The similarity solution for the steady stagnation flow towards an off-centered rotating disc is gives a system of non-linear partial differential equations. These nonlinear differential equations are numerically solved by applying well known Keller-Box Method. After finding the velocity distributions, the important designing subject, entropy generation of this system has been analyzed. Graphical results are presented to investigate effects of the rotation ratio α, off-centering, Reynolds number and axial height on the radial and azimuthal velocities and entropy generation. In order to show the effectiveness of the KellerBox method, the obtained results are compared with available solutions obtained using DTM. The obtained results demonstrate the reliability of the algorithm and the KellerBox method is an attractive method in solving the systems of nonlinear partial differential equations, and also the entropy generation is an important parameter depends on design and work conditions that should be in the attention of designers of these rotating systems.
The similar solution on the equations of the revised Cheng-Minkowycz problem for natural convective boundary layer flow of nanofluid through a porous medium gives (using an analytical method), a system of non-linear partial differential equations which are solved by optimal homotopy analysis method. Effects of various drastic parameters on the fluid and heat transfer characteristics have been analyzed. A very good agreement is observed between the obtained results and the numerical ones. The entropy generation has been derived and a comprehensive parametric analysis on that has been done. Each component of the entropy generation has been analyzed separately and the contribution of each one on the total value of entropy generation has been determined. It is found that the entropy generation as an important aspect of the industrial applications has been affected by various parameters which should be controlled to minimize the entropy generation.
In this paper, the performance of organic Rankine cycle with a two-stage turbine and internal heat exchanger, considering different dry hydrocarbons as working fluid, has been analyzed. This thermodynamic analysis is done using Engineering Equation Solver version 8.379 software. The influence of working fluid reheating has been studied and the critical temperatures for the thermal and exergy efficiencies are determined. Results show that thermal and exergy efficiencies increase with working fluid reheating and also through a two-stage turbine. RC-318 is a good replacement for R-236fa, R-113 has a better efficiency than R-236fa, R-245fa, and iso-butane and finally cyclohexane can achieve the highest efficiency. Although the maximum value of efficiencies for each one of working fluids are different, but all of these maximum values almost happen at a unique value of relative pressure of the cycle. The same result has been presented for variation of turbine inlet temperature. C⃝ 2014 Wiley Periodicals, Inc. Heat Trans Asian Res, 44(8): 738-752, 2015; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj).
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