Laboratory-scale Dryer Research Articles

INFRARED DRYING OF LEMON SLICES

A study was carried out to test and evaluate the use of infra-red radiation as heat energy source for drying lemon slices. A laboratory scale dryer was developed and tested at the laboratory of Agric. Eng. Dept. Fac. of Agric. Mansoura Univ. The experimental treatments included three different levels of radiation intensity (0.973, 1.093, and1.161 kW/m2), three different air temperatures (40, 50 and 60°C) and constant air velocity of 1 m/sec. The drying behavior was simulated using two different thin layer models (Lewis's and Henderson, and Pabis's). The studied models were compared with the obtained drying data, and the most suitable model for predicting the change in lemon moisture content during drying process was then assessed. Final quality of the dried lemons was also determined. The results show that, both studied models could describe the drying behavior of lemons satisfactorily. However, Lewis's model considered more proper for describing the drying behavior and predicting the changes in moisture content in terms of precision and application simplicity. The quality tests of the dried lemons showed that, radiation intensity of 0.973 kW/m2 with air temperature of 50°C recorded the best dried lemon quality in terms of higher retention of ascorbic acid (Vitamin C), citric acid and total soluble sugars.

Drying kinetics of RDX under atmospheric pressure and vacuum conditions

The drying characteristics of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are investigated in the ranges of 60–90°C of drying temperature under atmospheric pressure and vacuum conditions in a laboratory scale dryer. The effect of drying temperature and absolute pressure on the drying characteristics is determined. In order to estimate and select the suitable form of RDX drying curves, the curves are fitted to ten different semi-theoretical and/or empirical thin-layer drying models and coefficients are evaluated by non-linear regression analysis. The models are compared based on their coefficient of determination, such as mean bias error, root mean square error, reduced chi-square and modeling efficiency between experimental and predicted moisture ratios. It is deduced that Midilli–Kucuk model has shown a better fit to the experimental drying data as compared to other models. A diffusion model is used to describe the moisture transfer and the effective diffusivity for RDX drying is also determined at each temperature. Beside, the activation energy is also expressed using Arrhenius-type relationship under atmospheric pressure and vacuum conditions.

Drying Kinetics of RDX under Vacuum Conditions

The drying characteristics of Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are investigated in the ranges of 60-90°C of drying temperature under two vacuum conditions in a laboratory scale dryer. The effect of drying temperature and absolute pressure on the drying characteristics is determined. In order to estimate and select the suitable form of RDX drying curves, the curves are fitted to ten different semi-theoretical and/or empirical thin-layer drying models and coefficients are evaluated by non-linear regression analysis. The models are compared based on their coefficient of determination, such as mean bias error, root mean square error, reduced chi-square and modeling efficiency between experimental and predicted moisture ratios. It is deduced that Midilli-Kucuk model has shown a better fit to the experimental drying data as compared to other models. A diffusion model is used to describe the moisture transfer and the effective diffusivity for RDX drying is also determined at each temperature. Beside, the activation energy is also expressed using Arrhenius-type relationship under atmospheric pressure and vacuum conditions.

Intelligent approaches for linear controllers tuning with application to temperature control

Despite the new sophisticated controllers the linear PI/PID controllers keep the leading position in industrial implementations due to their simplicity, easy and well developed design and tuning, good system performance and robustness and universal application area. Various enhancements have been suggested to enlarge their range of operation with good performance. Fuzzy logic (FL) and genetic algorithms (GAs) offer proper intelligent solutions for improving the PI/PID controllers auto-tuning and adaptation to successfully deal with plant nonlinearity, inertia and changing parameters without plant model. The aim of this research is to develop a simple for engineering use method for design of a fuzzy two-level controller (FTLC) of a linear PI/PID controller and a FL supervisor. The FL supervisor tunes on-line the scaling of the basic PI/PID controller's gains depending on performance indicators. The basic FTLC parameters are off-line optimized using GAs and a proposed fitness function of system performance and energy efficiency which is estimated in system simulation with a GA developed T-S plant model. The method is tested in real time control of the temperature in a laboratory – scale dryer. The result is decreased settling time, overshoot and energy consumption in the whole range of operation of the nonlinear plant.

Impact of the spray drying conditions and residence time distribution on lysine loss in spray dried infant formula

The essential amino acid lysine plays an important role for the nutritional quality of infant formula. Unfortunately, it is easily damaged during spray drying which is usually used to produce infant formula powders. In this study, we showed that the extent of lysine loss can be controlled by adjusting the air inlet temperature and the air-to-liquid ratio. Depending on the spray drying conditions, 10.4 ± 2.9% lysine loss down to no lysine loss was determined after spray drying in laboratory scale and in pilot scale. A main impact on lysine loss could be attributed to the particle residence time which was shown to be longer for the short-form, pilot-scale spray dryer than for the tall-form, laboratory-scale spray dryer. Median particle residence time was 6 s in the laboratory scale dryer and 17 s in the pilot scale dryer. The air-to-liquid ratio of the spray dryer proved to be a good parameter to compare different types of spray dryers. The extent of lysine loss during storage of the spray dried powders was independent of the extent of lysine loss during spray drying. Lysine loss during storage can be reduced by low storage temperatures and low water contents of the powder. Coupling kinetics of lysine loss that take into account the physical state of lactose, i.e., glassy, rubbery, or crystalline, with the processing conditions and particle residence time during spray drying was shown to be a promising tool to improve the nutritional quality of spray dried infant formula.

Low-temperature convective drying of apple cubes

The paper presents results of an experimental investigation of convective drying of Idared apple in full recirculation laboratory scale dryer. The experiments were conducted with cube-shaped apple samples (side length 10 and 13 mm), without pre-treatment. The parameters of air stream over the tray with samples were fully controlled and adjusted in several sets of experiments, while always remaining in the following ranges: temperature 35–55 °C, relative humidity 10–30%, velocity 1–2 m/s. The drying kinetics of the apple samples was recorded, the results were analyzed and compared to the existing drying models. The analysis of the experimental results enabled derivation of correlations between drying parameters in a form k = f(T,RH), within Henderson & Pabis drying model MR = aexp(−kτ), as well as the calculation of effective moisture diffusivity during the process.

Study on Thin Layer Drying of <i>Rosa laevigata</i> Michx

The drying process of traditional Chinese medicine Rosa laevigata Michx was investigated in a laboratory scale dryer. Drying experiments were conducted at five temperatures of 40℃, 50℃, 60℃, 70℃ and 80℃. The experimental data were fitted to ten different thin layer drying models to select a suitable model for describing the drying process of Rosa laevigata Michx fruits. The results showed that the Midilli model had the highest value of R2 (0.999767), the lowest χ2 (0.000034) and RMSE (0.003616) among the ten models considered. The drying process of Rosa laevigata Michx fruits consisted of 1st falling rate period and 2nd falling rate period. The effective moisture diffusivity was found in the range of 1.49 - 30.20 × 10-11 m2·s-1. The value of activation energy obtained by plotting lnD versus 1/T is about 36 kJ·mol-1.

Kinetic Drying and Mathematical Modeling of Apple Slices on Dehydration Process

The hot air convective drying characteristics of thin layer apple slices were evaluated in a laboratory scale dryer. In this study, the required energy for dehydration of apple slices was supplied of the hot air drying. Drying behavior of apple slices was studied at 4 temperature levels (50, 65, 80, and 95°C), and at three levels of drying material thickness (3, 5, and 7mm) with the constant airflow velocity of 1m/s. Empirical data of experiments with variants of semi-theoretical and empirical models were evaluated. Finally, the results indicated that the Midilli et al. model was most adequate in predicting moisture transfer and root mean square error (RMSE), chi-square (χ2) and coefficient of determination (R2) were used for the determination of the best suitable model. The values of R2, χ2 and RMSE at 95°C of hot air temperature for 3mm of apple slices are obtained as 0.9979, 0.000092 and 0.01044 respectively.

Drying Kinetics of Extruded Pellets in Fixed Beds

To study the drying behavior of extruded feed pellets in a fixed bed, the drying kinetics were investigated in a laboratory-scale dryer. The effect of types of aeration, air temperature, and bed depth on drying curves and moisture nonuniformity was analyzed. The results showed that drying was mainly affected by the air flow direction, air temperature, and bed depth. The moisture nonuniformity was 2% for an alternating air flow direction drying, where as it was 7% for one-way drying at a bed depth of 15 cm at 33 min. Alternating direction drying improved moisture uniformity, but the drying rate was decreased at a bed depth of 20 cm. A constant drying stage was observed at a critical bed depth, where as an increasing drying rate stage was observed for a deeper bed. The pressure drop (ΔP/L) was studied by ventilation experiments considering the effect of air flow rate, moisture content, bed type, and bed depth. The result showed that pressure drop in a double bed was greater than that in a single bed with the same bed depth. The pressure drop increased with air flow rate and decreased with moisture content and bed depth.

Thermal Drying of Pepper Berries

This paper focuses on the drying kinetics at different temperatures of air in the chamber (lab scale dryer). A theoretical drying model was suggested. A number of experiments were carried out to study the drying characteristics of the fresh pepper berries in a lab scale dryer at six different temperatures which ranged from 30o C to 55o C at 5oC interval. In accordance with the experiments and the proposed model of drying of pepper fruits, the main parameters that contribute to accelerate the process can be distinguished. The parameters include the temperature of drying, the air humidity of the fruits surrounding and velocity of saturated water vapour transfer between the fruits and the surrounding. From the experiments, it was noticed that the change in size over time depends on the drying temperature. The drying process was accompanied by a number of processes that may be taken into account in refining the theoretical model. Characteristic drying time, according to the developed model exponentially depends on temperature, is proportional to the volume of pepper fruit, and inversely proportional to the coefficient of mass transfer. Mass transfer coefficient can be changed by changing of the air flow surrounding the berries in the drying chamber. This will work effectively in case when the drying is limited by high humidity in the surrounding.

Heat and Mass Transfer during Drying of Liquid Pasty Plant Extract by Vacuum Belt Drying

The present work is focused on heat and mass transfer during drying of instant coffee within a vacuum belt dryer. A series of drying experiments in a lab-scale dryer were performed. Using an advanced temperature measurement technique, the process could be optimized with respect to product quality. Thermal conductivity of coffee extract was investigated over the whole range from liquid extract to dry product. Additionally, the influence of porosity was analyzed. Based on the results, a numeric model was developed describing the coupled heat and mass transfer. The understanding of the process has been improved and the basis for a strong optimization tool has been found.

A basic investigation on instant coffee production by vacuum belt drying

The present work represents a basic investigation on instant coffee production by vacuum belt drying. A series of drying experiments in a lab-scale dryer were performed varying the process parameters optimizing the product's properties. Density, structure and flavor of the product were tested and compared to commercial products, which were produced by freeze or spray drying. It was found, that by optimized process parameters instant coffee can be produced, which fulfills present product requirements. Furthermore, the mass transfer throughout the drying process was analyzed, determining the effective diffusion coefficient by means of a thin film measurement technique. Additionally the sorption behavior of instant coffee was systematically investigated and could be described using a GAB sorption isotherm. No influence of the production process, coffee variety or temperature on the sorption behavior was detected.

Mathematical modeling of thin-layer drying of fermented and non-fermented sugarcane bagasse

This work reports hot-air convective drying of thin-layer fermented and non-fermented sugarcane bagasse. For this purpose, experiments were carried out in a laboratory-scale dryer assessing the effects of solid-state fermentation (SSF) on the drying kinetics of the processing material. The fermented sugarcane bagasse in SSF was obtained with the use of Kluyveromyces marxianus NRRL Y-7571. Drying experiments were carried out at 30, 35, 40 and 45 °C, at volumetric air flow rates of 2 and 3 m3 h−1. The ability of ten different thin-layer mathematical models was evaluated towards representing the experimental drying profiles obtained. Results showed that the fermented sugarcane bagasse presents a distinct, faster drying, behavior from that verified for the non-fermented material at the same conditions of temperature and volumetric air flow rate. It is shown that the fermented sugarcane bagasse presented effective diffusion coefficient values of about 1.3 times higher than the non-fermented material. A satisfactory agreement between experimental data and model results of the thin-layer drying of fermented and non-fermented sugarcane bagasse was achieved at the evaluated experimental conditions.

Computational Analysis of Fluid Dynamics in Pharmaceutical Freeze-Drying

Analysis of water vapor flows encountered in pharmaceutical freeze-drying systems, laboratory-scale and industrial, is presented based on the computational fluid dynamics (CFD) techniques. The flows under continuum gas conditions are analyzed using the solution of the Navier–Stokes equations whereas the rarefied flow solutions are obtained by the direct simulation Monte Carlo (DSMC) method for the Boltzmann equation. Examples of application of CFD techniques to laboratory-scale and industrial scale freeze-drying processes are discussed with an emphasis on the utility of CFD for improvement of design and experimental characterization of pharmaceutical freeze-drying hardware and processes. The current article presents a two-dimensional simulation of a laboratory scale dryer with an emphasis on the importance of drying conditions and hardware design on process control and a three-dimensional simulation of an industrial dryer containing a comparison of the obtained results with analytical viscous flow solutions. It was found that the presence of clean in place (CIP)/sterilize in place (SIP) piping in the duct lead to significant changes in the flow field characteristics. The simulation results for vapor flow rates in an industrial freeze-dryer have been compared to tunable diode laser absorption spectroscopy (TDLAS) and gravimetric measurements.

Drying Characteristics and Kinetics of Vacuum Microwave–Dried Potato Slices

Vacuum microwave dehydration characteristics and drying kinetics of potato slices were evaluated using a laboratory-scale dryer. The test materials were placed on a rotating tray to allow uniform exposure to the microwave field. The effect of drying conditions on the drying characteristics was investigated. As expected, higher drying rates were obtained with higher microwave power and lower vacuum levels. The effect of vacuum pressure on drying rate was not as significant as that of microwave power. The Henderson & Pabis model provided better simulation of the drying curves for potato slices. Empirical models are presented for the drying rate constant as a function of the microwave power and vacuum pressure for potato slices under the range of operating conditions tested.

Investigation of Drying Geldart D and B Particles in Different Fluidization Regimes

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Modelling variability in initial parameters for the simulation of rough rice drying using the covariance decomposition algorithm

The drying of rough rice kernels was studied using Monte Carlo modelling of batch behaviour at a constant low air temperature and relative humidity. In order to determine the effects of air temperature and initial moisture content on the drying constant and equilibrium moisture content, the tests were performed in a laboratory-scale drying system at various temperatures (15, 20, 25 and 30 °C) at a constant air velocity of 0.5 m s −1 and a relative humidity of 35±2%. The drying model to describe the batch behaviour was developed by coupling drying kinetics with a Monte Carlo method based on a covariance decomposition algorithm. It was concluded that the proposed drying model could successfully describe the batch drying of rough rice under the range of conditions studied.

A comparison of crystallisation approaches in spray drying

Simulations of crystallisation behaviour in a spray dryer have been performed using modifications to a model developed by previous workers and applied to lactose produced by a Buchi-290 laboratory scale dryer. Crystal growth behaviour has been modeled using Williams–Landel–Ferry (WLF) kinetics and also using lactose crystallisation kinetics from solution, with the assumption that no further crystal growth occurs when the material temperature is less than or equal to the glass-transition temperature. Explorations using all the approaches have suggested that the air inlet temperature is an important variable affecting the crystallinity of the product. This is confirmed by experimental evidence showing that the apparent degree of crystallinity for lactose is affected by the inlet air temperature over the range from 134 °C (∼55% crystalline) to 210 °C (∼76% crystalline). Comparing the trends predicted by the different approaches with experimental data from the literature suggests that WLF kinetics are most successful in predicting all the data, suggesting that the amorphous to crystalline transition cannot be neglected relative to the initial crystal growth from solution inside the droplets.

Partial Crystallization Behavior during Spray Drying: Simulations and Experiments

Simulations of crystallization behavior in a spray dryer have been performed using modifications to a model developed by previous workers and applied to a Buchi-290 laboratory-scale dryer. The potential crystallization behavior has been modeled using Williams-Landel-Ferry kinetics. Explorations using the model have suggested that the air inlet temperature is an important variable affecting crystallization in the dryer. The explorations suggested drying conditions that permitted reasonable drying while controlling the degree of crystallization. These conditions were examined and tested experimentally, also showing that the apparent degree of crystallinity was affected by the inlet air temperature over the range of inlet temperatures from 134°C (∼55% crystalline) to 210°C (∼76% crystalline). The simulation also predicted the trends in the experimental results from previous workers where their experimental results are considered in terms of the measurement techniques used in each case, suggesting that the simulation is a reasonable tool for developing operating conditions for drying equipment to give low or high degrees of crystallinity in the products.

The effect of temperature on the crystallinity of lactose powders produced by spray drying

The effect of varying the inlet air temperature over the range from 134 °C to 210 °C on the degree of crystallinity for spray-dried lactose powders (from ∼55% crystalline to ∼76% crystalline) has been studied experimentally in a Buchi-290 laboratory-scale dryer, since the temperature is likely to be important according to the Williams–Landel–Ferry theory for solid-phase crystallization. The increased crystallinity at higher-temperatures has been measured by water-induced crystallisation, X-ray diffraction, modulated differential scanning calorimetry and pore size and volume analysis, with all techniques showing consistent results. The results indicate that the degree of crystallinity in spray-dried products can be controlled by adjusting the operating conditions.