Surface Stickiness of Drops of Carbohydrate and Organic Acid Solutions During Convective Drying: Experiments and Modeling

Drying kinetics of low molecular weight sugars such as fructose, glucose, sucrose and organic acid such as citric acid and high molecular weight carbohydrate such as maltodextrin (DE 6) were determined experimentally using single drop drying experiments as well as predicted numerically by solving the mass and heat transfer equations. The predicted moisture and temperature histories agreed with the experimental ones within 6% average relative (absolute) error and average difference of ± 1°C, respectively. The stickiness histories of these drops were determined experimentally and predicted numerically based on the glass transition temperature (T_g) of surface layer. The model predicted the experimental observations with good accuracy. A nonsticky regime for these materials during spray drying is proposed by simulating a drop, initially 120 µm in diameter, in a spray drying environment.     

Effect of Pretreatments and Drying Methods on the Properties and Fishy Odor/Flavor of Gelatin from Seabass (Lates calcarifer) skin

Effects of different pretreatments of seabass skin and various drying methods on properties and fishy odor/flavor of resulting gelatin were evaluated. All gelatins contained α- and β-chains as the predominant components. Generally, a higher gel strength was found in the freeze-dried gelatin, compared with spray-dried counterpart (p < 0.05). Gel strength of gelatin decreased as the inlet temperature for spray drying increased (p < 0.05). All gelatin samples had creamy whitish color but became more yellow as the inlet temperature for spray drying increased. All gelatin gels were sponge- or coral-like in structure. Gelatin from skin pretreated with citric acid had lower fishy odor/flavor than that from skin pretreated using acetic acid. The lower fishy odor/flavor with coincidentally lower abundance of volatile compounds, including aldehydes, ketones, and alcohols, etc., was found in gelatin obtained by spray drying, in comparison with its freeze-dried counterpart. The lower fishy odor/flavor in spray-dried gelatin was in accordance with the lower thiobarbituric acid reactive substances and peroxide values. Thus, spray drying in conjunction with an appropriated pretreatment could be an effective method for production of gelatin with negligible undesirable fishy odor and flavor.     

COMBINED CONVECTIVE AND INFRARED DRYING OF A CAPILLARP POROUS BODY

Abstract

This work investigates the effect of spray drying conditions on some properties of tomato powder prepared by spray drying of tomato pulp. A pilot scale spray dryer (Buchi, B-191) with cocurrent regime and a two-fluid nozzle atomizer was employed. Sixty-four different experiments were conducted keeping constant the feed rate, the feed temperature, and the atomizer pressure, and varying the compressed air flow rate, the flow rate of drying air, and the air inlet temperature. Tomato powders were analyzed for moisture, solubility, density (bulk and packed), and hygroscopicity. Analysis of experimental data yielded correlations between powder properties and the above-mentioned variable operating conditions. Regression analysis was used to fit a full second order polynomial, reduced second order polynomials and linear models to the data of each of the properties evaluated. F values for all reduced and linear models with an R ² ≥ 0.70 were calculated to determine if the models could be used in place of full second order polynomials.     

Concentration and Drying of Tea Polyphenols Extracted from Green Tea Using Molecular Distillation and Spray Drying

The purpose of this study was to develop a method of combining molecular distillation and spray drying to concentrate and dry tea polyphenols extracts. Molecular distillation and spray drying of tea phenols extracts were performed using an orthogonal array design. The order of importance that influenced molecular distillation was distillation temperature > flux > rotational speed. The optimal conditions for concentration by molecular distillation were 70°C distillation temperature, 10 mL/min flux, and 1,200 n/min rotational speed. Inlet temperature was found to be the most important determinant of spray drying. The order of importance that influenced the spray drying was inlet temperature > feed flux > wind capacity > feed concentration. The optimal conditions for drying of tea polyphenols extracts by spray drying were determined as follows: 170°C distillation temperature, 3 mL/min feed flux, 30% feed concentration, and 30 m³/h wind capacity. Results of this study indicated that the combination of molecular distillation and spray drying was very suitable for the concentration and drying of tea polyphenols extracts. Using this approach to process tea polyphenol extracts can not only maintain the quality of tea polyphenols but also save time and energy.     

Characteristics and gel properties of gelatin from goat skin as affected by spray drying

Gelatin powder from goat skin prepared by spray drying at various inlet temperatures (160–200°C) was characterized. Predominant particle sizes were in the range of 4.65–5.14?µm. Gelatin powder was mostly concave in shape with varying sizes, depending on inlet temperatures used. All gelatin powders were creamy whitish. Powder generally became more yellowish as the inlet temperature of spray drying increased (p?p?p?p?>?0.05). Goat skin gelatin spray dried with inlet temperatures of 160 or 180°C had higher gel strength than commercial bovine gelatin (p?相似文献   

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.     

Effect of Drying Air Temperature on Drying Kinetics Parameters and Fructan Content in Helianthus tuberosus and Cichorium intybus

Abstract

Helianthus tuberosus and Cichorium intybus tubers accumulate fructans, non-digestible fiber, which has attracted great interest recently as a functional food. In this work a mathematical model for describing the tray drying of the tubers is proposed. It was found that the drying rate in the constant drying rate period was a function of the drying air temperature. Calculated values of the effective diffusivity coefficient are of the magnitude order of 10^?9 m²/s; for both tubers the value of this parameter depends on the drying temperature. Drying affects the fructan molecular weight distribution and fructose content in H. tuberosus and C. intybus tubers. These changes are dependent on the drying air temperature.     

Temperature Changes during Microwave-Vacuum Drying of Sliced Carrots

Abstract

The temperature changes during microwave-vacuum drying of sliced carrots were investigated. Sliced samples were dried to 7–10% moisture content (wet basis) at a wide range of microwave power and vacuum pressure levels. The experiments showed that for sample thickness less than 8 mm, the core temperature of the sample was the same as its surface temperature, with uniform temperature distribution within the sample. However, for sample thickness more than 8 mm, temperature gradient developed along the thickness of the sample. The experiments also showed that, with the decrease of moisture content X _w (dry basis), for samples with thickness ≤ 8 mm, the drying process of sliced carrots experienced three distinct periods: a warming-up period (X _w  = 7.68) without removal of moisture when the product temperature increased linearly with drying time until it reached the corresponding saturation temperature of water in the food at the vacuum pressure; a constant temperature period (2 ≤ X _w  < 7.68) in which most of moisture evaporated and flowed out of the sample efficiently with little resistance; and a heating-up period (X _w  < 2) in which the drying rate decreased and sample temperature increased rapidly. The mathematical models for predicting sliced sample temperature were also developed based on the energy conservation and regression of the experimental date.     

Simulation of a Spray Dryer Fitted with a Rotary Disk Atomizer Using a Three-Dimensional Computional Fluid Dynamic Model

Abstract

Spray dryers fitted with a rotary disk atomizer are widely used in many industries requiring high throughputs to produce powders from liquid streams. The interaction between droplets or particles and the drying medium within the drying chamber is still not well understood and hence difficult to model reliably. In this article CFD results are presented to describe the behavior of the performance of a spray dryer fitted with a rotary disk atomizer in a cylinder-on-cone chamber geometry. Four different turbulence models, i.e., standard k ? ε, RNG k ? ε, Realizable k ? ε, and Reynolds stress models were tested and compared to simulate the swirling two-phase flow with heat and mass transfer in the chamber. The results of this investigation can provide further insight into turbulent swirling flow modeling. The predicted results, such as, air flow patterns, air velocity and temperature, distributions, particle/droplet trajectories, drying performance etc., are obtained using the CFD code FLUENT6.1. Comparison with available limited experimental data shows that CFD results display reasonable agreement. Predicted results also show that the RNG k ? ε model performs better in this specific case.     

A Three-Dimensional Simulation of a Spray Dryer Fitted with a Rotary Atomizer

Abstract

Spray dryers fitted with rotary atomizers are commonly used in diverse industries to produce engineered powders on a large scale. Scale-up of such units is still largely empirical and based on prior experience and know-how. In the present study, a three-dimensional spray dryer with rotary atomizer is investigated numerically with a commercial CFD code. Continuous-phase, i.e., air, conservation equations are formulated in the Eulerian model while the droplet or particle equations are set up in the Lagrangian model. Two-way coupling between the continuous and dispersed phases is taken into account in the governing equations. The stochastic approach is used to predict the particle trajectories. The RNG k ? ? turbulence model was used. Typical results, viz. air velocity, temperature, humidity profiles, and particle trajectories are presented and discussed. Compared with the pressure nozzle spray dryer, more volume of drying chamber is used effectively by the rotating disc type spray dryer. It is found that evaporation and drying take place mainly in the region and in the vicinity of first contact between air and spray. A parametric study is presented and, where appropriate, comparison is made with experimental data obtained with the simulated spray dryer.     

Effects of spray drying on Lactobacillus plantarum BM-1 viability,resistance to simulated gastrointestinal digestion,and storage stability

The aim of this study was to evaluate the applicability of spray drying in the production of high-viability powder of L. plantarum BM-1. Firstly, in order to improve the survival of L. plantarum BM-1 during spray drying, different protectants were added before drying. The results showed that the highest survival rate of 75.70% and the lowest moisture content of 3.67% were achieved with the combination of reconstituted skim milk (RSM) and equal weight sucrose as protective agent. The cell counts reduction of free L. plantarum BM-1 was 2.58 log CFU/ml after exposure to 60°C for 1 min, whereas the reduction in spray-dried cells protected by RSM and sucrose was only 0.08 log CFU/ml. After 120-min incubation in simulated gastric condition, cell counts of free L. plantarum BM-1 decreased approximately 1.4 log CFU/ml, whereas no significant (p > 0.05) reduction in spray-dried cells was observed. Compared to the free cells, the spray-dried cells also showed higher survival under bile salts stress. In addition, the bacteriocin production of L. plantarum BM-1 was not affected during spray drying. Furthermore, the survival rate of spray-dried powder reached 98% after storage for 2 months at 4°C, and a nitrogen replacement package was shown to be better than a vacuum package and air-sealed package at room temperature. Therefore, the combination of equal weight RSM and sucrose is a promising protective agent for L. plantarum BM-1 during spray drying.     

Influence of Spray-Dryer Air Temperatures on Encapsulated Mandarin Oil

The influence of inlet and exit air temperatures (160–200 and 80–100°C, respectively) on the spray drying of mandarin oil was evaluated by using a three-level factor design. For optimization, dryer evaporative rate, volatile oil retention, and microencapsulation efficiency were considered as response variables. The response surface analysis produced significant (p < 0.05) polynomial regression equations that were successfully fitted for all response variables and no significant (p > 0.05) lack of fit was indicated for the reduced models. This observation confirmed an accurate fitness of the reduced response surface models to the experimental data. The multiple response optimizations indicated that an inlet air temperature of 200°C and an exit air temperature of 80°C were predicted to provide the maximum evaporative rate, volatile oil retention, and microencapsulation efficiency in the studied ranges.     

Ascorbic Acid Thermal Degradation during Hot Air Drying of Camu-Camu (Myrciaria dubia [H.B.K.] McVaugh) Slices at Different Air Temperatures

Abstract

Air drying of camu-camu slices was performed in order to estimate the effect of air temperature on the kinetics of ascorbic acid thermal degradation. Moisture variation during the air drying process was monitored gravimetrically by weighing the trays at predetermined time intervals. The experimental points were adjusted by Fick's diffusion model and by the Page empirical model. The effective diffusion coefficient (D_eff) ranged from 8.48 × 10^?10 to 1.34 × 10^?9 m²/s.The ascorbic acid content was evaluated in samples taken during the drying process using Iodine titration, and the results modeled by the Weibull equation. Concerning ascorbic acid retention the best drying condition required air at 50°C. The ascorbic acid retention was 78%, when the moisture content of the product reached 10% (wet basis).     

Effects of Spray Drying Temperature and Additives on the Stability of Serine Alkaline Protease Powders

In this study, after production by recombinant Bacillus subtilis (BGSC-1A751), carrying pHV1431::subc gene in the complex medium and separation of solids from the fermentation broth, serine alkaline protease (SAP) was dried in order to investigate the stabilization during spray drying and subsequent storage. The effect of air inlet temperature of the spray dryer between T = 70 and 130°C and the effect of protective additives, glucose and maltodextrin, at 0–2% (w/v) on SAP activity during spray drying and storage stability of obtained SAP powders at 4°C for a long period (6 months) were evaluated. Increasing drying air inlet temperature generally resulted in an increase in activity loss; moreover, higher absorbance peaks observed at wave number 1061 cm^?1 of the IR spectrums when drying temperature is increased indicates the structural change in the SAP molecule. In most cases presence of additives provided higher activities both after drying and during storage period compared to no additive case. Drying the enzyme with 1% (w/v) glucose at T = 110°C resulted in the highest enzyme activity after drying and storage processes.     

Supercritical CO2 Spray Drying of Ethyl Cellulose (EC) for Preparing Microparticles

Even though common spray drying has been widely used for drying food and related products, the effect of drying conditions of supercritical CO₂ spray drying on the particle sizes of dried products has not been well studied. The objective of this study was to study the effect of drying conditions and design parameters on the particle sizes of biomaterials dried with supercritical CO₂ spray drying. The ethyl cellulose (EC) microparticles were prepared with supercritical CO₂ as the dry medium using an experimental spray-drying apparatus. This research studied the influences of spray nozzle diameter, mass ratio of gas to liquid, solution concentration, temperature, and pressure on the physical characteristics of ethyl cellulose microparticles. The results indicated that the average size of the dried particles ranged from 1.07 to 9.84 µm. The spray nozzle with 8-mm diameter produced smaller microparticles with narrower distribution than the 4-mm spray nozzle. The average particle size increased with the increase of the ratio of gas to liquid. Also, the average size and distribution of the microparticles increased with the rise of temperature and solution concentration but decreased with the increase of pressure.     

Modeling Moisture Loss during Vacuum Belt Drying of Low-Fat Tortilla Chips

A continuous vacuum drying method was used to develop low-fat tortilla chips with good sensory properties. To better understand the process, drying models were developed to determine the effects of drying thickness and temperature on drying rate. Drying rates were determined at three conduction plate temperatures (80, 90, and 100°C) and three product thicknesses (0.8, 1.5, and 2.3 mm). An effective diffusion model and semi-empirical models were used to fit the data. In addition, a model was developed from the drying rate curves that incorporated a drying coefficient [k(t)] that varied with time and could be described by a two-term Lorentzian model. All models had good agreement between experimental data and predicted data, with R ² > 0.98. With consideration of other goodness-of-fit indicators (sum of squared errors [SSE] and χ²), the Page and variable coefficient models provided the best fit. The average effective moisture diffusivity was calculated using nonlinear regression and ranged from D _eff = 1.19 to 1.54 × 10^?9 m²/s. D _eff increased with temperature and was described by an Arrhenius equation with E _a  = 14.1 kJ/mol.

Continuous vacuum drying of a presteamed corn dough can be used to produce low-fat tortilla chips with high crispness and acceptable sensory properties. The drying rate models presented in this study will help predict appropriate drying times, optimize process conditions, and better understand the mechanisms of drying.     

Mathematical Modelling of Solar Kilns for Drying Timber: Simulation and Experimental Validation

Abstract

A complete solar kiln model (including the drying of hardwood timber) has been developed with particular reference to the seasoning of blackbutt (Eucalyptus pilularis) timber. The predicted internal air temperatures, relative humidities, and timber moisture contents have been compared with experimental data. The maximum difference between the actual and predicted moisture contents was 0.05 kg kg^?1. The agreement between the predicted and measured temperatures of the internal air is reasonable, and both the predictions and measurements have a similar cyclical pattern. The generally good agreement between the model prediction of the final moisture content and its measurement may be due to the careful measurement of the boundary conditions such as the solar energy input. The main uncertainties were identified as the heat exchanger output, the measurement of the initial moisture content, and the estimation of sky temperature. The significant uncertainty (18%) in the estimation of the initial moisture content is a key reason for the mismatch between the model predictions and the measurements.     

Effects of initial cell concentration,growth phase,and process parameters on the viability of Lactobacillus rhamnosus GG after spray drying

Abstract

During spray drying, probiotics encounter several stresses which can reduce their viability. To obtain powder with a sufficient amount of viable probiotics, we evaluated the effects of different process parameters, such as initial cell concentration and the bacterial growth phase, on the viability of the model probiotic Lactobacillus rhamnosus GG. Increasing the initial biomass did not positively impact bacterial viability after spray drying. For growth, we found that stationary grown bacterial cells were more resistant to the spray-drying process than mid-log grown cells, probably owing to an initiated stress response. Furthermore, a full factorial 3³ design was used to assess the influence of three different conditions of inlet temperature, feed rate, and atomizing air flow on the outlet temperature and bacterial viability after spray drying. As expected, inlet temperature had the largest influence on both outlet temperature and log-reduction in bacterial viability. An interaction effect was also observed between feed rate and inlet temperature. Considering the viability of L. rhamnosus GG, the optimal outlet temperature ranged between 50 and 60?°C for obtaining powders with the lowest log-reductions in viability.     

Pneumatic Drying of Iron Ore Particles in a Vertical Tube

Abstract

The drying and hydrodynamic characteristics of iron ore particles in a vertical pneumatic conveying dryer (0.078 m ID × 6.0 m high) have been determined. The pressure drop decreases along the height at the acceleration region, while it remains constant irrespective of the height in the fully developed region. The degree of particle drying in the dilute pneumatic region increases with increasing superficial inlet gas velocity at constant inlet gas temperature and solid injection rate. However, it decreases with increasing solid injection rates at identical superficial inlet gas velocity and inlet gas temperature. The degree of particle drying increases from 48.6 to 82.5% as the inlet gas temperature increases from 100 to 400 °C.