Drying Of Slices Research Articles

Evaluating of Microwave Drying for Hawthorn Slice as Alternative to Convective Drying

HIGHLIGHTS Microwave drying lead to improve the drying characteristics of Hawthorn slices. Page model was found as the best described the microwave drying data. Microwave drying at 360 W can be applied as an effective technology for drying of hawthorn slices.

Modeling convective thin-layer drying of carrot slices and quality parameters

The influence of thin layer convective dehydration parameters on drying kinetics parameters, chemical composition, and color parameters of carrot slices were investigated, and corresponding mathematical models were developed. In the carrot slices, convective dehydration process hot air temperature and the sample slice thickness were varied, while measured, calculated, and modeled responses were: time of dehydration, effective moisture diffusivity, the energy of activation, proteins and cellulose contents, lightness, redness, and yellowness. The obtained results showed that varied convective dehydration process parameters statistically significantly affected all investigated responses except activation energy. The most efficient drying model with the minimum thickness (3 mm) and the maximum drying temperature (70?C) had the shortest drying time (231 minutes). This model had the minimum resistance to mass transfer (the minimum effective moisture diffusivity, 2.04 ? 10?08 ? 7.12 ? 10?08 [m2s?1]), and the average maximum energy of activation (31.31 kJ/mol). As far as the carrot slices? chemical composition and color parameters were concerned, the model with the maximum thickness (9 mm) and the minimum drying temperature (35?C) was the optimal one. This model had the longest dehydration time (934 minutes), the maximum resistance to the mass transfer (8.87 ? 10?08 [m2s?1]), the minimum total protein content (5.26 %), and the darkest color (49.70). The highest protein content (7.91%) was found for the samples subjected to the highest drying temperatures and the lowest carrot slice thickness. In contrast, the process of convective dehydration had led to the lighter, reddish, and yellowish carrot slices. All developed mathematical models were statistically significant.

Energy consumption and thermal properties of drying banana (musa ssp) under varied relative humidity

The drying of banana slices was investigated under different relative humidity (RH) in a convective hot-air dryer. The experiments were conducted using 10, 20, 30 and 40% RH, 75oC and 2.0 m/s air velocity drying conditions. Drying kinetics, energy consumption and thermal properties were investigated. Eight mathematical models describing thin layer drying were employed and results were compared to their goodness of fit in terms of coefficient of correlation (R2), the root mean square error (RMSE) and the reduced chi square (χ2). The Midilli–Kucuk model could satisfactorily describe RH-convective drying of banana slices with R2, RMSE and χ2 in the ranges of 0.99947-0.99986, 0.00002-0.00008, and 0.0142-0.01618 respectively. For energy consumption, RH condition increased the energy consumption such that at every 10% increase in RH, a range of 17.9-41.0% increase in energy consumption was observed. In the case of thermal properties, endothermic peak revealed precise composition, fine particle size, and dispersion in a matrix of banana slices thus altering the transition in solid state. In effect, RH drying present new drying concept with prospecting thermodynamics absorbing properties. However, energy consumption issue needs to be addressed in further research.

Drying kinetics and the effect of blanching pretreatment on banana

The aim of this study was to estimate and select the drying kinetic model of thin-layer drying of banana slices and the effect of blanching pretreatment. In order, 16 semi-theoretical and/or empirical models were applied to the experimental data and compared according their coefficients of determination (R2), sum squared errors (SSE), and root mean square error (RMSE), which were predicted by non-linear regression analysis. Banana slices were subjected to the thermal blanching treatment, and then the samples were dried at 50 °C and 60°C for a period of 630 min. Chromatic characterization and shrinkage analysis were performed. Among the thin-layer drying models considered to determine the kinetic drying parameters, the semitheorical Two-term model gave the best fit for all drying conditions. Effective moisture diffusivity varied from 8.25 × 10−11 m2s-1 to 2.26 × 10−10 m2s-1 over the temperature range of the study. The increase in temperature led to a 60% average volume reduction. For color, the parameters L* and b* decreased, and a* increased in relation to the temperature increase, and blanching had a positive effect.

Performance evaluation of modified forced convection solar dryer with energy storage unit for drying of elephant apple (Dillenia indica)

AbstractThe development and performance of a modified force convection solar dryer (MFCSD) for drying elephant apple slices have been presented in this research. The MFCSD consists of two solar collectors and a drying chamber of 20 kg drying capacity. The secondary collector is integrated with thermal energy storage unit using a phase change material—paraffin wax. Performance analysis of the MFCSD was studied for drying elephant apple (Dillenia indica) slices. The proposed design enhanced the collector thermal efficiency by 12% as compared to a conventional glass collector. Drying of elephant apple slices in MFCSD will limit exergy losses and increase exergy efficiency. The estimated uncertainty of the collector chamber and the drying unit of the proposed MFCSD were obtained as ±3.3% and ±1.0%. Quality analysis (proximity analysis and textural properties) of the fresh as well as samples dried in open sun drying, tray drying, and MFCSD was carried out. The contents of carbohydrates (47.85 ± 2.66) and protein (21.24 ± 1.68) were high in samples dried in MFCSD when compared to samples dried in other two methods. The ash content of the sample dried in MFCSD was found to be 10.25 ± 0.15%, which was higher than samples dried in tray dryer. The payback period for drying elephant apple in MFCSD is 2.56 years, which is lower than the lifetime period (20 years) of the dryer.Practical ApplicationsA traditional method practiced by small farmers for drying high‐value perishable fruits is conventional open sun drying (OSD). Owing to slow drying rate and excessive heating, products dried under the open sun lose their nutritious and medicinal qualities. The present work details the construction of a low‐cost solar dryer for the drying of elephant apple. The aim of the drying kinetics to develop the architecture aspects of the solar dryer is to refine the drying systems. The results showed that the performance of modified force convection solar dryer (MFCSD) assisted with thermal storage could improve the quality of dried elephant apple slices and reduce drying time in comparison with an OSD method and a tray drying method. MFCSD would be a suitable alternative to the conventional dryers employed commonly in the industries for the drying of high‐valued agricultural products, and it can also be restructured to any size according the requirements.

Modelling the influence of hot air on the drying kinetics of turmeric slices

The influence of different drying temperatures and slice thicknesses on the drying kinetics of turmeric slices was studied to show how moisture is removed. The best model for predicting the drying kinetics was also determined. Turmeric slices (3 mm, 5 mm, and 7 mm) were dried at 40, 50, and 60 °C in a laboratory oven dryer. Four thin layer drying models (Newton, Henderson and Pabis, Logarithmic, and Page) were fitted to the experimental data and the selection was done based on the model with the highest correlation coefficient (R2), and lowest reduced chi-square (χ2), the sum of square error (SSE), and root mean square error (RMSE). Drying time varied between 420 min and 1140 min as the air temperature increased from 40 °C to 60 °C. The effective moisture diffusivity coefficient increased with increasing drying temperature and was found to be between 1.35×10-10 m2/s, and 5.00×10-10 m2/s, 3.00×10-10 m2/s and 10.91×10-10 m2/s, and 4.56×10-10 m2/s and 13.00×10-10 m2/s at 40 °C, 50 °C, and 60 °C, respectively. The values obtained for the activation energy for moisture diffusion were found to be 56.809, 56.060, and 45.561 kJ/mol for 3, 5, and 7 mm, respectively. The page model was found to best describe the oven drying of turmeric slices.

Study of the drying behaviour and color kinetics of convective drying of yam (Dioscorea hispida) slices

Drying is a crucial step in processing for enhancing the storability of yam (Dioscorea hispida) slices. In this present work, the drying of yam slices was carried out in a lab-scale auto weighing forced convective hot air drier at a temperature span of 50–70 0C after 30 min of boiling. The study focused on drying behavior, fitting mathematical models to drying and color kinetics, examining the texture and rehydration ratio of dries yam slices. To exhibit the mass and color change characteristics, experimental data were fitted to seven drying kinetics and two color kinetics models. Model fitness was compared and selected based on chi-square (X2), goodness of fit (R2), residual sum of squares (RSS), and root mean square error (RMSE). Moisture diffusivity ranged from 4.5133 × 10−10- 7.522 × 10−10 m2/s and increased with temperature. The activation energy of 23.53 kJ/mol was obtained. Midilli-kucuk model confirmed the superior fitting to experimental data followed by two-term model. Color kinetics was determined using L, a, b values, total color change (∆E), chroma, hue and browning index. L value reduced with drying time, while b and a value increased. Zero order kinetics fitted a and ∆E values adequately while first order kinetics described the changes in L and b values. It can be concluded that the Midilli-kucuk model can be used for predicting drying process behavor, system design of convective hot air drying of Dioscorea hispida for industrial scale up.

Simulation of temperature during vacuum microwave drying of mixed potato and apple slices

The increased use of vacuum microwave drying in food industry is attributed to shorter drying time and lower temperature. The temperature change of materials is difficult to model due to the vacuum condition. A simplified mathematical model is presented subject to some assumptions to predict the temperature distribution in slices made using a mixture of potato and apple purées. Dielectric loss factors of mixed slices were found to increase with temperature and water content. The model accounts for temperature and moisture-dependent dielectric loss factor which yields a useful predictive tool.

Conjugate modeling of flow and simultaneous heat and mass transfer in convective drying of porous substances

An in-depth understanding of the convective drying mechanism is significant for improving industrial production efficiency and reducing available energy consumption. In this research, a conjugate numerical model appropriate for representing the convective drying is developed and incorporated into the computational fluid dynamics framework, which adopts a non-equilibrium approach to depict the thermal transfer between the hot air and wet porous substances. The thermophysical properties of wet porous substances are formulated to change dynamically in response to the variation of moisture content. A concept of two-resistance dynamic equilibrium is introduced to characterize the interstitial mass exchange between phases, in which the void surfaces of wet porous substances are treated as phase interfaces. That numerical model is then validated by simulating the convective drying of apple slices for different airflow conditions. Calculation results show that the numerical model is capable of accurately predicting the time history of moisture content. The simulative results are in excellent agreement with experimental data as well. The flow distribution of field variables, the non-equilibrium thermal transfer, and the interstitial mass exchanges are also effectively captured. It indicates that the present conjugate numerical model can predict the pivotal physical phenomena involved in convective drying.

Experimental study of infrared – assisted heat pump drying of lime slices

This paper describes the experimental drying of lime slices using an infrared –assisted heat pump dryer. Experiments were carried out on a heat pump dryer model with a capacity of 1 HP integrated with 2000 W infrared radiator whose power can be varied from 0% to 100%. Experiments have been performed with the drying capacity of 1,2 kg/batch and the drying air velocity of 1,2 m/s. Three evaluations were considered: the effect of material thickness on drying time; the effect of temperature in drying chamber and intensity of infrared radiation on drying time, power consumption and product quality. The results showed that the drying process having 3 mm thickness of lime slices, the temperature in the drying chamber of 42,5¸45oC and the radiation intensity of 110¸300W/m2 was the good effective drying range. In addition, the study formulated a linear regression equation for the drying time relationship with drying chamber temperature and infrared radiation intensity. This mathematical model can be used as reference to determine actual drying time as well as a helpful tool for designing infrared - heat pump dryer.

Performance evaluation of cabinet solar dryer using ultraviolet (UV) sheet

This study presents experimental investigation into a novel UV cabinet type solar dryer designed for drying banana slices at the Chhattisgarh Swami Vivekanand Technical University (21 27′N, 81 43′ E). An experiment for the performance assessment of banana drying was conducted at the clear sky conditions. The solar dryer consists of 6 trays with the one drying chamber. The same technique is used for forced convection drying using the fan and the PV panel. Experimentally evaluated local metrological conditions such as solar radiation, atmospheric temperature, wind speed and air humidity. In the six trays for drying, 2 kg of banana slices were evenly divided and after a period of 16 h of drying, banana slices dried in the forced convection to moisture content of 13.75 % from an initial moisture content of 86.2%. On the other hand, natural convection drying reaches to 17.5% of the final moisture content, in the same time. Moisture ratio for the forced and natural convection drying varies in the range of 0.79–0.001 and 0.85–0.05, respectively. For the forced convection drying of banana slices the optimal and minimum drying efficiency of the designed solar dryer are 16.32 % and 0.29% whereas 13.75% and 0.15% of drying efficiency for natural convection drying are measured. The more efficient is forced convection drying in comparison with natural convection drying.

Drying of pineapple slices using combined low-pressure superheated steam and vacuum drying

Abstract A method of combining low-pressure superheated steam drying (LPSSD) and vacuum drying (VD) was proposed to improve the dried pineapple quality and increase the drying rate. It was found that the inversion temperature in low-pressure superheated steam drying of pineapple was 85.75 °C in terms of the first falling rate period. The combining drying (LPSSD–VD) reduced the maximum material temperature by 9.5 °C and 0.35 °C, and shortened the drying time by 50 min and 90 min compared with LPSSD and VD at the same drying temperature of 90 °C. The vitamin C retention rate of dried pineapple by LPSSD–VD was 29.33% and 15.94% higher than that of LPSSD and VD, respectively. The color of dried pineapple was also improved. Moreover, the sugar content of dried pineapple can be well controlled to meet the health demand of low sugar and ensure the taste of dried pineapple during LPSSD–VD process.

Infrared drying of pear slices: Drying kinetics, energy, and exergy analysis

AbstractOver the last few decades, the drying process has proven to be a fundamental operation within the food industry, as it prolongs the shelf life and reduces the levels of deterioration of the product. Infrared drying has gained great attention in recent years as it promotes more uniform and energy‐efficient drying. Given the above, this study aimed to perform infrared drying of pear slices at different temperatures, evaluating the drying kinetics, and the thermodynamic analysis. The pear slices 3‐mm thick were dried in an infrared dryer at temperatures between 50 and 100°C until constant mass. Different mathematical models were fitted to the experimental data to represent drying as a function of time. Energy and exergy analysis were performed by applying the first and second laws of thermodynamics. The Henderson and Pabis modified model satisfactorily represented the drying of pear slices. The effective diffusion coefficient increased linearly with increasing temperature, ranging from 1.15 × 10−9 and 5.08 × 10−9 m2/s. From Arrhenius's relations, the activation energy of the drying process of pear slices was 29.87 kJ/mol. The lowest specific energy consumption (10.28 kWh/kg) was observed for higher drying temperature. The drying temperature positively influenced the energy and exergy efficiencies of the process. The efficiency of the first law of thermodynamics varied between 40 and 99%. The increase in the energy required in the dryer, overcomes the destruction of exergy in the equipment.Practical ApplicationsInfrared radiation drying is a promising high‐efficiency technology. One of the main advantages of this method is the significant reduction in drying time compared with convective drying. For a complete evaluation of the drying system, analysis of the first and second laws of thermodynamics must be applied. Few studies on energy and exergy analysis of infrared dryers are found. A detailed literature review showed that there is no information on energy and exergy analysis of the infrared drying process of pear slices. It is believed that this study will contribute to the pear food industry by providing results from the best drying process in terms of kinetics, energy, and exergy.

Osmo-air drying of banana slices: multivariate analysis, process optimization and product quality characterization.

In the present work, osmotic dehydration (OD) was applied as a pretreatment to hot air drying of banana slices and the effect of OD parameters on mass transfer characteristics, color profile was analysed. Principal component analysis (PCA) of OD process revealed that solid gain, weight reduction, water loss and total soluble solids were positively correlated with each other but were found to be negatively correlated with moisture content (MC) of sample. Response surface methodology was used for optimizing the OD of banana slices and and the optimum conditions were 61.26°Brix sucrose concentration at 50°C for 6h, resulting in moisture reduction from 75 to 49.78%. PCA-biplot of osmo-air drying (OAD) process showed the association among response parameters, which further revealed a positive correlation of MC with bioactive components. Additionally, OAD samples were also studied for microstructure and Fourier Transform Infra-red analysis. Addition of calcium lactate to sucrose solution resulted in preserving the firmness and bioactive components during osmosis, in addition to fortifying the sample with calcium. The present study provides new possibilities for food industries in preserving the ripe banana and developing calcium fortified functional food products.

Combining ultrasound, vacuum and/or ethanol as pretreatments to the convective drying of celery slices

This work studied three emerging approaches to improve the convective drying (50 °C, 0.8 m/s) of celery. Celery slices of 2 mm thick were pretreated for 5 min using ultrasound (32 W/L, 40 kHz), vacuum (75 kPa vacuum pressure) and ethanol (99.8% v/v, as drying accelerator) applied individually or in combination. To evaluate individual effects of ultrasound and vacuum, the treatments were also performed with distilled water or air medium, respectively. Moreover, the cavitational level was characterized in each condition. Drying kinetics was evaluated tending into account the drying time required by each treatment and the Page’s model parameters. In addition, microstructural effects and shrinkage were evaluated. As results, ethanol combined with ultrasound significantly improved drying kinetics reducing drying time by around 38%. However, vacuum pretreatment did not affect drying kinetics even in combination with ethanol and/or ultrasound. Microstructural evaluation did not evidence cell disruption, suggesting changes in intercellular spaces, pores and/or cell wall permeability. The use of ethanol and vacuum showed a greater effect on shrinkage after pretreatment and after drying, respectively. In conclusion, at the studied conditions, the drying acceleration by vacuum and ultrasound is lower compared to the effect produced using ethanol.

Microbial inactivation and drying of strawberry slices by supercritical CO2

This work explores the feasibility to apply supercritical carbon dioxide (scCO2) to dry and increase the microbial safety of strawberries. Strawberry slices were dried at 10 MPa and 40 °C up to 6 h. The treatment was able to remove the 98% of the initial moisture content, corresponding to a weight loss of 90%. The method showed a limited inactivation power towards total mesophilic bacteria, while yeasts and moulds were under the detection limit of the technique (<10 log CFU/g). The process is efficient against different strains of pathogens (E. coli O157:H7, Salmonella spp. and L. monocytogenes), which were inoculated on the sample surface. Results highlight the potential of scCO2 drying as innovative food drying technology for the simultaneous drying and stabilization of the product without the use of high temperatures.

Performance of two terms exponential model on the drying kinetics of solar-dried tomatoes (Lycopersicum esculentum L.) treated with and without chemical preservatives

Open sun drying of horticultural produce results in contamination due to microbial and fungal attacks and could also be damaged by insects, pests, and rodents. Solar drying through solar collectors is, therefore, an important technique used for the preservation of foods and to extend the shelf life of produce, thereby reducing microbial attack and contamination. Therefore, an experiment was carried out to study the response of the drying kinetics of solar-dried tomatoes to the thin layer of preservatives on the drying and quality attributes. The tomato fruits were treated with natural preservatives (honey and aloe vera) and chemical preservatives (citric acid, sodium benzoate, and potassium meta-bisulfate). The tomato fruits were then kept at three (40, 45, and 50oC) different temperatures using a parabolic trough solar air heater for drying purposes. Both the drying temperature and preservative levels significantly (P< 0.001) affected the drying and quality traits of tomato slices. At a temperature of 50 oC and with citric acid as a preservative, the tomato attained the best average results for moisture lost hr-1, drying time, drying rate, total soluble solids (TSS) °Brix, fruit juice pH, titratable acidity (%) and vitamin C. Based on the average maximum results, 50°C temperature and citric acid as a coating material could be considered for attaining better quality attributes of dried tomatoes. A two-term exponential model on the moisture ratio of tomatoes was found to fit for correlation and regression.

Exergy and Energy Analyses of Microwave Dryer for Cantaloupe Slice and Prediction of Thermodynamic Parameters Using ANN and ANFIS Algorithms

The study targeted towards drying of cantaloupe slices with various thicknesses in a microwave dryer. The experiments were carried out at three microwave powers of 180, 360, and 540 W and three thicknesses of 2, 4, and 6 mm for cantaloupe drying, and the weight variations were determined. Artificial neural networks (ANN) and adaptive neuro-fuzzy inference systems (ANFIS) were exploited to investigate energy and exergy indices of cantaloupe drying using various afore-mentioned input parameters. The results indicated that a rise in microwave power and a decline in sample thickness can significantly decrease the specific energy consumption (SEC), energy loss, exergy loss, and improvement potential (probability level of 5%). The mean SEC, energy efficiency, energy loss, thermal efficiency, dryer efficiency, exergy efficiency, exergy loss, improvement potential, and sustainability index ranged in 10.48–25.92 MJ/kg water, 16.11–47.24%, 2.65–11.24 MJ/kg water, 7.02–36.46%, 12.36–42.70%, 11.25–38.89%, 3–12.2 MJ/kg water, 1.88–10.83 MJ/kg water, and 1.12–1.63, respectively. Based on the results, the use of higher microwave powers for drying thinner samples can improve the thermodynamic performance of the process. The ANFIS model offers a more accurate forecast of energy and exergy indices of cantaloupe drying compare to ANN model.

Plate versus mesh collecting electrode for electrohydrodynamic (EHD) drying

Electrohydrodynamic (EHD) drying is considered a highly efficient technology due to its ability to create powerful convective airflow with low energy consumption. EHD efficiency depends on multiple factors, such as voltage, current, environmental conditions, drying material, and electrodes geometry. This research is exploring the effect of collecting electrode geometry on the drying rate and energy efficiency of EHD drying. Although numerical studies predict a better performance of mesh collectors compared to solid plate collectors, experimental verification is still missing. This research addresses this gap by comparing the performance of plate versus mesh collecting electrodes in drying experiments with three discharge electrodes (nails, needles, pins) and two materials (wet paper and apple slices). Our experiments confirmed the benefits of mesh collector compared to the plate, namely up to 25% higher drying flux and a 20–35% smaller specific energy consumption. For example, EHD drying of apple slices with the mesh resulted in specific energy consumption of 719–731 kJ/kg compared to 935–968 kJ/kg with the plate collector. The better energy efficiency of the mesh collector provides a unique opportunity for the industrial upscaling of EHD drying technology.

Modelling and simulation of multi-coupled heat and mass transfer processes: A case study of solar biomass dryer

This research aims to develop and simulate multi-coupled heat and mass transfer models for the solar-biomass drying process of agricultural products. The model took into account all the possible resistances to the transport processes by coupling the diffusion, source, or sink terms of the transport models. A stable numerical solution of the models was achieved by the finite difference method via the Crank-Nicolson scheme with a well-relaxed stability criterion(≪0.5). The results of the drying simulation yielded drying rate constants of0.0318-0.03061h-1, average drying efficiency of 0.129 – 0.145 and drying time of 48–144 h, for solar drying of plantain slices with and without a biomass furnace as a supplementary heat source. The simulated transport variables were used to validate the measured results sequel to the practical Biot numbers (≪0.1), which accounted for the agreement between the experimental and simulated results. Also, the simulated drying rate constant was in agreement with the Arrhenius postulated evaporation rate constant for the two drying methods. Moreover, the solar-biomass drying of the sliced plantain from the initial moisture of 0.67kgwater/kgds to the final moisture of 0.15kgwater/kgds was accomplished within 48 h of continuous drying whereas the solar drying took 144 h of quasi-continuous drying to achieve the same result. The present work suggests the automation or regulation of heat from the biomass furnace to achieve quality drying within a short drying time with higher energy utilization efficiency.