---

Alfalfa crops were surveyed for the incidence of alfalfa mosaic virus (AMV), cucumber mosaic virus (CMV), peanut stunt virus (PSV), bean leaf roll virus (BLRV), bean yellow mosaic virus (BYMV) and bean common mosaic virus (BCMV) in the major growing areas in the southeast and central regions of Iran. Samples were collected between May 2009 and March 2011 and analyzed for viral infection initially by enzyme-linked immunosorbent assay (ELISA) followed by RT-PCR using capsid protein gene specific primers. In total, 634 symptomatic leaf samples were collected in four southeastern and central provinces of Iran representing 20 regions. Our results revealed a high incidence of AMV over a wide geographical area. AMV and BLRV were identified in most regions, whereas BYMV was found only in Yazd Province. PSV was detected in three regions, but not in Sistan- Balouchestan and Hormozgan Provinces. The highest incidence of viral infection amongst the surveyed provinces was recorded in Kerman (66.8%), followed by Yazd (39%), Sistan and Balouchestan (20.8 %), and Hormozgan (4.5%). AMV, BLRV, PSV and BYMV were present in 23.3%, 12%, 0.70% and 0.28% of the samples, respectively. CMV and BCMV were not detected in any surveyed region. Multiple virus infections were recorded in 42 samples. This is the first report on the detected occurrence of BLRV, PSV and BYMV in alfalfa in the southeast and central regions of Iran.

---

One of the main difficulties in employing fully coupled algorithms for solving Navier-Stokes equations is the high computation cost of coefficient matrix determination and solving the linear equation system. Therefore, the number of required iterations and computational costs may be reduced by increasing the convergence rate. This article deals with the formulation and testing of an improved fully coupled algorithm based on physical influence scheme (PIS) for the solution of incompressible fluid flow on cell-centred grid. The discretisation of improved algorithm is investigated and fully clarified, by comparing the methodology with two similar schemes. For a better insight, two benchmark problems are solved. The first problem is a steady lid-driven cavity with different Reynolds numbers between 100 and 10000. The second problem is steady flow over a backward facing step for the specified Reynolds number of 800. The history of residuals for present and previous methods are compared, in order to demonstrate the performance of the new discretization scheme. It is worth mentioning, the presented method is based on nine cells discretization. Therefore, the computational costs and memory usage of the proposed method are almost the same as previous ones. The results indicate that, the improved method converges in fewer iterations in comparison with prior methods. The new scheme can be utilized for development of the computational fluid dynamics solvers based on cell-centred grid arrangement.

---

In the present work, numerical simulation of steady, compressible and supersonic airflow in a magneto-hydrodynamic (MHD) generator has been studied. This flow considered to be ideal with low magnetic Reynolds number. A two-dimensional channel with four-pair electrodes and with various geometries and boundary conditions were utilized as a MHD Faraday generator model. The computational model consists of the Navier-Stokes equations coupled with electromagnetic source terms, Maxwell's equations and Ohm's law. Implicit based on density solver is used to solve the Navier-Stokes and the electric potential method is used to solve the Poisson's equation. First, the boundary conditions of constant temperature and constant heat flux were compared. Due to the less Joule heating and generation of higher electrical power, constant heat flux boundary condition was selected to continue working.

---

Ice slurry is called a mixture of fine ice particles with a fluid carrier such as water. The phase change ability of this mixture attracts the strong attention in the areas of thermal storage and refrigerant cooling of the secondary cycle. In this research, flow of ice slurry in horizontal tubes during the phase change is numerically investigated using FLUENT software. The two-phase nature of ice slurry mixture is studied using the Euler-Euler two-phase model based on kinetic theory of granular flows. The effect of ice particles phase change on heat and mass transfer between phases are investigated, the obtained results show that the local heat transfer coefficient for the use of the icy slurry mixture is increased 12% compare to the pure water. It is also determined by examining heat and mass transfer rate along tube, that the heat transfer coefficient for the pipe lengths larger than 10-15 times pipe diameter, remains constant. The variation of mean mass transfer is maximum at distance of 10-15 times of pipe diameter. The maximum value is 2-5 times larger than mean mass transfer in the pipe outlet. At the 20% end of the pipe, the decreasing trend of mass transfer accelerates.

---

In this research, the Asphaltene particles deposition is modeled using species transport equations. It is assumed that the deposition phenomenon consists of two steps: transport of Asphaltene particles toward the wall and attachment of them to the wall. Due to the small size of Asphaltene particles, their motion is simulated using species transport equation. Transport of Asphaltene particles is modeled by turbulent and Brownian diffusion and attachment mechanism is modeled employing first order chemical reaction. Effects of surface temperature and velocity is considered in the model. Finally the effects of velocity, surface temperature and Asphaltene concentration is investigated and compared with experimental data. The simulation results are agreed well with experimental data and the maximum error of is about 20 percentage. Also in addition of deposition rate, transport and attachment rate are investigated. The results indicate that Asphaltene attachment is more important than transport of Asphaltene, so accurate modelling of attachment has significant effect on prediction of Asphaltene deposition rate.

---

In recent years, pneumatic method of stigma separation has been considered by some researchers. In this regard, computer simulation of the process is necessary as well as determination of the engineering properties of the various flower parts. According to preliminary observations, the number of flower components, their characteristics, and the simulation of the separation process, all depend on the flower cutting location. In this study, cutting of flower was done in two modes. In the first mode, the flower was cut from the top of the receptacle and divided into three parts including petals (2), stamens (3) and a three-branch stigma. In the second mode, the cutting accomplished from the bottom of the receptacle and the flower divided into two parts including flower without stigma, and a three-branch stigma. Variations in weight, density and terminal velocity of different flower components were studied as a function of moisture content. According to the results of this study and in contrast to most of the published papers, vertical wind tunnels are not suitable for pneumatic separation of saffron stigma. In order to provide required information for computer simulation, the flower components were considered as spherical particles, and then their aerodynamic diameters were calculated using the proposed flowchart. The results showed that the difference in aerodynamic diameter values in the two-section cutting mode reach to significant amount of 70%. Results of present study also indicate that the appropriate stigma separator mechanism should have singular feeding system and ability to provide turbulent air flow. Preliminary results obtained from computer simulations are hopeful in the case of using dual internal tunnels equipped with rotational flow.

---

---

---

The main disadvantage of natural draft dry cooling towers is the influence of atmospheric conditions as ambient temperature and wind speed on the thermal performance. Wind disrupts the natural flow of air inside the tower creating vortices at the back and inside the tower that disrupts the air flow structure. When the wind blows, increasing the velocity of inlet air through the front louvers causes the air to pass through the behind louvers rather than outlet opening. The negative effect of this phenomenon reduces the cooling performance and consequently reduces the turbine production power in power plants. A good solution to this problem is to adjust the Louvers angle correctly. Therefore, in the present study, the thermal performance of the dry cooling tower was evaluated under the conditions of opening and closing the front louvers and changing their angle. In this regard, a natural draft dry cooling tower unit with the dimensions of the cooling tower located in combined cycle power plant was simulated in 3D using fluent software and the numerical results with the experimental data have been validated. The Realizable k-ε turbulent model is used to model the turbulent flow and the performance of the tower has been studied in three modes, including no wind, with the wind and the fully open louvers and with the wind and the semi-open louvers. According to the results, by partially removing the louvers to 60°, the heat transfer can be increased to 16% and the mass flow rate to 15%.