FLUID MECHANICS AND AERODYNAMICS JOURNAL
Year:2018 | Volume:7 | Issue:1 |Papers Count:6

Modeling of turbulent convective heat transfer of nanofluids in circular tubes with constant temperature and constant heat flux boundary condition have been performed using artificial neural network. 610 sets of data have been gathered using previous investigations and have been used to train neural network (ANN). The investigated nanoparticles are: TiO2, Graphene, SiC, CuO, SiO2, Fe3O4, and Cu. The base fluid for all these nanofluids is water. The neural network used has 6 inputs, which includes: nanoparticle density, nanoparticle size, nanoparticle volume fraction, flow Re number, type of boundary condition (constant heat flux or constant temperature) and the amount of heat flux or temperature related to these boundary conditions. Also, the output of neural network is Nusselt number. Comparing our results with previous investigation, showed that the proposed ANN topology are in good agreement. In this study, the proposed topology of R2=0. 9998 have been choosen between 400 examined ones.

In this research, a lattice Boltzmann model is proposed to simulate free convection flow through pressure filtration. High compressibility effect needs to be considered near the critical point. A Poiseuille flow has been used as the first example to examine the effects of boundary condition model used in this study. It has been shown that the encountered error is of second order, which is considered to be desirable. The effect of the present boundary condition on the stability of solution to a Rayleigh-Benard problem has also been demonstrated. Finally, the filtered pressure equations have been implemented to model flow of a supercritical fluid in a cavity. The results are in good agreements with available data in the literature.

To establish a variety of cavitating flow regimes, the combined body with wedge nose and rectangular afterbody is usually used. In this research work, the nose angle and the afterbody dimensions of model were 60° and 22cmx10cmx1cm, respectively. Its fabricated material is nearly smooth steel with roughness of 0. 01mm. Also, another model with 30° nose angle and the same dimensions of the afterbody is tested. Two mentioned bodies were installed at the test section of a high speed cavitation tunnel. If the speed and pressure of the flow in the tunnel are varied, first cavitation inception occurs, such as a white band at the interface. Then, a little decrease the cavitation number causes the sheet cavitation along the surfaces of the afterbody. However, they are not established simultaneously at the upper and lower planes of the afterbody. By increasing the length of the sheet cavitation, regular oscillation occurs. Observed cloud cavitation is due to the separation of sheet regime which occurs by the re-entrant jet. If cavitation number is decreased slowly, then the vapor sheet covers the upper and lower planes of the afterbody. At the same cavitation numbers, cloud cavitation regimes on the two mentioned planes are not equal. At an especial length of the sheet cavity, the rate of length increase will be intensified.

In this paper, the characteristics of three-dimensional incompressible flows were obtained along with artificial compressibility of Chorin. At first, compatibility equations and pseudo characteristics for three-dimensional flows were derived. Results showed that pseudo sound speed in incompressible flow is a function of compressibility parameter and the direction. The speed of sound is constant in compressible flows. By numerical solution of characteristics, four-dimensional pseudo hyper Mach cone was obtained. A code in MATLAB has been written to obtain numerical solution. In two-dimensional flows, one has three-dimensional Mach cone, instead of four dimensional one. This cross section is circle for compressible flows. In this work, natural and forced convections, were simulated in different dimensionless numbers: Reynolds, Prandtl, and Nusselt numbers. For these simulations, a new code has been written in FORTRAN. In the last part of this research, the influence of compressible parameter on accuracy and convergence was surveyed.

In this paper, the effects of added nanoparticles to oil with the aim of improving heat transfer were investigated. At first, thermophysical characteristics of helicopter oil (MIL-L-23699) were measured by cooperation of chemical laboratory of Iran Helicopter Support and Renewal Company (PANHA). Then, by collecting other data, geometry of the problem was produced and gridded through the use of Gambit software and was transmitted to Ansys Fluent 17. 2 for simulating the flow and heat transfer. The single-phase model and control volume technique have been used to solve this problem. The results reveal that by adding nanoparticles to helicopter oil, thermal properties, such as Nusselt number, considerably improve in comparison with pure oil. However, the improvement of heat transfer process for gold-oil nanofluid is more than the other nanofluids. Comparing the results also shows that adding nanoparticles to the base oil causes a slight pressure change, which has no special effect on nanofluid pumping. The results indicate that by increasing Reynolds number, Nusselt number and static pressure increase and friction coefficient decreases. It is also observed that in a constant Reynolds number, by increasing working temperature, Nusselt number, friction coefficient, and static pressure decrease and temperature increases. Therefore, adding nanoparticles to helicopter oil would lead to the improvement of heat transfer properties, better cooling of the size of engine, shrinking the engine lubrication system, the ability of tolerating high loads, the ability of flying at higher altitudes, and eventually the enhancement of power and efficiency of the engine.

In this study, we numerically and theoretically investigated the effect of magnetic field on shape of red cells. The two phase model was used for the dynamics of red cells. We considered red cells as deformable drops flowing through a flat microfluidic channel. We employed boundary element method (BEM) to numerically solve the two-dimensional Darcy equation by applying magnetic normal stress as a boundary condition at the interface of red cells and blood plasma. Our numerical and theoretical results indicate that red cells elongate in direction of magnetic fields. The final stable shape is a result of the balance between the surface energy and the magnetic energy of the drop. Our numerical and theoretical results are in good agreements with the experimental results.