جستجوی مقالات مرتبط با کلیدواژه « خشک کن » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

In order to prevent physical damage, it’s recommended to harvest lentils at a humidity of 20%, and then reduce it to less than 12%. Remaining the plant on the field as the conventional drying method reduces the quality and quantity of lentil product. The main purpose of this study is investigation of lentil quality characteristics in different drying conditions in order to determine an optimal condition and design a specified dryer system which can dry lentil with sufficient quality characteristics. In this study, lentil grains were dried using a hot air dryer at four temperature levels of 50, 60, 70 and 80°C and three air flow velocities levels of 1, 1.5 and 2m.s-1 until the grain moisture reached to 12%. Then their qualitative characteristics were examined. Increasing the temperature and air velocity accelerated the samples drying time consumption. With increasing temperature, air velocity had less effect on the drying time of the samples. Also, with increasing both temperature and velocity factors, the required compression force increased. On other hand, with increasing temperature, the brightness of the samples (L) decreased and the color of the samples changed from green (-a) to red (+a) and changes in color parameter b showed that the intensity of yellow color in samples have been reduced. Increasing the temperature reduced the amount of protein and carbohydrates in the dried samples, in contrast, by increasing air velocity they were better preserved. Temperature had a greater effect on the protein and carbohydrate content of the samples than the air velocity. Also, the studied factors did not have a significant effect on the amount of minerals in the samples. Based on the results obtained in this study, it’s recommended to apply the drying process at lower temperatures (50 and 60 ° C) and maximum air flow velocity (2m.s-1).

The aim of this study was to investigate the effect of temperature and air displacement rate on effective moisture diffusivity, specific energy consumption, drying rate, moisture ratio, and the extraction efficiency of Melissa officinalis essential oil in hybrid dryer as thin layer. This paper presents the thin layer drying behavior of Tarragon (Melissa officinalis) by a solar hybrid dryer. Experiments were carried out at the air temperatures of 40ºC, 50ºC, 60ºC, 70ºC and air velocity of 1m/s, 1.5 and 2 m/s. Effective moisture diffusivity values were achieved to be in the range of 7.1×10−12-1.05×10−11 m2/s. Specific energy consumption values were achieved to be in the range of 75.65-326.76 (MJ/kg). Also the effect of the air velocity on the drying time at a low temperature is greater than that at a high temperature. The highest amount of essential oil related to a temperature of 40°C and air velocity of 1-1.5 m/s was achieved with approximately 0.5 cc (v/w) and by increasing the temperature from 40°C to 70°C the amount of essential oil was decreased Significantly.

Exergy analysis is performed to determine the exergy yields and losses using the second law of thermodynamics. In this study, an infrared-hot air combined dryer system was studied for drying of parboiled paddy (Fajr variety) and the exergy analysis of its drying process was investigated in laboratory scale. Experiments were performed at 1 m/s inlet speed 0.32 and 0.49 W/〖cm〗^2 infrared radiation as well as three inlet air temperatures of 40.50 and 60 ° C. The results showed that the highest exergy efficiency was at 60 ° C with an average value of 66% and the lowest exergy loss was at temperature of 40 ° C with an average of 1.33 kJ/s. The average exergy efficiency for 0.49 W/〖cm〗^2 at three temperatures of 40, 50, 60 ° C was 8.6, 1.23 and 7.28% higher than the average exergy efficiency at 0.32 W/〖cm〗^2, respectively. This study shows a successful and efficient combination of infrared and hot air in parboiled paddy drying. This study shows a high exergy efficiency and efficient combination of infrared and hot air in parboiled paddy drying which increases the efficiency by increasing the inlet hot air and infrared radiation.

Three methods of solar drying (I), sun drying (II) and shade drying (III) used to reduce the moisture content of peppermint from 87 to 7% (wet basis). The increase of air-drying temperature (∆T) for peppermint dehydration in method II reached up to 4oC after absorbing of daily solar energy (Iave=957 W/m2). However, in the method I, this parameter (∆T) reached to 18oC after the ambient air passed through a double-pass heat collector (with only 1.26 m2 area). Although the enthalpy of drying air in the method I reached to 35 kJ/kg (40% more than the other methods because of the high heat intensity of solar collector Iave=840 W/m2), only ~16% of accumulated solar heat used to increase the peppermint temperature and evaporate its extra moisture. This is the reason that exergy in the inlet and outlet of the method I during drying peppermint reached to 24 and 38%, respectively. Furthermore, the drying capacity of peppermint in the method I was 100% more than the ones dried in methods II and III at the similar conditions. The total heat loss (because of connecting pipes and drying chamber) in the method I during peppermint drying was < 4% of the total heat collected in solar drier, which is negligible.

At the Sarcheshmeh copper complex, two rotary dryers are used to decrease the moisture content of the final concentrate. One of the most challenging problems was the blockage of hot gas chamber by the wet concentrate. This reduced the operational time and significantly increased the repair and maintenance costs. It was found that the main causes of blockage of hot gas outlet chamber was an excessive moisture content of the feed and the splashing of material into the chamber. The latter was due to the contact of the material with the body of the dryer and the underlying materials. In order to prevent the blocking of the hot air, the angle of the lifter plates was reduced from 90 to 75˚, the elbow angle of the hammer body increased from 135 to 155˚, and the ceiling of the hot air chamber was extended 70 cm into the dryer rotating section. After these modifications, in order to monitor the blockage process of the hot air chamber, the images of blockage level of the hot air chamber were captured and analyzed daily. Furthermore, the temperatures of the beginning and end of the combustion chamber was recorded and compared with the profiles before modifications. On account of these modifications, the operational period increased from 7 to18 days. In addition, the temperature of the dryer end point, which is an important indicator in determining the drying performance and moisture content of the product, was kept constant at about 90 °C. The temperature at this point before modifications was 50 °C which showed a significant increase in the drying performance.

Drying is one of the most important stages in the rice milling process. In present study the effect of two drying techniques (intermittent and continuous drying) on the some quality properties of parboiled paddy (Fajr cultivar) were investigated. The intermittent drying was performed in two stages with a tempering time between drying steps using a combination dryer of hot air – infrared (HIR) at the first stage (from 35 to 23%) and microwave dryer at the second stage (from 23 to 13%). While drying technique of continuous was done using HIR dryer in one stage for moisture content reduction of paddy from 35 to 13% (w.b.). The experiments were carried out at drying temperature of 40, 50 and 60 oC, infrared radiation (IR) intensity of 0.32 and 0.49 w/cm2, microwave power of 100, 200 and 300 W and tempering duration of eight times previous drying (the first stage). After drying, quality properties (head rice yield (HRY), color and toughness force (TF)) of parboiled rice and drying time were measured. Results revealed that the effect of drying techniques, air temperature, IR intensity and microwave power on the quality properties of parboiled rice were significant (poC (200-0.32) and 40oC (100-0.32), respectively. But, the maximum drying time, color value and TF were obtained using continues drying method with 61.04 min, 19.63 and 227.3 N, respectively. In conclusion, the intermittent dryer technique is appropriate and recommendable method for parboiled paddy of Fajr variety.

In present study two different mathematical models consisting of differential equations for energy, momentum and material exchange are developed in order to predict the performance of a fluidized bed dryer. In order to approach a realistic model the existing of surface and internal moisture is considered too. The validity of the models was examined by comparing the results of models by existing data reported in the literature [1]. The predicted final temperature of particles, and final moisture content are in good agreement with the experimental data. Finally the effects of various operating parameters including: gas velocity, gas temperature and gas humidity on final moisture content of the product were investigated.

In this project, a mathematical model used to study the process of calcium carbonate drying in a co-current spray dryer. In order to determine its performance, the drying kinetics equation obtained using the experimental data. The momentum equation on the suspending particle in air and the differential equations in three dimensions of the particle movement paths and the Reynolds number and the mass and heat transfer coefficients have been solved. Proportional to these relations, a computer program in MATLAB presented. The results obtained from this program predicted the experimental data very well.

Application of Computational Fluid Dynamics (CFD) technique for the prediction and investigation of flow and heat transfer in fluidized beds has been developed recently. In this paper the governing equations on fluidized beds has been reviewed theoretically. A CFD-based design of an experimental fluidized bed dryer for drying of sugar beet particles has been reported. Based on this technique, bed size, flow pattern and velocity vectors in the fluidized bed were investigated. For the designed bed, velocity profiles and pressure drop have been calculated in different regions of the bed.