جستجوی مقالات مرتبط با کلیدواژه « forced convection heat transfer » در نشریات گروه « مکانیک »

A strong magnetic field provides a new method of heat transfer with high heat flux. A numerical simulation for a heat sink with high heat flux under an external uniform magnetic field in three different directions is used to investigate the flow field and displacement heat transfer between liquid metal and hot surfaces. Due to its high density and large thermal and electrical conductivity coefficients, gallinsten liquid metal has been used as a working fluid. Discretization of the Navier-Stokes equations is performed by the upstream second-order finite volume method. The results show that the effect of applying a magnetic field in the Y and Z directions (perpendicular to the flow axis) on the heat sink with a Hartmann number of 88, improves the displacement heat transfer coefficient by 15% and 8%, respectively. The best efficiency in increasing the heat transfer was obtained by applying the magnetic field in the Y direction. By applying the magnetic field in the Y direction to the heat sink, the displacement heat transfer coefficient was increased by 11.9% for Hartman number of 44, 15% for Hartman number of 88, and 17.7% for Hartman number of 132, compared to zero Hartman number. By applying the magnetic field in Z direction to the heat sink, the displacement heat transfer coefficient was increased by 4.3% for Hartmann number of 44, 8% for Hartmann number of 88, 11.4% for Hartmann number of 132 and 22.1% for Hartmann number of 330, compared to Hartmann number of zero. Also, the results show that the effect of applying a magnetic field perpendicular to the flow axis has increased the velocity gradient. As a result, the pressure drop and friction coefficient of the heat sink have increased.

Increasing the heat transfer rate in various industries in order to improve the efficiency of equipment, prevent damage to parts and reduce costs is one of the essential discussions in the industry. One of the solutions to increase heat transfer is the use of active heat sink. In this research, an active heat sink with Galinsten liquid metal fluid was used and the discretization of Navier-stokes equations was done using the second order upstream finite volume method. The effect of applying the magnetic field in the Y direction (perpendicular to the flow axis) to the heat sink has caused the creation of a force against the flow direction called the Lorentz force, which has caused the M-shaped velocity distribution. According to the constant flux boundary condition, increasing the flow velocity in the vicinity of the walls has caused the surface temperature to decrease and the heat transfer to improve. The results showed that the effect of applying a uniform external magnetic field in both Y and X directions with a Hartmann number of 517 improved the Nusselt number by 38% and 13%, respectively, compared to a Hartmann number of zero. The effect of applying a magnetic field in the Y direction to the heat well with a Hartmann number of 517, 38%, Hartmann number of 258, 22% and Hartmann number of 129, 13% has improved the heat transfer.

Forced convection heat transfer of a cam-tube and a cylinder in external laminar flow and at Reynolds number in the interval 7×〖10〗^4to 1.2×〖10〗^5areexperimentally implemented.Nusselt number distribution and its varying in terms of Reynolds number for prototypes (Cam-tube and cylinder) are treated. The principle result indicates applying the Cam-tube instead of cylinder make it possible increase the heat transfer between 5 to 22 percent. The uncertainty of the gathered data was at minimum 12 percent and at maximum 22 percent. Furthermore,the results show that theHilpert’sequationisauthentic for the treated cam-tube.

Plasma actuator is one of the newest ways in vortex generation and flow control techniques which can enhance heat transfer rate by inducing external momentum to the boundary layer of the flow. In this paper, a 2-D numerical approach was implemented to analyze the presence of plasma actuator on the incompressible, turbulent, steady flow in a flat channel. In this approach, the flow field and heat transfer characteristics such as the stream function and heat transfer coefficient were evaluated through the variety of Reynolds number, at the presence and absence of applied voltages. The present computed results are firstly compared with the numerical data in case of rectangular flat channel and the results agree very well. The numerical results indicate that at a constant Reynolds number with the presence of a plasma actuator, the heat transfer coefficient will be increased but in a constant applied voltage the heat transfer coefficient will increase to the Reynolds of 250 and then will be decreased respectively. In addition, the size of generated vortexes significantly depends on the applied voltage and the upstream flow speed. On the other hand, according to the results, the flow speed affects the size of generated vortex and vanish the actuator effect at high Reynolds. According to the results, there is an optimized point for the applied voltage and flow speed.

In this paper, the flow and temperature fields affected by electrohydrodynamic actuator are numerically investigated for the incompressible, turbulent, and steady flow over a backward-facing step. Air is used as working fluid in heated backward-facing step cooling process. The electric field is generated by the wire electrode charged with DC high voltage. The numerical modeling is based for solving electric, flow, and energy equations with finite volume approach. The computed results are firstly compared with the experimental data in case of rectangular flat channel and the results agree very well. Then the effect of different parameters such as the radius of the wire, applied voltage, Reynolds number, and the wire position on the heat transfer coefficient is evaluated. The results show that the heat transfer coefficient with the presence of electric field increases with the applied voltage but decreases when the Reynolds number and the radius of the wire are augmented. Moreover, reduction of emitting electrode angle can significantly effect on the heat transfer enhancement. In consequence, one may able to find an optimum place for the emitting electrode position.

In this study forced convection heat transfer in a pebble bed cylindrical channel with internal heat generation was investigated experimentally. Dry air has been used as working fluid in heated spheres cooling process. Internal heating was generated uniformly, by electromagnetic induction heating method in a metallic spheres which have been used in test section. Spheres are made of stainless steel and their diameter is in the range of 5.5-7.5 mm. Present study was performed at steady state and turbulence flow regime, with Re number in the range of 4500-9500. Different parameters resulted by variation of spheres diameter, flow velocity and generated heat on forced convection heat transfer was studied. According to thermal and hydrodynamics studies, it can be said as Re number increases, heat transfer coefficient will increase. Also heat transfer coefficient has been increased by spheres diameter decrement. The generated heat has a little influence on heat transfer coefficient. The effect of pressure variations on forced convection heat transfer can be neglected. Porous channel has greater friction factor in comparison with an empty channel. The friction factor in empty channel is always less than 1 but for porous channel this parameter is in the range of 10-25.