IRANIAN JOURNAL OF MECHANICAL ENGINEERING (ENGLISH)
Year:2016 | Volume:18 | Issue:2|Papers Count:5

In this study, the effect of resonator length and working fluid on operation of heat-driven thermo acoustic refrigerator is investigated. The working fluid is considered to be Helium, Nitrogen and Argon. The simulation is carried out via a numerical method and the results are compared with DELTA-EC software. The results of these two methods are in good agreement with each other. The simulations show that increase in the resonator length results to increase in pressure amplitude for all mentioned working fluids and the frequency reduces by applying the Helium, Nitrogen and Argon respectively. Increasing the resonator length from 0.5m through 1.4m leads to reduction of the coefficient of performance for Nitrogen and Argon while this coefficient increases for Helium. The best coefficient of performance is gained for Helium gas and resonator length equal to 1.4 m.

In this study, using design of experiments, the effect of the total weight percentage of graphene nanosheets and nano clay and their weight ratio and weight percentage of compatibilizer (PPg-MA) on the tensile properties of polypropylene/ graphene/ nano clay/ PP-g-MA nanocomposites were investigated. Design of experiments and analysis of experimental data with Minitab 16 software and response surface methodology were carried out. Making nanocomposites, based on the melt mixing was performed. All combinations and pure states materials were mixed together in a co-rotating twin-screw extruder and then injection molded into standard tensile test samples. The tensile properties of all samples including tensile strength, Young's modulus and elongation at break was studied experimentally. Statistical models provided by response surface methodology had good agreement with experimental findings. Statistical analysis showed that with increasing the percentage of nanoparticles, tensile strength and elongation at break of nanocomposites reduced. Also increasing the percentage of nanoparticles increase the stiffness of nanocomposites without compatibilizer, however, with the increasing amount of compatibilizer, reduced modulus. Compounds morphology by Scanning Electron Microscopy (SEM) was performed. Micrographes showed better dispersion of the particles in lower percentages.

The phenomena of formation and detachment of droplets are one of fundamental issues in studying two-phase flows and have been seen in lots of natural phenomenon and processes, such as spraying processes, ink jet printing, emulsion, etc. Between different numerical methods, the lattice Boltzmann method (LBM) has been developed in to an alternative and promising numerical scheme for simulating multi-component fluid flows. In this project, formation and detachment of droplets were simulated, using LBM and particularly index function model. Results were validated using two-phase flows methods. After code validation, the formation and detachment of droplets in a cross-junction micro channel and under the electric field effects were studied. To survey different effects on this phenomenon, dimensionless numbers were studied. Finally, the effect of variation of permittivity, conductivity and capillary number for droplets were studied under different situations. Results show that the electric force have a positive effect in expedition of droplet formation, and also index function model proved its very use fulabilities. We have smaller drops with high frequency which shows that we can control the droplet formation.

This paper, paid to calculate and develop an equation to determine the amount of the natural gas leakage, from a small hole located on the surface of the buried gas pipe lines. The studied case designed and meshed by Gambit software and then numerical solution is done by using Fluent software. The pipe is located in the town border distribution pipelines, flow is turbulent and soil considered as a porous zone. The results indicate that at the small hole diameters, discharge speed reaches the sound speed and at the so-called, choking occurs in the flow. Also after permeation of natural gas into the soil, and hitting the soil particles and the air moving through soil, a pair of vortex is created inside the soil. Volumetric flow rate of leaked gas has a second order and linear relation with hole diameter and pressure of initial point. Finally, its paid to develop an equation to calculate the amount of leaked gas.

The standard Lattice Boltzmann Method, LBM, is usually able to predict the results of micro scale flows which are corresponding to the slip flow regime, while it has not sufficient accuracy for nano scale flows which are corresponding to the transition flow regime. In this paper, by improving the lattice Boltzmann method, pressure driven flow through non-porous nano channels and nano channels filled with porous media has been modeled for wide range of Knudsen numbers, Kn, covering the slip and transition regimes. The results show that the presented lattice Boltzmann model is able to predict the flow features in micro and nano scales for wide range of Knudsen numbers by modifying the relaxation time. In the presented research, the effects of the Knudsen number and porosity on the flow rate, Darcy number and pressure drop are reported. Also, for the first time, the Knudsen’s minimum effect for micro/nano channels filled with porous media is observed and evaluated. For the pressure driven flows in non-porous channels this effect occurs at Kn=1, while the results show that for the nano channels filled with porous media this effect occurs at Kn=0.1 because of the tortuosity effects.