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Showing 2 results for Gharehkhani
Abdolreza Gharehkhani, Ebrahim Abbaspour-Sani,
Volume 17, Issue 10 (1-2018)
Abstract
With development of micro-electromechanical phase shifter, the study of deformation and instability of micro-switches is very important. The static behavior and pull-in instability of the clamped-clamped micro-beam subjected to local electrostatic loads which is used in DMTL phase shifter is investigated. Taking into account of nonlinear effects caused by radius of curvature for the first time, the nonlinear differential equation of the system is obtained using Euler-Bernoulli beam theory and effects of small sizes by employing the principle of virtual work. By considering the local electrostatic static voltage applied on the micro-beam, the governing partial differential equation is further discretized with the aid of Galerkin’s method, and the effect of system parameters on static deflection and pull-in voltage of the micro-switches are investigated. It is found that curvature nonlinearity has a great effect on the mechanical behavior of the micro-switches. Increasing this parameter leads to hardening behavior in the micro-switches, and also static deflection is decreased with respect to linear beam theory. The results also indicate that with an increase in the applied voltage, nonlinear strains increase and nonlinear effects caused by radius of curvature will be significant. For instance, when the stiffness parameter is increased from 0 to 10, maximum deflections of the micro-switches for applied voltages of 1V, 2V and 3V decreases about 7.7%, 35.8% and 48.6 %, respectively.
S. Omiddezyani , I. Khazaee, S. Gharehkhani , M. Ashjaee, F. Shemirani, V. Zandian,
Volume 19, Issue 8 (August 2019)
Abstract
Today, nanofluid is attracting intense research due to its potential to augment the heat transfer rate and the cooling rate in many systems. On the other hand, new research progresses indicate that graphene nanofluids even in very low concentrations could provide higher convective heat transfer coefficient in comparison to the conventional nanofluids. For this reason, we used nanofluid containing the CoFe2O4/GO nanoparticles as working fluid to perform experimental investigation of its effect on laminar forced convective heat transfer in the flow passing through a copper tube, which is under a uniform heat flux. It should be noted that utilizing magnetic field on nanoparticles is one of the active methods for improving the heat transfer rate. To achieve this objective, the effect of external magnetic field intensity and also the effect of applying different frequencies on the improvement of heat transfer in Reynolds number and different concentration is also investigated and the optimum frequency were obtained. The results showed that the heat transfer of the studied hybrid nanofluid has been improved in the presence of constant and alternating magnetic fields and the amount of heat transfer increment, due to an alternating magnetic field, is more significant compared with a constant magnetic field. The results also show that in the absence of magnetic field, using ferrofluid with concentration of φ=0.6%, improves the average enhancement in convective heat transfer up to 15.2% relative to the DI-water at Re=571, while this value is increased up to 19.7% and 31% by using constant and alternating magnetic field, respectively.
