نشریه مکانیزاسیون کشاورزی
سال دوم شماره 2 (پاییز 1393)

Thin-layer drying of grapes pretreated with ultrasound and carboxymethyl cellulose (CMC) was investigated in a tunnel dryer at 65°C and 1.5 m/s air velocity. The results showed that with increasing ultrasound treatment time from 10 to 30 minutes, drying time is reduced and the effective moisture diffusivity is increased. Also, with increasing carboxymethyl cellulose concentration from 0.1 to 0.2 percent, drying time increased and from 0.2 to 0.3 percent, drying time decreased. Furthermore, in order to precioucely predict the drying process, data from experiments were fitted by the models such as Newton, Page, Henderson and Pabis, logarithmic, Midili, Wang and Singh, Seiiedlou and Aghbashlou and as well some new proposed models in this study. Multiple regression analysis was used to find the relations between the coefficients of the models with the defined variables. Thereafter, one of the proposed models was selected as the best model to describe the drying process of grapes under the selected experimental conditions.

Combine grain loss monitor is installed on the combine to measure the amount of grain losses in the separating and cleaning units. One of the advantages of this system is that it allows combine operator to choose the maximum forward speed for a given amount of grain losses. To achieve this goal, a load cell sensor was used. In order to prevent long straws covering the load cell, a mesh plate has been used. The basic blocks considered in designing the proposed system, were sensor, data-acquisition, central processing and power modules. The initial accuracy of the device was set on 0.1 g, since a large amount of noise is produced at the below levels of accuracy. The output data of the load cell was demonstrated on a LCD monitor. After assembling the designed blocks, laboratory experiments were conducted to evaluate the proposed system. Results showed that the setup angle of 37 was diagnosed as the best angle for installation.

Green bean has important role in the human diet and is one of the most important grains, because of having high levels of proteins and vitamins K, A and C. In this study the maximum cutting force and cutting energy for green bean were determined. Also, the effects of cutting angle (in three levels of 0, 30, 45 degree) and cutting speed on these characteristics were evaluated. Determination of these characteristics are important for design and optimization of the processing equipment for green bean. The results showed the effects of cutting angle and cutting speed on the green bean cutting force is significant at the %1 level. Cutting force was decreased by increasing the cutting angle and cutting speed. The interaction between cutting angle and cutting speed was significant at %1 level. The minimum amount of cutting energy with an average of 16/31 mJ was for cutting angle of 45 degree and cutting speed of 350 mm/min. Also, the results showed the effect of cutting angle on elastic modulus for green bean was significant and the amount of elastic modulus decreased by increasing cutting angle.

Forage chopping machine is applied for preparation and cutting forage in villages and small sized livestock units. The machine is placed on a flat and balanced site and chops hay and silage in various lengths depending on the type of livestock. This study was performed in order to obviate the needs of small and medium livestock units to a suitable chopper. By surveying on several models of choppers and using the results of previous studies, the proper design was selected. All of the parts and transmission system of the chopper were designed and modeled by CATIA software. Considering the plant material cutting processes, the mechanism of guillotine quick return for cutting system was selected. The required power of the machine was calculated to be 5.5hp based on mechanical-physical properties of alfalfa stems. The advantages of this machine over the other available choppers in the market are: simplified structure, using fewer parts, producing low dust and above the all, it has a separate feeding unit which increases safety. A 1450 rpm electro-gearbox with the reduction ratio of 1:20 was used in this machine. The type of power transformation system from electro-gearbox to cutting unit was quick return mechanism self-return scotch-yoke mechanism. Theoretical capacity of the designed chopper machine was estimated as 1.8 ton/hr.

Wheat is the most important crop in Iran and plays main role in the food supply chain. But, its production is associated with high losses. Hence, efforts to increase the production yield by reducing wastes are concerned. Unfortunately, according to some researchers in this field, the combine harvesting loss in Iran is about 20% or higher. One of the ways concerning to loss reduction is separation of harvesting processes and providing a desired mathematical model for them by investing and measuring of important parameters in losses. Cleaning process is one of these processes which has more effect on combine harvester performance. The performance of a cleaning shoe is expressed in terms of (1) grain loss or cleaning efficiency, (2) grain dockage, and (3) cleaning capacity. Material feed rate, fan speed and degree of sieve opening are operation parameters which were used in combine design and evaluating of its performance. In order to evaluate the effect of these parameters on cleaning efficiency, an experiment was conducted in 3×3×3 factorial pattern with randomized blocks design. The independent variables in the experiment were material feed rate, degree of sieve opening and cleaning fan speed. The first two variables and B×C interaction effect had significant effect on cleaning efficiency (P<0.01). But, fan speed and other interaction effects of these variables were not significant. Grain loss increased when feed rate was increased and it decreased when degree of sieve opening was decreased. Multiple regressions were used to express the relation between the dependent and independent parameters. The most compatible model (in the scope of this study) for grain loss (y2) was: which x1, x2 and x3 determined the material feed rate, fan speed and degree of sieve opening, respectively and a0, a1, a2 and a3 were constants.

Solar air heating collector is a simple device used for air heating by solar energy that can be applied for various kinds of tasks. In this study, a flat-plate solar air heating collector with a shutter window absorber and blower speed control system was designed and fabricated. The blower speed control system consists of three LM35 sensors, AVR microcontroller, two solar panels and a blower. Outlet air temperature was measured by control system providing variable speed to put it in specified temperature range. The collector was evaluated in outdoor open area for a week. Regarding the importance of different parameters affecting the collector efficiency, the temperature and velocity of air at the outlet were selected for modeling system performance. From conventional linear and nonlinear regression models, eight models which were more general and more likely to explain the relationship between two above-mentioned parameters were selected for statistical analysis. Based on the results, the fourth-degree polynomial regression model was proposed for interpretation of the empirical relation between temperature and velocity of air at the outlet of the collector. The model with coefficient of determination equal to 0.99 showed the best fit among the investigated models.

Upon determination of field machines, ownership and operating costs of agricultural machines are readily computed. However, timeliness cost is also influenced by field operations scheduling. If planting operation is performed in the smallest possible period around optimum planting time, timeliness cost is minimized. But in some conditions, planting operation cannot be completed in such period and for optimum scheduling of operations, a method is required to determine the best time for commencing planting operation. In this study, by definition of a parameter namely timeliness index (TI), a model based on a numerical method was developed to determine optimum planting start date (opls), in which total timeliness cost is minimized. After running the model by use of input data available from a real farm, opls was determined. By comparing, the TI resulted from opls with TI values resulted from deviated planting start dates from opls, the accuracy of the model was verified. increasing rate of TI value Also had a quadratic relationship with difference between planting start day and opls. Therefore, accurate determination of opls has an important role in decreasing timeliness cost.

There are different methods in order to model soil-wheel interaction which Bekker equation and Wismer models are two of them. These models have been selected in this study for tire rolling resistance prediction and comparison with experimental tests. Using an appropriate model for accurate prediction of rolling resistance, is useful for energy management. In this study, soil power-sinkage modules related to Bekker model were obtained. In this way, a series of plates with different widths was pushed into the soil while the force and corresponding sinkage were being measured. The soil cone index was recorded using a penetrometer in several replications to compare the rolling resistance calculated by both models and from experimental data. The experiments were performed with a single-wheel tester in controlled conditions at three levels of tire pressure and vertical load. The vertical load on the wheel was varied during the test, but its travel speed was kept constant at 2.3 km.h-1 . The results showed that Wismer model in all experiments had better ability to estimate rolling resistance than Bekker model. Bekker model with higher tire pressure provided better estimate for rolling resistance, since the wheel had been turned almost into a rigid wheel.