m.h. khoshtaghaza

One of the most important and sensitive steps after walnut harvesting is the separation of the kernel from its shell. Walnut rupture force is an appropriate criterion for design with high performance and better quality, which can be used as the basis for designing and adjusting the various parts of machines that are in contact with walnut. The lower rupture force caused the less energy requirement to separate the walnut kernel from the shell. The use of ultrasound in ambient fluids is well known to cause turbulence and biological cell rupture. These effects arise principally from the phenomenon known as cavitation which can scour surfaces and damage cellular material. Therefore the object of this study is to find the effect of ultrasound factors on the amount of walnut rupture force and quality of kernel extraction.

Walnut paper variety was selected from a Qazvin province orchard for this study. To determine the initial moisture content of the nuts, the samples were dried in an oven at 105°C for 24 h. Initial moisture content was found 5.5 (%w.b). The ultrasounds bath system (D-78224 Singen/htw, Elma, Germany) was used with a nominal frequency of 50 kHz and power of 1000 W. In this research, based on the pretest results and previous studies (Cao et al., 2010; Entezari et al., 2004) walnut samples were treated with three ultrasound time duration (5, 10 and 15 min) and three ultrasound bath temperature (20, 35, and 50ºC). Moisture content of the walnuts after ultrasound treatment was 8.8 (%w.b). After the walnut samples were treated by ultrasonic factors, a material testing machine (H50 K-S, Hounsfield, England) was used to determine the rupture force of the walnuts. The walnut was placed between two plates, and loaded at three loading speeds (0.5, 1.5, and 2.5 mm s-1) and pressed until the walnut ruptured. Rupture force was applied along with X and Y axes. The X-axis was in the longitudinal axis through the hilum to the tip (length) and the Y-axis was in the latitudinal axis (width) at right angles to the X-axis. Kernel extraction quality was classified into grades according to size and number of broken pieces of the kernel. Central composite design (CCD) of resound surface method was used to optimize the effect of ultrasonic factors on walnut kernel extraction.

The results indicated that the loading speed, ultrasound time duration, loading direction, and moisture content had a highly significant effect (P<0.01) and ultrasound bath temperature (P<0.05) on the rupture force and kernel extracting quality. Regarding the sum of squares of ANOVA results, the ultrasound time duration factor had the most effect on the rupture force and the loading direction factor had the most effect on kernel extraction quality. By increasing bath temperature and ultrasound time duration, walnut rupture force was decreased. The minimum walnut rupture force was obtained in 25 min ultrasound time duration, 50ºC bath temperature, 1.5 mm s-1 loading speed, and width loading direction for wet walnut. By increasing bath temperature, walnut kernel losses were increased. The best kernel extraction quality was obtained in 2.5 mm s-1 loading speed, 25 min ultrasound duration, 20ºC bath temperature, and longitudinal loading direction. The proposed optimal point was obtained at 64.4 N rupture force, and two half of the kernel at 1.3 mm s-1 loading speed,  25 min ultrasound duration, 50ºC bath temperature, and longitudinal loading direction for wet walnut.

The walnut ultrasound treated samples had minimum rupture force and the best quality kernel extraction. It was observed that by increasing the loading speed and ultrasound time duration, the percentage of whole kernels and the quality degree of broken kernels increased.

In this study, the effect of microwave drying method (at five power levels: 200, 400, 600, 800 and 1000 watts) on drying time, color change, amount of organic acids and vitamin C of sumac fruit (Rhus coriaria L.) was investigated. The experiment was conducted in a completely randomized design with three replications and the response surface methodology (RSM) was used to find the optimum points for the minimum drying time and color changes or the maximum organic acids and vitamin C during drying. The results showed that microwave drying had significant effect on the color, the amount of organic acids and vitamin C at 5% probability level but it had significant effect on drying time at 1% probability level. Among the different microwave powers, the highest and lowest organic acids were obtained at 1000 and 600 watts with values of 1.46 and 1.11 mg/100 g, respectively, and the highest and lowest vitamin C was obtained at 600 and 1000 watts with values of 0.40 and 0.26 mg/100g, respectively. The best situation for microwave drying (with the lowest drying time and color variations and the maximum phytochemicals) was obtained at 815 watts. Finally, the lowest color changes and the highest amount of organic acids and vitamin C were observed in the shade drying method.

Manual citrus harvesting is commonly performing hard, expensive and time consuming. In this study, a factorial experiment with a completely randomized design in three replications was performed to find out the effect of frequency (three levels of 5, 7.5 and 10 Hz), vibration time (three levels of 10, 15 and 20 seconds) on harvesting capacity and losses of Thomson cultivar of orange. The results indicated that the effect of frequency and vibration time was significant (P≤0.01) on the harvesting capacity and losses, but their interaction effects weren’t significant. The harvesting capacity significantly increased by increasing frequency, and the highest harvesting capacity was 62.8 % at 10 Hz frequency. Although the harvesting capacity increased by increasing the vibration time, but there was no significant difference in vibration times between 15 and 20 seconds at 10 Hz frequency. Also the fruit loss was increased by increasing the vibration time. Due to these reasons, frequency of 10 Hz and vibration time of 15 seconds were selected as the most suitable condition for mechanized harvesting of this cultivar of orange. Finally a linear mathematical model was developed based on the frequency and vibration time for the harvesting capacity and fruit loss of Thomson cultivar of orange.

Non-destructive ultrasonic testing is one of the methods utilized to evaluate quality of agricultural produce. Transducers used in this method are made for basically industrial applications. Since ultrasonic attenuation of waves in agricultural produce is very high, industrial transducers cannot be used in agriculture and needs to be modified. This is done with horns that concentrate energy on a small area at a certain distance from the transducer. In this paper, an exponential horn was designed, fabricated and tested using theoretical and computer-aided methods. Results showed that highly sophisticated horns can be designed using computer-aided method with a high accuracy. Analysis of the number of elements on the natural frequency of horn proved that the analysis was not precise at the low number of elements. Therefore, the number of elements should be increased when natural frequency of horn is almost fixed. The minimum number of elements was obtained to be 300. A comparison between theoretical and computer-aided methods showed a desirable performance of the computer-aided method with an error less than 1% without solving very complicated equations. Based on statistical analysis of the data, the effect of produce thickness (potato and carrot) on the velocity of ultrasonic waves in the horned probe was not significant. However, for the un-horned probe, velocity changed significantly with the sample thickness which is not desirable. Therefore, horned probe is more suitable for non-destructive ultrasonic tests than the un-horned probe.

The objective of this study was to determine some mechanical properties of chickpea which are basic with regard to the design of harvesting machines. At the present, chickpea is harvested manually with difficulty and low efficiency. Therefore two common methods in grain harvesting were studied meanwhile stem cutting force and pods stripping force were compared in the field and greenhouse conditions. The relationship of stem diameter and moisture content with shear stress was verified by the linear regression analysis. There was no significant difference between shear stress of chickpea stems planted in the greenhouse and field conditions and it varied from 2.8 to 9 MPa depending on the stem diameter. At 10.5 to 19% moisture content, there was no significant effect of moisture content on shear stress but the regression analysis showed that the effect of stem diameter on shear stress was significant. In terms of pod stripping force a significant difference was observed between greenhouse and field environments. The average of this force in the field and greenhouse were 8.8 and 6.2 N, respectively, at 12% moisture content (w.b.). As the field results did not correspond with those of the greenhouse for stripping, it can be concluded that greenhouse data may not be suitable for designing purposes and researchers should use the data from field condition.

One of the most important thermal properties of unhulled pistachio nuts, namely bulk thermal coductivity, was evaluated as the function of moisture content and temperature. The moisture content of nuts ranged from 20.9% on the wet basis to 51.8% (moisture content at harvest time) and the temperature ranged from +20°C to +40°C. In order to measure the thermal conductivity of agricultural materials, a specific probe was developed. Thermal conductivity was measured in transient state by calculating the maximum instant slope, using the line heat source which was assembled in the probe. Bulk thermal conductivity varied significantly with moisture content and temperature. It ranged from 0.1145 to 0.1904 W/mK and increased with moisture content in the range of 20.9-51.8% on the wet basis. Furthermore, increasing the temperature from 20 to 40°C raised the average thermal conductivity from 0.1448 to 0.1585 W/mK. The conducted tests on two varieties of nuts (Akbari and Kallehghoochi) demonstrated that the thermal conductivity of Kallehghoochi cultivar is lower than that of the Akbari cultivar at α=0.05. Quadratic regression equations were developed depicting the effect of moisture content and temperature on thermal conductivity.

Traditional paddy dryer systems in Iran cause considerable losses in rice production due to non-uniform drying. In order to decrease the amount of kernel fissuring and to increase the drying rate, fluidized bed method was applied in this study for rough rice drying at temperatures higher than normal. An experimental dryer was used for drying the samples. The drying experiments were set up to find kernel fissuring percentage and the drying times under three conditions: fixed, minimum, and full fluidized bed conditions at temperatures of 40, 60 and 80oC. Results showed that the amount of kernel fissuring, at minimum fluidization compared to fixed bed condition, decreased 57%, 68% and 75% at temperatures of 40, 60 and 80oC, respectively. This reduction at full fluidization compared to fixed bed condition, at the above temperatures, was 40%, 54% and 65%. The minimum fluidization method took the lowest and the fixed bed method took the highest drying time. It was concluded that the minimum fluidization drying method had the lowest fissuring and drying times at all experimental temperatures.