IRANIAN JOURNAL OF MECHANICAL ENGINEERING (ENGLISH)
Year:2015 | Volume:17 | Issue:2|Papers Count:5

To evaluate the performance of an engine, it is needed to test engine experimentally. A Large amount of energy is wasted in the engine test cell. In the present work, in order to generate power from the waste heat, an Organic Rankine Cycle (ORC) is used. The waste heat is recovered in three separate heat exchangers (preheater, evaporator and super heater). These heat exchangers are separately designed, and the whole system is analyzed from the energy and exergy viewpoints. Finally, a parametric study is performed to investigate the effects of heat recovery temperature characteristics on important thermodynamic and heat transfer parameters. The results show that applying the ORC, recovers the heat losses equivalent to 8.85% of the engine power.

In the following paper, the accuracy of full turbulent K-e and transitional K-w models in external aerodynamic capturing of NACA0012 in both incompressible regime (Re number of 6 million) and subsonic compressible regime (Mach number of 0.3 to 0.9 and Re number of 1 million to 100 million) have been comprehensively investigated until using comparison between both results, the differences between full turbulent and transitional flow (combined fully laminar+transition region+ fully turbulent) assumptions in aerodynamic coefficients specified accurately. Among these investigations, some sorts of sensitivity analysis, including changes in free-stream Mach number, free-stream Reynolds number, free-stream angle of attack, grid density and free stream turbulence level have been done. Also the effects of transition inception point and affecting parameters, and the magnitude of the conformity between numerical results and theoretical concepts about transition and related effective parameters on the magnitude of lift, drag, lift-slope, pressure distribution, and pressure/friction lift-and-drag coefficients have been investigated in detail. To confirm the validity and the accuracy of the results, the numerical results have been compared with some published references.

Ambient temperature variations and cross winds are the most important environmental parameters affecting the performance of cooling towers, which can result in considerable economical losses to a power plant. In this paper, field and analytical study of these parameters and their effects on the performance of Heller cooling towers from economical point of view have been presented for a typical 240 MW power plant. Results show that at constant ambient temperature, with the increase in wind speed up to 6 m/s, the performance of the steam section of the power plant decreases by an average of 2.52%. Similarly, under still-air condition (no-wind condition), a 10oC increase in the ambient temperature results in about 3.4% decrease in the performance of the steam section. The percentages of decrease in the performance of the steam section of the power plant are equivalent to reduction in the produced power amounting to 16.8 MW and 24 MW, respectively.

In this research a software is developed to simulate the partial cavitation over the axisymmetric and quasi three-dimensional bodies using a Boundary Element Method (BEM).According to desirable convergence of axisymmetric simulation in BEM, first the axisymmetric cavitation flow is simulated and this result is used to simulate quasi three-dimensional bodies. In order to simulate the cavitation flow, the source and dipole rings are distributed on body and cavity boundaries, Using Green's theorem integral expression and to simulate closure of cavity, two models is used: simple closure model and re-entrant jet model. The constant length of the cavity is initial prediction and the cavitation number and shape of cavity are the main results of this simulation. The validation of solution, the Navier-Stokes equations based on mixture model is compared to BEM results in convergense and accuracy. Compression between this results and other experimental and numerical simulation show the ability of BEM in simulation of cavitation flows with desirable convergence and relatively good accuracy.

Applications of heat transfer enhancement by tube inserts (turbulators) have been used in many industries such as power plants, refineries and petrochemicals plants. The main objective is typically viewed primarily as a means to improve and to intensify the thermal performance, size and capital cost reduction of heat exchangers and air coolers. This article introduces a procedure for considering of heat transfer enhancement in a typical air cooler using different turbulators such as Wire coils, Twisted tape and Wire matrixes. Due to increase of the effective surface area, increase of eddies and back mixing in fluid and consequently increase of heat transfer rate, the required heat transfer area is reduced significantly. The case study shows application of wire coil inserts is more effective than others and goes beyond the size reduction. The comparison is revealed that about 20 percent improvement in total cost for 10 years operation of the existing air cooler equipped with the turbulator.