient because at the beginning, water moistens the sample external surface so evaporation does not depend on internal sample characteristics, but only on external convective heat and mass transfer rates. Mass and energy balance equations are solved and the result converted into a general initial drying rate equation, in which all dryer characteristics are grouped into one dimensionless parameter. The initial drying rate equation is mathematically maximized and the optimum working conditions determined. The result shows that initial drying rate always increase with increases of either the superheated steam temperature or velocity, but once these two variables are fixed, there exists at least one “optimum” pressure at which the initial drying rate is a maximum. Finally, the initial drying rate and optimum condition equations are applied to three model dryers, a dryer for a flat sheet, a fixed bed dryer and a rotary dryer. In each case, numeric values are computed and plotted as drying rate versus pressure curves, in which the optimum drying rate is also included. Also presented is a chart to compare the optimum pressures as functions of temperature and steam velocity for the three dryers.     

Generalized Kinetics of Drying of Fibre Materials

Dependences for describing the kinetics of drying of fibre materials in concrete conditions and generalizing dependences obtained by solving a one-dimensional isotropic diffusion equation are proposed. A comparison was made with the experimental data for different drying conditions and types (convective, conductive, with suction) for different fibres and fabrics in a thin layer. The generalizing dependence of the drying kinetics was analyzed. It was found that the dependences obtained describe two drying periods with sufficient accuracy and can be used as generalizing dependences. The method of calculation with the proposed equations is given.     

Improvement of Manufacturing Technology for Ultrastrong and High-Modulus Carbon Fibres

1. The quality of CF, their strength and modulus of elasticity in particular, can be increased by the following methods: reducing the porosity of the initial PAN fibres by selecting the optimum conditions for spinning, plasticization drawing, finishing, and drying; decreasing the nonuniformity of the fibre diameter due to suppression of deformation resonance during spinning by selecting the jet formation and hardening conditions; decreasing the fibril and crystallite size by reducing the precipitator and solvent concentration gradient in the precipitation zone (spinning into mild baths); creating optimum conditions for mesophase self-ordering of the material at 450–550° C during precarbonization; increasing the cohesive energy by increasing the density to 1.8–2.1 g/cm³. 2. Replacing convective tempering of PAN twists in thermooxidative treatment by conductive tempering reduces the treatment time by 3–4 times. __________ Translated from Khimicheskie Volokna, No. 5, pp. 11–15, September–October, 2005.     

Effective trends in revamping polymerization, extraction, and drying equipment for chemical fibre plants

Effective trends in revamping of polymerization, extraction, and drying equipment in chemical fibre plants to increase competitiveness and finished product sales by creating new and updating existing equipment for polymerization, extraction, and drying of polycaproamide are reported. __________ Translated from Khimicheskie Volokna, No. 5, pp. 57–61, September–October, 2006.     

Investigation and calculation of diffusion processes in thin fibre materials and fibre-forming polymers

A solution to the boundary-value problem for diffusion processes in thin fibre materials and fibre-forming polymers is presented. Quantitative estimations for the diffusion coefficients applicable to washing and drying of thin fibre materials and fibre-forming polymers were obtained. __________ Translated from Khimicheskie Volokna, No. 3, pp. 7–8, May–June, 2007.     

Correlation between the conditions of fabrication and structure of cotton cellulose for viscose formation

The effect of different regimes for each stage of fabrication of cotton cellulose on its supermolecular structure was evaluated by electron microscopic methods. It was shown that rigorous conditions of fabrication of cotton cellulose cause destruction and loosening of the surface and inner layers of the fibre. This indicates an increase in the reactivity of the cellulose and is promising for processing it into viscose fibres. Translated from Khimicheskie Volokna, No. 1, pp. 22–26, January–February, 1998.     

Theoretical principles of experimental determination of fibre flexural rigidity

An exact differential equation for the equilibrium of an elastic fibre loaded on the free end with a concentrated force and over the entire length of the elastic line of the distributed power load caused by the weight of the fibre was obtained in conditions of large movements. A method was developed for determining the flexural rigidity of the fibre which consists of bending the fibres and numerically solving the equation from the geometric nonlinear theory of bending of elastic fibres. __________ Translated from Khimicheskie Volokna, No. 4, pp. 19–21, July–August, 2007.     

Ballooning in spinning textile-metal fibre

Analytical expressions for the contact load and tensions of the components that ensure the equilibrium structure of textile-metal fibres in the spinning conditions are reported. Differential equations for contour movement of a rotating fibre were obtained and solved; using the experimental data, the fibre tension in the balloon was calculated. __________ Translated from Khimicheskie Volokna, No. 3, pp. 43–46, May–June, 2007.     

Prices for petrochemical raw materials and synthetic fibres and yarns in the first half of 2006

The price situation for crude oil, petrochemical raw materials, commercial granulate, and synthetic fibres and yarns on world and regional markets in the first half of 2006 was distinguished by instability. Fluctuations in the price of crude, especially the increase in February–April 2006, caused the cost of almost all types of raw materials for commercial polymers and synthetic fibres to increase. The lowest prices for petrochemical raw materials and products of processing them were observed in Asia, while relatively high prices were observed in Western Europe. The prices of cotton in the US and Western Europe were $400–500 and $600–700/ton lower than for 1.7 dtex polyester fibre for the first time in the USA and Western Europe. The price of PES fibre was $110/ton higher over six months in Western Europe, and the price of cotton, on the contrary, was $25/ton lower. __________ Translated from Khimicheskie Volokna, No. 6, pp. 68–77, November–December, 2006.     

OPTIMIZATION OF CONVECTIVE DRYING PROCESS BASED ON ECONOMIC INDICATORS

ABSTRACT

Drying of lightly salted sardine (Sardinella aurita) was accomplished using three air temperatures (35°C, 40°C, 50°C) and three air velocities (0.5 m/s, 1.5 m/s, 2 m/s); the effects of drying conditions on drying kinetics were studied. As for all biological products, air temperature is the main factor influencing the drying kinetics. However, over a given temperature which seems to correspond to protein modification (50°C), and at a high air flow rate (2 m/s and 2.5 m/s) a crust formation on the surface of the fish, due to the combined effect of heat and salt was observed. This phenomenon inhibited the drying rate. From the drying curves, two falling rate periods were observed. The dimensionless drying rate versus a dimensionless moisture content data were regressed by the Marquardt Levenberg non-linear optimization method to obtain an empirical equation describing the salted sardine characteristic drying curve.     

Model for drying during fluidized-bed combustion of wet low-rank coals

An unsteady state heat conduction model with a convective boundary condition is proposed for the drying of low-rank, high-porosity coals, such as lignites, during fluidized-bed combustion. The drying front is assumed to be the receding surface of a wet core. The solution technique for this moving boundary problem is based on the heat balance integral approach with immobilization of the moving boundary by a change in space variable. The governing cubic equation describing the drying curve in dimensionless form may be solved easily by the Newton—Raphson method. The model predictions are compared with experimental data for Mississippi lignite with excellent agreement. A correlation for estimation of total drying time is proposed. The temperature profiles obtained may be used for the study of the coupled drying and devolatilization in fluidized-bed combustors. The profiles could also be of importance in the study of formation of fissures/cracks in lignites subjected to intense heating conditions encountered during fluidized-bed combustion.     

From Laboratory Experiments to Design of a Conveyor-Belt Dryer via Mathematical Modeling

Abstract

A conveyor-belt dryer for picrite has been modeled mathematically in this work. The necessary parameters for the system of equations were obtained from regression analysis of thin-layer drying data. The convective drying experiments were carried out at temperatures of 40, 60, 80, and 100°C and air velocities of 0.5 and 1.5 m/sec. To analyze the drying behavior, the drying curves were fitted to different semi-theoretical drying kinetics models such as those of Lewis, Page, Henderson and Pabis, Wang and Singh, and the decay models. The decay function (for second order reactions) gives better results and describes the thin layer drying curves quite well. The effective diffusivity was also determined from the integrated Fick's second law equation and correlated with temperature using an Arrhenius-type model. External heat and mass transfer coefficients were refitted to the empirical correlation using dimensionless numbers (J _h , J _D  = m · Re ⁿ ) and their new coefficients were optimized as a function of temperature. The internal mass transfer coefficient was also correlated as a function of moisture content, air temperature, and velocity.     

Determination of the critical twist for polypropylene yarn

An equation that reflects the effect of the basic properties of the fibre and the linear density of polypropylene yarn on its twist was obtained. Determination of more accurate values of the yarn twist with this equation is due to the nonlinear character of the dependence of the twist on the properties of the fibre and the linear density of the yarn. __________ Translated from Khimicheskie Volokna, No. 6, pp. 64–65, November–December, 2006.     

Adsorption isotherm of a disperse dye

An absorption isotherm equation similar in form to Langmuir’s equation was obtained for monomolecular adsorption of a dye on the inner surface of a fibre for the process of dissolution of a dye in amorphous regions of a fibre using the assumptions concerning formation of dye—macromolecule fragment solvates in the ratio of 1:1. Linearity of the function 1/C_F = f(1/C_S) is possible both in adsorption of the dye with formation of a monomolecular layer (Langmuir) and in dissolution of the dye in the amorphous part of the fibre-forming polymer with formation of solvates. __________ Translated from Khimicheskie Volokna, No. 2, pp. 61–63, March–April, 2006.