جستجوی مقالات مرتبط با کلیدواژه « Lorentz force » در نشریات گروه « مکانیک »

Nowadays different kind of active and passive methods used in order to reduce energy consumption and air pollution in buildings. Simultaneous use of phase-change material (PCM) and green roofs with triple-skin facades (TSF) and triple glazed windows (TGW) in residential buildings equipped with Building-integrated photovoltaics (BIPV) can lead to 70% annual energy saving. On the other hand, PCM type and applying methods in different climate conditions impacts energy saving in these conditions. So for the first time, in this research Multi objective optimization of a residential buildings equipped with above technologies was done by the help of genetic algorithm. Reduction of required heating and cooling loads was chosen as optimization’s objectives and three climate conditions of Iran was selected. Results indicate that maximum energy saving is 73.3%. Maximum Cooling load reduction is 92.2% which is happened in biome-dry tropical climate conditions. In addition, Maximum reduce in Co2 emission is 60.6% for Tehran.

This article investigates the effect of magnetic and electric force fields with positive or negative voltages on wave propagation and phase velocity of nanosystems, including structure-fluid interaction. To this end, nanofluid conveying cylindrical carbon nanoshells with axial movement embedded on electromagnetic visco-Pasternak media are considered. Herein, it is assumed that the elastic visco-Pasternak medium includes springs in the form of airy coils. Thus, applying an electric field to the system cause to make a magnetic field and a magnetic-electric-elastic (MEE) nanosystem is obtained. The magnetic field will affect both the structure and the flowing fluid respectively by applying the Lorentz force and using the Knudsen and Hartmann numbers and then the phonon scattering occurs. The governing equations under hydrodynamic, electric, magnetic, and shear forces are derived based on the cylindrical-sinusoidal-nonlocal high-order shear deformation (CSN-HSDT) proposed theory using the energy method and generalized Navier-Stokes equations. The results obtained in this research can be used in the design and manufacturing the health measuring instruments, energy harvesting, and drug transporting vessels on a nano-scale.

Transporting molten metals is one of challenges in industries. Dangers for human, oxidation, torbulance and reduction of equipment life are problems of the transportation. Electromagnetic pumps have solved problems of using molten containers and also mechanical pumps. In this paper, by examining the effect of main parameters in the design of a direct current electromagnetic pump with a rectangular cross section (magnetic field size, electric current applied to the fluid, channel height and width) by the surface response method, the pump output including flow velocity and The Lorentz force is optimized. The results show that the amount of electric current applied to the fluid has the greatest effect on the response surfaces. It is also found that changing the channel width had little effect on responses. However, reducing the channel height has a positive effect on the response levels. By creating a magnetic field of 0.3 Tesla and a current of 12 amps on a channel with dimensions of 30 X 10 mm, the fluid with a velocity of 0.27 m⁄s is displaced by a volumetric force of 5000N⁄m^3. The method used in this paper optimized the output parameter of the pump. Experimental tests verify the results of simulations, including the maximum pumping height, pump flow and fluid velocity in the pump.

This study investigated the effect of an omnidirectional magnetic field on the heat transfer performance of a saline water-Al2O3 magnetic nanofluid (MNF) cavity. The cavity was a quarter-circle with a cold left wall and a heated right wall, whereas other surfaces were insulated (adiabatic). All surfaces were assumed constant. The governing equations were solved numerically based on control volume and SIMPLE algorithm. The nanoparticle concentration ranged from 0 to 0.04 percent, the Hartmann number (Ha) was between 0 and 9, and the Rayleigh number (Ra) was 105. Findings indicated that increased nanoparticle concentration and magnetic field intensity enhance the reductive effect of the Lorentz force. Increasing the magnetic field intensity has an insignificant effect on the thermal performance of the fluid with zero nanoparticle concentration. As the nanoparticle concentration increases, the electrical conductivity of the fluid increases too which leads to a significant increase in the reductive effect of the magnetic field so that a 2% increase in nanoparticle concentration at Ha = 4.5 reduces heat transfer by more than 45%, whereas this reduction is higher than 65% at a nanoparticle concentration of 4% and Ha = 9.

In this paper, magnetogasdynamics with outlet Knudsen of 0.2 is studied in a pressure-driven microchannel. By using a developed code, the effects of changing magnetic field parameters including power and length with implementation of slip velocity at the walls has been simulated numerically. The geometry is a two dimensional planar channel having a constant width through all. The flow is assumed to be laminar and steady in time. In order to analyze the variation of velocity, pressure, Lorentz force and induction magnetic field, the governing equations for flow and magnetic fields have been solved simultaneously using the lattice Boltzmann. No assumption of being constant for parameters like Knudsen and volumetric forces are made. Another feature of this research is to improve the quantity of results which is a major problem in this method and many studies have been done in this area. This study represents the results tending to that of analytical relations by using a second order accuracy for calculation of slip velocity and correction of pressure deviation curve in compare with the past studies if a proper relaxation time is determined. The simulation results show a change in Fx profile to M if the length of external magnetic field length reduces to 40% of the whole. Removing applied magnetic field from both ends of the channel will increase pressure gradient at the intermediate part and displaces the section at which the maximum pressure deviation occurs. Slip velocity and centerline velocity behave different for the reduced magnetic field length.

The MHD equations solution for small plasma Beta using characteristics-splitting schemes which have low numerical dissipation is frequently diverged. Simultaneous increasing of magnetic energy (due to high discharge current) and kinetic energy (due to strong gas-dynamic expansion) leads to decreasing of internal energy and finally the pressure value is negative near the electrodes tip. In this research، to obtain a stable solution، the HLLE approximate Riemann solver has been used. This method can produce necessary numerical dissipation to prevent entropy violation. To achieve a high order accurate solution، new modification of MUSCL technique has been employed. This method is called OMUSCL2 technique which has lower dispersion and dissipation errors. For simulation of non-equilibrium ionization mechanism، a 7-species chemistry model has been implemented. Numerical results of a lab-scale thruster are presented، whereby comparison with other experimental and numerical data shows good agreement between the predicted and measured enclosed current and thrust.

In this paper the effect of electromagnetic field lengths to change simultaneously is simulated on the temperature distribution and flow velocity of a MHD micropump considering the lateral electromagnetic diffusive regions. The geometry of flow is a two-dimensional channel between two parallel plates and the flow is assumed to be incompressible، steady and laminar. In addition، thermophysical properties such as the dynamic viscosity and electric conductivity of fluid are considered to be the function of temperature. The governing equations of both flow and electromagnetic fields have been solved using the finite volume numerical method a comprehensive analytical solution including velocity، pressure and temperature filed distributions has been derived for an special case. The numerical results show that by changing the length of electromagnetic fields and considering the fluid (water) properties as a function of temperature، for flow in a 1000 mm2 cross-section channel، magnetic field intensity 0. 025 Tesla and electric field strength 20 volt/mm، the flow rate reaches 250 mLit/s and the mean cup temperature from 25 0C at entrance reaches to 40 0C at the exit of channel. However for constant properties، the flow rate and the mean cup temperature reach 70 mLit/s and more than 60 0C respectively.

Using Lorentz forces under effects of electro-magnetic fields for flow control is a suitable procedure. Lorentz forces may be added as a source term in the governing fluid flow equations. For this phenomenon, the numerical modeling of subsonic flow with the Mach number of 0.2 for turbulent flow regime using a finite-volume TVD scheme with implicit time marching for solving the two-dimensional compressible Navier Stokes flows and the Baldwin-Lomax turbulence model around aerofoils are investigated to control undesirable effects of flow separation. By using Lorentz forces, it was shown that the separation was delayed or avoided over NACA0015 aerofoil and hydrodynamic performance was enhanced. Employing flow control using the Lorentz force, the lift coefficient was increased and the drag coefficient was not changed, considerably. Hence, the stall angle was increased.

Internal-force-driven flows in which the force acting on channel cross sections have a perfect uniform distribution create a fully-developed velocity field. Even if the driving force is inserted on a part of channel, the velocity profiles are parabolic. In this situation, firstly the driving force with non-uniform axial distribution can be removed temporarily and then one can use an equivalent pressure gradient alternatively throughout the channel. In this case, although the distribution of pressure gradient and the driving force change but the resulting velocity profiles remain unchanged. The main advantage of this replacement is that the solution of the equations in the 3-D geometries can be converted to a 2-D solution using Poisson equation in the channel cross section. After determining the velocity distribution in the cross section, one can inversely calculate the actual pressure distribution easily. This will be done by resuming the real axial force. One of the applications of this simplification is that the simulation of MHD channel flows can be carried out easily. Good agreement between the results of the new solution method and the results of the perfect solutions shows that the present method with enough accuracy can be used for prediction of velocity and pressure fields in microfluidic networks and can be reduced the heavy costs of 3-D analysis.

In this study، a two-dimensional، axisymmetric، computational Algorithm has been developed to simulate the plasma flowfield in a MPD thruster for the purpose of determining the flow behavior and electromagnetic characteristics distribution. The solution employs Roe’s flux vector difference method in combination with Powell’s characteristics-splitting scheme. To ensure the stable high-accuracy solution، new modification of MUSCL technique so called OMUSCL2 method is used. According to being supersonic strong gasdynamic expansion near the electrodes tip، HHT entropy correction is employed. Further improvements to the physical model، such as the inclusion of relevant classical transport properties، a real equation of state، multi-level equilibrium ionization models، anomalous transport، and multi-temperature effects، that are essential for the realistic simulation MPD flows، are implemented. Numerical results of a lab-scale thruster are presented، whereby comparison with experimental data shows good agreement between the predicted and measured enclosed current and electric potential.

Internal-force-driven flows in which the force acting on channel cross sections have a perfect uniform distribution create a fully developed velocity field even the axial distribution of these forces is non-uniform. In this situation، firstly the driving force with non-uniform axial distribution can be removed temporarily and then one can use an equivalent axial uniform body forcealternatively throughout the channel. In this case، although the distribution and the driving force change but the resulting velocity profiles remain unchanged. The main advantage of thisreplacement is thatthe solution of the equations in the 3-D geometries canbe converted to a 2-D solution using Poisson equationin the channel cross section. After determining the velocity distribution in the cross section، one caninverselycalculate the actual pressure distribution easily. This will be done by resuming the real axial force. One of the applications of this simplification is that the simulation of MHD channel flows can be carried out easily. Good agreement between the results of the new solution method and the results ofthe perfect solutions shows that the present method with enough accuracy can be used for prediction of velocity and pressure fields in microfluidic networks. Consequently the heavy costs of 3-D analysis are reduced considerably.