مجله پژوهش های مکانیک ماشین های کشاورزی
سال هفتم شماره 2 (پاییز و زمستان 1397)

In this paper, an indirect active solar air dryer was designed and constructed. The dryer performance in terms of energy absorption and heat generation was investigated under the impact of air mass flow rate in active and passive modes. Based on the laws of mass and energy conservation, the dryer dimensions were designed and then the dryer was constructed in faculty of agriculture at Shahrekord University. The first and second laws of thermodynamics were applied to analyze the energy and exergy and the influencing components. Experiments on mint were carried out on July 4, 5 and 6, 2015 both in active (fan on) and passive (fan off) modes of the dryer. The experiments were initiated at 9 AM continued to 7 PM, and the effect of air speed at three levels (0.5, 1 and 2 m s-1) was evaluated. Results showed that energy consumption in both the active and passive modes is independent of air flow rate and is more influenced by the moisture content of the mint. The highest exergy efficiency was observed in natural convection mode of the dryer.

In the present study, a pilot thin-layer rotary tray dryer was designed and fabricated and equipped with an air-to-air cross-flow plate heat exchanger. Experiments were conducted to assess the effects of the experimental variables (air temperatures of 50, 65 and 80°C, air velocities of 1 and 2 m/s, tray rotation speeds of 0, 6, and 12 rpm with and without application of the heat exchanger) on the thin layer drying dynamics, effective moisture diffusivity and activation energy of apple slices. According to the statistical results (RMSE, SSE and R2), the Midilli et al. model was the best fitted for describing the drying behavior of apple slices. Results indicated that temperature has the most important effect on drying time (75.5%), followed by air velocity (17.6%) and tray rotation (7.8%). The highest effective diffusion was found to be 8.37×10-9 m2s-1 at air temperature, air velocity and speed rotation of 80 ºC, 2 ms-1 and 12 rpm, respectively. The lowest effective diffusion was 2.7×10-9 m2s-1 at air temperature, air velocity and speed rotation of 50 ºC, 1 ms-1 and 0 rpm, respectively. The activation energy value of apple slice varied between 16.41- 24.16 kJ/mol. The use of heat exchanger reduced energy consumption of the dryer by 33%. The results of this study can be applied for recovering the waste heat from exhaust air and improving the performance of forcedconvection dryers.

In this study, an acoustic system is proposed for online estimation of precision planting indices. The technique was based on rising the acoustic amplitude with impacts of seeds on a plate. By exceeding a defined acoustic threshold, each impact was registered as a meaningful event imported into an acoustic system algorithm for estimating precision planting indices. To evaluate the proposed system, a feeding platform was designed being able to apply different patterns of seed spacing with predefined precision planting indices. During the tests, dropped seeds from the feeding platform impacted to the plate and their spacing is estimated according to the time interval between seeds and simulated speed of planter. According to the ISO standard, calculated seed spacing was automatically separated in three ranges of spacing. The precision planting indices including multiple index, miss index, precision in spacing and quality of feed index were estimated based on the theoretical seed spacing. Considering the estimated precision planting indices with 99% coefficient of determination with referenced data in feeding platform and the acoustic system spacing measurement, the proposed acoustic system was evaluated as a powerful technique for laboratory evaluation of precision planting.

The in-transit vibrations caused by uneven roads have a significant effect on mechanical damage of agricultural products. Olive (Olea europaea L.) fruit is one of the sensitive fruits to mechanical bruising. In this study, the effects of frequency and acceleration of simulated in-transit-vibration using a vibrating table were investigated on mechanical damage of two olive cultivars. The experiments were conducted using a factorial experiment in a completely randomized design with 3 replications. The factors included vibration accelerations (0.3g, 0.5g and 0.7g), vibration frequencies (5, 7.5 and 10 Hz) and cultivars (Conservolea and Roghani). The effects of frequency and acceleration on the mechanical damage of olive fruit were significant at probability level of 1%. Increasing vibration frequency and acceleration led to first increase and then decrease in mechanical damage. The effect of cultivar on mechanical damage was not significant. The frequency of 7.5 Hz had the most mechanical damage for both cultivars; therefore, it should be controlled during transportation. The combination of 7.5 Hz and 0.5g for Roghani and 7.5 Hz and 0.7g for Conservolea caused the most mechanical damage to the fruit.

Sugarcane is one of the most important products in the area of agriculture. The solid part of sugarcane, fiber (bagasse), is the major byproduct of sugarcane industry and one of the largest cellulose sources. Another measurable index in sugarcane is Brix which is considered as sugar content as well as maturity index. Due to the importance of fiber, Brix index and moisture content of sugarcanes’ stalk, in this paper has been tried to provide nondestructive method for estimation of aforementioned parameters. To this end mechanical vibration of sugarcane stalks was evaluated as a cantilever beam. After placing samples in suitable place, they were excited and natural frequency, damping and damping ratio was calculated; these features were given to artificial neural network as inputs to predict brix, fiber percent and moisture content of sugarcane’s stalk (as outputs). The correlation coefficient for fiber, brix and moisture content were R2=0.97, R2=0.71 and R2=0.55 respectively. The support vector machinewas used to classify sugarcane parameters. The results showed that support vector machine classify fiber and Brix with the accuracy of 91.43 and 83.73%, respectively.

In this study, to investigate the tractor performance parameters, a Massey Ferguson 399 tractor was equipped with liquefied petroleum gas and diesel fuel system. The study was based on three steps: (i) equipping the tractor with dual fuel systems, (ii) evaluating on asphalt road (bitumen) and (iii) disk operations on a farm. The heavy disk plow was performed at working depth of 25 cm. The results were analyzed by factorial experiment based on randomized complete block design. The study was conducted by 5 levels of fuel combination (D100, D80, D60, D40 and D20) and a forward speed of 3.5 and 7 km/h in asphalt and 7 and 12 km/h in farm with engine speed of 1800 rpm. The highest and lowest diesel fuel consumptions were obtained at D100 and D20 treatments with 15 and 4.2 l/h, respectively and the highest and lowest LPG consumptions were obtained in the D20 and D80 combination with 7.9 and 2.4 kg/h, respectively. The drawbar power in various combinations of fuel was not changed significantly. By increasing the ratio of LPG and diesel fuel combination, specific fuel consumption was reduced from 0.4 to 0.6 l/kWh. In two farm and asphalt conditions, the best combination of fuel was obtained in D60 that showed the highest power drawbar and the lowest specific fuel consumption. In this combination, the overall energy efficiency of tractors was approximately about 20%.

Nowadays, with progress in different sciences and entering logging software and decision-make systems, decision has been deviated from trial and error in agriculture mechanization and aimed to predict prospective and targeted accordingly. Therefore in this research, the Analytic Hierarchy Process (AHP) with the help of EXPERT CHOICE11 software was employed to select the most appropriate hole-digger for usage in gardens. Three different types of hole-diggers including manual hole-digger, hydraulic hole-digger and three point hitch hole-digger were evaluated in this study. The criteria of selection consisted of the device's price, maneuverability in confined space, ergonomics, ease of utilization and work progression. The importance of device's price, maneuverability in confined space, ergonomics, work progression and finally ease of utilization were equal to 0.366, 0.277, 0.168, 0.121 and 0.068, respectively. The manual hole-digger, which is the cheapest type of diggers, is selected and introduced with 0.403 final value among the three types of hole-diggers as the most appropriate choice option. Inconsistency ratio was calculated equal to 0.05 that is acceptable amount in saaty’s opinion.

In this research, draft requirement of subsoiler tine plus fuel consumption, slippage, drawbar power, traction efficiency and overall energy efficiency of MF399 and JD3140 tractors at four speeds of 1.8, 2.3, 2.9 and 3.5 km/h and two depths of 40 and 50 cm were compared. Tractor type, speed and depth plus interaction effects had a significant effect on all parameters other than draft and drawbar power. Generally, JD3140 showed a better performance as the increase in speed from 1.8 to 3.5 km/h caused the increase of draft, fuel consumption, slippage, drawbar power and overall energy efficiency in two depths of 40 and 50 cm of 7, 4, 23, 108.3 and 89%, respectively but caused the decrease of traction efficiency of 13.8%. Furthermore, 10 cm increase in depth caused the increase in draft, fuel consumption, slippage and drawbar power of 21.3, 31.6, 20.6 and 21.4%, respectively but caused the decrease in traction efficiency and overall energy efficiency of 9.7 and 25%, respectively. The results of optimization of studied parameters using response surface methodology (RSM) show that depth of 42.9 cm and speed of 2.4 km/h resulted in the optimized condition about the performance of the tractor-subsoiler set.