EFFECT OF VIBRATION ON THE DRYING RATE DURING THE FALLING RATE PERIOD

The results of an experimental study on the drying characteristics in vibrated fluidized beds of corn plumule, silica gel and citric acid are presented. Application of vibration was found to enhance the drying rate during the falling rate period. In the optimum range of vibration parameters, the critical moisture content decreased significantly as compared with that in conventional fluidized beds of the same material.     

EFFECT OF VIBRATION ON THE DRYING RATE DURING THE FALLING RATE PERIOD

The results of an experimental study on the drying characteristics in vibrated fluidized beds of corn plumule, silica gel and citric acid are presented. Application of vibration was found to enhance the drying rate during the falling rate period. In the optimum range of vibration parameters, the critical moisture content decreased significantly as compared with that in conventional fluidized beds of the same material.     

AN APPROXIMATION METHOD FOR THE DETERMINATION OF THE DISTRIBUTION OF TEMPERATURE AND OF MOISTURE CONTENT IN THE FALLING RATE PERIOD OF DRYING

The present paper deals with the periods of dif- ferent drying mechanism. A calculation method is pre- sented for the temperature distribution of the material during these periods and for distribution of moisture content in the falling rate period. The test material was a 100 x 100 x 30 mm gypsum plate.     

AN APPROXIMATION METHOD FOR THE DETERMINATION OF THE DISTRIBUTION OF TEMPERATURE AND OF MOISTURE CONTENT IN THE FALLING RATE PERIOD OF DRYING

The present paper deals with the periods of dif- ferent drying mechanism. A calculation method is pre- sented for the temperature distribution of the material during these periods and for distribution of moisture content in the falling rate period. The test material was a 100 x 100 x 30 mm gypsum plate.     

DRYING OF STICKY GRANULAR MATERIALS DWING THE CONSTANT RATE PERIOD IN A VIBRATED FLUIDIZED BED

Experimental results on the drying characteristics in a vibrated fluidized bed IVFB) for sticky and agglomerating materials under various conditions of the operating parameters are presented.The dynamics of the \'FB of wetted materials and the effects of parameters, such as vibration amplitude and frequency, initial moisture content, initial bed height, particle size, and air velocity and temperature on the drying rate during the constant rate period were studied experimentally.     

DRYING OF STICKY GRANULAR MATERIALS DWING THE CONSTANT RATE PERIOD IN A VIBRATED FLUIDIZED BED

Experimental results on the drying characteristics in a vibrated fluidized bed IVFB) for sticky and agglomerating materials under various conditions of the operating parameters are presented.The dynamics of the 'FB of wetted materials and the effects of parameters, such as vibration amplitude and frequency, initial moisture content, initial bed height, particle size, and air velocity and temperature on the drying rate during the constant rate period were studied experimentally.     

AN EXPERIMENTAL STUDY OF THE FALLING RATE PERIOD OF SUPERHEATED STEAM IMPINGEMENT DRYING

ABSTRACT

The drying of paper under impinging jets of superheated steam and air during the falling rate period was investigated in the range of jet temperatures 150 < Tj < 450^oC and basis weights 30 < B < 150 g/m². The equilibrium moisture content of Kraft and TMP paper was measured. The adsorption energy of water on pulp fibers near the boiling point appears lower than the value extrapolated from Prahl s (1968) measurements made in air at lower temperatures. The critical moisture content was determined for superheated steam and air impingement drying. Complete drying rate - moisture content histories are presented for a series of typical conditions.     

TEE EFFECIS OF EXTENDED THIN FILM EVAPORATION AND EXPWNAL DIFFUSION RESISTANCE DURING THE CONSTANT DRYING RATE PERIOD

ABSTRACT

Extended thin film evaporation with external diffusion resistance is analyzed for the constant rate period of the drying process, in which a polar liquid evaporates from porous bodies made of glass. The extended thin film is defined as the Liquid film in which the disjoining pressure dominates the fluid flar field and works as the driving force replenishing the evaporating Liquid. The results of the analysis shows that due to the existence of the evaporating thin Liquid film, the evaporation fran the extended thin film can compensate the reduction of evaporation rate caused by the increase of the dry spots and keep the drying rate the same as or even greater than that of the completely wetted surface. The external diffusion resistance makes the vapor concentration near the porous solid surface remain constant and therefore keeps     

TEE EFFECIS OF EXTENDED THIN FILM EVAPORATION AND EXPWNAL DIFFUSION RESISTANCE DURING THE CONSTANT DRYING RATE PERIOD

Extended thin film evaporation with external diffusion resistance is analyzed for the constant rate period of the drying process, in which a polar liquid evaporates from porous bodies made of glass. The extended thin film is defined as the Liquid film in which the disjoining pressure dominates the fluid flar field and works as the driving force replenishing the evaporating Liquid. The results of the analysis shows that due to the existence of the evaporating thin Liquid film, the evaporation fran the extended thin film can compensate the reduction of evaporation rate caused by the increase of the dry spots and keep the drying rate the same as or even greater than that of the completely wetted surface. The external diffusion resistance makes the vapor concentration near the porous solid surface remain constant and therefore keeps     

INFLUENCE OF THE DRYING MEDIUM PARAMETERS ON DRYING INDUCED STRESSES

A thermomechanical model of drying of capillary-porous materials whose material constants depend on moisture content and temperature is presented in the paper. The finite element method is used for the solution of two-dimensional problem of convective drying of a prismatic bar. The moisture distributions, temperature distributions, drying induced strains and stresses for various drying medium parameters are determined. The effect of these parameters on moisture distribution and in particular on drying induced stresses is discussed.     

INFLUENCE OF THE DRYING MEDIUM PARAMETERS ON DRYING INDUCED STRESSES

ABSTRACT

A thermomechanical model of drying of capillary-porous materials whose material constants depend on moisture content and temperature is presented in the paper. The finite element method is used for the solution of two-dimensional problem of convective drying of a prismatic bar. The moisture distributions, temperature distributions, drying induced strains and stresses for various drying medium parameters are determined. The effect of these parameters on moisture distribution and in particular on drying induced stresses is discussed.     

DISSERTATIONS AND THESES IN DRYING WRITTEN IN CZECHOSLOVAKIA IN THE PERIOD 1975 - 84

Research and development of drying processes and equipmect has a long tradition in Czechoslovakia (1). There are at least 10 top reoearch centers where drying of varicus materials has been studied. Remarkable attention to drying theory and application is also paid at Czechoslovak universities which yields numerous theses dealing with various aspects of the drying process. The total of 52 M.Sc. theses oriented to drying and/or dryers had been published in the last decade. Moreover, 22 Ph.D. theses were carried out in the same period. This represents an important source of theoretical and experimental results. However all theses had been mitten in the Czech or Slovak language, and therefore their wide international application is rather limited. They are summari-zed in the following list.     

DISSERTATIONS AND THESES IN DRYING WRITTEN IN CZECHOSLOVAKIA IN THE PERIOD 1975 - 84

Research and development of drying processes and equipmect has a long tradition in Czechoslovakia (1). There are at least 10 top reoearch centers where drying of varicus materials has been studied. Remarkable attention to drying theory and application is also paid at Czechoslovak universities which yields numerous theses dealing with various aspects of the drying process. The total of 52 M.Sc. theses oriented to drying and/or dryers had been published in the last decade. Moreover, 22 Ph.D. theses were carried out in the same period. This represents an important source of theoretical and experimental results. However all theses had been mitten in the Czech or Slovak language, and therefore their wide international application is rather limited. They are summari-zed in the following list.     

THE INFLUENCE OF STORAGE/TRANSPORTATION CONDITIONS ON DRYING STRESSES AND THE PRONG TEST

From the time lumber is removed from the kiln to the time the remanufacturer uses it, it can be exposed to many different humidities With exposure to severe humidities, cupping in the final product can occur. This paper considers if humidity conditions during storage and transportation can significantly influence drying stresses and prong lest response. To determine the influence of exposure to different humidities, dried lumber was slowly equilibrated to 7,5% moisture content. It was than cut into blocks. The blocks were exposed to various humidity scenarios lo simulate actual storage and transportation conditions. Stress levels, moisture content and prong response were recorded. The analysis showed that stress level and prong response were strongly influenced by exposure to different humidities. The analysis also indicated that returning lumber to 7.5% equilibrium moisture content did not return the stress level or prong response to the original values. These combined results confirm that the prong test cannot be used as an indicator of how well the lumber has been dried or conditioned after it has been stored and transported. This makes seller/buyer disagreements difficult to resolve.     

THE INFLUENCE OF STORAGE/TRANSPORTATION CONDITIONS ON DRYING STRESSES AND THE PRONG TEST

ABSTRACT

From the time lumber is removed from the kiln to the time the remanufacturer uses it, it can be exposed to many different humidities With exposure to severe humidities, cupping in the final product can occur. This paper considers if humidity conditions during storage and transportation can significantly influence drying stresses and prong lest response. To determine the influence of exposure to different humidities, dried lumber was slowly equilibrated to 7,5% moisture content. It was than cut into blocks. The blocks were exposed to various humidity scenarios lo simulate actual storage and transportation conditions. Stress levels, moisture content and prong response were recorded. The analysis showed that stress level and prong response were strongly influenced by exposure to different humidities. The analysis also indicated that returning lumber to 7.5% equilibrium moisture content did not return the stress level or prong response to the original values. These combined results confirm that the prong test cannot be used as an indicator of how well the lumber has been dried or conditioned after it has been stored and transported. This makes seller/buyer disagreements difficult to resolve.     

FINITE ELEMENT SIMULATION OF THE THERMO-HYDRO STRESSES IN A VISCOELASTIC SPHERE DURING DRYING

The objective of this study is the formulation of a finite element model that could be used to analyze the stress crack formation in a viscoelastic sphere resulting from temperature and moisture gradients during the drying process. Numerical solutions to the simultaneous moisture and heat diffusion equations describing moisture removal and heat intake process for the sphere are obtained. The distribution and gradients of temperature and moisture developed inside the sphere during drying are established. The calculated temperature and moisture gradients are used in a finite element analysis of the thermo-hydro viscoelastic boundary value problem to simulate the stresses in the body.

The model is used to solve a sample problem of drying a soybean kernel. The simulated drying curve for the soybean model is obtained and compared favorably with the experimental results reported in the literature. Tangential stress, as a criteria for failure, is shown to change from compressive to tensile stress as it approaches the surface. It reaches its peak value at the surface in one hour and then decays slowly. The effect of different drying conditions is studied and the results are discussed.     

FINITE ELEMENT SIMULATION OF THE THERMO-HYDRO STRESSES IN A VISCOELASTIC SPHERE DURING DRYING

The objective of this study is the formulation of a finite element model that could be used to analyze the stress crack formation in a viscoelastic sphere resulting from temperature and moisture gradients during the drying process. Numerical solutions to the simultaneous moisture and heat diffusion equations describing moisture removal and heat intake process for the sphere are obtained. The distribution and gradients of temperature and moisture developed inside the sphere during drying are established. The calculated temperature and moisture gradients are used in a finite element analysis of the thermo-hydro viscoelastic boundary value problem to simulate the stresses in the body.

The model is used to solve a sample problem of drying a soybean kernel. The simulated drying curve for the soybean model is obtained and compared favorably with the experimental results reported in the literature. Tangential stress, as a criteria for failure, is shown to change from compressive to tensile stress as it approaches the surface. It reaches its peak value at the surface in one hour and then decays slowly. The effect of different drying conditions is studied and the results are discussed.     

PHYSICAL CHARACTERISTICS AND DRYING RATE OF ECHINACEA ROOT

ABSTRACT

Echinacea angustifolia or the purple coneflower is an important medicinal plant that boosts the immune system. It is believed that the active ingredients are predominantly located in the root. Physical characteristics and drying rates of the root of E. angustifolia from a farm in Saskatchewan, Canada were studied. Root consisted of a main (central) root and secondary root branches. Cleaned roots exhibited wide variations in mass ranging from 15 to 95 g. The central root diameter varied from 9 to 20 mm with an average of 14 mm. The average initial moisture content of the fresh root was 57% (wb). The specific densities of the fresh and completely dried root were 1040 and 1370 kg/m³, respectively; and the corresponding bulk densities of loosely piled roots were 305 and 410 kg/m³. Roots were dried in a convection oven at temperatures of 23, 30, 40, 50, 60 and 70°C. Equations for estimating drying rates, drying constants, and equilibrium moisture content were developed. Increased drying temperatures reduced echinacosides but did not affect alkamides 1 and 2 which are known to be also responsible for medicinal value of E. Angustifolia.     

TEE EFFECT OF EXTENDED THIN FILM EVAPORATION DURING TEE CONSTANT DRYING RATE PERIOD

ABSTRACT

The extended thin film evaporation is analyzed during the constant drying rate period. The extended thin film is defined as the liquid film which the disjoining pressure dominates the fluid flow field and works as the driving force of replenishing the evaporating liquid. The results of the analysis show that the extended thin film evaporation can compensate the reduction of evaporation rate due to the increase of dry spots and keep the evaporation rate nearly constant. Experimental data in the literature are in good agreement with the results of this work. This implies that the extended thin film evaporation may be an important part of the mechanism for drying.