Convective Tray Dryer Research Articles

Computer-Aided Neuro-fuzzy Algorithm for Prediction of Ginger(Zingiber officinale) Rhizome Drying

Neuro-fuzzy modeling technique has been used for the development of computer-based adaptive process control systems for most postharvest operations instead of convectional mechanistic modeling technique owing to its good prediction without prior knowledge of process operation. Therefore, adaptive neuro-fuzzy inference system (ANFIS) modeling and prediction of ginger (Zingiber officinale) rhizome moisture content in a forced convective tray dryer was investigated in this study. Computer codes for an exhaustive search and grid partitioning were written in the Matlab software environment and used for the analysis of experimental data obtained from the ginger rhizome drying experiment. The data were trained and checked using the grid-partitioning ANFIS method for the development of neuro-fuzzy network for ginger drying prediction. The prediction accuracy of the network was evaluated by varying input and output Membership Function (MF) types. The exhaustive search analysis shows that drying time (DT) has the highest effect on the moisture content, followed by air drying temperature (ADT), air relative humidity (ARH), and air flow velocity (AFV). Moreover, combination of DT and ADT as two interactive variables; and combination DT, ADT and ARH as three interactive variables show highest effect on ginger moisture content removal during the process. Generalized bell (gbell) MF with two MF for each input variable and constant output MF 2 type were obtained as the best ginger drying ANFIS network with corresponding R and MSE of 0.9667 and 0.0971, respectively. Therefore, this study shows the reliability of the ANFIS model for the prediction of ginger rhizome drying in a tray dryer.

Computer-Aided Neuro-fuzzy Algorithm for Prediction of Ginger(Zingiber officinale) Rhizome Drying

Neuro-fuzzy modeling technique has been used for the development of computer-based adaptive process control systems for most postharvest operations instead of convectional mechanistic modeling technique owing to its good prediction without prior knowledge of process operation. Therefore, adaptive neuro-fuzzy inference system (ANFIS) modeling and prediction of ginger (Zingiber officinale) rhizome moisture content in a forced convective tray dryer was investigated in this study. Computer codes for an exhaustive search and grid partitioning were written in the Matlab software environment and used for the analysis of experimental data obtained from the ginger rhizome drying experiment. The data were trained and checked using the grid-partitioning ANFIS method for the development of neuro-fuzzy network for ginger drying prediction. The prediction accuracy of the network was evaluated by varying input and output Membership Function (MF) types. The exhaustive search analysis shows that drying time (DT) has the highest effect on the moisture content, followed by air drying temperature (ADT), air relative humidity (ARH), and air flow velocity (AFV). Moreover, combination of DT and ADT as two interactive variables; and combination DT, ADT and ARH as three interactive variables show highest effect on ginger moisture content removal during the process. Generalized bell (gbell) MF with two MF for each input variable and constant output MF 2 type were obtained as the best ginger drying ANFIS network with corresponding R and MSE of 0.9667 and 0.0971, respectively. Therefore, this study shows the reliability of the ANFIS model for the prediction of ginger rhizome drying in a tray dryer.

Effect of ultrasound-assisted drying on drying kinetics, color, total phenols content and antioxidant activity of pomegranate peel

The study investigated the effect of ultrasound (US) pre-treatment on drying kinetics, color, total phenols content and antioxidant activity of pomegranate peel (PP). The US pre-treatment was carried out at a frequency of 24 kHz at room temperature for two time periods of 5 and 10 min. The pretreated PP were then dried in a convective tray dryer at two different temperatures (70 and 80 °C). The US pre-treatment had a significant influence on reducing the drying time (approx. 45 % reduction) of PP. Five thin-layer drying models were fit to study the drying kinetics in which Midilli's model gave the best-fit curve. The effective moisture diffusivity (Deff) of PP ranged from 5.44 × 10−09 to 1.49 × 10−08 m2/s. The PP activation energy (Ea) decreased with increased exposure time. The color values (ΔΕ*) increased with increasing treatment time and temperature, however, no significant difference among color values was observed. The total phenol content and antioxidant activity were higher in US-treated peel powder than in untreated (UT) PP. The US pre-treatment of 10 min and dried at 70 °C successfully reduced degradation of total phenolic content and antioxidants and is recommended for PP drying pretreated with US

INFRARED DEHYDRATION OF BLANCHED QUINCE SLICES: STUDY ON PROCESS AND MASS TRANSFER CHARACTERISTICS

In the present work, moisture removal characteristics of quince slices in a convective tray dryer were studied. The blanched slices (with thicknesses of 3, 5 and 7 mm) were dried at drying temperatures of 50, 60 and 70 °C and air flow rates of 1, 1.5 and 2 m/s. The analytical model proposed by Dincer and Dost was used to determine the mass transfer parameters. The obtained Biot numbers (0.108‒0.293) revealed that both the internal and external resistance control the moisture diffusion within the samples. The moisture diffusivity and convective mass transfer coefficient were found to be in the ranges of 1.578×10-7‒7.331×10-7 m2/s and 2.040×10-5‒3.507×10-5 m/s, respectively. The activation energies for moisture diffusion and surface mass evaporation were determined to be in the ranges of 17.607 to 48.019 kJ/mol and 5.270 to 27.430 kJ/mol, respectively.

Effect of treatment and drying method (Solar and convective) on physico-chemical quality of dried moringa leaves

Moringa is one of the promising crop high nutritional and therapeutic values. While drying of moringa leaves, there is significant loss in physical, chemical and nutritional composition of leaves. So, the present study was conducted to investigate the effect of different treatment and drying method (solar and convective) on physico-chemical quality of moringa leaves. Moringa leaves that were sorted, washed and surface dried were considered non-treated whereas leaves that were blanched at 7.5 min after sorting were considered treated. The following samples were dried in three dryers viz., PAU advanced domestic solar dryer, PAU domestic solar dryer and convective tray dryer. Samples that were treated had better physico-chemical quality than untreated sample. Similarly, samples dried in PAU advanced domestic solar dryer had better quality retention i.e. had low moisture content, low colour change, higher protein content, higher ascorbic acid and higher total antioxidant activity.

Studies on drying characteristics of (Tinospora cordifolia) Giloy stem

Natural drug from the plants are gaining popularity because of several advantages such as often fewer side effect, better patient tolerance, relatively less expensive and acceptance due to a long history of use, especially herbal medicines provide rational means for the treatment of many diseases that are obstinate and incurable in other system of medicine. Drying practices are important in giloy for increased active principle retrieval through improved post-harvest processing. Convective tray dryer was used for drying of Giloy stem using. Three different air temperature and air velocity was taken as a process parameters. The effect of these process parameters on the drying characteristics of (Tinospora cordifolia) giloy stem was studied. The effect of dryring air temperature and air velocity on drying time was quite evident. The initial drying rate was maximum i.e. 0.039278 g w/g dm- min at 60°C air temperature and 2m/s air velocity and was minimum 0.0275 g w/ g dm-min at 40 °C and 1m/s air velocity. The maximum drying rate was observed at initial stage of drying for all air temperatures and velocity and the drying rate decreased with drying time.

Process optimization for dehydration of shelled peas by osmosis and three‐stage convective drying for enhanced quality

Peas are highly seasonal and perishable in nature, thereby requiring suitable preservation methods to be available throughout the year. Osmotic drying is one of the suitable methods for preserving perishable and semi-perishable produce. Osmotic drying of green peas was carried out in ternary solutions of water, sodium chloride (NaCl), and sucrose having different solution concentrations and osmotic temperatures. Three-stage drying of osmotically pretreated green peas was carried out in convective tray dryer at air temperatures of 70°C (for first 3 hr), 60°C (for next 2 hr), and 50°C (till final moisture content of below 10% wb). The samples were analyzed for moisture content, color change, sphericity, hardness, and rehydration ratio (RR). The osmotic drying process was optimized using response surface methodology (RSM). The optimized process conditions for maximum sphericity, hardness, and RR and for minimum moisture content and color change were determined as sodium chloride solution (10% w/w) and osmotic temperature of 34.41°C. Practical applications Osmotic drying of foods is advantageous when used in combination with other drying techniques as it reduces total drying time, inhibits enzymatic browning, and also reduces energy costs. This study would help to understand the effect of osmotic solution concentration and osmotic temperature on quality of osmo-convective dried peas. Optimization of process parameters would provide the best combination of osmotic solution concentration and osmotic temperature for achieving better product quality in terms of moisture content, color, hardness, rehydration ratio, and sphericity. The high-quality product hence obtained using optimized process parameters will find utilization not only in soup mixes, ready-to-eat snack foods but also as fresh-like peas upon rehydration during off-seasons.

Thin-layer drying of cassava chips in multipurpose convective tray dryer: Energy and exergy analyses

Energy and exergy data of the drying of thin-layer cassava (Manihot esculenta) chips in a multipurpose convective-type tray dryer at 50 °C were collected to evaluate the technical performance of the drying system. The energy and exergy parameters, i.e. energy utilization, energy utilization ratio, energy efficiency, exergy inflow and outflow, exergy loss, and ex-ergetic efficiency were analyzed. The results indicate that the energy utilization, exergy inflow, exergy outflow, and exergy efficiency increased in the ranges of 9.53–24.66 kJ/s, 5.67–11.34 kJ/s, 2.21–8.04 kJ/s, and 38.90 %270.86 %, respectively, with increasing drying time. The results also show that the energy utilization ratio, energy efficiency, and exergetic improvement potential tend to decrease in the ranges of 0.49–0.68, 47.48 %–62.62 %, and 0.96–2.33 kJ/s, respectively, with increasing drying time. Additionally, stable exergy losses were observed during the drying process, within the range of 3.30–4.27 kJ/s during drying. Further research and development that could be used to improve the performance of this drying process are also suggested.

Empirical Drying Model for the Mass Transfer and Drying Kinetics of Treated and Untreated Saba Banana Slices

Banana fruit is a delight in most Nigerian homes, which is usually eaten fresh, but recently, dried bananas have found their way into the daily snacks. Unfortunately, this precious fruit suffers a huge post-harvest loss due to its high moisture content. This work includes the fitting of the drying process to empirical models to predict the drying process using a locally fabricated convective tray dryer. To prevent discolouring during drying, samples were treated with a 1:4 lemon juice. Drying was carried out (for both treated and untreated samples) at temperatures of 40 0C, 50 0C, 60 0C, and 70 0C. Four empirical models were examined (Newton, Peleg, Henderson-Pabis, and Logarithmic models), and the model with the highest R2 and least RMSE values was adopted as the best fit for each drying temperature. Results showed that the Peleg model favoured air-drying and at temperatures of 50 0C and 600C for untreated and treated samples, respectively, while other models considered, best described the drying at other temperatures, for both treated and untreated samples.

Numerical Simulation of air Temperature and air flow Distribution in a Cabinet tray Dryer

The quality of dried product can be enhanced in cabinet tray dryers through a uniform distribution of drying air flow and temperature. In this work, a numerical investigation is conducted to examine the consequence of air movement on the quality of product dried in a convective tray dryer. The temperature and velocity contours of air in the drying chamber are numerically determined for three different geometries of cabinet tray dryer and are compared. A good harmony is found between the predicted data from CFD and experimental data from the literature. This work will enable us to optimize the drying chamber design for uniform dispersal of air flow and temperature and to improve quality of dried product for large scale applications.

Experimental Evaluation of a Diesel Cogeneration System for Producing Power and Drying Aromatic Herbs

The focus of this work was to evaluate the thermal performance of a cogeneration system used to produce power and dry aromatic herbs. The waste heat from the exhaust gases of the diesel engine was recovered to heat air using a thermosyphon heat exchanger. The heated air was employed in a convective tray dryer in order to dry Origanum vulgare, Mentha spicata, and Ocimum basilicum. The experiments were carried out at full load in a stationary compression ignition engine coupled to a generator. The maximum global energy efficiency of the cogeneration system was 40.14%, and the effectiveness of the heat exchanger achieved 39%.

The Effect of the Drying Method on the Quality of Dried Kiwi Slices

Abstract— Drying is known as a food preservation method which increases the food’s storage time by water reduction. Traditional drying consisted of open sun-drying, but different industrial dryers have been widely used in recent times. The new dryers consist of convective, infrared, ultrasound, freeze fluidized bed and freeze dryers. All of these dryers reduce the water content but under different mechanisms which leads to the end products with different qualities. In this study we aim to compare the difference in quality of kiwi fruit slices dried by three different dryers: 1. Convective tray dryer, 2. Microwave dryer and 3. Freeze dryer. The tray dryer experiments were conducted in two air temperatures of 60 and 80oC in the constant air velocity of 0.8 m/s. The microwave dryer operated in 3 output powers of 180, 270 and 360 W. The condenser temperature and pressure in the freeze dryer reduced to -50oC and 0.1 mbar, respectively. The operating conditions and time were regulated so that the moisture content of all dried samples reduced to nearly 10% in the wet basis. The three parameters of color change, ascorbic acid and antioxidant reduction were selected as the measuring criteria for the comparison of the product qualities. The experiments show that the freeze drying caused the minimum color change while the microwave drying in the maximum power of 360W caused the maximum amount of color change. The concentration of ascorbic acid was measured in the fresh fruits and dried samples by standard methods. The measurements proved that the ascorbic acid content of the freeze dried samples was 80% of the fresh fruits. The ascorbic acid content of other samples was much lower. The antioxidant activity of the dried samples and the fresh fruits was also measured by standard methods and the experimental data also showed that the freeze drying causes the minimum reduction in the antioxidant activity.

Experimental and Theoretical Investigation of Pumpkin Drying in Fluidized Bed Dryer

Thin layer drying characteristics of pumpkin cube were experimentally investigated in a fluidized bed dryer. Experiments were performed at three different drying temperatures: 50, 60 and 70 °C. Pumpkin used in the experiments had an initial moisture content of 95% wet basis (1930 % dry basis). The drying air velocities were set to 3.5 m/s to achieve fluidization. Experimental results show that large drying rates are obtained in the fluidized bed dryer, which are much higher than those obtained with conventional methods and convective tray dryer. In just 120 minutes moisture contents lower than 6% wet basis were achieved. Pumkin drying was mathematically modeled using the Lewis, Henderson ve Pabis, Page, and logaritmic models, all of which are semi-emperical models widely applied in the literature. Using Fick’s first law effective diffusivities were calculated and compared with those in the literature. Effective diffusion coefficients obtained in the fluidized bed dryer were up to 70% higher than the diffusion coefficients obtained in convective tray dryers. Temperature dependence of effective diffusion coefficients was described by an Arrhenius-type relationship.

Assessment of mathematical models of drying of jabuticaba peels through performance indicators

Brazil is a country with a huge diversity of native fruits, and one of them is jabuticaba. The jabuticaba peel is the main part of the fruit due to the high level of bioactive compounds besides fibers and minerals. Therefore, it is necessary to use this residue that can be reused for several purposes, such as extraction of natural colouring. Drying technology is applied with the objective of increasing the shelf life of the jabuticaba skin which has a high level of water. In the present work, an evaluation of mathematical drying models through performance indicators which were accuracy factor (A f ), bias factor (B f ), root mean square error (RMSE) and standard error of prediction (%SEP) was done for studying the drying kinetic of the jabuticaba pell. The drying process was conducted in a convective tray dryer at 43 ⁰C for 352 min. According to the results, the two terms model and the Midilli model were the ones that better fitted the experimental data, and the Page model was the third one. However, the convenience of using the Page model is due to the computational and numerical advantage because it is needed to estimate only two parameters.

<b>Thermophysical properties of yacon (<i>Smallanthus sonchifolius</i>): experimental determination and effect of moisture content

The knowledge about thermophysical properties of foods is especially important in thermal processing, influencing the design, optimization and cost reduction of the process, as well as the quality and safety of the final product. This article deals with the determination of some thermophysical properties of yacon, namely, specific mass, specific heat, thermal conductivity and thermal diffusivity during the osmo-convective drying. Yacon is a root with approximately 90% w.b. of moisture content, whose high concentration of fructooligosacharydes and antioxidants has gained attention in the food research field. Yacon slices were osmotically dehydrated for 2 hours in a sucralose solution and then dried in a convective tray dryer for 2 hours, varying the osmotic solution’s temperature and stirring rate and temperature of the drying air. All thermophysical properties were determined during the drying process at 30-minute intervals. The thermophysical properties were determined not only experimentally but also calculated by models available in literature based on the product’s centesimal composition. A satisfactory agreement between experimental and predicted results was obtained. Further, empirical models obtained by nonlinear regression were successfully fitted to the experimental data, as a function of moisture content, within a 94% - 3% w.b. range.

Ascorbic acid degradation of papaya during drying: Effect of process conditions and glass transition phenomenon

The aim of the present work was to study the degradation of ascorbic acid during hot air drying of papaya cubes and to verify its relationship with glass transition. A convective tray dryer was used in the drying experiments, which were carried out at air temperatures (Tair) of 40, 50, 60 and 70°C and air velocities of 1.0 and 1.32m/s. The lowest Tair induced higher retention of this nutrient at end of drying. At 70°C, papaya sample remained in the rubbery state until the end of drying, since product temperature (Tp) was above the glass transition temperature (Tg) along the process. This state is characterized by great molecular mobility inside the food, which facilitates the degradation. At 40°C, the rate of nutrient degradation was very slow as Tg was close to Tp and papaya has suffered phase transition from rubbery to glassy state.

MATHEMATICAL MODELING AND THIN-LAYER DRYING KINETICS OF BAMBOO SLICES ON CONVECTIVE TRAY DRYING AT VARYING TEMPERATURE

This study investigated the thin-layer drying characteristics of bamboo slices in a convective tray dryer with three different temperatures viz., 55, 65 and 75C and fit the experimental data to four drying models to identify the best fit model and drying temperature. The drying rate curves of slices typically demonstrate a smooth diffusion controlled drying behavior. The drying rate at the beginning of the process was generally lower at 55C, with a marked difference between it and the other temperatures. The difference between MRs increased gradually at the commencement of drying and the time required for reaching equilibrium moisture content decreases with increasing temperature. The average value of coefficient of determination (r2) and RMSE revealed values varied between 0.94–0.99 and 0.014–0.073, respectively. Page and logarithmic models obtained the highest r2 and least RMSE at all temperatures and better reflected the drying mechanism of bamboo slices than exponential model. Rehydration ratio elevated when salt solution used for rehydration and the weight gain was more irrespective of temperature. Superior rehydration was noticed when the slices were dried at 65C, and it was relatively poor at 75C and 55C. Products dried at 65C recorded highest scores for visual appearance and colour at the end of drying. PRACTICAL APPLICATIONS Consumers are inclining towards taking health-promoting products from nontraditional sources. Bamboo shoots are now an important food crop in the international food market. Bamboo shoot being low in fat, high in dietary fiber and rich in mineral content, like an ideal vegetable, has been used traditionally the world over. The market for bamboo shoots is growing steadily, and more and more people are developing a taste for them. Processing while keeping nutrients intact and enhancement of shelf life of the value-added products assume great significance for business potential due to seasonal availability of bamboo shoots. It would demand process standardization for small-scale processing units. Therefore, the use of hot air in controlled cabinet drying through convective air is far more rapid and provides uniformity and hygiene for industrial food drying processes. Therefore, this study deals in detail about dynamics of thin-layer drying kinetics of bamboo slices and its quality evaluation by rehydration and sensory process.

Glass transition phenomenon on shrinkage of papaya during convective drying

A differential scanning calorimeter was used to determine the Tg of papaya pieces equilibrated with several water activities. Thermograms revealed the existence of two Tg. The first, which presented lower value, is due to the matrix formed by sugar and water. The second one, less visible and less plasticized by water, probably corresponds to macromolecules. The data of Tg were satisfactory correlated by the Gordon–Taylor model. A convective tray dryer was used for the drying experiments, which were carried out at air temperatures of 40°C and 70°C and air velocity of 1.0m/s. The shrinkage behavior was accomplished by total area and apparent volume alterations along drying. Samples were photographed during process, and their length and lateral areas were measured using the ImageJ® software. As result, the effect of air temperature on shrinkage was significant and the highest temperature (70°C) induced higher extent of shrinkage values. At this condition, papaya sample was in a rubbery state, characterized by great matrix mobility, and remained so until the end of process, since product temperature (Tp) was above the Tg along the process. At lower temperature (40°C), shrinkage stopped at a critical value of moisture content (0.21g/g, wet basis), which coincided with the point in which the Tg was close to Tp.

Convective drying rates of thermally blanched slices of potato ( Solamum tuberosum): Parameters for the estimation of drying rates

Thermal blanching is a pre-drying treatment applied to some food products in order to inactivate enzymes for preservation of flavours and colour. This process leads to modified surface layers in the products. Drying of such products involve moisture transfer across such layers leading to build-up of moisture concentration gradients within the material being dried. In this study microscopic investigation of surface layers of blanched potato confirms that the presence of such surface layers. Rates of drying of thermally blanched slices of potato ( Solamum tuberosum) of different thicknesses are obtained experimentally in a laboratory convective tray dryer at 85 °C and 95 °C. A model ( Fernando et al., 2008) for estimation of dehydration rates of materials with surface layers which describe three parameters ( l / D ) , r and K p · H· C o related to the drying material and the process is employed in order to evaluate the respective parameters based on the experimental data with the aid of a Matlab optimization program. Consistent values of the parameters were obtained for different thicknesses indicating applicability of the parameters in the model for characterization of species for drying of the blanched materials. Drying rates regenerated using the averaged parameters showed compatibility with experimental data with a correlation coefficient of 0.992.

Modeling of the Seedless Grape Drying Process using the Generalized Differential Quadrature Method

AbstractMathematical modeling of the grape drying process is important in understanding the transport phenomena involved in the production and processing of dried grapes. Drying models proposed in the literature have simplifying assumptions, and thus ignore important phenomena such as shrinkage and changes in transport properties which occur during the drying process. Consequently, a mathematical model is developed for the seedless grape drying process, which considers the effects neglected in previous models. Since an analytic solution to this nonlinear model is impossible, the generalized differential quadrature method is used to solve the models' equations. The model is validated with experimental data obtained from a laboratory scale convective tray dryer operating at 50–70 °C and an air velocity of 1.5 m/s. Model predictions are in close agreement with experimental data due to the inclusion in the model of shrinkage and variation in moisture diffusivity. Model results can serve as a framework to improve the performance of existing and novel dryers, and also in the design of process simulators for dryers.