JOURNAL OF MECHANICAL ENGINEERING AMIRKABIR (AMIRKABIR)
Year:2010 | Volume:41 | Issue:2|Papers Count:10

Combustion zone temperature in porous burners (PBs) is lower than free flame burners, which leads to a reduction in NOx emission. Furthermore, because of enough resident time for complete combustion, amount of CO emission will be reduced. In this research, pollutant emissions are investigated for a 5 kW porous burner integrated with a heat exchanger. Navier-Stockes, energy and the chemical species transport equations in a porous media with local thermal equilibrium assumption between the solid and gas are solved. 2D temperature field and species concentrations are presented in the premixed methane -air combustion. The effect of excess air on CO and NO emission are investigated. Results are acceptable with comparison of experimental data, also the results of this simulation are better than some simulations in quantitative and qualitative sense.

According to high dependence of spectral behavior of gases to temperature, pressure, wave length and concentration, it is needed that such properties be explained by simpler mathematical models. Moreover, appropriate numerical methods should be used to solve the radiative transfer equation for radiation intensity in the media, heat flux divergence and temperature field. Solution of the radiative transfer equation has been made by several researchers for gray gas in one-dimensional case. In this article, the radiative transfer equation is solved for two-dimensional case (long rectangular section) considering the spectral behavior of media (CO2, H2O gases) through combining the box model and zone method. Because of the nongray behavior of the industrial gases, solving this equation can improve the gray gases assumptions in the model.

In this paper, the effect of the liner material model on the result of numerical simulation of Explosively Formed Projectile (EFP) is examined. Johnson-Cook, Steinberg, and Zerilli-Armstrong models are used for the simulation. All models are shown that have a good agreement with the experimental results. Zerilli-Armstrong model predicts final EFP shape with more accuracy in comparison with the other models. The results of simulations indicate that Johnson-Cook and Steinberg models predict the projectile length better than Zerilli-Armstrong model. The velocity of projectile predicted by all models agrees well with the experimental measurement.

This paper is concerned with the inverse heat transfer between two parallel plates filled with a porous medium under a non-equilibrium condition. Sequential Function Specification Method (SFSM) and Conjugate Gradient Method (CGM) with Adjoint equations are employed to estimate the transient wall heat flux at the porous boundary. Combination of the non-thermal equilibrium model and inverse heat transfer methods is the novelty of this paper. Results showed that sensor locations and existing noise in the measured data have important effects on the calculated heat flux.

In this paper development of turbulent flow around a triangular obstacle, its vortex generation and resulting effect on neighboring turbulent boundary layer of a flat plat, are studied. Vortex shedding controlled in size and position by changing side length and relevant angles of the triangle. The distance from the plate changed gradually from a point stuck to the plate to points far inside the free stream. As a result in each step, a stagnation point forms on frontal area, a jet at the beneath of the obstacle and one, two or three vortices after the rear face. Each of flow developments contributes to local heat transfer coefficient of neighboring flat plate. Most effective part seems to be the last vortex at downstream to the obstacle. Its local contribution to total enhancement is about 80% when total heat transfer compared to that of a single flat plate of a similar flow field. The overall heat transfer enhancement over the affected area is about 60%.

In this research, applications of the Boundary Element Method to viscous flow are investigated. The BEM formulation allows a boundary-only solution for linear stokes flow. For higher speed flows in which the non-linear convective effects cannot be ignored, a volume integral must be retained. The proposed formulation is based on analogy between Navier's equations in elastostatics and Navier-Stokes equations expressed by using a penalty function. By using penalty function formulation, pressure term is eliminated and Navier-Stokes equations are converted to Navier equations in elastostatics. In many previous works, potential fundamental solution was used for solving viscous fluid flow with BEM but in this research elastostatics fundamental solution is used. Finally, some two-dimensional examples are provided to validate the presented approach. It is found that the boundary element method gives accurate solutions and it is more economical than other methods since the application of the method requires discretization only on the boundaries of the domain and thus it reduces the spatial dimensions of the problem by one.

This paper shows the effect of shear stress of liquid-vapor interface with and without mass transfer on thermal performance of a thermosyphon by the integral method. In this analysis, governing equation solved for laminar flow to find velocity profile, thickness of liquid film as well as heat transfer coefficient. In this study, a thermosyphon with 30.5cm length and 2.42cm inner diameter is analyzed. Methanol is used as a working fluid at saturated temperature of 63oC. Results show that the shear stress of liquid-vapor interface decreases the rate of heat transfer.

Manufacturing of blades in air turbine motors according to complicated shape and critical working conditions needs a high technology. The root of blade under applied forces should have high surface quality and dimensional accuracy in comparison with the other blade components. In this study, the surface quality due to different types of available wire-cut machines for machining of compressor blade root has been investigated. To this end some samples has been machined by different wire-cut machines. Afterwards the different components of surface integrity (such as surface roughness, surface topography, hardness, thickness of affected surface layers, microcrackes and pits, residual stresses) has been studied. Finally, the machining of the root of compressor blade with this process has been discussed and concluded.

In some applications a single variable, either a process variable or product variable, characterizes the state of the process. In the other applications, multiple variables characterize the state of the process. However, in some practical situations, the quality of a process or product is characterized by a relationship between two or more variables instead of by the distribution of a single quality characteristic. This relationship, which can be linear, nonlinear or even a complicated model, is referred to as profile by researchers. Up to now, several methods have been proposed for monitoring simple linear profiles in both Phases I and II. In this paper, for improving phase II monitoring of linear profiles, a method has been proposed which applies Cumulative Sum control charts. Average run length criterion and simulation studies are used in order to evaluate the performance of the proposed method. The results show the suitable performance of the proposed method. Finally, the effect of reference value on the performance of the proposed method is evaluated.

The Multiple Facility Location Problem (MFLP) is to locate certain facilities so as to serve a given set of customers, whose locations and requirements are known. When the locations have to be selected from a given set of candidate locations, the problem becomes a Discrete Multiple Facility Location Problem (DMFLP). In this study, a special case of DMFLP is discussed where multiple facilities that are of different type are to be placed (location decision) and assign customers to these facilities (allocation or assignment). Both cases with and without interactions among new facilities are considered in this problem. In this paper, efficient lower and upper bounds are used to propose a branch-and-bound scheme as an exact method. Also, new heuristic method is provided for both cases and compared for large-job sizes. Computational results on randomly generated data in comparison with optimal solutions indicate that the heuristic method is accurate and efficient.