Experimental Drying Research Articles

NIR monochrome imaging for monitoring of apple drying process: Light-emitting diode and Band-pass filter imaging techniques

The convergence of drying technology and Digital Twins is enabling a transition from traditional drying methods to a new phase where the process can be continuously monitored. A crucial aspect is the development of digital model of kinetic reactions. In this context, hyperspectral imaging has been widely used, however, it has limitations due to its high cost and computational intensity, which restrict its application to lab-scale settings. To address this limitation, this study introduces technically simple and cost-effective imaging techniques of Light-emitting diode (LED) and Band-pass filter (BPF). These techniques were implemented at 980 nm and 1450 nm to measure moisture content, Soluble Solids Content (SSC), and shrinkage of apple slices undergoing drying at 60 °C. Images of apple slices during the drying process were captured to train Gaussian Process Regression (GPR) models. Moisture content achieved the highest accuracy, with GPR models yielding R-squared values of 0.996 and 0.992, and RMSE values of 1.74% and 2.21% for LED and BPF, respectively. Similarly, SSC (R-squared ≥0.874 and RMSE ≤7.85%) and shrinkage (R-squared ≥0.967 and RMSE ≤5.23%) were well predicted. Furthermore, accurate prediction results for external apples demonstrated the models reliability and robustness. In line with the concept of digital twins-based smart drying, the 980 nm LEDs embedded into an experimental dryer exhibited high accuracy (R-squared ≥0.968 and RMSE ≤4.6%) in inline prediction of moisture content. This represents a significant step towards the development of digital twins-based smart dryers using cost-effective and technically simple imaging sensors.

KARAKTERISTIK PENGERINGAN BIJI PINANG MENGGUNAKAN EXPERIMENTAL DRYER

Abstract
 Areca nut seeds at harvest generally have a high water content, so to reduce the water content of betel nuts, namely drying or drying the betel nuts, they must be dried because if they contain high water content, the betel nuts will be easily damaged. To obtain the drying characteristics, thick sliced, medium sliced, and thin sliced areca seed layers were dried using an experimental dryer.
 This study aims to analyze temperature changes in the dryer during the drying process, determine the drying characteristics of areca nut meat including moisture content versus time, drying rate versus time and drying rate versus moisture content. The betel nut meat taken from the Malalayang One area is then sliced into 3 thicknesses, namely thick, medium and thin. Observations of temperature changes were carried out at the temperature of the material in each thickness, the ambient temperature, the plenum temperature and the temperature above the dried material. The temperature data is plotted and analyzed graphically. The water content was analyzed descriptively calculated based on the hourly weight loss. drying rate obtained from calculations and analyzed graphically.
 The results showed the temperature distribution in the plenum room, drying room, material temperature and drying room temperature. The water content decreased inversely with the change in time, the longer the drying time, the lower the water content in Areca seed, showing a pattern of decreasing water content in this experiment by showing an exponential pattern. Drying time for Areca nut seeds using this drying tool takes 9, 5, and 4 hours for thick, medium, and thin slices. The moisture content of Areca seed at the end of drying was 9.0%, 4.8% and 3.07 for thick, medium and thin slices, respectively. The drying rate of Areca seed relative to the drying time decreased the drying rate. The average drying rates for thick, medium, and thin slices were 7.92%/hour, 15.10%/hour, and 19.31%/hour, respectively.
 Keywords : Drying, Areca Nut, Experimental Dryer

NIR laser-based imaging techniques to monitor quality attributes of apple slices during the drying process: Laser-light backscattering & biospeckle imaging techniques

This paper seeks to investigate the potential use of laser-based imaging techniques in non-invasive quality inspection of apple slices during drying. For this purpose, Laser-light Backscattering (LLBI) and Biospeckle (BSI) Imaging techniques were investigated. Images at 980 nm and 1450 nm were captured. The data was used to develop Gaussian Process Regression (GPR) and Partial Least Square Regression (PLSR) models in order to estimate quality attributes of moisture content, vitamin C, and soluble solids content (SSC). Overall, the predictions accuracies were slightly in favor of GPR models. Moisture content was best estimated with R-squared = 0.92 and RMSE = 7%, and R-squared = 0.93 and RMSE = 6.54% when GPR models were trained on 1450/980 nm data acquired by LLBI or 980 nm data acquired by BSI, respectively. LLBI-based GPR models predicted vitamin C with R-squared ≥ 0.79 and RMSE ≤ 0.83 mg/100 g fresh weight (FW), slightly better than that of BSI (R-squared = 0.80 and RMSE ≤ 1.01 mg/100 g). The most accurate predictions of SSC for LLBI (R-squared = 0.88 and RMSE = 6.39%) and BSI (R-squared = 0.82 and RMSE = 7.99%) were achieved at 980 nm. Furthermore, BSI monitoring system was embedded into an experimental dryer to study the interaction between sample temperature and biospeckle activity. Results showed an increase in biospeckle activity at the beginning of drying followed by a gradual decrease towards the end of drying. The findings of present study indicate the potential use of simple and promising monochrome imaging systems in monitoring of the drying process that can be considered as alternatives to more expensive imaging sensors such as hyperspectral imaging.

Microscopy of maize grains subjected to continuous and intermittent drying

Drying is an important step in the post-harvest processes as a way of product conservation and quality preservation. In this context, this study aimed to evaluate the effect of continuous and intermittent drying of maize grains with different rest periods on the integrity of their micro- and macroscopic structures. Maize grains were harvested with a moisture content of 0.3399 ± 0.001 dry basis (db) and subjected to continuous and intermittent drying with 4, 8, 12, and 16 hours of rest period. An experimental fixed-bed dryer, with controlled drying air conditions at a temperature of 100 °C and air flow of 1.5 m3 min.−1 m−2 (12 m3 min.−1 m−3), was used. Continuous drying was completed with a moisture content of 0.1628 ± 0.0003 db, whereas intermittent drying was interrupted with 0.2195 ± 0.0002 db and resumed after rest. The drying rate, integrity through grain images, the conformation of particles through scanning electron microscopy, and cell membrane integrity were evaluated. The drying rate increased with an increase in the rest period, the increase in rest period reduced the intensity of cracks, and the reduction in rest period led to higher dispersion and reduction in the size of starch granules and lower integrity of cell membranes.

Potencial fisiológico de sementes de feijão guandu sob embalagens, condições de secagem e armazenamento

Neste trabalho objetivou-se avaliar o potencial fisiológico de sementes de feijão guandu submetidas a diferentes condições de secagem durante o armazenamento em diferentes embalagens. O experimento foi instalado em delineamento inteiramente casualizado, em esquema fatorial de 3x4x5 (três condições de secagem: secagem em estufa, secagem em secador experimental e secagem meia sombra; quatro tipos de embalagem: garrafa Pet, caixa Tetrapak, saco de Nylon e galão Pet de 5 L com vela e cinco períodos de armazenamento: 0, 30, 60, 90 e 120 dias). O potencial fisiológico das sementes foi avaliado pelo teste padrão de germinação, teor de água, condutividade elétrica, emergência e envelhecimento acelerado. O tipo de embalagem influencia o potencial fisiológico de sementes de feijão guandu durante o armazenamento. O acondicionamento de sementes de feijão guandu em garrafa Pet permite maior conservação da germinação e vigor durante os 120 dias de armazenamento. A condição de secagem em meia sombra garante maior potencial fisiológico das sementes de feijão guandu durante os 120 dias de armazenamento.

Bir Tartım Otomasyonunda, Platform Tipi Yük Hücrelerinin, S-tipi Olarak Kullanılması

Tarımsal ürünlerin dayanımını artırma gayretlerinden birisi de kurutmadır. Ürünlerin kuruma karakteristiklerini incelemek için yapılan çalışmalarda kütle oldukça önemlidir. Bu çalışmada, kurutma denemeleri için tasarlanmış 3 numune kabına sahip, sıcak hava ile çalışan bir deneysel kurutucu sisteme otomatik tartım sistemi yapılmıştır. Kurutma makinelerinde kapların ağırlıklarını ölçmek için operatör sürekli belirli zaman aralıklarında kapları yerinden çıkartarak, tartıp tekrar yerine koymaktadır. Kurutma süresi, ürün çeşidi ve miktarına göre 72 saate kadar sürebilmektedir. Bu çalışmada, ürünlerin kütle kaybını ölçmedeki zorluklara çözüm getirmek amacıyla bir tartım otomasyonu gerçekleştirilmiştir. Üç hazneli kurutucu için üç adet yük hücresi kullanılarak ürünlerin kütlesi istenen zaman aralıklarında anlık olarak ölçülmüştür. Bu çalışmada Arduino Mega, HX711 24 bit ADC kartı ve kullanıcı ile etkileşim bileşenlerine sahip Nextion ekran kullanılmıştır. Askı tip yükleri ölçmede sıklıkla kullanılan S-tipi yük hücreleri yerine çubuk şeklinde platform tipi yük hücreleri kullanılmıştır. Daha ucuz olan platform tipi yük hücreleri, hazırlanan aparatlarla S tipi yük hücresine dönüştürülmüştür. Bu sayede platform tipi yük hücrelerinden daha duyarlı ve ucuz birer S tipi yük hücreleri elde edilmiştir. Yapılan testlerde ölçmeye ait önemli parametreler elde edilerek sistemin başarımı kanıtlanmıştır.

Drying kinetics and effective diffusion of watermelon seeds

Studying the drying kinetics allows describing the process by mathematical models and obtaining information that helps to understand the phenomenon in question. Considering that watermelon (Citrullus lanatus) seeds have high moisture content and need to be subjected to drying, the objective was to select the model that best represents the drying behavior of watermelon seeds and determine the diffusion coefficient, activation energy and drying rate of these seeds at different temperatures. The seeds were dried in an experimental dryer at temperatures of 40, 45, 50, 55 and 60 °C, with air velocity of 0.8 m s-1, in four replicates. The models were fitted with non-linear regression analysis using the Gauss-Newton method. It was concluded that the models that best represent the drying kinetics of watermelon seeds are Approximation of Diffusion for temperatures of 40, 50 and 55 °C and Page for 55 and 60 °C. The highest drying rates are observed at the highest temperatures. The diffusion coefficients presented magnitude of 7.69684×10-10 and 1.27585×10-9 for the range from 40 to 60 °C, and the activation energy was 12.2641 kJ mol-1.

Drying kinetics and effective diffusion of buckwheat grains

ABSTRACT Buckwheat has become important in the food sector as its flour does not contain gluten. Since buckwheat is a relatively new crop in the agricultural environment, there is little information available regarding its processing. Drying is one of the most important post-harvest stages of buckwheat. The aim of the present study was to describe the drying process of buckwheat grains. Buckwheat grains with a moisture content of 0.41 ± 0.01 (dry basis, d.b.) were harvested, followed by drying in an experimental dryer at the temperatures of 40, 50, 60, 70, and 80 °C, at an air speed of 0.8 m s-1. The drying rate was determined, and the mathematical models generally employed to describe the drying process of several agricultural products were fitted to the experimentally obtained data. Model selection was based on the Gauss-Newton non-linear regression method and was complemented by Akaike Information Criterion and Schwarz’s Bayesian Information Criterion. It was concluded that the drying rate increased with an increase in temperature and decreased with an increase in drying time. It is recommended to use the Midilli model to represent the drying kinetics of buckwheat grains at the temperatures of 40, 60, and 70 °C, while the Approximation of diffusion model is recommended for the temperatures of 50 and 80 °C. The magnitudes of effective diffusion coefficients ranged from 1.8990 × 10-11 m2 s-1 to 17.8831 × 10-11 m2 s-1. The activation energy required to initiate the drying process was determined to be 49.75 kJ mol-1.

UTILIZATION OF DRYING AIR TEMPERATURE AND RELATIVE HUMIDITY FOR SAVING THE REQUIRED TIME AND ENERGY FOR DRYING ROSEMARY PLANTS

The purpose of this study is to test and evaluate the effect of drying temperature on the behavior of moisture content and relative humidity of the drying air and drying time of orchid plants at four different levels of temperature. An experimental dryer was designed and installed with local components, which can control the temperature under study to the levels of (35, 40 , 45 and 50 oC) with a corresponding relative humidity of to the levels of (32.2, 28.3, 24.5 and21.2) respectively. The air speed was adjusted at (1.5 m / s) to achieve maximum utilization of energy used in drying. The average primary moisture content of the rosemary was 80% on a wet basis. There is an inverse relationship between the temperature and relative humidity of the air inside the dryer where the relative humidity of the air decreases from 32.2% to 21.2% when the temperature increased from 35 to 50 oC . There is an inverse relationship between temperature and final moisture content values ​​where the final moisture content is reduced from 80 to 32.65% on a dry basis with temperatures increasing from 35 to 50 ° C. There is a difference between the temperature in and out of the drying air and the difference is greater at the beginning of the drying process has decreased to reach the lowest value at the end of the drying process. The highest value of the relative humidity outside of the air was at the beginning of the drying process and it was reduced during the drying process until it reaches its lowest value at the end of the drying process. There is an inverse relation between temperature and drying time, the higher the temperature the lower the drying time.

Technology and instrumentation stevia solutions of spray drying

The relevance of the use and development of sweeteners is reflected in the article. The main requirements for sweeteners were given: the sweetness quality, color and odor absence, a pleasant taste, harmlessness, complete elimination from the body, good solubility in water, chemical resistance. Due to its beneficial properties, the sweetener obtained from stevia leaves is increasingly used. A method of obtaining stevia extract with subsequent drying is presented. The leaves and stems of the Stevia rebaudiana Bertoni plant were used for the experiment. The extract was obtained using water-alcohol extraction at a temperature of 85–87 ?С, a water module of 1.0: 4.5, and a duration of 115–118 min. using three rinsings, the water and alcohol extracts were combined. The extract filtered from suspended impurities on a deep filter was concentrated under a vacuum of 0.08 MPa at a temperature of 60 ° C to a content of 35%. The resulting concentrate was dried on an experimental spray dryer. The temperature of the dried particles did not exceed 60 ° С, and the drying process lasted 15–30 s. High-quality stevioside powder was obtained due to instant drying and low temperature of sprayed solution particles. Thus obtained sweetener from stevia does not need intermediate purification from ballast substances and does not require further modification to improve organoleptic properties - to enhance sweetness and reduce the residual bitter aftertaste characteristic of some natural glycosides. The authors believe that the resulting sweetener makes it possible to develop new products with dietary and therapeutic purposes.

Artificial drying of safflower seeds at different air temperatures: effect on the physiological potential of freshly harvested and stored seeds

Abstract: The air temperature used in the drying process can determine the initial physiological quality and storage potential of a seed lot, which is the object of this study. Safflower seeds, harvested at a moisture content of 25.8%, were subjected to drying in an experimental dryer at air temperatures of 40, 50, 60 and 70 °C until reaching a moisture content of 6.6 ± 0.6%. Immediately upon drying and every 60 days after that, up to 240 days of storage under uncontrolled conditions, seed samples were collected to determine physiological quality. Increasing drying air temperature resulted in higher water removal rates, promoting immediate and latent damage to seed physiological quality, evidenced by the reduction in the percentage and speed of root protrusion, first count, and germination, mainly at temperatures of 60 and 70 °C. For the maintenance of safflower seed germination and vigor up to 240 days of storage, it is recommended that drying air temperature does not exceed 40 °C, especially when seeds present moisture contents close to or higher than 25.8% at the drying moment.

The effect of material mixing on heat transfer in the process of contact drying

This paper deals with the process of heat transfer in contact drying. Heat transfer during contact drying for a stagnant bed without mixing and drying with a mechanically agitated bed were theoretically and experimentally investigated for a contact paddle dryer. The effect of material mixing on the process of heat transfer was evaluated. For a theoretical description of heat transfer in a contact dryer, the penetration model was used. Experiments with green wood chips were realized on an experimental paddle dryer. In both cases, the stagnant bed and the mechanically agitated bed, the theoretical values were slightly higher compared to the experimental results. Mixing intensifies the process, it showed an increase to roughly twice in heat transfer for the tested experimental dryer.

Drying Kinetics of Tomato, Okra, Potato and Mango in a Forced-Convective Solar Tunnel Dryer

The design of a solar drier requires detailed information about drying kinetics of the products to be dried. The objective of our work is to characterize drying kinetics of tomato, okra, potato and mango and calculate the main drying parameters namely the drying rate, the moisture ratio and the effective diffusivity from the derivative form of the Fick’s second law of diffusion. We found that solar drying of tomato, okra, potato and mango occur in both constant and falling-rate phases. Sound experimental conditions and specifically continuous measurements and data collection during experiments, emerged as a major factor allowing the observation of both a constant-rate and falling-rate phases. Two models namely the Henderson & Pabis Model and the Page Model were used to characterize the evolution of moisture ratios <i>(MR)</i> over time. For each of the abovementioned crops, the Page Model appeared to give a better description of <i>MR</i> = <i>f(t)</i> with χ² varying from 0.0051 to 0.0978. As per the Effective Moisture Diffusivity, its values were 8.866×10^-09, 4.651×10^-09, 4.969×10^-09 and 5.177×10^-09 for mango, tomato, potato and okra respectively. Calculated drying constants were compared with the ones obtained by other authors in similar experimental conditions. The experimental dryer we used was a forced convective solar tunnel dryer. All experimentations were conducted in Niamey (Niger) from 7 to 9 June 2018, 3 to 4 Mars 2019, 24 to 26 April 2018 and 1 to 3 May 2018 for mango, tomato, potato and okra respectively.

Dehydration Kinetics of Cassava, Yam and Potato Slices Using a Refractance WindowTM Dryer

This study aims to investigate the drying characteristics of cassava, yam, and potato slices using a laboratory scale batch Refractance Window™ (RW) dryer. The experimental dryer was constructed by modifying a laboratory water bath. The bath was covered with a transparent Polyethylene terephthalate (PET) plastic film held in-place with angled edges. The cassava, yam, and potato slices were dried on the Refractance WindowTM dryer, and the variation of the moisture content of the slices during the drying process was measured. The water temperature beneath the plastic film was maintained at 60oC. The dehydration data were fitted to thin-layer drying models. Regression analysis suggested that the Haghi and Ghanadzadeh model best describes the dehydration behaviour for the 3 mm thick slices for the cassava, yam, and potato tubers. The coefficient of determination (R2) values of 0.999, 0.998, and 0.998 for the cassava, yam, and potato slices respectively were reported in all the models studied. The drying curves, the drying rate curves, and the Krischer curves, from the experimental drying data, was plotted. Observations indicate that the cassava, yams, and potatoes slices dried to below 0.11 g water/g-solid moisture content in about 150 min. This study was performed to facilitate the understanding of the design, modelling, and operations of a continuously operating RW dryer. Keywords: Refractance Window Drying, Thin Layer Drying Models, Yams, Cassava, Potatoes.

DRYING KINETICS OF NIGER SEEDS

The objectives of this study were to describe the process of drying niger seeds through the fitting of different mathematical models to the experimental drying data, to select the best model that represents the phenomenon, and to determine the diffusion coefficients and thermodynamic properties of the product. Seeds with an initial moisture content of 30% (wet basis) were collected and dried at 40, 50, 60, 70, and 80 oC in a fixed bed experimental dryer. After drying, different mathematical models were fitted to determine the diffusion coefficient by applying liquid diffusion theory, which allowed for calculation of the energy activation, enthalpy, entropy, and Gibbs free energy values. The Page model was selected to represent the drying process of niger seed drying, as it is a traditional and simpler model. The effective diffusion coefficient increased as the temperature increased. The activation energy for liquid diffusion at the temperature range of 40 to 80 oC was 46.83 kJ mol-1. The enthalpy and entropy specific values decreased as the drying air temperature increased. The Gibbs free energy values also increased as the drying air temperature increased.

Performance Evaluation of a Biomass Fuelled Cabinet Dryer

In an attempt to reduce post-harvest losses of agricultural produce to considerable level in rural area in developing countries, a study was conducted to evaluate the performance of a developed biomass fuelled cabinet dryer. The effect of drying air temperature on unripe plantain sizes at 5, 10 and 15 mm dried in a thin-layer dryer was investigated within a temperature range of 50–70 °Cat regular interval of 30 minutes until equilibrium moisture content were reached. The performance evaluations of the experimental biomass cabinet dryer were conducted for thermal efficiency of charcoal and sawdust fuels respectively. It was found that experimental curves of the plantain drying rate versus time showed that drying rate increased when hot air drying increased with time. Moisture transfer occurred during the falling rate period of drying. Moisture loss of the plantain slices at 5 ,10 and 15 mm reached an equilibrium moisture content at 150, 180 and 240 minutes respectively when charcoal fuel was fired. While moisture loss on the plantain slices at 5, 10 and 15 mm reached an equilibrium moisture content at 120, 240 and 270 minutes respectively when sawdust fuel was fired. The maximum overall drying efficiency of the biomass fuel cabinet dryer when plantain slices were dried was calculated to be 89.67 %.

New Experimental Rotary Dryer of Olive Stone: Design, Control and Modeling

Drying is the most important process to treat olive oil mill wastes. Olive stone is a by-product obtained in the olive oil extraction process. Crushed olive stone is separated from olive oil mill waste in the olive oil mills by means of mechanical procedures. Olive stone is mainly used as a biomass product for generating thermal energy for space heating in commercial buildings, residences and homes. Olive stone moisture content ranges from 20 to 30% (wet basis). Drying of olive stone is fundamental for its revaluation as biofuel, and the vast majority of this by-product is dried in rotary dryers. To improve the drying efficiency of olive stone in these dryers, we have designed and modeled an experimental rotary dryer that is intended to solve the heat and mass transfer equation in the sectioned models, both in a steady-state model and transient model, and to contribute to the development of a control system that is much more perfect.

KINETICS OF COLOUR CHANGE OF TOMATOES DURING DRYING

Colour is one of the pharameters determining the quality of dried tomatoes. The changes in colour of the skin of tomatoes during drying in an experimental dryer at various temperatures were measured every two hours by using Minolta CR 200 colorimeter and the colours were represented in Hunter-&lt;em&gt;Lab&lt;/em&gt; scale. The objective of this research was develop a model for predicting colour changes of tomatoes during drying. The decrease in darkness as represented by dL value varied from 10 to 16%, while decrease in chroma value (dL) varied from 20 to 37% of initial values. An empirical logarithmic equation with six constants was derived to fit the data of chroma changes during drying at various temperature and times. The model of colour change of tomatoes can be used for determining the optimum drying temperature to produce acceptable colour of dried tomatoes at reasonable cost.

KINETICS OF COLOUR CHANGE OF TOMATOES DURING DRYING

Colour is one of the pharameters determining the quality of dried tomatoes. The changes in colour of the skin of tomatoes during drying in an experimental dryer at various temperatures were measured every two hours by using Minolta CR 200 colorimeter and the colours were represented in Hunter-&lt;em&gt;Lab&lt;/em&gt; scale. The objective of this research was develop a model for predicting colour changes of tomatoes during drying. The decrease in darkness as represented by dL value varied from 10 to 16%, while decrease in chroma value (dL) varied from 20 to 37% of initial values. An empirical logarithmic equation with six constants was derived to fit the data of chroma changes during drying at various temperature and times. The model of colour change of tomatoes can be used for determining the optimum drying temperature to produce acceptable colour of dried tomatoes at reasonable cost.

Experimental dryer design for agricultural products

This study consisted of designing and building an experimental dryer that allows working with different temperatures and velocities of the air, aiming to perform studies on thin- and thick-layer drying of agricultural products. The project was divided into three stages: heat source designing, dryer geometric parameters, and fan selection to meet operational demand. Heating was made by a set of six electrical resistances totaling 12 kW and the drying bed in thin layer was composed of two trays with diameter of 0.20 m. Operational demands were met using a centrifugal fan with a power rating of 735.5 W. The used methodology was able to size the experimental dryers for thin- and thick-layer drying working at distinct temperatures and air velocities.