IRANIAN JOURNAL OF MECHANICAL ENGINEERING (ENGLISH)
Year:2019 | Volume:20 | Issue:4 |Papers Count:10

In this paper, the analytical investigation of two thermal and mass transfer effects for nonhomogeneous catalytic reaction mixture into a micro-channel has been achieved considering the continuous regime properties. In this problem, the Knudsen number is considered smaller than 0. 1 where the flow is in the continuous or slip regime. The governing equations are consisting of energy, mole fraction and catalytic conversion where the wall effects have been achieved from thermal and mass jump boundary conditions. The solution results at three different values of Knudsen number are compared with experimental data, and at all points, when the Knudsen number is equal to 0. 01 the best validity by experimental data be available. The results of slip-jump solution, with maximum error of 2. 54%, has a better validated experimental values than based modeling data without slip and jump condition, with maximum error of 26. 6%. The greatest increase in fuel conversion occurs at low-level Reynolds number, with a value about 80. 04%. Increasing thermal jump effect coefficient, normalized temperature reduces while with increase in mass jump effect coefficient, fuel conversion decreases and surface mole fraction increases.

In this paper, an approach to the prediction of two-phase flows based on two-fluid models and conservative shock capturing method is presented. The advantage of this approach is that the interface is allowed to develop naturally as part of the transient calculation. Another novelty is the comparison of well-posedness criteria of three two-fluid models. The well-posedness criteria for single pressure model is greater than free pressure model, and the numerical diffusion for single pressure model is little than two pressure model. It has been chosen 0. 0000001, 0. 000001, 0. 00001, 0. 0001 and 0. 001 for pressure relaxation term in two pressure model 1. It has shown that by increasing pressure relaxation, the result of the two pressure model 1 and two pressure model 2 tending two each other, and this is an Confirmation of equality of pressures in two-fluid model 2.

Recent developments in automotive industry tend reseachers to design engines of lower volumes and higher efficiencies. Volume reduction enhances the generated heat per volume which in turn requires effective cooling methods to avoid thermal stresses on the engine walls. Nowadays nanofluids are extensively welcomed and employed as effective working fluids with efficient cooling potentials. In the present study effects of adding nanoparticles to the pure water as the cooling working fluid in the radiator is assessed. The employed nanoparticle is TiO2. A 3D model of engine with the cooling passages is simulated by CFD both for the pure fluid (water) and nanofluid. It will be shown employing 1%)vol( TiO2 nanofluid improves cooling heat transfer up to 37% in comparison with the pure water.

Nanofluids are suspensions of nanoparticles in fluids that show significant enhancement of their properties at modest nanoparticle concentrations. Nano fluid is a smart fluid. The flow and heat transfer of a mixture of two different types of Nanofluids (water-alumina and water-copper oxide) in a localized ventilated compartment will be investigated by a finite volume method for three different situations. The results will be presented in the form of flow lines, constant temperature, and Nusselt numbers. Inlet fluid is at cold temperatures and walls with outlet ports in extreme conditions. The particle size is 33 nm and the tests are carried out at ambient temperature. The studied parameters include input fluid intensity (500≥ Re≥ 100), Riley number effects (105≥ Ra≥ 103), Nanofluid concentration (0. 05≥ Φ ≥ 0). The numerical results show that, for example, in the first position, in Reynolds 100 and Riley 103 in pure water state, the mean Nusselt was as much as 7. 7 and reached 8. 61in the concentration of 0. 33. Which will increaseby 17. 78% to Nusselt. In general, increasing the volume fraction of nanoparticles will increase the flow of Nusselt and heat transfer. The type of nanofluid is also effective in the amount of heat transfer.

Today، application of advanced materials has made opportunities to reduce energy consumption of buildings and improve life’ s quality. Smart glasses are among new materials designed to prevent energy loss through windows which could be categorized as Electrochromic glasses, liquid crystals, Gasochromics, Thermochromics and SPDs. In this article introducing various types of smart glasses, their characteristics and thermal performance had been compared. In order to evaluate the impact of smart glasses on energy consumption of building, a small office in Bushehr, Iran has been studied using Designbuilder simulation software. According to the results, SPD glass has the best performance reducing cooling load of building. Gasochromic, Electrochromic and Thermochromics glasses would also reduce the cooling load respectively. While the amount of solar heat gain varies in different months of the year, the average annual solar heat gain is the lowest using SPD glasses. Application of SPD glass would result in 48. 3% reduction in buildings cooling load compare to ordinary glass. The amount of reduction for Gasochromic, Electrochromic and Thermochromics glasses would be 45. 8%, 34. 1% and 17. 23% respectively. So application of smart glasses in hot and humid climate of Bushehr can reduce solar heat gain and thus cooling load of buildings.

Increasing the volumetric efficiency of internal combustion engines has always been one of the goals of the engine designers. Utilizing turbocharged systems is one of the common ways to achieve this aim. In these systems, compact heat exchangers are used to reduce the temperature and increase the density of the air at the outlet of compressor. This article seeks out the best geometric layout for an aftercooler to have the lowest pressure drop and the highest temperature decrease of the passing air through the heat exchanger and at the same time leads to the lowest manufacturing cost. To obtain this purpose, a bar and plate heat exchanger is considered and after deriving all the geometric, flow and thermal equations, a comprehensive objective function is defined. Then, using the genetic algorithm method and considering six design variables, the best design values for variables are found to maximize the objective function. All calculations are done analytically and using coding in MATLAB software. The results show that the designed aftercooler beside an appropriate weight and a very low pressure drop, reduce the engine inlet air temperature significantly and brings it to an acceptable level to enter the engine.

The purpose of this study was to investigate the effect of surface changes to reduce the drag coefficient in a triangular array heat exchanger. Experiments were carried out in an opencircuit wind tunnel. The range of distance to diameter is between 2 to 4 and the Reynolds number is between 5. 2×104 to 6. 9×104. The diameter and length of the tubes are 41. 5 mm and 42 cm, respectively. Tubes are made of copper. On each tube, 10 holes were created from zero to 180 degrees. The outer diameter of each hole is 3 millimeters. Shark skin is used as a surface accelerator. In these experiments, the effect of increasing the space ratio is studied. The results show that the coefficient of drag force decreases 14. 5 to 25. 4 percent for tube with shark skin. The greatest reduction in the drag coefficient is in Reynolds number 69920 and in the ratio of distance to diameter 2.

In this paper, a combination of a gas turbine unit with thermal and membrane desalination are evaluated technically and economically. A V94. 2 Siemens gas turbine model with capacity of 150MV is selected for power generation. This system benefits by thermal and membrane desalination that work simultaneously. So that, preheated water of condenser in thermal unit is used as feed water into the membrane unit. By this combination, the desalted water is divided between thermal and membrane units. After modeling process, economic analysis has been performed and the cost of selling water in each of unit is calculated. As a benefit of converting gas unit into Water and power co-generation system in this analysis, the cost of water by thermal and membrane unit are calculated in 0. 7, 1. 45 dollars Per cubic meter respectively. Finally by two-objective optimization and by considering of a gas power plant efficiency and also the capacity of desalination, an optimized condition of this combination is proposed.

Interest in plasma actuator as an active flow control has grown rapidly in the last years. Plasma actuator consists of a pair of electrodes that are separated by a dielectric material. Applying voltage to the electrodes, results in a body force that act on the flow field and is used in order to control it. Plasma actuator by imparting momentum is able to tangentially accelerate the flow field that can be used for flow control purpose such as boundary layer transition control, drag reduction, lift enhancement, and flow separation control. This work involves the documentation and control of leading-edge separation control that occurs on an axial compressor cascade at high angle of attack. To study the effect of control technique, a 2-D numerical investigation were performed in presence of varying plasma actuator voltage and location in different flow characteristics such as stream line, pressure and lift-to-drag ratio. The results show that plasma actuator reduce energy losses and a lift-to-drag ratio enhanced of up to 18% can be obtain by using plasma actuator at 15% of the blade chord length. The control effect obtain by the plasma actuator in low Reynolds number is more effective and increasing the applied voltage improves the performance of the compressor cascade by increasing the induced body force.

In the present study, to extend the Stokes' second problem, the bottom edge of viscous incompressible semi-space resting fluid is excited in two dimension, simultaneously. This two-dimensional excitation which is the effect of velocity of two-dimensional travelling wave, is boundary condition for the two-dimensional linear Navier-Stokes equations. The time-space exact solution for fluid velocity and pressure show that the amplitude of oscillating velocity has fast damping in space till 1. 87 micron from excited surface. After this height, the amplitude of oscillating quantities has a slowly damping. In the first region (in fast damping region), phase difference between pressure and velocity is changing, but after that there is a region with constant phase difference. The space variation in velocity components of surface wave, together with the coupling of velocity components in main equations, produces pressure wave. It has been found that kinematic effect of vertical and horizontal harmonic motion cause damped rotational motion in fluid.