Showing 4 results for talesh bahrami
Behnam Ahmadi, Hamid Reza talesh bahrami, Hamid Saffari,
Volume 16, Issue 5 (7-2016)
Abstract
Superhydrophobic surfaces received many applications in various industries such as desalinization, heat exchanger, anti-fog and self-cleaning surface production. In this study a wet etching process were used to produce superhydrophobic copper surfaces. The specimens were etched by multiple ferric chloride and deionized water solutions to create micro-nano structures on their surfaces. The electronic scanning electron microscopy (SEM) images of the resulted surfaces show a formation of micro-nano structures with specific templates. Contact and sliding angle measurement of surfaces after etching process show that contact angles of specimens improve to nearly 140o while sliding angle of all samples were 180o , which is the same as a rose petal property. In the next step, to promote hydrophobicity of surfaces, increase contact angle and decrease sliding angle, specimens were immersed in an ethanol and stearic acid solution with a specific concentration. As well as, effects of etching time and etchant concentration on the sliding and contact angles with/without stearic acid modification were investigated. Results show that contact angles increased and sliding angles decreased remarkably so that it reduced to lower than 10o in some cases and lotus effect were achieved.
Hamid Reza talesh bahrami, Saeed Zareie, Hamid Saffari,
Volume 17, Issue 3 (5-2017)
Abstract
In In this paper nanofluids condensation heat transfer on an inclined flat plate is investigated. To do this, thermal resistances of single droplets are calculated and the total heat flux is evaluated using population balanced theory. The nanofluids include alumina, titanium dioxide and silver as nanoparticles and water as a base fluid. Effects of different surface inclinations, nanofluids types, and nanoparticles concentrations are investigated on the heat transfer. Nanofluids properties consisting of thermal conductivity, density, dynamic viscosity, and latent heat are extracted from literature and introduced into the equations. The results are compared with some experimental data in the same conditions. The Nusselt theory is used to compare the heat transfer rate of filmwise condensation with dropwise condensation. Inspecting the results shows that the heat transfer coefficient of a vertical plate is maximum, and decreases with decreasing in inclination due to lower washing rate of small droplets by sliding droplets. The results also show that the heat transfer coefficients of various nanofluids are different but they are constant all over the surface. As well as, addition of nanoparticles to the base fluid increases heat transfer rate. It can be seen that water-silver nanofluid has the maximum heat transfer rate among three beforehand mentioned nanofluids in the same conditions and the heat transfer rate increases with increase in volume fraction of nanoparticle for a specific nanofluid.
Hadiseh Soltani, Sadjad Ghasemloo, Hamid Parhizkar, Hamidreza talesh bahrami,
Volume 18, Issue 2 (4-2018)
Abstract
Plume reversion due to missile ascending and related flow expansion and its interaction with missile body especially with missile base has been an important concern of investigators and missile designers. The aim of the current is investigation of effects of different parameters on the interaction of plume and missile body. To do this, heat flux on the missile body at different conditions including different flight conditions, turbulence modeling, base length and nozzle modeling has been studied. In the following, plume induced flow separation is studied. To model flow field, Gambit 2.4.6 and Ansys Fluent 17 are used for grid generation and flow simulation respectively. The results show that with increasing in flight height, plume at the base of missile gradually expands and finally covers the base completely. As well as, it can be seen that plume expands more rapidly in the base region and reduces heat flux when the nozzle is not considered. The reduction of heat flux is different in various parts of the base, ranging from zero to a maximum of 83% in areas far away from or near the nozzle. In the end, the effect of the base length was investigated. The results showed that as the base length is increased, the vortices are further expanded and this expansion leads to increased heat flux so that when the base length is doubled, the heat flux is increased by 20% at most
H.r. talesh bahrami, H. Parhizkar, S. Ghasemlooy,
Volume 19, Issue 5 (May 2019)
Abstract
one of the key issues in the design of high-speed modern devices such as giant aircraft and high-speed trains. In this regard, it is to design these devices in such a way to have at least aerodynamic noise. The cylinder, as a bluff body, is widely used in the design of various devices, such as a landing gear. Therefore, the reduction of cylinder noise can be widely used. In the present study, numerical solution is used to present a method for reducing the noise generated by flow on the cylinder. This is done by flow suction from the grooves the cylinder. Acoustic numerical calculations were performed, using LightHill's acoustic analog approach in the form of wave equations of Ffowcs-Williams & Hawkings model. The numerical solution is performed in the three-dimensional unsteady form, using the large eddy simulation turbulence model. The characteristics of the grooves, such as their dimensions and distance the generated acoustic noise have been studied. The results show that the active control method presented in this paper is an effective and yet simple way to control noise. The cylinder used in the present study produces a noise of about 110 dB at a speed of 250 km/h. According to the results, it can be said that by optimally arranging the number of slots and creating a proper flow suction, its sound level can be reduced to about 60 dB.
