جستجوی مقالات مرتبط با کلیدواژه « Free convection » 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.

In this paper, a new method is introduced to solve the inverse problems based on the repression tree (RT). To investigate the method’s efficiency to handle the nonlinear inverse heat transfer problems, two case study problems are done in this paper; first one is estimation of the free convection heat transfer coefficient of a horizontal copper cylinder and the second is estimation of the heat transfer coefficient in the surface of a quenched copper cylinder in a fluid using the cylinder temperature history. The input data were produced by solving the direct heat transfer equations of the cylinder and Churchill-chu imperial correlation and to test the method’s sensitivity to the random errors in input data, an artificial noise with normal distribution was added to the temperature results of the direct solution. The regression tree’s results were also compared with the sequential function specification (SFS) and the artificial neural network (ANN) methods. For the first case study problem, the root-mean-square error (RMSE) of RT, SFS, and ANN methods are 0.0129, 0.1231 and 0.0217, respectively, and for the second problem 8.844, 54.09 and 71.634 are the RMSE values. The comparison shows that the presented method has a good potential to solve the nonlinear inverse heat transfer problems with low error and time lag to online estimate the unknown parameter.

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 study the free convection heat transfer of a nanofluid, including water and nanoparticles suspended in a square cavity is simulated numerically for a laminar flow. Open source framework i.e. OpenFOAM was used to develop the equations and make changes in the desired terms such as relative velocity between the nanoparticles and the base fluid. To achieve the purpose of the research and to ensure the accuracy of the numerical algorithms used in this framework, at first the free convection inside the cavity was investigated using two-phase mixture model and the results of the present study were compared with the results presented in the literature. Then, with the help of existing mathematical equations, important parameters in simulating the forces acting on nanoparticles in the free convection inside the cavity were studied and as a result, the forces that had a significant impact were selected as the most important and corrected relative velocity was entered in the continuity, momentum, heat transfer and continuity equation of the second phase (nanoparticles) as a parameter called JP. This simulation was performed using the PIMPLE algorithm (SIMPLE + PIZO). To consider free convection, nanofluid’s density changes with Boussinesq relationship. The mixture two-phase model has used for modeling with higher speed and more accuracy and also effective thermophysical properties of nanofluid, related to JP parameter have been used in order to increase the accuracy of work. As a result, the effect of these forces on different conditions was investigated.

In this paper, the effect of aerodynamic heating on temperature distribution inside supersonic bird cabin in different insulation conditions, the existence of gravity force and different flight height has been investigate using a computational fluid dynamics method with the finite volume approach. The coupling boundary condition in the shell wall use to simultaneously to solve the equations in solid and fluid. The air assumed as an ideal gas and the Boussinesq approximation used to changes density with temperature. In - cabin temperature distribution changes in terms of the free Convection heat transfer is simulated transiently up to a flying time of 70 seconds. The results are presented as temperature contour in the middle section of the model, temperature - time and temperature - location diagrams for different times. In this research, experimental and numerical method s are validated the temperature distribution inside and outside the model, which shows good accuracy.

In this investigation experimental measurements have been done over a wide range of wave parameters, water temperatures and air velocities for . The measurements were performed over a wide range of on a large heated wave flume equipped with a wind tunnel. The effects of forced, free and mixed convection regimes on the water evaporation rate in surface gravity Waves have been investigated. The experimental results shows that wave motion on the water surface increase the rate of evaporation for all air flow regimes. Also Results reveal the evaporation rate increases with air velocity but increasing of , , has different effects on evaporation rate. For free convection regime evaporation rate increases with, , . For forced and mixed convection regime at medium values of , the leeward air flow structures which form barrier for the vertical transport of vapor, decrease water evaporation rate. Results reveal that the effect of induced turbulence at the wavy interfacial surfaces on the water evaporation increment is more than the effect of interfacial area increment percentage.

This study has mainly focused on derivation of aerodynamic data for an airship in particular conditions especially at high angles of attack. When such data are inserted into a flight simulator as a closed loop, it is vital to make use of special computational means and methods, so that the ability to send and receive flight conditions would be achieved through an “in-the-loop” manner. Therefore, using an open source environment such as OpenFOAM is suggested in this regard. Through this study, the aerodynamic coefficients of the airship are calculated by three different CFD approaches and empirical data collected from wind-tunnel tests while geometrical parameters were set for angles of attack between -10 to 20 degrees. In order to achieve aerodynamic goals, air simulation is of great importance. So, the aerodynamic results are compared based on the three methods of calculating fluid "computing" in the loop, the wind tunnel test and the analytical method of the geometric parameters of the ship's aircraft. In this study, the stability of the aircraft, the longitudinal and lateral aspects of the aircraft is examined. Also, by examining the ratio of the coefficients of the lift to the drag, based on the angle of attack, the angle of attack that the aircraft has the best performance is determined.