Hot Air Convective Drying Research Articles

Evaluating polyphenol and ascorbic acid contents, tannin removal ability, and physical properties during hydrolysis and convective hot-air drying of cashew apple powder

Abstract Cashew apple is a source of by-products in the cashew industry. Powder products provide convenience to the process of use, transport, and preservation of nutrients. In this study, the production of soluble powder from cashew apples was developed through the investigation of hydrolysis process (time, temperature, and enzyme tannase) and convective drying conditions (temperature and maltodextrin content). The following indicators are evaluated, such as the total polyphenol content (TPC), total tannin content, total ascorbic acid, solubility, turbidity, and color. The results have shown that TPC increased by 1.67 times, and more than 50% of tannins was removed after the hydrolysis process. At the same time, the efficiency of the process over 30% under all processing conditions was evaluated. These results are the foundation for the development of cashew apple powder and related products, thereby improving the economy of the cashew industry in Vietnam and the world.

Meta-heuristic optimization for drying kinetics and quality assessment of Capparis spinosa buds

This paper was conducted to model the drying kinetics of Capparis spinosa buds using dragonfly swarm optimized nonlinear regression and to compare the impact of drying treatments on their quality. Experiments included hot-air convective drying (HACD) from 40 to 120 °C, vacuum drying (VD) at 40, 60, and 80 °C, microwave drying (MD) ranging from 200 to 1000 W. Out of 30 models tested, the drying kinetics fitted best with Jena Das model in both HACD and VD and modified Midilli for MD. The comparison between the drying treatments used indicated that when taking into account the quality of the dried caper, VD at 80 °C was the most effective, resulting in a high-quality caper with a well-preserved color (ΔE = 7.47), high bioactives (TPC = 30.18mgGAE/gDW and TFC = 10.27 mg QE/gDW) and radical scavenging abilities (DPPH = 0.249 and ABTS = 4.448 mg/mL) at the expense of long duration (6h) and high specific energy consumption (50.667 kWh/kg). On the other hand, when considering the drying behavior MD ranked best with samples dried at 1000 W showing high diffusivities 2.04e−8 m2s−1 low energy consumption (MER 0.1216 kg/h), and short drying times (12 mn). This research is critical in selecting better drying conditions for increased usage in the culinary, cosmetic, and pharmaceutical sectors.

Comparison of Mango (Mangifera indica) Dehydration Technologies: A Systematic Review

The convective hot-air drying technology can cause physicochemical, nutritional, and organoleptic losses in the mango (Mangifera indica). The present Systematic Review was carried out with the objective of comparing mango dehydration technologies to identify the effects on the physicochemical, nutritional, and organoleptic properties of the fruit. Through a review of published scientific and conference papers in the Scopus database, adjusted to the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) methodology, a total of 134 documents dated between 2000 and December 6 of 2022 were obtained; 76 of these documents were finally included in the bibliographic and theoretical analysis. Selection parameters emphasizing the relationship between the articles and the research topic, evidenced by including at least one of three dehydration technologies and the fruit of interest with an experimental or theoretical approach to the dehydration subject; review articles and surveys were excluded. Correlation graphs of bibliographic variables were made using the data mining software VantagePoint (version 15.1) , which was graphically restructured in Microsoft Excel with the support of statistical analysis. Of the resulting articles, it was found that the countries with authors who participated most in scientific production like India, Brazil, Colombia, the United States, and Thailand, were those related to mango production or importation. Furthermore, the freeze-drying technology allows operating at lower temperatures than convective hot-air drying, contributing to the preservation of ascorbic acid, among other compounds. The refractance window has the shortest operation time to obtain moisture values between 10 and 20%. The dehydrated samples using the refractance window are smooth, homogeneous, non-porous, and comparable to the color obtained with freeze-drying, which is acceptable for industrial applications.

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.

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.

Development of Powder from Amaranthus by Convective Hot Air Drying at Varied Temperatures and its Quality Evaluation

Development of Powder from Amaranthus by Convective Hot Air Drying at Varied Temperatures and its Quality Evaluation

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

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

Analysis of drying characteristic, effective moisture diffusivity and energy, exergy and environment performance indicators during thin layer drying of tea in a convective-hot air dryer

The objective of this study is mainly to analyze the drying kinetic parameters, effective diffusivity, and thermodynamic performance indicators (energy, exergy, heat, and mass transfer coefficients) of tea under different drying conditions of different drying temperatures (DT) and thin layer thicknesses (TT). Experimental drying was conducted at drying temperatures of 70°C, 80°C, and 90°C with thin layer thicknesses of 10 mm, 15 mm, and 20 mm. The results show that a higher drying temperature and a lower thin layer thickness can increase evaporation moisture content and shorten drying time. By evaluating and comparing the fitting of five drying models adopted by the coefficient of determination (R2) and chi-square (χ2), it can be found that the logarithmic model is the best to describe drying behavior. The effective moisture diffusivity shows a positively correlated trend with the increase in DT and TT, with the value of activation energy ranging from 14.030 to 22.344 kJ mol−1 K−1. The specific moisture evaporation rate (SMER), energy efficiency, exergy efficiency, and sustainability index (SI) descend as the TT increases at all DT; the specific energy consumption (SEC) and improvement potential (IP) rate perform in an opposite manner, but the TT remains unchange. The conclusion drawn from the thermodynamic parameters is opposite to the aforementioned. As the TT increases, the heat and mass transfer coefficients show a significant decrease trend. In addition, the heat and mass transfer coefficients are given as functions of DT and TT, and further knowledge shows that the mass transfer coefficient is positively correlated with DT but the heat transfer coefficient is negatively correlated. In conclusion, this article provides new insights into the effects of drying characteristics, energy consumption characteristics and heat and mass transfer characteristics in the process of tea drying under different drying conditions, and provides certain theoretical reference bases for promoting the optimization of industrialized tea drying production machinery design and drying process optimization.

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.

Fundamental drying and agglomeration experiments with bio-fraction and refuse derived fuel for the development of pyrolysis reactor feed.

The EU's circular economy concept necessitates increasing the recycling ratio of municipal solid wastes. There are many existing mechanical-biological processing plants in Hungary for the preparation of residual municipal solid wastes (RMSWs). The two most important products of these plants are the bio-fraction and the refuse derived fuel (RDF). Currently, there are problems with both of these material streams in Hungary, since most of the bio-fraction is still landfilled, and the local thermal utilisation of the RDF has not been implemented yet. The high moisture content of the produced bio-fraction and RDF causes difficulties for the downstream operations; therefore, there is recent engineering interest in drying and agglomeration of these materials. The authors have carried out systematic and parallel drying and briquetting experimental series to study the effect of the material, material composition, mass (volume or surface) of the material, particle size distribution and pre-treatment with a cutting mill on drying intensity in a 1 m3 oven and their effect on briquettability by a laboratory briquette press. The initial slope of the relative moisture loss as function of time was determined. Process engineering design methods of convective hot air-drying can be further developed taking into account the research results. Results can be used for the design of the feed of a pyrolysis reactor once reactor experiments have provided the optimal feed requirements.

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.

Physico-chemical and Functional Properties of Drumstick Leaf Powder

The study was conducted to analysis of physico-chemical properties of drumstick leaf powder. Drumstick leaf were dried in a convective hot air dryer at 30oC, 40oC and 50oC. The air velocity inside the dryer was 2-3 m/s, the drying process takes 6 hrs, 27hrs, and 19 hrs time to dry the product at 30⁰C, 40⁰C, and 50⁰C.&#x0D; The experimental drying data of drumstick were applied to six Moisture ratio models, namely, the Newton model, modified Page model, Henderson and Pabis, Logarithmic, Two term and Exponential Model was found to be the best for explaining the drying characteristics of drumstick leaf. The effective moisture diffusivity varied from 3.651 ×10-11, 4.503×10-11 and to 7.343×10-11 over the temperature range studied, with activation energy of 28.281 kJ/mol for drying of drumstick leaf. The drumstick leaf powder contains moisture 10.85 to 15.56 %, protein 22.88 to 23.979 %, fat 1.80 to 2.42 %, fibre 11.53 to 12.16 %, ash 3.69 to 4.93 %, carbohydrate 40.94 to 849.25% The flour had average water absorption capacity (3.081to 4.22l g/cc), bulk density (3.081 to 0.445 g/cc) were recorded.

Thermal Degradation Kinetics of Immature Melon Manis Terengganu (MMT) Heated by a Convective Hot Air Dryer

Thermal Degradation Kinetics of Immature Melon Manis Terengganu (MMT) Heated by a Convective Hot Air Dryer

MODELING AND SIMULATIONS OF WET POROUS MEDIUM CONVECTIVE DRYING

In the convective drying of a wet porous medium by hot air, the medium surface exposed to the air fluid may experience three stages, namely the fully wet, partly wet, and fully dry stages. At the fully wet stage, the medium surface is fully covered by a water film, with the convective moisture transfer taking place all over the medium surface; at the partly wet stage, the medium surface is partly covered by water film, with the convective moisture transfer occurring only at the wet surface where free water is present. In this research, a theoretical model is presented to simulate the convective drying of a wet porous medium, and experiments on hot-air convective drying of a wet porous sand layer are carried out to investigate the sand-layer temperature and water content variations during the drying, in which the sand layer thickness is 4 mm, the initial water-film thickness is 0.4 mm, and the hot-air temperatures are 45, 60, and 75&amp;deg;C, respectively. Inverse calculations are conducted to get some insight into the water-film coverage function based on the experimental data, which are necessary for quantitatively evaluating the effective moisture transfer surface area when calculating the convective moisture transfer at the partly wet stage. By combining the coverage function with the wet porous medium drying model, a comprehensive model is obtained. Calculations are implemented to simulate the convective drying of the wet porous sand layer, and the effects of the two constants included in that function on the wet sand-layer drying characteristics are discussed. The calculation results are compared with the experimental data; they agree very well, supporting the effectiveness of the current model in simulating the sand-layer convective drying process.

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.

Comparison of ANN and ANFIS modeling for predicting drying kinetics of Stevia rebaudiana leaves in a hot-air dryer and characterization of dried powder

ABSTRACT In this investigation, the drying of Stevia rebaudiana leaves was carried out in a lab scale convective hot-air dryer at a varying temperature of 30–80°C to analyze the drying behavior, fit mathematical, Artificial Neural Networks (ANNs), and Adaptive Neuro-Fuzzy System (ANFIS) models to predict the drying kinetics of leaves. Further, dried leaf powders were analyzed for color properties, ascorbic acid and total phenol contents, antioxidant activity, water activity (aw), water solubility index (WSI), hygroscopicity (HG), density (bulk, tapped, and particle), bulk porosity, and flowability indices (Hausner ratio (HR), Carr index (CI), and angle of repose (α)). The results showed that ANFIS model with R2 of 0.9998, offers a more accurate forecast of the drying kinetics of leaves dried in a convective hot-air dryer in comparison to mathematical and ANN modeling. The convective drying significantly (p < .05) effected the L*, a*, b*, hue angle and chroma values of dried leaves. Increase in the drying temperature from 30 to 80°C resulted in a decrement of 50.90% in aw, 10.10% in tapped density, while enhancement of 23.26% in WSI, 32.93% in HG, 54% in particle density, and 10.59% in bulk porosity of dried leaf powder. Notably, ascorbic acid and antioxidant activity decreased with rising temperatures, while total phenols enhanced up to 50°C. The bulk density of dried samples remained largely unchanged with increasing temperature, while the flowability of the Stevia powder improved. Thus, these findings provide valuable insights for producers regarding the drying characteristics and properties of Stevia leaf powder.

Analysis of exergetic performance for a combined ultrasonic power/convective hot air dryer

Recently, the effectiveness of combined use of non-thermal technologies to improve hot air dryers’ performance from both the energy and quality point of views has been proven. However, no study has been reported on thermodynamic analysis of such hybrid systems. The present work dealt the influence of ultrasonic power combination with convective hot air dryer on exergetic performance of the system. Potato cubes were dried at different drying air temperatures (45–65 °C) and velocities (0.5–1.5 m/s) and ultrasonic powers (0–0.08 kW). Based on the findings obtained through the experiments, the exergy loss varied averagely from 240.58 to 600.83 kJ, and was decreased continuously with increasing the power level. The average exergy destruction ranged from 169.61 to 1554.23 kJ, and was decreased at the higher air temperatures and velocities. Combination of ultrasonic power with hot air intensified the exergy destruction. The average exergy efficiency varied from 24.19 to 91.42% and from 11.67 to 38.27% for the drying chamber and process, respectively.

Effects of freeze drying and convective hot-air drying on predominant bioactive compounds, antioxidant potential and safe consumption of maoberry fruits

The effects of freeze drying and convective hot-air drying of maoberry fruits (Antidesma bunius L.) on their phenolic and ascorbic acid contents and antioxidant activities, as well as the levels of 5-hydroxymethylfurfural (HMF) and food-associated microorganisms, were investigated. Results showed that fruits dried to the desired final moisture content (∼15%) using convective hot-air drying at 50–100 °C exhibited lower retention of ascorbic acid, total phenolics, total flavonoids and total anthocyanins compared with fruits dried using the freeze drying process, with greater retention observed in fruits exposed to lower temperatures. Lower drying temperatures also resulted in dried fruits with higher antioxidant activities, and no significant differences in antioxidant potential were observed in freeze-dried and 50 °C-dried fruits. All dried fruit products obtained from the studied conditions showed negligible HMF levels (<100 ppm) and possessed lower pathogen loads than the microbiological limits for ready-to-eat products. Therefore, the products should cause no adverse health effects. As suggested by a principal component analysis, convective hot-air drying at 50 °C could be a potentially inexpensive drying method for preserving bioactive compounds and inactivating key pathogens in maoberry fruits, despite its low efficiency in reducing fungal contamination of the dried products.

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