An Experimental Study on Drying of Green Apples

Drying behavior of green apples in a laboratory dryer was examined. Prior to drying, the apples were cut in 8 mm thick slices, which were then treated with citric acid solution and blanched hot water at 80°C. Next, they were dried at 65°C with an air velocity of 2.0 m/s. The shortest drying time (270 min) was obtained with apples pretreated with citric acid solution. The drying data were fitted with 11 mathematical models available in the literature. Selection of the best model was investigated by comparing the determination of coefficient (R ²), reduced chi-square (χ²), root means square error ( RMSE ), and mean relative percentage error (P) between the experimental and predicted values. The results showed that the Wang and Singh, logarithmic, and Verma et al. models gave the best results in describing thin-layer drying of apple slices. The effective moisture diffusivity of pretreated samples with citric acid solution was higher than the other samples.     

DRYING OF SUGAR BEET PULP USING A LABORATORY AIR DRIER

ABSTRACT

Drying curves for sugar beet pulp were obtained in a laboratory-scale air drier. Dehydration conditions were: temperatures in the range of 35 to 90 ^°C, air flow velocities of 0.5 to 2.0 m/s, and air moisture content of 0.005 to 0.06 kg water/kg air. Using data from thin layer experiments, a mathematical model was derived to describe the dehydration behaviour under the described conditions. The model was able to predict data obtained from deep bed experiments. Results from this work could be used to develop a design methodology for dryers that operate at relatively low temperatures (<90^°C).     

Drying Kinetics and Sorption Isotherms of the Nejayote

Abstract

The nixtamalization is an alkaline cooking process in corn tortillas industry that uses large quantities of water (5:1 corn weight) and producing a byproduct called nejayote. In this work, drying kinetic of insoluble fraction from nejayote was obtained using a hot air cabinet dryer at 60, 75, and 90°C. The air rate and water content were 1.5 m/s and 0.028 kg of water/kg of dry air, respectively. Sorption isotherms were measured by the COST method with sulfuric acid solutions at 30, 45 and 60°C. Results showed a difference in drying kinetics/drying time between drying temperatures of 60 and 75°C, and practically no difference between 75 and 90°C. This was probably due to the development of a superficial crust on the product. The shape of sorption curves was as expected; no temperature effect was identified but it is a common behavior for products with high sugar content. Finally the sorption isotherm was predicted based on primary chemical compounds (carbohydrates, proteins, crude fiber, and calcium hydroxide).     

Liquid holdup determination in packed columns for sulfur dioxide absorption

Total, static and dynamic holdups have been measured for 0.012 m ceramic Raschig rings with air rates from 0 to 700 kg m⁻² h⁻¹ and sodium citrate solution rates from 2000 to 60 000 kg m⁻² h⁻¹ at 40°C using the draining method. Equations presented for estimating holdups are discussed.     

Equilibrium solubility of H2S and CO2 and their mixtures in a mixed solvent

The solubility of hydrogen sulphide, carbon dioxide, and their mixtures has been measured at 40° and 100°C in a mixed solvent consisting of 20.9 wt% MDEA (methyldiethanolamine), 30.5 wt% sulfolane (tetrahydrothiophene-1, 1-dioxide), and 48.6 wt% water. The results have been compared with those for aqueous 2.0 mol/dm³ MDEA and an analogous mixed solvent, containing AMP (2-amino-2-methyl-1-propanol), which are available in the literature. These data were used to modify the solubility model of Deshmukh and Mather (1981) to account for the mixed solvent effects on the system thermodynamics. Results show that the model is useful as a first approximation in predicting acid gas solubilities; agreement with experiment was generally found to be within £15%.     

Thin-Layer Drying of Green Peas and Selection of a Suitable Thin-Layer Drying Model

The thin-layer drying of three varieties of green peas was carried out in hot air-drying chamber using an automatic weighing system at five temperatures (55–75°C) and air velocity of 100 m/min. The green peas were blanched and sulphited before drying. The variety Pb-87 dried at 60°C was judged to be best for quality on the basis of sensory evaluation and rehydration ratio. The Thomson model was found to represent thin-layer drying kinetics within 99.9% accuracy. The effective diffusivity was determined to be 3.95 × 10^?10 to 6.23 × 10^?10 m²/s in the temperature range of 55 to 75°C. The activation energy for diffusion was calculated to be 22.48 kJ/mol. The variation in shrinkage exhibited a linear relationship with moisture content of the product during drying. The Dincer number at drying air temperature 60°C and drying air velocity 100 m/min was determined to be 2,838,087. The difference between temperatures of drying air and that of green pea kernels was found to decrease with drying time for all the drying temperatures taken for investigation.     

Novel self‐supported natural and synthetic polymer membranes for air humidification

Novel self‐supported natural and synthetic polymer membranes of chitosan‐hydroxy ethyl cellulose‐montmorillonite (CS‐HEC‐MMT) and polyvinyl alcohol (PVA)‐polystyrene sulfonic acid (PSSA) are prepared by solution casting method followed by crosslinking. These membranes are employed for air humidification at varying temperatures between 30°C and 70°C and their performances are compared with commercial Nafion^® membranes. High water fluxes with desired humidified‐air output have been achieved for CS‐HEC‐MMT and PVA‐PSSA hybrid membranes at air‐flow rates of 1–10 slpm. Variation in the air/water mixing ratio, dew point, and relative humidity that ultimately results in desired water flux with respect to air‐flow rates are also quantified for all the membranes. Water flux values for CS‐HEC‐MMT are less than those for Nafion^® and PVA‐PSSA membranes, but the operational stability of CS‐HEC‐MMT membrane is higher than PVA‐PSSA and comparable with Nafion^® both of which can operate up to 70°C at repetitive cycles of humidification. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Sodium Humate as a Promising Coating Material for Microencapsulation of Beauveria bassiana Conidia Through Spray Drying

Microencapsulation of Beauveria bassiana (Bb) conidia with sodium humate (SH) was undertaken successfully through spray drying at a high inlet air temperature of 175°C with corresponding outlet air temperature of 86.5 ± 1.3°C using 0.2% SH. The obtained product was a free-flowing, dark-brown powder containing microcapsules of Bb conidia coated with sodium humate (Bb-SH). These microcapsules measured 2.47–3.57 µm and possessed an uneven, fluffy surface. The colony-forming units (CFU) of Bb-SH microcapsules spray-dried at 175°C were 21.54 LCFUg^?1, on par with 21.59 LCFUg^?1 for Bb conidial powder not subjected to spray drying. Bb-SH microcapsules resulted in a high mortality of 93.0% against six-day-old Helicoverpa armigera larvae within five days after treatment. Bb-SH microcapsules readily dispersed in water, releasing sodium humate from the conidial surface. Germination of conidia was not affected by sodium humate as visualized by scanning electron microscopy of the cuticular surface of treated larvae. Bb-SH microcapsules showed good viability (21.11 LCFUg^?1) at the end of six months of storage at room temperature (～30°). Thus, sodium humate is a promising biopolymer for encapsulation of Bb conidia for extended shelf-life at room temperature.     

Drying of polyvinyl alcohol in a closed-circuit dryer

The sorption isotherm and the drying rate curve represent the basis for the design of a dryer for solvent wetted polyvinyl alcohol (36 wt.% methyl acetate, 62 wt.% methanol, 2 wt.% water). In this study the sorption isotherms of polyvinyl alcohol wetted with a mixture of methyl acetate and methanol were measured at 40, 60 and 80 °C, and the drying rate curves of solvent-wetted polyvinyl alcohol layers 3, 10 and 20 mm in height in a dry air stream (air temperatures 30, 60 and 100 °C, air velocities 0.2 and 1 m s⁻¹) were investigated. The hygroscopic equilibrium moisture content can be determined by means of the sorption isotherm, and the belt area of the dryer by means of the drying rate curves.     

A parametric study of a platinum ruthenium anode in a direct borohydride fuel cell

Data on the performance of a direct borohydride fuel cell (DBFC) equipped with an anion exchange membrane, a Pt–Ru/C anode and a Pt/C cathode are reported. The effect of oxidant (air or oxygen), borohydride and electrolyte concentrations, temperature and anode solution flow rate is described. The DBFC gives power densities of 200 and 145 mW cm⁻² using ambient oxygen and air cathodes respectively at medium temperatures (60 °C). The performance of the DBFC is very good at low temperatures (ca. 30 °C) using modest catalyst loadings of 1 mg cm⁻² for anode and cathode. Preliminary data indicate that the cell will be stable over significant operating times.     

The solubility of carbon dioxide and hydrogen sulfide in a 35 wt% aqueous solution of methyldiethanolamine

The solubility of hydrogen sulfide and carbon dioxide in an aqueous solution containing 35 wt% methyldiethanolamine (MDEA) (3.04 kmol/m³, 4.52 mol/kg) has been measured at 40° and 100°C at partial pressures of the acid gas up to 530 kPa. Some data for hydrogen sulfide in a 50 wt% solution of MDEA (4.38 kmol/m³, 8.39 mol/kg) were also obtained. Also, densities of CO₂-aqueous MDEA solutions were measured at 40°C.     

A new eco-friendly mass formulation based on industrial mining residues for the manufacture of ceramic tiles

New eco-friendly mass formulations based on the scheelite and kaolin residues were developed to manufacture ceramic tiles. The start raw materials (scheelite residue, kaolin residue, feldspar and plastic clay) were characterized as to their chemical composition, main mineralogical phases, and particle size distribution. Three ceramic masses with 37 wt% of kaolin residues and different contents of the scheelite residues (2 wt%, 5 wt%, and 10 wt%) were formulated. The mass formulations were uniaxially pressed (19.6 MPa) to obtain samples with dimensions of 60 mm × 40 mm x 7 mm, which were dried at 110 °C/24 h, and sintered at different temperatures (1150 °C, 1200 °C, and 1250 °C). Dilatometric experiments measured thermal expansion coefficients. The results are in agreement with the literature, i.e., 6.0 μm/m°C^?1, 6.1 μm/m°C^?1 and 6.4 μm/m°C^?1 to samples with 2 wt%, 5 wt%, and 10 wt% of scheelite residues, respectively. The potential of the mass formulations studied was evaluated by linear shrinkage, water absorption, apparent density, apparent porosity, flexural strength, and mineralogical phase identification. The results were compared with the literature experimental data and International Technical Standards. It was concluded that the samples investigated have suitable properties for use as ceramic and porcelain tiles. Also, the pseudowollastonite and mullite phases were identified in the sample with the lowest concentration of scheelite residue. These phases are responsible for increasing flexural strength.     

Temperature effects on polyphenol oxidase activity in organic solvents with low water content

The effect of temperature studies on polyphenol oxidase immobilized on glass beads were carried out in organic solvents. The optimum temperature for catalysis depended on the solvent and varied in a range from 26°C for dichloromethane to 50°C for toluene, benzene and 1,1,1-trichloroethane. Optimum temperature and activation energy were independent of the water content of the system whereas the inactivation energies decreased as the water content of the system was decreased. The enzyme was stable in toluene up to 50°C although residual activity depended on the water content of the system. Thermoinactivation of polyphenol oxidase in toluene gave an activation energy for enzyme decay of 111.5 kcal mol^?1 which is consistent with a conformational process. Among the agents employed to protect the enzyme against thermal denaturation 1 % (w/v) short-chain polyols added to the buffer and 0.5 mmol dm^?3 p-nitrophenol added to toluene more than doubled the half-life of the enzyme.     

Comparative Investigation of Dynamic Foam Behavior of Air–Water and CO2–Water Systems

The purpose of this study was to understand and compare the dynamic foam behavior of the surfactant Tween‐20 in air–water and CO₂–water systems. The foam height in the CO₂–water system was less than that in the air–water system, but the foam stability was better in the CO₂–water system. The effect of temperature on axial dye displacement and foam bubble size was studied, where the foam generation ability of the surfactant was directly proportional to the temperature, while the foaminess was inversely proportional. The observed highest foam volume for the air–water system was 3922 ± 181 cm³ and for the CO₂–water system 3195 ± 181 cm³ at 5.0 g L^–1 of surfactant at air flow rate of 1 liter per minute (LPM) at 52 °C. The half‐life for the air–water and the CO₂–water system was 110 and 40 s, respectively, at 5.0 g L^–1 of surfactant at the air flow rate of 1 LPM and 28 °C. In wet foam, the liquid holdup range for the air–water system was 0.38–0.52% and for the CO₂–water system 0.51–0.72% in the concentration range 1.0–5.0 g L^–1 at 1 LPM gas flow rate.     

Experimental Study on Optimization of the Agglomeration Process for Producing Instant Sugar by Conical Fluidized Bed Agglomerator

This study was conducted to determine the optimal processing conditions for manufacturing instant sugar. The instant sugar was produced with a batch fluid bed agglomerator under the following conditions: inlet air temperature 60–90°C; water flow rate 1–3 mL min^?1; and spraying time 1–10 min. The optimal conditions were estimated using response surface methodology as follows: inlet air temperature of 74.4°C, water flow rate of 2.85 mL min^?1, and spraying time of 10 min. Subsequently, particle density of 1,550 kg m^?3, poured density of 470.13 kg m^?3, tapped density of 599.8 kg m^?3, porosity of 62.1%, mean diameter of 324.66 µm, flowing time of 6.39 s, yield percentage of 78.96%, and desirability of 0.46 were obtained as optimal amounts. The results showed that the quadratic effects of water flow rate and spraying time on flowing time and particle density as well as the effects of spraying time and inlet air temperature on mean diameter and flowing time were significant. Within the temperature range of 60–90°C, the impact of spraying time and water flow rate on instant sugar properties had preference over inlet air temperature. Moreover, the optimal instant sugar required less dissolution time compare to various industrial sugar samples.     

The temperature effects on hydraulic conductivity of compacted bentonite

The hydraulic conductivities of water saturated Ca-bentonite with dry densities of 1.4, 1.6, and 1.8 Mg/m³ were measured within the temperature range of 20 to 80°C. The hydraulic conductivities of all the compacted bentonites are lower than 10⁻¹¹ m/s, and the relationship between the logarithm of the hydraulic conductivity and the bentonite dry density can be fitted to a straight line. The hydraulic conductivities of bentonites increase with increasing temperature, and the hydraulic conductivities at 80°C increase up to about three times those at 20°C. The measured values are in agreement with those predicted from the hydraulic conductivities at 20°C assuming that only fluid properties are changed with changing temperature. The change in viscosity of water with increasing temperature contributes greatly to the increase of hydraulic conductivity.     

Experimental investigation of the evaporation behavior of urea-water-solution droplets exposed to a hot air stream

The behavior of droplets of urea-water-solution (UWS) evaporating under the influence of a hot stream of air was investigated experimentally, under temperatures ranging from 100°C to 400°C. The droplets were suspended on a glass microfiber to minimize the influence of heat conduction, through the fiber, on the evaporation rate of the droplet. The flow rate of air, under all experimental conditions, was measured and these data were used to estimate the average velocity of air around the droplet. Experiments were also conducted on droplets of pure water and the results were compared. The initial mass fraction of urea, in the solution, did not appear to have a significant effect on the evaporation constant, but it did affect a few essential aspects of the evaporation behavior. The evaporation of water droplets was in accordance with the d² law at all temperatures, whereas the evaporation of UWS droplets was ambient-temperature dependent.     

Preparation of chemically crosslinked gels with maleate‐denatured poly(vinyl alcohol) and its application to drug release

Maleate‐denatured poly(vinyl alcohol) (M‐PVA) was crosslinked with heating. The mechanism of crosslinking was studied with several procedures: titration, Fourier transform infrared, and solubility. The carboxyl groups of M‐PVA consisted of carboxylates and a few free carboxyl groups. The crosslink was the ester linkage between hydroxyl and carboxyl groups. Several kinds of M‐PVA tablets were prepared under different conditions: pressures of 200–600 kgf/cm² and grain sizes of 75 (pass) to 250 μm (on). The swelling behavior of these chemically crosslinked tablets was studied in a buffer solution of pH 7.4, mainly at 37°C. Moreover, the effect of temperature from 5 to 50°C and the effect of repeated swell–dry cycles on the behavior of the tablets in a buffer solution [106 μm (on), 200 kgf/cm²] were studied. The release of p‐acetamidophenol from those tablets in the pH 7.4 buffer solution was studied. The different release patterns were due to the differences in the swelling behavior. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1178–1184, 2002; DOI 10.1002/app.10411     

Evaluation of Mass Transfer Resistances from Drying Experiments

A new approach to experimental evaluation of mass transfer resistances from drying experiments is proposed. A composite model of ginseng root mass transfer, based on one-dimensional treatment of diffusive and convective resistances as additive components of radial mass transfer, was developed. Mass transfer resistance was evaluated from a linear relationship between measured flux and thermodynamic driving force. Partitioning of mass transfer resistance into diffusive (core and skin) and convective (air boundary layer) resistances was done by modification of boundary conditions: (a) high (3 m/s) and low (1 m/s) air velocity; (b) skin removal. Total radial mass transfer resistance was evaluated as (146 ± 6) ? 10⁶ s/m at 38°C, significantly decreasing to (48 ± 1.5) ? 10⁶ s/m at 50°C. Boundary resistance was evaluated as (54 ± 5) ? 10⁶ s/m at 38°C and (26 ± 3) ? 10⁶ s/m at 50°C in the entire range of moisture contents. Core and skin resistances were both moisture dependent: core resistance increased from initial value of (6 ± 1) ? 10⁶ s/m to (61 ± 6) ? 10⁶ s/m toward the end of drying, whereas skin resistance decreased from initial value of (92 ± 5) ? 10⁶ s/m to (25 ± 5) ? 10⁶ s/m at the endpoint of drying. However, the sum of core and skin resistances, which represents composite diffusive resistance of intact ginseng root, was constant and independent of moisture content: (91 ± 4.6) ? 10⁶ s/m at 38°C and (22 ± 1.6) ? 10⁶ s/m at 50°C. The relationship between mass transfer resistance R and drying rate factor k = 1/RC was used for verification of the composite model.     

The solubility of methane in aqueous solutions of monoethanolamine,diethanolamine and triethanolamine

The solubility of methane in 3 kmol/m³ solutions of monoethanolamine, diethanolamine, and triethanolamine was measured from 25° to 125°C and pressures up to about 13 MPa. Measurements were also made for the solubility of methane in water at 25° to 125°C and pressures up to 18 MPa in order to confirm the accuracy of the experimental technique. It is demonstrated that methane is more soluble (in terms of mole fraction) in the amine solution than in pure water. Furthermore, the solubility is an increasing function of the size of the alkanolamine. The solubility data were modeled using a Henry's-law approach and the results summarized in terms of salting-in coefficients.