Drying Technology

The aim of this study was to determine the changes in physical properties of Paulownia (Paulownia elongata) wood, a fast-growing species, during heat treatment at three different temperatures (160, 180, and 200°C) and durations (3, 5, and 7 h). After heat treatment, changes in swelling, density, color, and equilibrium moisture content at 35, 65, and 85% RH were investigated. The results indicated that the minimum and maximum decrease swelling ratios were 6-46% for tangential, 4-32% for radial, and 12-64% for longitudinal. The equilibrium moisture contents were 1-26% for 35% RH, 1-33% for 65% RH, and 1-38% for 85 RH, respectively; the density of air-dried and oven-dried samples decreased by 1-16% and 1.5-15%, respectively, and color changes values (L*) were 10-40%.

The effect of harvesting regime, drying mode and storage period on quantity of essential oil in the leaves of Patchouli (Pogostemon cablin) grown under humid tropical conditions of Northeast India is reported for the first time. Leaf samples of first year harvests had the highest oil content (g/100g of dry weight) as compared to subsequent year’s harvests. All the three harvests of second year showed considerable yield reduction whereas third year harvests yielded the lowest oil. Further, first harvests of leaves during the entire three years crop cycle yielded the maximum oil. Declining trend in oil yield was recorded in second and third harvests of subsequent years. Leaf maturity stage also had significant effect on oil content. Out of the three maturity stages viz. full vegetative, semi-mature and fully mature; semi matured leaves had the highest oil content. Spread followed by heap drying of patchouli leaves resulted highest yield of oil. Storage of well dried leaves up to 135-150 days produced highest oil yield. Based on the studies, it is concluded that the essential oil profile of patchouli leaves greatly influenced by harvesting cycle, post-harvest drying mode and storage period.

Rice is the staple food for more than three billion people worldwide. Although considerable progress has been made with respect to improved breeds and production practices, losses during postharvest handling remain considerable. Drying and storage of paddy are two key stages where management can be improved. For rice, grain moisture content of 14% prevents microbiological activity, while a level of about 12% minimizes quality losses over prolonged storage periods. Due to the need for simple and economical technologies, an inflatable solar dryer (ISD) was developed based on adaptations of the Hohenheim-type solar tunnel dryer. To form a drying tunnel, transparent polyethylene (PE) film attaches by zipper to a reinforced black polyvinyl chloride (PVC) film. To reduce heat loss, a flexible multilayer floor was used along the drying area. The tunnel does not need a substructure as it is stabilized adequately from pressure created by two axial flow ventilators. During experiments, paddy was spread on the floor and mixed with a special roller bar. The ISD has been evaluated for paddy in the Philippines during both rainy and dry seasons and was subsequently optimized. Sun drying and shade drying were carried out in parallel for comparison and product was evaluated for moisture content and quality in terms of milling recovery and head rice yield. Moisture content was reduced from 23% to 14% within 26-52 h of continuous operation during the rainy season and 16% to 14% within 4-26 h of drying during the dry season. In both seasons, the final moisture content of 12% was reached after prolonged drying periods. Quality was not found to be affected with respect to drying treatment. The ISD showed advantages over sun drying, despite longer drying periods. Citation: Salvatierra-Rojas A, Nagle M, Gummert M, de Bruin T, Müller J. Development of an inflatable solar dryer for improved postharvest handling of paddy rice in humid climates. Int J Agric & Biol Eng, 2017; 10(3): 269–282.

En este estudio se determinó la cinética de secado de la pulpa de ahuyama y se evaluó la degradación de carotenoides totales a temperaturas diferentes. Para la determinación de la cinética de secado, se deshidrataron cubos de ahuyama de 2 cm a 65, 75 y 85°C a velocidad de aire de 10 m s-1. Se calcularon los tiempos para la obtención de la humedad en equilibrio, los cuales fueron de 11 , 7 y 6 h a 65, 75 y 85°C, respectivamente, y las curvas de secado se ajustaron al modelo de Page (R2  ≥0,99). Las pérdidas de carotenoides totales al final del proceso de secado fueron de 70,8; 83,2 y 87,8% para 65, 75 y 85°C, respectivamente, sugiriendo que, con propósito del aprovechamiento de su contenido de
carotenoides, resultaría más conveniente emplear temperaturas de secado relativamente bajas.
[The squash (Cucurbita moschata) is a promising crop due to its high content of carotenoids. In this study, the drying kinetics of its pulp (2 cm cubes) was determined at 65, 75 and 85°C with 10 m s-1 air velocity. Total carotenoids losses were assessed at the end of the cubes drying process. The equilibrium humidity was reached after 11, 7 and 6 h at 65, 75 and 85°C, respectively. The drying curves were adjusted to the Page model. Carotenoid losses were 70.8; 83.2 and 87.8% for 65, 75 and 85°C, respectively, which suggests that it would be more convenient to use
relatively low drying temperatures when the dried product is intended to be a better vitamin A source. ]

The objective of this study was to determine the isothermal drying kinetics of Acacia mangium wood blocks by employing a relative humidity-controlled drying chamber. A model was developed based on solution of Fick's second law and evaluated through the coefficient of determination (R 2 ), sum of square error (SSE), root mean square error (RMSE), and reduced chi-square (χ 2 ). This model was compared to semi-theoretical models which are commonly used to describe the drying behavior of biomass in previous studies. The porosity and shrinkage characteristics of dried specimens were also evaluated. Based on the findings in this work, it was determined that the proposed model resulted in an excellent fit with experimental data for all four drying temperature levels of 30, 35, 40, and 45 ∘ C to describe the isothermal drying kinetics of Acacia mangium . It appears that volumetric shrinkage of the samples decreased quadratically with decreasing moisture ratio. The activation energy of the drying process was determined to be 41.07 kJ/mol.

Soysal Y, M Keskin, A Arslan, YE Sekerli. 2018. Infrared Drying Characteristics of Pepper at Different Maturity Stages. International Conference on Energy Research (ENRES2018), 1-2 November 2018, Alanya, Turkey, Proceedings Book, pp.293-304. ........... ............. ........ ......... .............. ............... ............. ............. ............. ............ ............
Abstract: The influence of maturity stages on the infrared drying kinetics and moisture diffusion characteristics of pepper slices were investigated. Increasing the drying temperature decreased the drying time considerably. Compared to the green pepper samples, drying time of the red pepper slices was 1 to 7 min longer depending on the drying temperature. Entire drying process for both green and red pepper slices took place mainly in falling rate period. Among the 11 mathematical models tested to fit the moisture ratio changes during the drying of pepper slices, the Midilli et al. (2002) model gave the best fit for all data points. The value of the drying coefficient k increased with the increase in the drying temperature. Considerable increases were observed in the effective moisture diffusivity values with the increase in infrared drying temperature. Depending on the drying temperature range studied, the Deff values of the green pepper samples varied from 0.5363x10-10 to 1.1369x10-10 m2s-1 and red pepper samples from 0.6079x10-10 to 1.2561x10-10 m2s-1. The Deff values of the red pepper slices dried at 50°C and 70°C were significantly higher than those of the values for green pepper slices (P<0.001). Activation energies (Ea) were predicted as 34.69 kJ/mol for the green pepper slices and 33.46 kJ/mol for the red pepper slices. The closeness of Ea values implies that the unripe (green) pepper is as sensitive as the ripe (red) pepper to infrared drying temperature. Moreover, the ripening of the pepper from green to red did not change much of its structural properties controlling its heat transfer characteristics. The moisture content and drying rate versus drying time profiles also supports these findings. ............. ........... ............ ........... ........... ............ ............. ............. ............ ............. ............. ...............
Özet: Bu çalışmada, biberin olgunlaşma düzeyinin, biberin kızılötesi kuruma kinetiği ve nem yayılma özellikleri üzerine etkisi araştırılmıştır. Kurutma sıcaklığının arttırılması, kuruma süresini önemli ölçüde azaltmıştır. Kırmızı biber dilimlerinin kuruma süresinin, yeşil biber ile karşılaştırıldığında kuruma sıcaklığına bağlı olarak 1 ila 7 dakika daha uzun olduğu görülmüştür. Hem yeşil hem de kırmızı biber dilimleri için tüm kurutma işlemi, genel olarak azalan oran şeklinde gerçekleşmiştir. Biber dilimlerinin kurutulması sırasında nem oranındaki değişikliklere uyum yönünden test edilen 11 matematiksel model arasından Midilli ve ark. (2002) modelinin en uygun model olduğu tespit edilmiştir. Kurutma katsayısı (k), kuruma sıcaklığının artmasıyla artış göstermiştir. Kızılötesi kurutma sıcaklığındaki artışla birlikte etkili nem yayılma değerlerinde önemli artışlar gözlenmiştir. Çalışılan kurutma sıcaklıklarına bağlı olarak, Deff değerleri; yeşil biber için 0.5363x10-10 ila 1.1369x10-10 m2s-1 ve kırmızı biber için 0.6079x10-10 ila 1.2561x10-10 m2s-1 arasında değişmiştir. 50°C'de ve 70°C'de kurutulan kırmızı biber dilimlerinin Deff değerleri, yeşil biber için olanlardan anlamlı miktarda yüksektir (P <0.001). Aktivasyon enerjisinin (Ea) yeşil biber için 34.69 kJ/mol ve kırmızı biber için 33.46 kJ/mol olduğu tahmin edilmiştir. Ea değerlerinin birbirine yakınlığı, olgunlaşmamış (yeşil) biberin, olgunlaşmış (kırmızı) biber kadar kızılötesi kurutma sıcaklığına hassas olduğu anlamına gelmektedir. Ayrıca, biberin yeşilden kırmızıya olgunlaşması, ısı transfer özelliklerini kontrol eden yapısal özelliklerinin çoğunu değiştirmemiştir. Kuruma zamanına göre nem içeriği ve kuruma oranı özellikleri de bu bulguları desteklemektedir.

The effect of air flow rate on the change of biomass (organic waste material) temperature and moisture content during an autothermal drying process is discussed. The laboratory-scale experiments were performed using a 240-dm3 horizontal composting reactor equipped with an air supply system, biomass temperature measuring system, and air humidity and temperature sensors. An organic fraction of municipal solid waste with the addition of a structural material was used as a substrate in this process. As a result of the autothermal biodrying process, the initial moisture content of organic waste ranging from 0.8 to 0.9 kgH2O/kg of raw waste mass decreased by 50%. Water balances were calculated before and after biodrying, and the difference was less than 10%. The heat of combustion and the calorific value of dried wastes ranged respectively from 6,750 to 12,280 kJ/kg and from 8,050 to 10,980 kJ/kg. The biodrying efficiency varied from 0.73 to 0.97, depending on process conditions. Energy balances showed that average biological energy production rates varied between 1.66 and 6.90 W/kg of raw waste mass.