---

In this study, a numerical method is used to investigate the effects convergence primary nozzle on the air ejector performance used in Polymer Electrolyte Membrane Fuel Cell (PEMFC). Simulations have been performed by solving the compressible form of two-dimensional Navier–Stokes equations. The turbulence model have been employed to estimate the turbulent region. A comparison of the computed results with the published experimental data exhibits agreement in terms of entrainment ratio at defined operating conditions. The ejector with convergence nozzle was widely used in the aerospace science, jet engine and Polymer Electrolyte Membrane Fuel Cell, because it has many advantages such as jet noise reduction, prevent condensation of water vapor inside the ejector and improvement of conventional converging-diverging nozzle. According to several applications and advantages of convergence nozzle, effects of primary converging nozzle on the flow characterization and the ejector performance have studied at any part of its. Based on particular application of the ejector with convergence primary nozzle in PEMFC, performance improvement is the purpose of this study. The results have been compared with air ejector with convergence-divergence primary nozzle. The results show that the air ejector performance has been enhanced under changing primary nozzle structure. This means that the ejector can consume available energy in its operation processes optimally beside increasing drawn secondary flow.

---

Condensing flow in nozzle and stationary blades of steam turbine has always been the subject of many studies. Due to the lack of precise relationship between surface tension and small droplet radius, the radial dependence of surface tension has been ignored in calculations and surface tension of flat surface instead of droplet surface tension is used. Gibbs-Tolman-Koenig-Buff equation expressing the radial dependence of surface tension that Kalova provides as a relationship of changes in surface tension versus radius of the surface by fitting response from the exact solution of GTKB equation. The aforementioned relationship is known as Kalova surface tension equation. The present study considers the effect of the Kalova surface tension correction on nucleation and droplet growth in condensing flows in an ultrasonic Laval nozzle. Since Tolman coefficient (δ) is an important parameter in Kalova surface tension equation, by fitting response from Tolman equations a correlation for Tolman coefficient temperature changes suggested for the first time. Kalova Surface tension in addition to the direct impact of the droplets crisis radius, to obtain droplet free energy crisis is also impressive that the impact of both them in the modified classical nucleation equation have been studied for the first time. The results of analytical modeling one-dimensional adiabatic supersonic flow with applying the Kalova surface tension correction and using the proposed equation for Tolman coefficient temperature changes indicate an improvement to the 12% in radius of the droplets and 5% in pressure distribution in the region of condensation shock.

---

Cooling of high temperature systems such as gas turbine blades is one of the most important systems in industrial. In this paper, three dimensional cooling performance on a flat plate is calculated by a 3D finite-volume method and the realizable k-ε turbulence model which is the improved of the standard k-ε turbulence model and it can generate data more appropriate for fluid injections and jets. In this investigation, 4 different cases have compared together to find the best cooling case with maximum effectiveness. These cooling cases are including 2 cases of film cooling with console and cylindrical holes, one case of impingement cooling and one case of transpiration (with porous wall) cooling. For validation, the adiabatic cooling effectiveness for the console has been compared with the experimental data. These comparisons have been shown a good agreement between experimental and numerical data. The adiabatic cooling effectiveness, the effects of density ratio (by air and CO2 as a coolant) (DR) and blowing ratio (M) are studied in all cases. The adiabatic cooling effectiveness for console and transpiration cooling cases have compared together for studying the penetration of coolant fluid in the main stream (hot fluid) and showing the temperature and effectiveness distribution . The main purpose of this paper is finding the best cooling techniques with maximum effectiveness and the results have been shown which the designed transpiration cooling model has the best effectiveness respect to other cooling techniques.

---

In present study, the entropy analysis for laminar MHD flow over a stretching sheet with variable heat flux in presence of heat source and constant suction is done. The flow is influenced by uniform transverse magnetic field. The PDE governing differential equations including continuity, momentum, and energy are reduced to ODE ones by similarity solution. Then, the ODEs are solved by applying the 4th-order Runge-Kutta method. To validate, the result of this study and the published result are compared and the agreement is achieved. Bejan number is used as a design criterion parameter for a qualitative study about the cooling. The effects of suction parameter, heat source parameter, magnetic parameter, Prandtl number and heat flux parameter on dimensionless velocity and temperature, dimensionless entropy generation and Bejan number are shown in several plots. The results show that with increasing Prandtl number, suction, heat source parameter, magnetic parameters and parameters related to heat flux, the Bejan number is decreased, decreased, increased, decreased and decreased, respectively. The results of this research can be used for the increasing of the cooling in the surface in the coating.