Stefan Cenkowski

REVIEW OF THIN-LAYER DRYING AND WETTING EQUATIONS

ABSTRACT Thin-layer equations contribute to the understanding of the heat and mass transfer phenomena in agricultural products and computer simulations for designing new and improving existing commercial drying processes. Many different equations have been developed to represent thin-layer drying behaviour of the grains. Many thin-layer drying and rewetting equations are reviewed and discussed. Some suggestions for future coordinated research work arc given.

Grain bulk density as affected by diatomaceous earth and application method

Abstract The effect of the enhanced diatomaceous earth (EDE) insecticide Protect-It ™ was studied at different concentrations on the bulk density of wheat, corn, barley, rye and oats at three moisture contents (12, 14 and 15% m.c., dry basis). The greatest changes in bulk density occurred when the concentration of EDE ranged from 50 to 200 parts per million (ppm). At concentrations greater than 500 ppm, bulk density decreased little with increased EDE concentrations. The bulk density reductions in all five grains tested were significantly higher for the grain at a dry basis moisture content of 15% than at 12%. The reduction in bulk density as a result of the EDE application was described mathematically using empirical equations. The bulk density of wheat was measured before and after the wet (suspension) or dry (dust) application at 100 and 300 ppm of EDE under laboratory conditions. The dry application caused a significantly greater reduction in wheat bulk density than did the wet application. Application of only 10 ppm of either marine or fresh-water DE significantly reduced the bulk density (about 1.3–1.8%, w/w, respectively) of 13.9% m.c. wheat without dockage. Twenty five various DE obtained from different regions of the world were tested for bulk density changes when applied to wheat at various concentrations. All DE decreased wheat bulk density, though there were significant differences between DE. The most active DE formulations against stored grain insects, such as Protect-It ™ , Dryacide ® , Insecto ® , Dicalite, DE Eu and DiaFil, also had the greatest effect on the bulk density.

Deep-Bed Grain Drying - A Review of Particular Theories

ABSTRACT Theories developed for explaining the drying phenomena in grain drying systems are referred to as particular grain drying theories. The objectives of this paper are to review various particular grain drying theories and to suggest directions for future research in this area. Grain drying models are classified as non-equilibrium, equilibrium, and logarithmic type. Four non-equilibrium models (stationary bed, cross-, concurrent-, and counter-flow) were reviewed. Under low temperature and low airflow conditions, drying in a stationary deep-bed occurs at near equilibrium. The derivation of an equilibrium grain drying model and its necessary assumptions were discussed. Logarithmic models were developed and applied by many researches mostly to low temperature drying in stationary deep-beds. A semi-empirical thin-layer equation is commonly used in the reported grain drying models. The inclusion of this equation is an important factor, that determines the cognitive and practical values of a grain drying ...

DEHYDRATION OF SUGAR-BEET PULP IN SUPERHEATED STEAM AND HOT AIR

The drying characteristics of sugar-beet pulp in superheated steam and hot air at three temperatures (130, 157, and 183°C) and three velocities (0.24, 0.32, and 0.37 m/s) of drying media (air or steam) under atmospheric pressure were studied. The drying rate was higher and the drying time was shorter in superheated steam than in hot air of the same temperature. The drying rate increased and the drying time decreased with increased temperature for both superheated-steam drying and hot-air drying; however, the effect of temperature on superheated-steam drying was greater than on hot-air drying. At 157°C, increasing the velocity of the drying medium did not affect the drying characteristics of the samples dehydrated with hot air, but increased the drying rate at moisture contents greater than 0.5 kg/kg dry basis (d.b.) for superheated-steam drying. Sugar-beet pulp dehydrated with either superheated steam or hot air under the same drying conditions (157°C and 0.32 m/s) had the same water activities.

A METHOD OF DETERMINATION OF THE DIFFUSION COEFFICIENT BASED ON KERNEL MOISTURE CONTENT AND ITS TEMPERATURE

ABSTRACT Mathematical analysis of convection drying in the falling rate period was used to determine the overall coefficient of diffusion as a function of temperature and moisture content. The mass diffusion equation and its series solution was adopted for a single wheat kernel, assuming that it can be represented by a sphere as a model system. The results of the experimental data and the calculations are presented in the graphical form.

Effects of Superheated Steam Processing on the Textural and Physical Properties of Asian Noodles

Asian noodles were simultaneously cooked and dried in superheated steam at temperatures from 110 to 150°C and steam velocities of 0.5, 1.0, and 1.5 m/s. Textural and key physical properties of color, breaking stress, and starch gelatinization were measured to ascertain the effects of the superheated steam processing. Textural properties of adhesiveness, springiness, cohesiveness, chewiness, resilience, and hardness determined from a TPA were found to be generally unaffected by steam velocity. All properties but springiness increased with an increase in processing time. Increasing temperature decreased adhesiveness, springiness, cohesiveness, and resilience but increased hardness and chewiness to a small degree. Processing time greatly affected noodle color, resulting in browning at greater processing times. Results show that velocity was not a significant factor (p > 0.05) on the breaking strength of noodles. Temperature was only significant (p < 0.05) at 110 and 120°C and breaking stress decreased with increasing temperature. There were small decreases in breaking stress with processing time. Combined gelatinization of both amylopectin and amylose was an average of 80.5% for all superheated steam processed samples.

Superheated Steam Drying of Distillers' Spent Grains on a Single Inert Particle

The article presents the results of drying a distillers’ spent grain fraction (DSG) of a stillage in superheated steam (SS). The study aimed at determination of the effect of SS parameters on drying kinetics of DSG deposited as a pasty layer on the 50-mm solid Teflon sphere. Drying was conducted at approximately 2 to 4 kPa above the atmospheric pressure, with steam temperature ranging from 110 to 160°C and steam velocity of 1 m/s. Samples were dried with SS at different processing times ranging from 60 to 360 min, depending on the SS temperature. During the initial warmup period of SS processing, the pasty DSG gained moisture due to steam condensation on its surface, which further evaporated at constant material temperature (apparent constant rate period). That period ended as soon as the condensate evaporated and temperature of the product passed the saturation point of steam. Only the falling drying rate period was observed. The drying rates increased from 0.02 to 0.83 L/min with the increase in steam temperature from 110 to 160°C, respectively. The effective diffusivity of moisture in DSG increased with the increase in steam temperature according to the Arrhenius-type relationship. The values of the effective diffusivity ranged between 3.24 × 10−10 and 2.48 × 10−9 m2/s, with the activation energy of 53.74 kJ/mol.

Effects of superheated steam on Geobacillus stearothermophilus spore viability

Aims:  To examine the effect of processing with superheated steam (SS) on Geobacillus stearothermophilus ATCC 10149 spores.

Characteristics of carbon dioxide sorption by stored wheat

Abstract The sorption of carbon dioxide gas (CO2) by wheat was determined in glass flasks at four temperatures (0, 10, 20 and 30 °C) and four moisture contents (m.c.) (12, 14, 16 and 18% wet basis). The gaseous concentrations were analyzed by gas chromatography and the vacuum developed from the sorption of CO2 by wheat was measured with a mercury manometer. The calculated amount of CO2 sorted at equilibrium was a non-linear function of both temperature and moisture content. Sorption of CO2 by wheat decreased with increasing temperature from 0 to 30 °C at 14% m.c., and the initial rate of sorption increased with increasing m.c. from 12 to 18% at a temperature of 20 °C. Sorption was modelled using non-linear regression at two conditions (0–30 °C at 14% moisture content and 12–18% moisture content at 20 °C). The maximum mass of CO2 sorbed in 60 h was 0.510 g/kg of wheat at 18% m.c. and 0 °C and the lowest was 0.224 g/kg at 18% m.c. and 30 °C. A linear relationship existed between the initial CO2 concentration and the concentration after 60 h when 250 g of wheat of 14% m.c. at 20 °C was exposed in 500 ml flasks.

Age-dependence of intracranial viscoelastic properties in living rats

To explore the effect of maturation on intracranial mechanical properties, viscoelastic parameters were determined in 44 live rats at ages 1-2, 10-12, 21, 56-70, and 180 days using instrumented indentation. With the dura mater intact, the apparent modulus of elasticity, the indentation modulus, and viscous behavior were measured in vivo, as well as 1 h after death. In a separate group of 25 rats, brain water, and protein content were determined. A significant increase of the elastic and indentation moduli beginning at 10-12 days after birth and continuing to 180 days was observed. The creep behavior decreased in the postnatal period and stabilized at 21 days. Changes in intracranial biomechanical properties corresponded to a gradual decrease of brain water, and an increase in total protein content, including glial fibrillary acidic protein, myelin basic protein, and neurofilament light chain. Elastic properties were not significantly different comparing the live and dead states. However, there were significant postmortem changes in viscous behavior. Viscoelastic properties of living rat intracranial contents are shown to be age dependent, reflecting the physical and biochemical changes during postnatal development. This may be important for understanding why young and mature brains respond differently in situations of brain trauma and hydrocephalus.