Search

This paper presents a revised model for the titled "Unsteady Mixed Nano- Bioconvection Flow in a Horizontal Channel with Its Upper Plate Expanding or Contracting" [18]. In this paper, the authors used a two phase model for the nanofluid presented in International Journal of Thermal Sciences 77 (2014), Mar., pp. 126-129 [15] in which the nanofluid particle volume at the wall is passively rather than actively controlled. Here, we observed that the boundary conditions are not satisfied in all curves of the nanoparticle volume fraction, i. e. the curves do not match the boundary conditions presented in eq. (19). The second note is that all values of are positive which contradicts with the results presented in [15]. Since the equations are coupled then it can be said that not only the behaviors of are wrong but also all the results presented in that paper is not correct. The main reason for conducting this investigation is performing a revision for the mentioned paper and presenting a set of curves to show the corrected behaviors for dependent variables. [ABSTRACT FROM AUTHOR]

The paper presents a numerical simulation of two-phase turbulent flow in straight horizontal channels of pneumatic transport with non-circular cross-section. For the granular flow simulation, we have chosen the flow of solid particles of quartz, flour, and ash in the flow of air, which is transporting fluid. During the modeling of the flow, the transported solid particles are reduced to spherical shapes. A correction of the stress model of turbulence is performed by taking into account the influences of the induction of secondary flows of the second order in the gas phase. The full Reynolds stress model was used for modeling the turbulence, and the complete model is used for the turbulent stresses and turbulent temperature fluxes. All numerical experiments were conducted for the same initial flow conditions and a single uniform grid was adopted for all numerical experiments. The flow is observed in a straight channel of a square cross-section and dimensions of sides of 200 mm and the length of 80 Dh. During the simulation, the fineness of the numerical grid was also tested, and the paper shows results of the numerical grid of the highest resolution beyond which the fineness does not influence the obtained results. The paper offers graphics of velocities of the solid particles transported by the transporting fluid (air) along the channel. [ABSTRACT FROM AUTHOR]

In this study heat transfer and fluid flow analysis in a wavy channel is numerically studied, while a magnetic field is applied in transverse direction to the main flow stream. Recently in a numerical study, we have observed that usage of wavy channel instead of straight one enhances heat exchange between the core flow and hot walls. On the other hand, the usage of magnetic field transverse to hot walls can enhance heat transfer in a straight channel. In this paper, we would like to examine if presence of these two methods simultaneously is useful for enhancement of heat exchange. For this purpose, the governing equations are numerically solved in the domain by the control volume approach based on the SIMPLE technique. Numerical studies are performed over a range of Reynolds number, Hartmann number, and the wave amplitude. From this study, it is concluded that heat transfer in channels can be enhanced by the usage of magnetic field or usage of wavy channel instead of a straight one. But simultaneous usage of magnetic field and wavy channel is not recommended. [ABSTRACT FROM AUTHOR]

In this study, thermo-physical and geometrical parameters affecting entropy generation of nanofluid turbulent flow such as the volume fraction, Reynolds number, and diameter of the channel and microchannel with circular cross-section under constant flux are examined analytically. Water is used as a base fluid of nanofluid with nanoparticles of Ag, Cu, CuO, and TiO2. The study is conducted for Reynolds numbers of 20000, 40000, and 100000, volume fractions of 0, 0.01, 0.02, 0.03, and 0.04, channel diameters of 2, 4, 6, and 8 cm and microchannel diameters of 20, 40, 60, and 80 micrometers. Based on the results, the most of the generated entropy in channel is due to heat transfer, and also, with increasing the diameter of the channel, Bejan number increases. The contribution of entropy generation due to heat transfer in the microchannel is very poor and the major contribution of entropy generation is due to friction. The maximum amount of entropy generation in channel belongs to nanofluids with Ag, Cu, CuO, and TiO2 nanoparticles, respectively, while in the microchannel this behavior is reversed, and the minimum entropy generation happens in nanofluids with Ag, Cu, CuO, and TiO2 nanoparticles, respectively. In channel and microchannel, for all nanofluids except for the water-TiO2, with increasing volume fraction of nanoparticles, the entropy generation decreases. In channel and microchannel, the total entropy generation increases as Reynolds number augments. [ABSTRACT FROM AUTHOR]

An analytical method to calculate the temperature distribution of heavy particles in the channel of the plasma torch on the known distribution of the electronic temperature has been proposed. The results can be useful for a number of model calculations in determining the most effective conditions of gas blowing through the plasma torch with the purpose of heating the heavy component. This approach allows us to understand full details about the heating of cold gas, inpouring the plasma, and to estimate correctly the distribution of the gas temperature inside the channel. [ABSTRACT FROM AUTHOR]

This article presents a computational analysis of the turbulent flow of air in a pipe of rectangular section provided with two waved fins sequentially arranged in the top and the bottom of the channel wall. The governing equations, based on the k-e model with low Reynolds number used to describe the turbulence phenomena, are solved by the finite volume method. The velocity and pressure terms of momentum equations are solved by the SIMPLEC algorithm. The profiles of axial velocity, the velocity fields and the drag coefficient were obtained and presented for all the geometry considered and for selected sections, namely, upstream, downstream, and between two waved baffles. This contribution lead to results which were analyzed by the use of the solid, plane baffles, waved and inclined with active degrees of 0° up to 45° with a step equal to 15° and directed towards the left. Over the range of the study, the undulation of the baffles induced with an improvement on the skin friction of about 9.91% in the case of a = 15°, more than 16% in the other cases, and concerning the pressure loss, the undulation of the baffles was insured improvements starter from 10,43% in all cases compared with the baffles of plane form. [ABSTRACT FROM AUTHOR]

We numerically studied flow-induced vibrations of two tandem cylinders in transverse direction between two parallel walls. The effect of the horizontal separation between two cylinders, ranging from 1.1 to 10, on the motions of the cylinders and the flow structures were investigated and a variety of periodic and non-periodic vibration regimes were observed. The results show that when two cylinders are placed in close proximity to each other, compared with the case of an isolated cylinder, the gap flow plays an important role. As the separation ratio is increased, the fluid-structure interaction decouples and the cylinders behave as two isolated cylinders. [ABSTRACT FROM AUTHOR]