Falling Rate Period Research Articles

EFFECT OF DRYING KINETICS ON THE QUALITY OF THE GREEN CAPSICUM

The effect of power (Watt) of microwave assistance drying on consumption of energy, drying efficiency and kinetic studies in green capsicum (Capsicum annum) was studied. For describing green capsicum drying behavior two mathematical models (Lewis model and Parabolic model) are used. Based on their root mean square error, χ2 and R2, values of predicted and experimental moisture content to models are compared. The drying time of green capsicum was decreased from 47 minutes to 22 minutes due to increasing power of microwave from 180 Watt to 900 Watt. The drying process was showing a falling rate period. In Lewis model the result shown most appropriate model for the study. For co-relation of moisture content with effective moisture diffusivity a third-order relationship was found. The effective moisture diffusivity of Green Capsicum samples increased as the moisture content decreased. Over the microwave power spectrum tested, the effective diffusivity ranged from 1.5 X 1012 m2/sec to 4.3 X 108 m2/sec, with an energy activation of 31.74 W/g. As microwave power and moisture content increased, so did energy efficiency.

MATHEMATICAL MODELLING OF HOT AIR DRIED APPLE AND EFFECTS OF VARIETY, SHAPE AND TEMPERATURE ON DRYING BEHAVIOR AND QUALITY CHARACTERISTICS

In this study, drying kinetics and quality characteristics of apple cv. Starking, Gala and Granny Smith circles and squares were studied at two different drying temperatures, 60 °C and 70 °C. Drying times were varied between 85-165 min. Depending on variety, shape and temperature. The falling rate period was observed and drying rate changed depending on the drying parameters. Four mathematical models were fitted to experimental data and Logarithmic model was found to be the best for all the samples. Total phenolic contents and antioxidant capacities of dried apple samples varied in the range of 4.11-8.36 mg GAE/g dry matter and 4536.43-7370.47 mmol AEAC 100/g dry matter, respectively and showed a tendency to increase or decrease after drying depending on the variety and shape interaction. Shape had also significant effect on antioxidant capacities of samples as well as the variety (p<0.05). The results of variance analysis demonstrated that there were significant differences among color values of apple samples dried at 60 ºC and 70 ºC.

The Influence of Drying Temperatures and Methods on the Drying Characteristics of ‘IkanBakar’ Paste

Drying is one of the popular preservation methods in food products. This work was done to investigate the influence of the drying temperatures and methods on the drying characteristics of ‘ikanbakar’ paste. The ‘ikanbakar’ paste was dried by using oven drying and vacuum drying methods at temperatures of 50°C, 60°C and 70°C. The drying rate was estimated from the moisture content and drying time data. The drying curve showed the falling rate period as the drying rate decreased with increasing time. For colour analysis of the paste, the L* values from the oven drying method were lower than those from the vacuum drying method, ranging from 7.4210 to 7.2752. This showed that the colour of paste from oven drying was darker than vacuum drying. The mathematical models used to describe the drying curve of ‘ikanbakar’ paste were Lewis, Page, Two-term, and Midilliet. al. model. The performance of these models was evaluated by comparing their root mean square error (RSME) and chi-square (X²) values, and it was found that the most suitable model was the Two-term model. There were insignificant differences between the effective moisture diffusivity (Deff) values for the ‘ikanbakar’ paste in both drying methods.

Osmotic, osmovacuum, sonication, and osmosonication pretreatment on the infrared drying of Ginkgo seed slices: Mass transfer, mathematical modeling, drying, and rehydration kinetics and energy consumption.

This study evaluated the mass transfer, drying, and rehydration kinetics (drying and rehydration curve, moisture diffusivity [Deff ]), energy consumption (specific energy consumption [SEC], moisture extraction rate (MER), and specific moisture extraction rate [SMER]), and mathematical modeling of infrared dried Ginkgo biloba seed (GBS) using the various nonthermal pretreatments namely: osmotic (OS), osmovacuum (V + OS), ultrasound (US, ginkgo seed immersed in a distilled water with US), and osmosonication (US + OS, ginkgo seeds immersed in an OS solution with US). Results showed that various pretreatments affected mass transfer, drying, and rehydration characteristics, and energy consumption, which was confirmed by principal component analysis. In terms of mass transfer, US pretreatment recorded the highest weight loss while the osmosonication pretreatment registered the highest solid gain. The entire drying process occurred in the falling-rate period. The Deff values were within the normal range of agroproducts (10-11 to 10-8 m2 /s). The modified Page-I and Weibull model best fitted the drying and rehydration kinetics, respectively, with the coefficient of determination (R2 )>0.991, root mean square error, residual sum of squares, and reduced chi-square closer to zero, compared with the other models. The untreated GBS (control) had the lowest energy efficiency (lowest SMER and MER) and the highest SEC than the pretreated GBS. Among the various pretreatments, the US pretreatment of GBS was superior, with the highest Deff , MER, SMER, and drying rate, and lowest drying time and SEC. Based on the findings, sequential US pretreatment and infrared drying is a feasible drying technique for GBS that could be used commercially. PRACTICAL APPLICATION: Ginkgo tree cultivation in China has exceeded market needs with 60,000 tons per annum of GBS produced. Hence, there is a compelling need to explore new chances to use GBS availability irrespective of the seasonality and address the problem where GBS utilization is limited to the early phases of home-cooked dishes. Although drying increases the shelf life of ginkgo seeds, there is a higher operation cost. Thus, pretreatment can reduce energy consumption and augment the product quality is ideal. This research reported the impact of nonthermal pretreatments on ginkgo seeds' mass transfer, drying, and rehydration characteristics. The present results will provide a comprehensive understanding of the engineering application of ginkgo seed pretreatment, allowing for the best technique to be selected.

Spray drying of desulfurization wastewater: Drying characteristics, product analysis and potential risk assessment

The Wastewater Evaporation System (WES) was a reliable and economical way to treat desulfurization wastewater. However, the evaporation mechanism was not clear, and the evaporation product properties were lack of awareness. In this study, the evaporation and product properties were revealed by the single droplet drying (SDD) method and spray drying system. It was found that the evaporation process of wastewater involved the constant rate and falling rate period. The component of the evaporation product from the SDD and spray drying method were similar, mainly consisted of MgCl2, CaCl2, NaCl and CaSO4. Besides, the potential risks of WES were assessed. After wastewater evaporation, the Electrostatic Precipitator (ESP) removal efficiency was enhanced due to the aggregation of fine particles and the enhanced specific resistance. For the influence of WES on comprehensive fly ash utilization, the chloride mass fraction in the final product was lower than 0.06% and could meet strict regulations.

The experimental study and modelling the drying kinetics of mussels using ultrasound assisted vacuum drying

In the present study, chemical compositions, drying kinetics, quality parameters and energy consumptions for mediterranean or black mussel (Mytilus galloprovincialis) subjected to ultrasound assisted vacuum drying (UAVD) were analyzed between the range of 50–70 ​°C. During drying only falling rate periods were observed. Obtained conclusions demonstrated that the moisture content and drying rate were influenced by the ultrasound assisted vacuum drying method and the drying air temperature. The ultrasound assisted vacuum drying shortened the drying period and increased the effective moisture diffusivity (Deff). Drying led to a considerable increasing of protein and fat content. Six well-known thin layer drying models were compared with regards to coefficients of determination. The Alibas model was selected as the best one. The activation energy was calculated as 3.80 ​kW/kg. High “L∗" and low "ΔE" values were obtained for dried mussels. Using of ultrasound assisted vacuum drying technique resulted in very low energy consumption.

Comparative Study on Different Drying Techniques for Determining the Moisture Content of Cereals/Millets and Pulses

Cereals/millets and pulses are an important parts of healthy and balanced diet and hence helps in bridging the gap of protein hunger malnutrition and micronutrient deficiencies. To increase the shelf life of perishable and non-perishable food items, drying is one of the primary and oldest processing techniques that the food grains are subjected to. The convection oven drying method is one of the commonly used methods for the estimation of moisture in marketing enterprises and industries but as the time consumption is quite higher in this process a replacement but quick and dependable technique is essential. One variety rice (Luit variety), one variety of millets and one variety of pulses (samples) were used for the study. Experiments with temperature varying from 30-60 °C and varied time intervals (15 minutes) were conducted in a microwave oven and convection oven using the samples. The main parameters used for the study were temperature and time which was recorded after a time interval of 15 minutes1. The results stated that the process of drying takes place at a falling rate period i.e. with the rise in temperature the moisture content decreases. At a very long process the drying rate, the curve slop becomes less sharp and slowly tends to be horizontal at longer period of time. The values are calculated when the moisture content of the samples becomes constant. Drying food grains for a longer time period have adverse effect in the nature of the samples along with it can result in income loss of marketing industries.Salient findings from the study can be that the alternative means for the convection oven drying can be microwave oven drying as it can be a favorable method for the estimation of moisture content in food grains.

Evaluation of the drying process and toxic metal contents in yerba mate cultivated in southern Brazil

The drying kinetics of yerba mate leaves from southern Brazil was investigated theoretically and experimentally in a drying oven at 70°C. The effect of drying conditions on the moisture ratio, drying rate, and effective diffusivity of yerba mate leaves was evaluated. Five drying models were fitted to experimental data. Additionally, the concentrations of As, Cd, Pb, Ni, Cr, and Hg in the yerba mate leaves were determined using inductively coupled plasma optic emission spectrometry (ICP-OES). The results revealed that all samples only showed a falling rate period without a constant rate of drying. The Midilli model showed the best fit of experimental data. All samples showed levels of Hg higher than those permitted by Brazilian legislation. Monitoring programs and other studies are required to prevent the intake of yerba mate products contaminated with toxic metals.

Vacuum oven drying of mussels: mathematical modeling, drying characteristics and kinetics study

PurposeThe aim of this work was to study the effect of the different temperatures on drying kinetics and quality parameters of vacuum oven-dried mediterranean or black mussel (Mytilus galloprovincialis) specimens.Design/methodology/approachDrying process was performed at 50, 60 and 70 °C and a vacuum drying pressure of 0.1 kPa. The proximate composition analysis was done. Drying rates of the mussels were computed. Mathematical modeling was carried out. Effective moisture diffusivity, activation energy and total energy consumption were calculated. Color measurement was conducted.FindingsDrying took place entirely in the falling rate period. The obtained results indicated that the drying air temperature has a remarkable influence on the moisture content and drying rate. Drying resulted in a significant increasing of protein and fat content. The Deff values ranged from 1.44 × 10−9–3.23 × 10−9 m2/s, with the activation energy 4.47 kW kg−1. The Alibas model is the most proper model to define the drying curves. This method provided high energy efficiency and quality in dried products.Research limitations/implicationsFresh mussels grown in Eceabat location were used as the study sample. In the drying process, 50, 60, 70 °C temperatures and 0.1 kPa pressure was used. These are the limitations of the research.Originality/valueThis work is the first to report the influence of vacuum oven drying on the color changes and drying kinetics of black mussels.

Scale-up and optimization of the spray drying conditions for the development of functional microparticles based on chia oil

A factorial design was performed for the microencapsulation of chia oil by spray drying at pilot-scale, to validate the results obtained previously at laboratory scale in a Büchi-B290. The effects of drying-air inlet (Tinlet) and outlet (Toutlet) temperatures in a Niro Production Minor on the solid yield, thermal efficiency, theoretical droplet evaporation times, and physico-chemical properties of powders were analyzed. The theoretical droplet evaporation times (0.31−0.54 s) were calculated considering the constant and falling rate periods and a negligible relative velocity between spray and air. Critical diameters between 31.77–41.57 μm were estimated for microcapsules, depending on the process conditions. After scale-up of the spray drying operation, higher solid yields (74.24–79.79%), thermal efficiencies (27.56–73.19%), encapsulation efficiencies (96.97–98.57%), and enhanced flowability of products, compared with experiments at laboratory scale, were observed. Moreover, the scale-up did not affect the chemical composition of microencapsulated oils, their fatty acid composition before and after in-vitro digestion processes. A global optimization was performed at pilot-scale and the process conditions that simultaneously optimized all the responses was 160 °C × 90 °C (Tinlet × Toutlet).

Reinforced contact between sludge and hot wall for enhancing conductive drying by applying external load: Heat and mass transfer analysis

Conductive drying is widely used in sludge management for emission reduction and energy recovery. However, interfacial vapor film between sludge and hot wall inhibits drying efficiency. This study employed external load to reinforce the contact of sludge with hot wall for facilitating interfacial heat transfer. Subsequently, a drying model was developed for heat and mass transfer mechanism analysis. The influence of external loads was explored on conductive drying behavior at 180 °C and 0, 25, 100 kPa. The drying rates were increased with external load. The drying process consisted of the warm-up, constant rate, and two falling rate periods. Without external load, moisture migration was dominated by liquid water diffusion induced by capillary force in the first falling rate period. However, at 100 kPa, the convective flow of water and vapor dominated the moisture migration in the first falling rate period due to increased interfacial heat transfer, evaporation rate, and gas pressure. Then vapor diffusion was predominant owing to enhanced gas diffusivity. Besides, this study provided essential information on design optimization of industrial applications, such as moisture content prediction for searching for equilibrium points between energy consumption and resource recovery and the critical factors for enhancing moisture migration.

Experimental and modelling studies of convective and microwave drying kinetics for microalgae

Conventional microalgal drying consumes huge time and contributes to 60–80% of downstream process costs. With the aim to develop an effective and rapid drying process, the present study evaluated the performance of microwave based drying (MWD) with a power range of 360–900 W and compared with the conventional oven drying (OD) at 40–100 °C. MWD was found to be efficient due to uniform and volumetric heating because of dipolar interaction, with an effective diffusivity of 0.47 × 10−9−1.63 × 10−9 m2 s−1, comparatively higher than OD. Activation and specific energy of 32.43 W g−1 and 42.9–56.07 kWh kg−1 was projected respectively, and a falling rate period with best fit for Newton and Henderson-Pabis model was observed for MWD. Uniform heating from internal sub-surface avoided cell distress, resulting in 14.4% higher lipid yield and significant preservation of biochemical components that can be processed into bioenergy and valuable products in microalgal biorefinery.

Strawberry-hydrocolloids dried by continuous cast-tape drying to produce leather and powder

Cast-Tape Drying (CTD) is an innovative and competitive technique to dehydrate fruit and vegetable pulps on a continuous scale, to produce leathers, flakes, and powders. The hydrocolloids maltodextrin, starch, and pectin were added to a strawberry pulp as carrier agents (CA). Ostwald and Herschel-Bulkley's models fitted well to rheological data of strawberry pulp and strawberry-CA suspensions. A pseudoplastic behavior was observed for all samples, which is ideal for spreading on the CTD support. All drying curves showed a constant and a falling rate period, and the time to reach a constant moisture content was dependent on the sample (between 20 and 40 min). After drying, products were removed as leathers, and the CA addition contributed to the easier detachment of the materials from support. All leathers were homogeneous, with thicknesses in the range of 0.2–0.4 mm, and the strawberry-CA leathers exhibited a slight color difference compared to the pure strawberry. Sorption isotherms of the strawberry leathers adjusted well to the GAB model. The volatile compounds in the strawberry pulp were strongly modified by drying, with the addition of maltodextrin and pectin promoting the preservation of some of the strawberry original volatiles; however, pectin has shown a few new compounds. The presence of hydrocolloids in strawberry powders increased the Tg and the dispersion (except when maltodextrin was added) in water, compared to pure strawberry powders.

Drying Kinetics and Modelling of Convective Drying of Kedondong Fruit

Kedondong is an underutilized fruit cultivated in a small scale in Malaysia and it contains nutrients that can be preserved through drying. The dried product can be sold as a premium fruit snack that could generate revenue for the producer. We studied the drying of peeled and unpeeled kedondong fruits using hot air (60-80°C). This study aims to investigate the drying kinetics (drying rates and effective diffusivities) of kedondong fruits and model the drying curves using thin layer models. Ten thin layer models were employed and solved using non-linear regression. Drying kinetics showed that only falling rate periods were observed, which implied that internal diffusion was the dominant mechanism for moisture release. Mathematical models showed that Modified Hii et al. (I) and (II) models were able to predict the drying curve well with the highest R2 (0.9992-0.9999), the lowest RMSE (8.0 x 10-4 - 2.5 x 10-3) and the lowest χ2 (4.0 ×10-5 - 2.0 x 10-4). Peeled samples showed higher effective diffusivities (average 3.2 x 10-11 m2/s) than unpeeled samples (average 2.7 x 10-11 m2/s). The activation energy was lower in peeled samples (25.8 kJ/mol) as moisture diffusion could occur more easily than unpeeled samples (32.1 kJ/mol). Results from this study provide kinetic information that can be used in scaling up of dryer and optimizing dryer performances.

Drying kinetics and thermodynamic analysis of tomato in a tunnel dryer

In this study, drying kinetics and thermodynamic analysis of tomato were conducted in a tunnel dryer. Drying experiments were performed at three temperatures (100, 115, and 130 °C) and an air velocity of 1.45 m/s. From the drying curves, only a falling rate period was observed. Under these conditions, a characteristic drying curve was determined. It is observed that at the 40 minutes of the drying process, the outlet gas enthalpy achieved a maximum value that is very close to the inlet value and remained constant until the end of the process. Entropy exhibited similar behaviour to enthalpy. The maximum value of the exergy efficiency curve corresponds to the maximum value observed within the drying rate curves. This maximum value represents the stage when the available energy is efficiently used in moisture removal. As the drying rate decreases the available energy is started to be less employed.

Enhancement of conductive drying of sewage sludge with mechanical compression: Drying kinetics, and interfacial heat transfer behavior

Improving sludge drying efficiency is of tremendous importance for public health, subsequent treatment, and comprehensive utilization. The interfacial thermal resistance between sludge and hot wall greatly limits the conductive drying performance. This study employed mechanical compression to decrease the interfacial thermal resistance. The drying kinetics and interfacial heat transfer behavior were investigated at mechanical loads of 25 to 200 kPa, temperatures of 120 to 210 °C, and sludge thicknesses of 1.0 to 3.0 mm, and were compared to those in the conventional drying process without mechanical load. The increase of temperature and mechanical load and the decrease of thickness improved drying rates. The drying experienced one warm-up period and two falling rate periods. The breakthrough of interfacial vapor film was responsible for the rapid rise in drying rates initially. At the thickness of 3.0 mm, 210 °C, and 100 kPa, the effective moisture diffusivity was increased by 2.5 times, and the apparent activation energy was reduced by 34% compared to the traditional process in the first falling rate period, implying that mechanical compression facilitated moisture migration and bound water desorption. The effective moisture diffusivity in the first falling rate period was increased by 35% compared to the diffusivity in the second falling rate period because of the pressure-driven flow. The decrease in drying rates was due to the transformation from the pressure-driven flow to vapor diffusion-limited flow in the first falling rate period. Additionally, this study provided essential information on developing a new sludge treatment method and establishing the drying model.

EFFECT OF THE DRYING METHOD ON THE QUALITY AND DRYING CHARACTERISTIC OF MINT LEAVES (Mentha spicata L.)

Mint leaves are vegetables used for tea especially in the northern part of Nigerian because of their nutritional and medicinal values. Fresh mint leaves are perishable and to extend their shelf-life drying the leaves is a common practice among the people. The application of a proper drying method is essential to preserve its nutritional and medicinal values. Lack of information on the drying characteristic that could be used for the design of its dryers is a major bottleneck in its processing. This accounts for the poor colour, taste, flavour of dried mint leaves found in the market.In this study, three methods were used to dry mint leaves, sun, oven and shade drying methods. Proximate analyses were carried out on the samples dried with the three methods. Samples drying characteristics were investigated using an oven at 40, 50, 60 and 70 °C. The results show that the drying method significantly affected all the proximate compositions at 5% level. Shade drying has the highest crude protein and ash contents of 7.74% and 8.48% respectively. Carbohydrates were more (30.13%) when open sun drying was employed. Oven drying favoured lowest moisture content of 7.20%, highest crude fiber of 49.34% and highest crude fat contents of 9.22%. To dry mint leaves to equilibrium moisture content, it took 140 min for samples at a drying temperature of 40 °C, 120 min at 50 °C, 90 min at 60 °C and 70 min for 70 °C. Drying of the leaves occurred in a falling rate period.

Drying kinetics, heat quantities, and physiochemical characteristics of strawberry puree by Refractance Window drying system

AbstractAttempts were made to understand the drying kinetics, different heats involved, and change in physiochemical properties during Refractance Window (RW) drying of strawberry puree on an in‐house fabricated RW drier. RW drying of puree was conducted at 75°C water temperature with 1.5 mm thickness. The drying was carried out from initial moisture content 614% (db) to 5.1% (db) with1.2 m/s exhaust air velocity. RW drying took place only in the falling rate period. The sensible heat of strawberry puree, convective heat loss from puree surface to air, and convective heat loss from the bottom surface (hot water to air) of the dryer were 70, 205, and 61.96 W, respectively. The evaporative capacity of 5.28 kg m−2 hr−1 was calculated at experimental parameters. This confirms that the drying system is advantageous. RW dried strawberry puree was rehydrated as exact of fresh strawberry puree considering total solids. Total phenolic content and ascorbic acid were significantly (p < .05) reduced from 246.33 mg gallic acid equivalent (GAE) (fresh strawberry puree) to 204.67 mg GAE per 100 g (reconstituted RW dried strawberry puree); 33.31–28.54 mg/100 g, respectively. Color characterization through L*, a*, b*, darkness factor (b*/a*), chroma (C), and hue angle (h*) revealed that reconstituted RW dried puree sample was darker compared with fresh puree.Practical ApplicationsAmong various drying methods of fruit purees, hot air drying is the most widely used. It results in an unpleasurable taste and color. During the falling rate drying period, the less thermal conductivity of fruit puree restricts heat transfer in conventional drying. Refractance Window (RW) drying adopts low‐temperature drying for less time, which leads to advantages like effective and economical drying. RW drying technology can be promising at the commercial level in product quality and much‐reduced production cost.

Infrared Drying Kinetics and Color Qualities of Organic and Conventional Sweet Red Peppers

This study compares the infrared drying kinetics, effective moisture diffusivity, activation energy and color qualities of organically and conventionally produced sweet red peppers (Capsicum annum L.) dried at three different temperatures (60, 70 and 80°C). Results showed that the entire drying process for both organic and conventional sweet red peppers took place mainly in falling rate period. Increasing the drying temperature decreased the drying time considerably. No significant difference was found between the drying times of organic and conventional red peppers. The Midilli model yielded the best fit for all data points for organic and conventional peppers. The drying coefficient of the Midilli model increased with the increase in the drying temperature. The effective moisture diffusivity and activation energy values of organic pepper samples were found slightly higher than those of the conventional samples. This result was found to be compatible with the drying coefficient of Midilli model and characteristic drying rate curves. Higher drying temperatures resulted in brighter red pepper powder color which is more preferable by consumers. Infrared drying at 60°C for organic pepper samples produced the best pepper powders in terms of color quality. Moreover, infrared drying at 60°C and 70°C was also judged as the acceptable drying applications in terms of color quality since they gave the nearest redness to yellowness ratios and higher brightness values as compared to the color of fresh peppers. Overall, infrared drying at 70°C instead of 60°C resulted in about 22% savings in drying time and can be used to produce high quality organic or conventional sweet red pepper powder with better color quality.

Drying of Sisal Fiber: A Numerical Analysis by Finite-Volumes

Vegetable fibers have inspired studies in academia and industry, because of their good characteristics appropriated for many technological applications. Sisal fibers (Agave sisalana variety), when extracted from the leaf, are wet and must be dried to reduce moisture content, minimizing deterioration and degradation for long time. The control of the drying process plays an important role to guarantee maximum quality of the fibers related to mechanical strength and color. In this sense, this research aims to evaluate the drying of sisal fibers in an oven with mechanical air circulation. For this purpose, a transient and 3D mathematical model has been developed to predict moisture removal and heating of a fiber porous bed, and drying experiments were carried out at different drying conditions. The advanced model considers bed porosity, fiber and bed moisture, simultaneous heat and mass transfer, and heat transport due to conduction, convection and evaporation. Simulated drying and heating curves and the hygroscopic equilibrium moisture content of the sisal fibers are presented and compared with the experimental data, and good concordance was obtained. Results of moisture content and temperature distribution within the fiber porous bed are presented and discussed in details. It was observed that the moisture removal and temperature kinetics of the sisal fibers were affected by the temperature and relative humidity of the drying air, being more accentuated at higher temperature and lower relative humidity, and the drying process occurred in a falling rate period.