Convective Air Drying Research Articles

Drying of avocado peels using carbonation-ultrasonication as pretreatment: energy consumption, antioxidant capacity and rheological properties

Fruit processing by-products, especially peels are underused and mostly discarded as waste. The aim of this study was to assess the effect of ultrasonication (US) combined with carbonation (CUS) on the convective drying process of avocado peels at different temperatures, adding value to this waste. For this, the avocado peels were treated with dry ice for 15 min and subjected to US (400W/10 min, 30°C) before convective air drying (50-70°C). The energy consumption, antioxidant capacity, water adsorption isotherms, rehydration rate, and dynamic rheology of dried avocado peels pretreated by CUS were compared with a control process (without pretreatment) and only US pretreatment. The combined treatment (CUS70) resulted in a 2.6-fold reduction in drying time and a 2.3-fold decrease in energy consumption, with CO2 preserving bioactive compounds and antioxidant capacity after the drying process. Differences were also observed in the rehydration capacity of the samples (CUS), with an increased water absorption capacity, along with a reduction in the viscoelastic properties of the peels. The results present new perspectives for the application of CUS in the food industry, paving the way for the development of creative, innovative, and simple approaches for the management and recycling of agri-food waste, with the potential to extend this knowledge to new food matrices.

Investigating drying behavior and quality of Neem leaves using a novel biomass gasification-powered climate control unit with built-in humidity control

Traditional food drying methods, such as open sun drying (OSD) and hot air convective drying (HAC), are widely employed due to their simplicity. However, these methods are inefficient and often yield lower-quality and contaminated products. To address these limitations, we utilize a novel Climate Control Unit (CCU) powered by biomass gasification. The CCU allows independent control of temperature ranging from 0−70°C as well as humidity 10−90%. Our primary objective was to investigate the various drying methods to preserve essential nutrients, reduce power-consumption, and promote environmental-sustainability. In this study, we focused on Neem leaves, a valuable medicinal ingredient, and investigated their drying behaviour and quality using the CCU as a dryer. We implemented diverse control strategies, including temperature control, humidity control, and combined temperature and humidity control. The drying experiments were conducted across different temperature ranges: moderate 45−55°C15−30%, low 25−35°C15−30%, and high 65−75°C15−30%. For comparison, we evaluated the results against OSD and HAC. Next, we assessed various thin-layer drying models to describe the optimal drying kinetics of Neem leaves. Furthermore, we focus on quality aspects, including chlorophyll, phenolic, and tannin content and the thermal performance of the system. Overall, our study elucidates the need to balance drying time and product quality while selecting drying methods. Moderate temperature with humidity control drying appeared to be optimal with a slight compromise on drying time (final moisture content ≈13%drybasisin7hours, and preserving chlorophyll (≈95%) and phenolic content (≈55%)); however, high-temperature drying seemed optimal with a slight compromise on product quality (final moisture content ≈6%in3hours, and preserving chlorophyll (≈70%) and phenolic content (≈45%)). The peak drying efficiency of ≈21%, ≈28%, and ≈38% was obtained during temperature, humidity, and combined temperature and humidity control at moderate temperature drying respectively. The drying cost (≈0.29 $/kg) was observed minimal in case of combined temperature and humidity control. We believe the diverse control strategies reported in this study are expected to find viable applications in drying technology for various perishables, such as wood, tea seasoning, and processing in leather industries, among others.

Comparison of drying methods for biochemical composition, energy aspects, and color properties of alfalfa hay

AbstractAlfalfa is a crucial feed source for livestock, necessitating proper drying to achieve optimal moisture levels before consumption. This study aims to reveal alfalfa's drying characteristics and quality properties, defined as the queen of feed, by drying it under different drying conditions. Alfalfa samples were dried using different drying techniques: Open-sun, shade, greenhouse, hybrid (microwave-air-convective), air-convective, microwave, and freeze-drying. The influence of drying techniques on the drying kinetics, energy aspects, biochemical properties, mineral composition, fatty acids, carotene, and color attributes of alfalfa were investigated. Present findings revealed that shade and high-temperature drying conditions increased the crude fiber content (23.18%) of alfalfa samples. The highest protein values were found in open-sun drying (22.01%) and 60 °C air-convective drying (22.10%). The highest values for mineral composition were determined in freeze drying, and the greatest Zn (33.68 ppm) and Fe (135.45 ppm) contents were determined in 100 °C air-convective drying. The highest saturated fatty acids open-sun (21.27%) and freeze dryer (21.07%), unsaturated fatty acids at 60 °C (84.51%) and 80 °C (84.26%), poly unsaturated fatty acids at 60 °C (78.36%), 80 °C (78.14%) and 100 °C (77.74%) were obtained. The drying kinetics of alfalfa were best modeled with the Jena&Das, and in terms of a* (greenness) values, the hybrid drying yielded the best results. The lowest total energy consumption (54.00 kWh) was seen in 200W + 80 °C hybrid drying and the highest (324.72 kWh) in 100 °C air-convective drying. The color attributes and energy consumption findings showed that hybrid drying could efficiently be used for alfalfa drying. In addition, freeze drying was determined to be the best drying method in terms of nutrient preservation.

Sun-Dried and Convective-Dried Octopus vulgaris Quality Parameters and Estimated Shelf Life During Ambient Temperature Storage

ABSTRACT Drying process was used in this study as a preserving method of octopus quality during storage. Octopus vulgaris quality attributes in terms of pH, water activity, color properties, total volatile basic nitrogen (TVB-N), trimethylamine (TMA), total viable count, and yeast and molds (YM) were evaluated. Samples were dried under sun drying and convective air drying and stored at ambient temperature. During storage, TVBN and TMA obtained were within the recommended level for good quality of dried samples. Accelerating shelf-life test was evaluated based on TVB-N, TMA, and YM, with shelf lives of 388 and 603 days for convective air drying and sun drying, respectively.

Effect of Blanching Temperature and Convective Hot Air-drying Temperature of Orange Peel Slices on Its Quality Evaluation

Drying characteristics of orange peel was investigated by blanching and convective hot air drying of orange peel slices (of 3mm thickness) at the temperature 40ºC, 50ºC and 60ºC. Drying models i.e. Lewis, Henderson and Pabis and Page were fitted to the experimental data on moisture ratio with respect to time. The page model fitted well r^2≥0.976 and MSE≤0.0012 among all the models tested for the experimental data. Effective diffusivity (Deff) at time (t) for orange peel were 0.086×10-8m2/s, 1.834×10-8m2/s and 2.017×10-8m2/s which was blanched at 72ºC:10 min, 82ºC:8min and 92ºC:5 min and dried at 40ºC; 0.0903688×10-8m2/s, 1.077×10-8m2/s and 1.898×10-8m2/s which was blanched at 72ºC:10 min, 82ºC:8min and 92ºC:5 min and dried at 50ºC; 1.168×10-8m2/s, 1.422×10-8m2/s and 1.579×10-8m2/s which was blanched at 72ºC:10 min, 82ºC:8min and 92ºC:5 min and dried at 60ºC. The activation energy (Ea) for moisture diffusion was found to be 2.244×104 kJ/mole, 2.523×104 kJ/mole and 1.262×104 kJ/mole. The quality parameter i.e. T.S.S was in 20 to 60(°B), acidity was in the range of 0.32 to 18.09 %, reducing sugar was in the range of 19.05 to 6.21 % non-reducing sugar was in the range of 2.56 to 10.13%, total sugar was in the range of 9.08 to 25.8%, pH was in the range of 5.4 to 3.6%, ascorbic acid was in the range of 18.2 to 34.76%, yellowness index was in the range of 77.76 to 154.40 and protein was in the range of 8.60 to 11.24% on orange peel powder prepared from blanching at 72ºC: 10 min, 82ºC: 8min and 92ºC: 5 min dried at 40⁰C, 50⁰C and 60⁰C respectively were determined and discussed.

Convective Hot Air Drying of Aloe vera Slices and its Quality Evaluation

Convective Hot Air Drying of Aloe vera Slices and its Quality Evaluation

Experiment study on particle pulverization-assisted convective air drying of sewage sludge

Sewage sludge drying is a pivotal step in sludge reduction, harmlessness, and resource utilization. Pulverizing sewage sludge can significantly increase the surface area of sludge particles available for contact with the air medium, consequently strengthening the convective drying process of the sludge. In this paper, the adopted deep drying system mainly combined sewage sludge pulverization and sewage sludge drying functions. Parametric studies were carried out to investigate the effects on the drying process. The moisture content of the sewage sludge decreased from 50.3% to 26.8% when the linear speed of the rotating blade tip of the pulverizing dryer and induced draft fan reached 28.3 m·s−1, 62.8 m−1, and air velocity reached 9.5 m·s−1, respectively. Furthermore, this work also preliminarily reveals the mechanism of the pulverizing dryer. The pores on the sludge particle surfaces are destroyed during the drying process. As the linear speed of the rotating blade tip in the pulverizing dryer increased, the hydrophilicity and the average particle size of the sewage sludge particles decreased, with the particle size representing the highest volume fraction being reduced by 62% in the particle size distribution. The pulverizing dryer not only breaks up the sludge to increase the surface area of the sludge in contact with the air but may also have a centrifugal effect. As the intensity of the pulverizing dryer increases, Nuclear Magnetic Resonance (NMR) measurements show a leftward shift in the peak of the weakly bound water in the sludge and a noticeable shortening of the transverse relaxation time. Overall, the results suggested that pulverizing is a suitable assistive method to improve the drying effect of the sewage sludge.

Comprehensive study on potato drying in convective air dryer: experimental observations, mathematical modeling, and model validation

We studied the drying kinetics of sliced potatoes (Solanum tuberosum) using a tray dryer. An experiment was conducted on how the drying rate was impacted by air temperature, sample thickness, and air velocity. The study was conducted under varying temperature ranges (50°C, 60°C, and 70°C), air velocities (0.6 ms−1, 0.7 m s−1, and 0.8 m s−1), and potato slice thickness (2 mm, 4 mm, and 6 mm). The findings revealed that a higher air temperature was correlated with an increase in the drying rate, while thicker layers demonstrated a decrease in the drying rate. We further evaluated five mathematical models, with the Page Model emerging as the most suitable based on the lowest residual standard error (RSE) and Akaike's Information Criteria (AIC), which are 0.06421 and -1123.947, respectively. After plotting the predicted moisture ratio against the experimental moisture ratio, we observed an exceptional predictive accuracy (R2 > 0.99) across various conditions. These findings underscore the critical importance of precise parameter control for optimizing potato drying processes in industrial settings, providing valuable insights for enhanced efficiency and resource utilization. Further exploration into real-time optimization and scalability can extend the practical applications of this study.

Hot air convection drying characteristics and microstructures of Pt/C catalyst layers in proton exchange membrane fuel cells

Large-scale fabrication of membrane electrode assemblies for proton exchange membrane fuel cells normally uses hot air convection drying of the catalyst layer (CL). The temperature, velocity, and relative humidity of the hot air affect the CL microstructure and, consequently, the power generation rate. This study experimentally investigated the impact of the hot air temperatures (30 °C, 50 °C, 70 °C and 90 °C), velocities (0.5, 1.0, 1.5 and 2 m/s) and relative humidities (5%, 10%, 20% and 30%) on the CL drying characteristics and microstructures. The mass loss was recorded by an electronic balance as the slurry coating dried with the CL microstructure then evaluated using a scanning electron microscope and nitrogen absorption-desorption measurements. The drying was almost completed for all cases within 90 s. A correlation was then developed for the CL hot air convection drying moisture ratio which was best fit by the two-term exponential model. The correlation accurately predicted the data for low relative humidities with average differences within 10%. The hot air temperature, velocity and relative humidity can significantly affect the CL pore size. High temperatures and velocities formed thicker CLs, while high relative humidities led to thinner CLs. These results indicate that the CL microstructure can be regulated by controlling the drying conditions.

Experimental investigation, performance analysis, and optimization of hot air convective drying of date fruits via response surface methodology

A laboratory-scale hot air convective dryer (HACD) was used to dry date fruits surplus at 0.5 ± 0.02 kg kg−1 to a safe moisture level of 0.35 kg kg−1 under drying temperatures (T) of 50–70 °C with airflow rates (Q) of 0.18 and 0.28 m3 h−1. Kinetics, modeling, energy, economic feasibility, and color difference of the date fruits were analyzed and then optimized using response surface methodology (RSM) with two drying factors and eight responses. The drying time to reach the desired moisture level ranged from 9 to 28 h under different drying conditions. The proposed mathematical model expressed the moisture behavior over drying time with the highest R2 = 0.9998 and 0.9999, respectively, for 0.18 and 0.28 m3 h−1. Effective moisture diffusivity (Deff) was calculated using the starting accessibility parameter and varied between 9.9 × 10−8 and 3.3 × 10−7 m2 s−1. The energy analysis revealed that the specific energy consumption (SEC) varies between 22.04 and 43.05 kWh.kg−1 and the drying efficiency (η) are 16.91, 16.14, and 25.38% for 50, 60, and 70 °C, respectively. The RSM optimization using a multi-level design with two centurium points denoted the optimum responses for the highest drying temperature. The lowest payback period (Pb) of the drying system was estimated to be 0.45 years for T = 70 °C and Q = 0.28 m3 h−1. The optimum drying time, Deff, total energy consumption (Et), SEC, η, and total color change (ΔE) were estimated to be 9 h, 3.3 × 10−7 m2 s−1, 33.91 kWh, 22.04 kWh.kg−1, 27.69%, and 1.69, respectively.

Evaluation of the environmental performance of the production of polyphenol-rich fruit powders: A case study on acerola

This study evaluated the environmental performance by life cycle assessment (LCA) of five popular drying processes (freeze drying, spray drying, spouted bed drying, convective hot air oven drying, and foam mat drying) to obtain polyphenol-rich acerola powders from acerola juice and pomace. To the best of our knowledge, this is the first report in the literature showing the total polyphenol content (TPC) as the target quality index to evaluate the LCA of fruit-based dried ingredients, taking the potential functionality into consideration. Acerola powders had low moisture content (1.43%–5.20%) and water activity (0.301–0.433), and remarkably high TPC (79–287 mg GAE/g). LCA results showed that the re-purposing of readily available and burden-free pomace is a smart and eco-friendly solution to secure polyphenol-rich fruit powders with lower environmental impact (<10%) and resource availability (<50%). On the contrary, juice-derived powders have higher potential ecological impact associated to agricultural cultivation. Oven drying exceeded in 75–80% the impact to the ecosystems of other drying processes, which jeopardizes process viability. Drying attributes that dictate environmental performance were identified, such as powder productivity and carrier selection, with maltodextrin having >60% lower impact than albumin in 9 out of 10 mid-point categories evaluated. High powder productivity (35.8 g/h and 34.7 g/h for juice- and pomace-derived powders, respectively) and robustness endorse spray drying as an eco-minded drying strategy for the efficient processing of naturally polyphenol-rich materials. This research provides comprehensive data to support the upcycling of fruit pomaces as smart feedstocks to produce phytochemical-rich food ingredients.

Influence of ultrasound pretreatment on drying characteristics of cocoyam (Xanthosoma sagittifolium) slices during convective hot air drying.

Convective hot air drying of cocoyam is risk-free and inexpensive to a significant level. However, hot air drying causes negative changes to the color, texture, flavor and nutritional content of cocoyam as a result of the prolonged drying. Recently, the innovative technology of ultrasound pretreatment has been applied in food processing to reduce the processing time, conserve energy and preserve the quality of the food product. Thus, there is need to investigate the effect of ultrasound pretreatment with distilled water (UDW) and ultrasound with osmotic dehydration (UOD) for different ultrasonic times (10-30 min) on the drying kinetics of cocoyam slices during convective hot air drying. Ultrasound pretreatment was applied at a frequency of 20 kHz and an output power of 600 W for UDW and UOD. The ultrasound-pretreated samples were further dried in a convective hot-air drying oven at 70 °C. UDW and UOD samples, respectively, had a 25% and 46% reduction in drying time compared to untreated samples. The UOD samples had the lowest activation energy (10.697 kJ), as well as the highest moisture diffusivity (3.782 × 10-10 m2 s-1 ) and mass transfer coefficient (2.006 × 10-8 m s-1 ), among the untreated and UDW samples. Wang and Singh, Page and Peleg models were found to be the most fitted models with respect to the drying characteristics of cocoyam for untreated, UDW and UOD samples, respectively. Ultrasound pretreatment technology is a potential non-thermal process that can be incorporated as a pretreatment method in the convective drying of cocoyam to reduce processing time, conserve energy and enhance cocoyam product shelf life. © 2023 Society of Chemical Industry.

Improving the energy effectivity of biomass drying for utilisation in energy systems by combining convective and contact drying

The article deals with reducing the energy consumption of biomass drying before combustion in energy plants. The combination of traditionally used convective hot air drying and less applies contact drying is analyzed. To determine the basic drying characteristics, the experiments on a contact dryer and a convective hot air dryer were carried out with wet wood chips. A heat balance model of a system with serial connection of a convective air dryer and a contact dryer was compiled. In the model, the utilization of condensation heat from the waste vapor leaving contact drying to preheat the drying air for convective drying was considered. Based on these results, the system could be optimized to achieve the lowest energy consumption, drying time, and dryer sizing. This solution can significantly improve the energy efficiency of drying moist biomass before combustion from 3.29 and 2.76 MJ per kg of evaporated water for only convective drying and only contact drying, respectively, to 1.48 or 1.33 MJ per kg of evaporated water, depending on the order of the dryers in their connection.

New Emerging Technique to Intensify Convective Air Drying Process: Impact of Interval Starting Accessibility Drying (ISAD) on Quality Attributes of Strawberries Fruits

New Emerging Technique to Intensify Convective Air Drying Process: Impact of Interval Starting Accessibility Drying (ISAD) on Quality Attributes of Strawberries Fruits

β-Carotene and Lycopene Degradation Kinetics of Tarhana Dough During Convective Air Drying and Traditional Drying Methods

In this study, tarhana doughs were dried with convective air drying at 30, 40 and 50 oC temperatures and 0.5, 1.25 and 2 m/s air velocities, and with traditional drying (sun-drying method). By this way effects of drying air temperature and velocity on degradation kinetics of β-carotene and lycopene during air drying of tarhana samples were investigated and the results compared with traditional drying method. The degradation reaction of β-carotene and lycopene was found to be following the first-order kinetic model. The reaction rate constant values of the β-carotene degradation were determined in the range of 0.0003-0.0025 min-1, and the activation energy values were determined in the range of 6.15-49.05 kJ/mol. The reaction rate constant values of the lycopene degradation were determined in the range of 0.0001-0.0007 min-1, and the activation energy values were determined in the range of 20.5-34.3 kJ/mol. β-carotene and lycopene content of tarhana samples decreased with the increase in drying temperature, and the rate of degradation reactions of these components increased with the increase in temperature and air velocity. As a result, it was determined that β-carotene and lycopene were better preserved at 1.25 m/s air velocity at 30 oC.

Development of Powder from Spinach by Convective Hot Air Drying at Varied Temperature and its Quality Evaluation

Development of Powder from Spinach by Convective Hot Air Drying at Varied Temperature and its Quality Evaluation

Process conditions sensitive (PCS) thin-layer mathematical model of hot air convective drying

In this work, a model sensitive to changes of process parameters such as temperature, air velocity, air initial relative humidity, and wet material layer thickness has been developed and verified by two different experimental methods. A laboratory convective batch dryer was used to measure drying behavior of 11 types of products at various process conditions to determine the model parameters. An independent solar drying system was used to experimentally verify the model. The model can predict drying kinetics at any point within a defined range of process conditions: model parameters were determined for temperature range of 40–50 °C, air velocity of 0.6–1.2 m/s, initial air relative humidity of 27–45%, and layer thickness of 4–12 mm. However, the model was verified also for extrapolated air velocity and humidity with good agreement between experimental and model data despite the use of a different independent experimental system.

Convective hot air drying of grapes: drying kinetics, mathematical modeling, energy, thermal analysis

Convective hot air drying of grapes: drying kinetics, mathematical modeling, energy, thermal analysis

Modification in starch structure of soaked and germinated lentil seeds under various thermal processing methods, including conventional, microwave, and microwave-assisted techniques

Adding lentil flours as an affordable and sustainable plant-based ingredient in food formulation plays vital role in promoting human health and reducing the environmental footprint of human diet. Also, the inclination toward sustainable food products requires the introduction of green technologies as the substitution of conventional heating. A proper substitution demands investigating the impact of different heat transfer mechanisms of conventional and green volumetric heating processes on starch gelatinization and enhancement in starch structural, functional, and nutritional properties. Hence, modified lentil flours through soaking/germination pretreatment followed by volumetric heating (microwave-infrared and vacuum-microwave drying) and conventional heating (roasting and convective air drying) were examined in this study. The results showed that using microwave-infrared not only significantly decreased processing time but also created a similar gelatinization degree compared to the lentils treated by roasting at 240°C. Vacuum-microwave also found a suitable substitution for convective air drying, producing similar modified starch at a shorter processing time. Almost all thermal treatments improved total starch digestibility; however, microwave-infrared drying and roasting increased rapidly digestible starch while vacuum-microwave and convective air drying enhanced slowly digestible starch. Generally, soaking/germination followed by the mentioned dryings leads to modified flours by changes in their starch structure, resulting in the effective utilization of pulse flours as a promoting food ingredient.

Hot Air Convective Drying of Ginger Slices: Drying Behaviour, Quality Characteristics, Optimisation of Parameters, and Volatile Fingerprints Analysis.

Ginger is one of the most popular spices and medical herbs with its unique pungent flavour and taste. Although there has been much research into the drying methods of ginger, the effect of drying parameters in hot air convective drying on ginger quality needs to be explored in depth. This study investigated the differences in drying behaviour and quality characteristics of ginger with the variables of temperature, thickness, and loading density. The moisture states and diffusion pattern in the different stages during the drying process were analysed using low-field NMR techniques. The results of quality evaluation showed that the temperature greatly influenced the colour and gingerol content of dried ginger, and the thickness of a ginger slice greatly influenced the rehydration rate. Optimal drying conditions were determined by considering a combination of specific energy consumptions with quality retention based on the response surface methodology: a temperature of 66.41 °C, thickness of 2 mm, and loading density of 5 kg/m2. HS-GC-IMS combined with multivariate chemometrics was used to achieve the characterisation of flavour profiles and fingerprinting of dried ginger. The principal component analysis and correlation analysis revealed that the alterations in ginger quality were intimately related to moisture diffusion during drying.