JWSS - Journal of Water and Soil Science

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Rice is only second to wheat as a major food for Iranians. It has to be dried for processing and/or storing due to excessive moisture content after harvesting. In most parts of Iran, rice is sun-dried by spreading it on the ground under solar radiation which leads to excessive losses such as attacking birds and rodents, grain contamination, wind and rainfall hazards, as well as thermal and moisture stresses. The present research aims to investigate the feasibility of thin layer solar drying process of rough rice to determine the appropriate bed depth of seed. A mixed mode passive solar dryer was used. In this system, hot air is provided by natural convection through an air solar collector. Thin-layer drying process was investigated using the thin layer mathematical models (Newton and Page models). One of the main aims of this research was to find an appropriate depth that can be regarded as thin layer. Therefore, bed grain depths of 2, 4 and 6 cm were selected for the experiments. The results illustrated that the bed depth of 2 cm showed the thin layer drying behavior whereas bed depths of 4 and 6 cm did not.

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The application of solar energy for drying cereals and other agricultural commodities has been increasing lately. This is due to the fact that solar energy is free, renewable, inexhaustible and environmentally friendly. This research is a new approach for employing solar energy as the main energy source for drying purposes. The drying test rig was designed, fabricated and evaluated. The grain solar dryer is an active mixed mode type with a semi-continuous discharge system. The rig consists of six solar air collectors, a heating channel, a drying chamber and an air distributing system. Rough rice was selected as cereal grain to be dried in the dryer to evaluate the system of the drying rig. In this research the effect of mass flow rate and time of crop discharge, on the rate of crop drying were evaluated. The experiment was conducted as a factorial experiment on the basis of a completely randomized design with three replications. The first factor was mass flow rate at three levels of 0.011, 0.0066 and 0.0048 kg/m²s and the second factor was the time of crop discharge at two levels of 15 and 30 min. The dryer capacity, the amount of energy consumed (electrical and solar) during drying process, and the efficiency of collectors were also evaluated. According to Duncan's multiples range test, the effects of mass flow rate of drying air, and the interval time of discharge, were highly significant on the moisture content of discharged rough rice. The maximum efficiency of the collectors was 37.13% and the fraction of energy consumed by heating channel during the drying process, compared with solar energy, was 6-8 percent. The maximum capacity of the dryer was about 132 kg of rough rice from 11 AM to 2 PM reducing the initial moisture content from 27% to 13%. On the whole, the evaluation results indicated that the dryer could reduce the moisture content of the crop to the storage safe moisture content during appropriate time with highenergy efficiency.

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The vertical pipe intake is an economical structure relative to the other alternatives. VPI usually installed near the water surface and prevents from the coarse sediment entrance to the system. The strong vortex in VPI entrance is a major problem which may reduce the system efficiency. Recognizing the vortex affected parameters, helping engineers to design anti vortex structures. In this study an experimental model is built to study the effect of tangential velocity, flow direction at approach channel outlet on the discharge coefficient of vertical pipe intake. By dimensional analysis it is indicated that the vortex in VPI could be defined by the dimensionless numbers (Reynolds, Weber, Froude, Circulation and Submergence). The relationship between the Froude, Circulation and Submergence numbers are presented. By using this relation one can determine the Submergence number and then calculate the discharge coefficient of vertical pipe intake.

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In this work, a cabinet solar dryer for thin layer drying of Cuminum cyminum was evaluated in two conditions (Indirect and Mixed). Four levels of drying air flow rates (three active and one passive) were adopted. The experiments were performed in a completely randomized Block design pattern in three replications. Drying durations were kept constant (90 min) for all the experiments. Average initial moisture content of Cuminum cyminum was 43.5 %( db) and the product was set to be dried for 90min in the solar dryer (average 8%d.b). The effects of the drying air flow rates and modes of drying were highly significant in final moisture content of Cuminum cyminum. Duncan test was selected to evaluate the effects of different factors on average moisture content of the samples. The results showed that the passive air flow system in mixed mode drying conditions for drying the Cuminum cyminum was best. The drying duration for the mentioned condition was 55min to dry the product from 43.5% to 8 %( db). The experiments were conducted each sunny day of August-September 2007 from 11.30 till 13.The average solar irradiance was recorded 750 W/m2 average ambient air temperature was32°C and average ambient relative humidity was20%. Using the dryer in the best selected conditions reduced the moisture content of the product from 43.5% to 4.95% after 90 min.

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Internal erosion is the second major reason for earth dam's failure after overtopping. One of the effective factors in internal erosion in earth dams is the clay minerals used in dams as well as the effects of compaction efforts on soil in sample preparation. In this research, internal erosion and the effect of clay minerals and compaction effort on internal erosion were investigated. For this purpose, Kaolin clay and Na Montmorillonite (Bentonite) separately and with different percentages of mixture were used to investigate the effect of different percentages of Bentonite on internal erosion. Two hammers of standard compaction and modified compaction test were also used to investigate different compaction efforts in internal erosion. The results showed that as compaction effort increased in constant water content, erodibility also increased to about 3%. In addition, it is found that erodibility of kaolin clay is more than bentonite, which reaches 65%. Finally, by adding 12% bentonite to kaolinite, erodibility decreased to a great extent.

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Excess pore water pressure in clay core dams during construction and primary filling reservoir (first impounding) causes initiation and progression of hydraulic fracture. In this research, the instrumentation data during construction and first filling reservoir (first impounding) was analyzed. It measured internal deformations, pore water pressures and total vertical stresses and compared with the analysis results in Masjed-e-Soleiman dam. To do this analysis, GEOSTUDIO 2004 V. 6.02 software was used. The staged construction of the dam was the model in the form of 2D coupled consolidation. The Non-linear elastic model for the core material and Linear Elastic model for other zones were incorporated into the models. For exact assessment and to obtain correct parameters of the constitutive model, the triaxial tests were performed on the core material of Masjed-e-Soleiman Dam and acceptable results were obtained.

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Hydraulic conductivity is an important parameter in the design of geotechnical structures such as earth dam, floor construction, retaining walls and environmental structures. In unsaturated soils, hydraulic conductivity is a function of moisture content and soil water suction i.e. soil moisture characteristic curve. In this study, the values of unsaturated hydraulic conductivity in two soil types (Ramjerdi and Molasadra core dam series) at 5 different compactions using Gardner method were measured. Then, the unsaturated hydraulic conductivity was estimated by different models using the soil moisture characteristic curve and was compared with measured values. The results showed that Fredlund and Xing models predict the soil moisture characteristic curves more accurately compared with van Genuchten model. For Ramjerdi soil series and up to nearly 0.25 volumetric water content, (VGM) and (FM) models indicated a good estimation for unsaturated soil conductivity. Also, for Molasadra core dam none of the models resulted in acceptable estimations for unsaturated hydraulic conductivity.

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One of the most essential and appropriate groundwater model components is accurate information of the recharge values among input data often introduced to the model as the percentage of rainfall of aquifers. The recharge values are influenced by many temporal and spatial factors. Firoozabad plain is one of the suitable plains for agriculture in the Fars province in which utilization of groundwater resources has been banned since 23 September 2002, due to the declining water level and negative balance. The main purpose of this study was to estimate the recharge values of groundwater aquifer by using SWAT in the MODFLOW model. Firstly, surface water was simulated via SWAT model, and sensitivity analysis, calibration, validation and uncertainty analysis of results were performed by SWAT-CUP software. After extraction of aquifer recharge values from the calibrated model, the groundwater of basin was simulated via MODFLOW model in both steady and unsteady conditions. Following the model calibration, the hydrodynamic coefficients of plain were determined and sensitivity of model was checked in terms of hydraulic conductivity and discharge rate of pumping wells. As for the confidence, the model was revalidated, which proved in simulating the behavior of the aquifer very well.

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Erosion is one of the main factors of destruction of hydraulic structures. Therefore, soil improvement is necessary to improve soil quality and reduce soil erosion. Due to the adverse effects of substances such as lime and ash and also the increasing usage of nanotechnology in various branches of engineering sciences, using nanoparticles as new additives is an efficient way. In this study, to investigate the effect of nanosilica additive on soil, erosion function apparatus (EFA) is used. Samples containing nanosilica with 0, 1, 1.5, 2 and 4 percent (w/w) of dry soil were compacted in the standard compaction mold. They were tested in a close flume and with variable discharges. Erodibility parameters showed that by addition of 1.5% nanosilica to the dry soil, erodibility decreased by 92% as compared with untreated soil. The optimal amount of nanosilica was chosen as 1.5%. The results showed that samples compacted with the optimum moisture content causes the least erodibility. Scanning Electron Microscope (SEM) tests results showed that by addition of nanosilica to the dry soil, soil structure becomes more dense which reduces the risk of erosion.
 

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