Design and Construction
A. Khalo ahmadi; O. R. Roustapour; A. M. Borghaee
Abstract
IntroductionProviding new solutions to control wet waste is one of the most important issues in maintaining public health. Drying will reduce the harmful effects on the environment by reducing moisture and the smell of wastes as well as easy transportation and disposal costs. The purpose of the design ...
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IntroductionProviding new solutions to control wet waste is one of the most important issues in maintaining public health. Drying will reduce the harmful effects on the environment by reducing moisture and the smell of wastes as well as easy transportation and disposal costs. The purpose of the design and development of the household dryer is to dry food waste in order to reduce its volume and prevent the spread of its pollution in the air, water, and soil. To study the drying behavior of food waste, an experimental cabinet dryer was designed, fabricated, and evaluated for drying food waste.Materials and MethodsThe dryer consisted mainly of the drying chamber, electric heater, fan, air inlet channel, mesh tray, air distribution plates, temperature sensor, and control panel. Different parts of the dryer were made of a stainless galvanized sheet. The dryer was modeled using Catia 2019 software and its various parts were designed. The heating power was calculated as 2.7 kW. A centrifugal fan with an air volume of 310 m3h-1, 2800 rpm, and 110 Pa was used to supply airflow in the dryer. In the drying process, a tray with medium and lateral air passage was fabricated and applied. Food waste was obtained from fruit and vegetable waste, homemade food, and fruit shops. And nonfood items such as glass, paper, plastics, and metals were separated from the waste and crushed with a shredder, and reduced to sizes less than 20 mm. First, the product was placed in the environment for one hour and then pressed with a mechanical press with the same pressure to eliminate part of the water. An anemometer UT363 model made in China was used to measure the air velocity. The temperature was measured and controlled by a temperature thermostat of G-sense model made in Iran. The effect of three temperatures of 50, 60, and 70 °C and three inlet velocities of 1, 1.5, and 2 m s-1 on the kinetics and intensity of drying of food waste and energy consumption of food waste with a thickness of 3 cm was investigated. Moisture ratio and drying intensity diagrams were extracted. Diffusion, activation energy, and energy consumption were determined.Results and DiscussionDrying kinetics diagrams showed that temperature had a significant effect on moisture variation of food waste during drying. Drying period decreased with increasing temperature. The slope of the drying intensity diagrams increased with the increase of the dryer temperature. Drying rate was decreased at the temperature of 70 °c and it had a steeper slope that indicates the more intensity of the drying process in this condition. The drying process of all three samples occurred in the falling rate stage. The air duct on the side and in the middle of the tray caused hot air conducted above the tray and increased energy consumption. Effective moisture diffusivity of food waste during the drying process was in the range of 3.65×10-9-4.56×10-9 (m2 s-1). The effective moisture diffusivity at temperatures of 50 °C and 60 °C was less than 70 °C. Because at the temperature of 70 °C, the membrane resistance of the cell destroyed by high heat and increased the diffusion coefficient in the material.ConclusionIncreasing temperature caused the drying period decreased and the drying occurred in the falling rate stage. Temperature and the interaction of velocity and temperature had a significant effect on the drying process. The highest drying intensity and the lowest drying time were observed at the temperature of 70 °C and a velocity of 2 m s-1. Energy consumption had the maximum value at the temperature of 70 °C and a velocity of 2 m s-1 and a minimum value at the temperature of 50 °C and a velocity of 1 ms-1. The amount of activation energy for the food waste mass at three velocities was equal to 10417.44 J mol-1.
M. Rad; H. Goli; F. Mirahmadi
Abstract
Introduction Strawberry plays an important role in human health because of its micronutrients and natural antioxidant content. Increasing storage time and decreasing microbial processes, weight and volume, and eventually facilitating export, has bolded the need for drying this product. The most common ...
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Introduction Strawberry plays an important role in human health because of its micronutrients and natural antioxidant content. Increasing storage time and decreasing microbial processes, weight and volume, and eventually facilitating export, has bolded the need for drying this product. The most common drying method is sun drying. This technique requires large areas and lengthens the time to complete the process which is undesirable economically. Furthermore, the final product may be contaminated by dust and insects, and the exposure to solar radiation results in color deterioration. In order to improve the quality, traditional sun drying techniques can be replaced by a more rapid and efficient drying method such as hot-air drying. In recent years air impingement technology has got more attention in the field fruit slices drying due to high heat and mass transfer, decreasing drying time and increasing product quality. The objectives of this study were to investigate the effects of drying conditions on the drying kinetics and quality characteristics including the rehydration ratio of the strawberry slices in an air impingement jet dryer. Materials and Methods An air jet impingement dryer with controllable temperature, air velocity, and the relative nozzle-to-product distance (H/D) was used in this study. The experiments were conducted under different temperatures (45, 55, and 65°C), air velocities (6, 9, and 12 m s-1) and H/D ratios (4, 5, 6, 7, and 8). The initial moisture content, effective moisture diffusivity, activation energy, and rehydration ratio were evaluated. Results and Discussion The effects of drying temperature and air velocity on the moisture ratio and the drying rate are shown in Figs 2 and 3. As it can be seen, the moisture ratio of strawberry slices decreased with the increase of drying time. The analysis of variance for drying time indicated that increasing drying temperature and air velocity could reduce the drying time. In addition, the effect of drying temperature on drying time was more significant than that of the air velocity. It is clear that the drying rate decreased with moisture content. There was a rapid decrease in drying rate during the initial period and slow decrease at the later stages of the drying process. It is also found that the drying process generally took place in the falling rate period. It is observed that the moisture ratio decreased as H/D ratio fall. The response of drying time was affected significantly (p < 0.05) by H/D ratio. The effective moisture diffusivity increased with increasing drying temperature and air velocity. Based on the results reported in this study, the Wang and Singh model with the lowest Root Mean Square Error (RMSE=0.02) and the highest Coefficient of determination (R2=0.996) provided the best fit to describe the experimental drying data of strawberry slices. The statistical analysis shows that drying temperature and air velocity have significant (p < 0.01) effect on the rehydration ratio (RR) of slices, while the interaction effect was not significant. The means comparison shows that the RR of dried slices decreased as drying temperature and air velocity rose. H/D ratio significantly (1%) affected rehydration ratio. The means comparisons shows that the rehydration ratio increased when H/D value varied from 4 to 8. Also, the results of color change represented that color change of dried samples decreased with increase of temperature and air velocity and increased with increase of the H/D ratio. Conclusion a) Increasing drying temperature and air velocity dropped the drying time. In addition, the effect of drying temperature on drying time was more significant than that of the air velocity. b) A constant rate period was not observed in drying of strawberry slices and the whole process of strawberry slices was carried out in the falling rate period. c) The moisture ratio decreased as H/D ratio dropped, which in turn resulted in saving drying times. d) The Wang and Singh model was found to be the best model to describe the drying kinetics of strawberry slices. e) The effective moisture diffusivity of strawberry slices ranged from 1.62×10-10 to 3.24×10-10 m2 s-1. f) The values of activation energy of strawberry slices were found to be 12.88, 15.055 and 16.746 kJ mol-1 for air velocities of 6, 9 and 12 m s-1, respectively. g) The rehydration ratio of dried slices dropped as the drying temperature and air velocity rose and increased with increase of the H/D ratio. h) The color change of dried samples decreased with the increase of temperature and air velocity and increased with the increase of the H/D ratio.
S. M. Ataei Ardestani; B. Beheshti; M. Sadeghi; S. Minaei
Abstract
Fluidized bed dryers have not yet been used for drying products such as mint leaves. This could be due to high porosity and low mechanical resistance resulting in poor quality of fluidization. Applying vibration has been recommended to overcome problems such as channeling and defluidization, and hence ...
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Fluidized bed dryers have not yet been used for drying products such as mint leaves. This could be due to high porosity and low mechanical resistance resulting in poor quality of fluidization. Applying vibration has been recommended to overcome problems such as channeling and defluidization, and hence improving the fluidization quality. In this research, a laboratory scale vibro-fluidized bed heat pump dryer was designed and constructed for drying mint leaves. The experiments were conducted at vibration frequency of 80 Hz and amplitude of 3 mm. The velocity and temperature of the inlet air was controlled by an automatic control system. Experiments were carried out at 40, 50 and 60 °C, and two methods: heat pump drying (HPD) and non-heat pump drying (NHPD). The results revealed that drying process primarily occurred in the falling rate period. Effective moisture diffusivity of the samples increased with increase in drying air temperature and varied from 4.26656×10-11 to 2.95872×10-10 m2 s-1 for the HPD method, and 3.71918×10-11 to 1.29196×10-10 m2 s-1 for the NHPD method and was within the reported range of 10-9 to 10-11 m2 s-1 for drying of food materials. The activation energy was determined to be 84 kJ mol-1 for the HPD and 54.34 kJ mol-1 for the NHPD, both have very good agreement with the results of other investigators. The coefficient of performance and specific moisture evaporation rate showed the acceptable performance of the heat pump system. Moreover, the energy consumption of the dryer for the NHPD method was more than the HPD method.
