نشریه مهندسی مکانیک مدرس
سال بیست و دوم شماره 12 (آذر 1401)

This study has experimentally investigated the effect of Fe3O4 and secondary flow injection on convection heat transfer and friction coefficient on a horizontal pipe. Secondary flow injected to main flow to make more turbulence to five different models. Water and Fe3O4 have been considered in5865 to 18800 Reynolds range and three0.01%,0.03% and0.06% volume concentrations. Length and diameter of test tube considered 65 cm and 1.7 cm, respectively, the diameter of secondary flow injection holes considered 3 mm and 4.5 mm, the ratio of volumetric flow rate to total flow considered 10% and 20% and distance between secondary flow injection holes considered 4 and 2. The results show that the increase of diameter of secondary flow injections holes, the ratio of secondary flow volumetric flow rate to total flow and the decrease of distance between secondary flow injection holes are effective on coefficient of utilization increase. The highest coefficient of utilization achieved   =20%,  =2 in each model using water fluid in d=4.5 state. In this state, the mean of coefficient of utilization achieved 1.256, 1.266, 1.31, 1.45 and 1.52 for first, second, third, fourth and fifth models in all Reynolds, respectably. The above state has the highest thermal performance in the fourth and fifth models. The mean of coefficient of utilization in all Reynolds increased 0.91%, 3.97% and 4.98% for the above state in the fourth model using Fe3O4 with three0.01%,0.03% and0.06% volume concentrations to water fluid, respectively. Similarly, this increase achieved 1.58%, 4.56% and 5.66% in the fifth model, respectively.

The concept of Zero Energy Building [5] has been introduced globally to reduce energy consumption and carbon emissions in the building sector. Renewable energy systems such as Solar Thermal collectors, Photovoltaic collectors, and Heat Pumps are used to implement ZEBs. This study proposes a Building Integrated Photovoltaic Thermal-Air Source Heat Pump (BIPVT-ASHP) to realize ZEB in a small-scale building. To evaluate the performance of the system, a BIPVT-ASHP hybrid system model was designed, and also the building load model was defined based on the actual building conditions. Then, the heating and cooling performance of the BIPVT-ASHP system was dynamically simulated for one year using TRNSYS software. Then the system was numerically evaluated from energy, economic and environmental perspectives. According to the results of this study, for this system, the initial non-renewable energy consumption was 1.29 kWh/m2 per year, which was less than the heating energy threshold for the ZEB, and the proposed system met well the ZEB conditions. In addition, it was shown that for a given area, photovoltaic/thermal technology leads to a further reduction in non-renewable primary energy consumption but less solar thermal energy production compared to traditional separate production using photovoltaic [2] collectors.

Melt conductivity of metals makes it possible to apply force directly to the melt by electromagnetic forces. The movement of melt performs without using any mechanical parts, and it also reduces the risk of corrosion of metal parts in contact with molten metals. In this research, a discontinuous molten flow is generated from a designed nozzle, and after a cooling process, the droplets convert to metal powders or granules. In this pump, drop-on-demand formation is based on eddy currents and alternating electromagnetic forces inside the melt. The most important effective parameters in the induction coil are the current, voltage, and frequency. In order to control the operation of the pump, it is necessary to understand its effects and to find the optimal conditions. The results of studies show that the most effective parameter affecting the number of drops released per unit of time is the voltage of the coil and then the frequency and finally the pulse on time. In this project, by studying various effective parameters, a device was designed to generate molten droplets. The results showed at the voltage of 280 v, pulse-On time of 1.5 ms, and also by increasing frequency from 5 to 20 Hz, the number of droplets increased from 144 to 246 drops. The highest number of drop outputs occurred at the frequency of 20 Hz, Voltage of 280 v, and pulse-On time of 1.5 milliseconds.

In this Study, the necessary force of the isothermal forging process of disc piece of aluminum alloy AA7075 was analyzed and calculated by theoretical methods and finite elements method. In the simulation of the isothermal forging process in Deform software, were selected the temperature of 400 °C, the speed of top mold of 0.1 mm/s and the shear friction coefficient of 0.075 as process parameters. The necessary force of isothermal forging was obtained 80 tons in 6.18 mm Motion Course for disc piece by analyzing the simulation results of finite element method in DEFORM software. The axisymmetric slip line field method was used to estimate the forming force of the isothermal forging of the closed die before of the flash filling, which obtained 23.54 tons. The comparison forming force of isothermal forging of disc piece by theory method with the results obtained from finite element simulation showed that the forming force corresponds very well with the force-displacement diagram is compatible. The geometry of billet, the final top and bottom dies and assembly drawing of isothermal forging process of disc piece of aluminum 7075 dies were calculated by assuming a constant volume in plastic deformation.

Numerical methods as one of the subcategories of theoretical models can predict the behavior of energetic materials with appropriate accuracy and away of experimental tests limitations. In this investigation, computational fluid dynamics tool has been used to predict the blast wave propagation with Consideration of geometrical obstacles. Two solvers (extendedSonicFoam and blastFoam) from the open source technology module, OpenFOAM  have been used for simulations and To enhance confirmation with reality, large eddy simulation method was employed for turbulence modeling. In addition to the ideal gas equation of state (EOS), the BKW EOS, which is a complete EOS with an explicit temperature dependence, have been used to correlate the various thermodynamic parameters. Several gauges were positioned to record the pressure-time signals and the experimental data reported in the resources were used for validation. It should be noted that the maximum error of simulations was 12.29% for different blast wave parameters. deviation from standard for ideal gas numerical results was greater than that of real gas assumption and blastFoam solver has been predicted maximum positive phase overpressure, arrival time and positive phase impulse, which are the important parameters of blast wave, with less error in comparison to extendedSonicFoam solver.

Once a composite laminate is subjected to quasi-static tensile or fatigue loading, some damage modes initiate and propagate in the laminate. The first damage mode is the matrix crack that forms in the layers with an angle to the loading direction. Although not leading to breakage, these cracks reduce the equivalent mechanical properties of the composite laminate. In this paper, a new nonlinear analytical model is presented and used to predict the stiffness degradation of the cross-ply composite laminates. For this purpose, a new third-order polynomial function is proposed as the Helmholtz free energy of the composite, and the appropriate equations are derived. A microscopic experimental test is designed and accompanied by the analytical model to investigate the damage progression in a glass/epoxy cross-ply laminate. Also, finite-element micromechanical models with periodic boundary conditions (PBC) are proposed and used to determine the damage constants. The model is validated against the 3D micromechanical models and the quasi-static uniaxial loading-unloading experimental tests. The validation shows a very good agreement between the model and the experiments.