rasool kalbasi

In this paper, the dynamic modeling of a D-type boiler was performed during a step increase in loading. The D-type boilers are used in industry to produce process saturated steam. In these types of boilers, heat absorption occurs in two sections of the furnace and the convection section. The pipes of the convection section are indirectly exposed to heat, causes the flow direction to change from the upper drum to lower drum and vice versa. One of the special features of this boiler is that the drum circulation loop is natural and as a result, the hydraulic balance equations of the system must be considered. In the present modeling, the equations of water-side were considered in one-dimensional and the equations of flue gas-side were considered in three-dimensional space using the zonal method. The transient continuity and energy equations of the water-side form a system of nonlinear ordinary differential equations which were solved using the Runge–Kutta method. To solve the water and gas-side equations in two-way coupling method, a Fortran computer program has been developed. Investigation of the boiler operating parameters during start-up can help to improve the existing control system. The comparison of the present results with the test data of the desired boiler showed that maximum modelling errors are equal to 4.8, 1, and 6.8 percent for steam pressure, drum water temperature, and outlet steam of boiler during start-up, respectively. Also, the boiler response to a step increase in consumer steam demand is less than 20 seconds.
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A severe case of stenosis in coronary arteries results in turbulence in the blood flow which may lead to the formation or progression of atherosclerosis. This study investigated the turbulent blood flow in a coronary artery with rigid walls, as well as 80% single and double stenoses on blood flow. A finite element-based software package, ADINA 8.8, was employed to model the blood flow. The hemodynamic parameters of blood, such as the Oscillatory Shear Index (OSI) and the Mean Wall Shear Stress (Mean WSS) were obtained by both k-ε and k-ω turbulence models and then compared. According to the results, the negative pressure predicted by the k-ω turbulence model was several times greater than that by the k-ε turbulence model for both single and double stenoses. This, in turn, leads to the collapse of artery walls and irreparable injuries to the downstream extremity. Furthermore, the k-ω model predicted a larger reverse flow region in the post-stenotic region. In other words, the k-ω turbulence model predicts a larger part of the post-stenotic region to be prone to disease and the k-ε turbulence model predicted a higher rate of plaque growth. Moreover, the k-ω model predicted a much more intense reverse flow region than the k-ε model, which itself can lead to blood pressure disease.

Solar energy is used for domestic, industrial, and power plant consumption. From a nation-wide perspective, it has attracted increasing attention due to creating opportunities, reducing fossil fuels consumption, and also meeting the requirements for reduction of environmental pollutants. Given its geographical location which has endowed Iran with a desirable level of solar energy as a renewable source of energy, it is the first paper aimed to conduct a potentiometric study of constructing a 20 kW power plant in 31 capital cities in Iran, considering all the existing losses. PVsyst 6.7 and Meteonorm 7.1 software packages are used for analysis. Results showed that the required area for monocrystalline solar panels was less than that for polycrystalline ones and for polycrystalline less than thin-film panels. Furthermore, solar cells with higher manufacturing technology incurred lower costs, so that monocrystalline cells produced the cheapest solar-powered electricity, while the electricity generated by thin-film panels was the most expensive. In addition, it was found that ventilation had less impact on monocrystalline solar cells than polycrystalline, and less on polycrystalline panels than thin-film ones. The highest (39˚) and lowest (27˚) annual optimum tilt angle were related to Bojnoord and Bandar Abbas, respectively. Also, the results revealed that the highest (0.833) and lowest (0.771) annual performance ratios were obtained for Ardabil and Ahvaz, respectively. The highest (35276) and lowest (24031) amount of annual energy injected to the grid (kWh) were associated with Zahedan and Sari, respectively. Average annual energy injected to the grid (kWh) for the studied stations was 30942. For a more detailed evaluation of the effect that each type of losses had on the energy produced, annual loss diagrams, which are the most important outputs of PVsyst software, were evaluated for Zahedan and Sari stations.

In this paper, a hybrid solid oxide fuel cell (SOFC) and micro gas turbine (MGT) power system is parametrically studied to evaluate the effect of different operating conditions. The SOFC/MGT power system includes SOFC reactor, combustion chamber, compressor and turbine units, and two heat exchangers. The effects of fuel utilization, temperature, and pressure are assessed on performance of the hybrid SOFC/MGT power system using energy and exergy analyses. This study reveals that the main exergy loss occurs in the external reformer and the maximum achievable output power is about 7kW for the hybrid system. Finally, the promising first law thermal efficiency of up to 83% is achieved when the second law efficiency enhances to 65% for the hybrid system.