مجله مهندسی مکانیک امیرکبیر
سال چهل و هشتم شماره 3 (پاییز 1395)

In this paper, the problem of optimal distillation columns sequence determination for a multicomponent distillation system with heat integration between condensers and reboilers of various columns with using mathematical programming approach considered. Existence of nonlinear constraints also discrete and continuous variables in optimization model is reason that the problem will be a Mixed-Integer-Non-Linear-Program (MINLP). MINLP model that obtained from mathematical programming is solved with GAMS. Some of proposed method features are generality and flexibility for defining new operating conditions. In proposed MINLP model, the effect of heat integration on optimal sequence has been considered by simultaneous optimization of sequencing and energy demand. Energy saving using heat integration has become possible by regarding column pressure as a variable in optimization model. The Results obtained from solution of MINLP model for a four components separation, shows 25% saving in total annual cost that includes investment, operation costs and energy consumption. . .

One of the most significant emissions of gas turbine is NOx. In present work a gas turbine combustor is simulated with the aim of reducing NOx. In most research and industrial cases, steam is injected into the combustor separate or premixed with air for reducing NOx emissions. In CLN technique, steam is injected into the combustor premixed with fuel. CFD simulation is done for an axisymmetric non premixed combustor and the ability of different combustion models on NOx and temperature prediction is investigated. Results show EDC model which can implement different mechanisms predicts NOx production more accurate than other models. Also the influence of injection of premixed steam-fuel into the combustor is investigated and is compared to the injection of premixed steam-air and no steam injection cases. Steam injection into the combustor is done by increasing mass flow rate via increasing the nozzle diameter in constant inlet velocity. Results show that the injection of premixed steam-fuel causes 5.8 percent and 4.7 percent further decrease in NOx and CO production in comparison with other case.

The present paper reports numerical results of mixed-convection heat transfer with nanofluid in a horizontal ventilated cavity heated from below and provided with an thin partition on the heated surface. Free flow at cold temperature enters the cavity and takes heat from a heat source. Discretization of the governing equations are achieved through a finite volume method and solved with the SIMPLE method. The effects of the governing parameters, such as the Richardson number, , the baffle position from the inlet, , solid volume fraction, ,and the nanoparticle type on the fluid flow and heat transfer characteristics are studied in detail. The results show that increases in Richardson number results in reduction of the average Nusselt number and increase in solid concentration leads to increases in the average Nusselt number. Also, the results predict an optimal value for baffle position.

At the present research, Film Cooling around a gas turbine blade has been studied numerically via Partially Navier-Stokes Simulation (PANS) approach which is one the most success approaches of Very Large Eddy Simulation (VLES) in turbulence flow. For detail investigation of flow around gas turbine blade (airfoil with film cooled holes on leading edge) has been simulated in three dimensions and inlet temperature and blade surface temperature has been considered: 409.5° C and 297.7° C respectively. Inlet Reynolds number is 8.42 X 105. Inlet flow is fully turbulent and turbulence intensity has been set on 0.052 meanwhile secondary flow effect in up and bottom of blade has been waived. Numerical calculation has been done by Fluent and partially averaged Navier- Stokes equations (PANS) have been applied to fluent by UDF’s. The obtained results from Partially Navier-Stokes Simulation (PANS) method have been compared with existed experimental data and other RANS two-equations models in other researches and it demonstrate that Partially Navier-Stokes Simulation (PANS) approach results has admissible correspondence with experimental data in addition these results are accurate than RANS two- equations models.

In the present study , we have investigated the external free convection of a nanofluid near a vertical heated surface embedded in a saturated porous medium using the thermal non - equilibrium assumption. The vertical surface has a linear temperature distribution with a uniform mass suction or injection. Assuming the Brownian motion and thermophoresis as the primary driving mechanisms of free convection of the nanofluid , suitable volume averaged equations are employed. We have also followed similarity solution method for transforming the governing equations in to the ordinary differential equations. The new set of ordinary equations is solved numerically by the Shooting method and the flow and temperature fields are determined completely. The obtained numerical results are employed for calculating the Nusselt numbers for both the solid and liquid phases in the physical domain. Moreover , the Sherwood number for the nanoparticles is determined over a wide range of parameters.

In the present study, falling a single droplet and two adjacent droplets under gravity force, in the vertical channel with side walls and for different situations of wall effects are simulated, using the inter molecular potential model of lattice Boltzmann method. Dynamic behavior of falling droplet is simulated. The simulation results are shown in the falling droplet with initial lateral position on the centerline (vertical axis of symmetry) of channel, the droplet has been moved down straight along the centerline with no lateral motion. For the falling movement of the droplet near wall, due to various effects on droplet, it has been diverted from its initial vertical axis. If Eotvos number is not very low (Eo>5)... .

Tail is one of the main components of aircraft to provide stability, control and trim. As yet, different type of Tails are designed and produced by manufacturers that each one has specific advantages. Since each tail has its own desired aerodynamic properties; it must stabilize, trim and control the aircraft. In this research, the effect of H type tail on aerodynamic coefficient of an aircraft is investigated experimentally using wind tunnel. Tests are done in incompressible wind tunnel of Aerospace Central Research made by ISI Company at Reynolds numbers 5300000, 720000, and 800000. The size of model is one fifth of a small aircraft which an external fuel tank is mounted under each wing. This model has control surfaces such as: ruder and elevator with variable angles. Results show the variation of aerodynamic coefficients and stability domain with attack angle of the aircraft model without external fuel store and zero angle of attack and with external fuel tank.

In this work, stability of V shaped flame in a premixed swirl burner is studied. The effect of firing rate (input energy per unit area), equivalence ratio and axial velocity of fuel and air mixture on the stability of a V shaped flame is studied. For swirl generation, a 45o angle swirler is used in the air inlet, which yields a flow with a swirl number of 0.78. Observations show that V shaped flame is formed in a lean mixture of fuel and air (1> fi) . When firing rate increases, it is observed that flow velocity at V flame formation instant is independent of flow rate and increases linearly from 1 m/s to 5 m/s. flame lift off occurs in larger equivalence ratio and mixture velocity when firing rate increases. With increasing mixture velocity, flame quenching occurs in smaller equivalence ratios and larger firing rates. Hence, stability limit of V flame increases with increasing cross section.

A novel approach for microfluidic droplet generation via “solvent shifting” is presented in this paper based on an experimental investigation. In a 3D co-flow configuration with a jet of ethanol/oil mixture surrounded by water flow, the lateral diffusion leads to supersaturation followed by a phase separation and consequently formation of oil nanodroplets. Due to the solutal Marangoni effect the nanodroplets migrate inward and they get collected at the channel centerline. For high concentrations of the oil the density of the nanodroplets is so high that they can merge and produce microdroplets. If the mixture contains 10% oil, the average diameter of the produced microdroplets is within the range 10-30 µm for various jet flow rates. The size of microdroplets increases with the flow rate of the jet. Overall, for the first time we show that it is practical to generate microdroplets of different sizes by solvent shifting approach in a microfluidic setup.