سال:1392 | دوره: | شماره: |تعداد مقالات:10

A multistage irreversible Carnot heat engine system operating between a finite thermal capacity high-temperature fluid reservoir and an infinite thermal capacity low-temperature environment with a generalized heat transfer law [q µ (D(Tn))m] is investigated in this paper. Optimal control theory is applied to derive the continuous Hamilton-Jacobi-Bellman (HJB) equations, which determine the optimal fluid temperature configurations for maximum power output under the conditions of fixed initial time and fixed initial temperature of the driving fluid. Based on the universal optimization results, the analytical solution for the case with Newtonian heat transfer law (m=1, n=1) is further obtained. Since there are no analytical solutions for other heat transfer laws, the continuous HJB equations are discretized and the dynamic programming (DP) algorithm is performed to obtain the complete numerical solutions of the optimization problem. Then the effects of the internal irreversibility and heat transfer laws on the optimization results are analyzed in detail. The results obtained can provide some theoretical guidelines for the optimal design and operation of practical energy conversion and transfer processes and systems.

The present investigation consists of an analytical treatment of a steady boundary layer flow of an Eyring-Powell model fluid due to a stretching cylinder with temperature dependent variable viscosity. The heat transfer analysis is also taken into account. Using usual similarity transformations the governing equations have been transformed into non-linear ordinary differential equations and are solved by a powerful technique, the homotopy analysis method. Two models of variable viscosity, namely, Reynolds' and Vogel's are considered. The convergence is carefully checked by plotting h-curves. The emerging parameters intrinsic to the problem are discussed through graphs.

Least squares is a robust and simple method in function approximation. Collocated Discrete Least Squares (CDLS) is a meshless method based on least squares technique. In this paper CDLS is used with a non-incremental projection method for the solution of incompressible generalized Newtonian fluid flow equations in the simulation of laminar flow of power-law fluids. The scheme is used to solve two benchmark problems named lid-driven cavity flow and flow past a circular cylinder for the power-law fluids.

In the present study, the impact of Heat Pipe Based Heat Exchangers (HPHEX) on the performance of an air-conditioning system in a library building was investigated. According to the fieldwork study, the air conditions established by the existing system are not within the comfort zone recommended by the ASHRAE. Therefore, enhancing the performance of the existing system by adding HPHEX was studied. HPHEX with different numbers of rows were examined in the system to determine the proper configuration. TRNSYS software was used to investigate the hourly effect of HPHEX on the system in terms of provided air conditions and energy consumption. According to the results, the system behavior in terms of provided air conditions is appropriate and marginally inside the comfort area with the added eight-row HPHEX. In addition, it was shown that by adding HPHEX to the system, a significant amount of energy recovery could be achieved.

Above all, existing blast furnace production comes about through innovations in the area of injection of alternative fuels as a partial substitute for metallurgical coke. These fuels have one common aspect, when they are used in metallurgical based industries, the hydrogen content in reducing gas is significantly increased. For variant calculations of the course of blast furnace smelting and the optimising of alternative fuels, a system of models of blast furnace smelting was developed at the VSB, Technical University of Ostrava. This system enables respect for basic limits and establishes the needed technological data for calculation of the injection efficiency of these fuels into blast furnaces. Some non-traditional alternative fuels have not been used in the process yet, here or abroad, and the use of the prognostic model system enables, in this way, a preliminary efficiency estimation of their application without the necessity of carrying out expensive and risky operating experiments. Following the first testing results, the influence of the share of hydrogen on the reduction process acceleration, and in the efficiency increase of iron production, is not negligible in any case.

Regarding the use of the velocity distribution of turbulent flows of big square plane nozzles, the authors propose the modeling of a turbulent free jet in a wind-tunnel. The free jet mixes with the surrounding fluid, creating turbulence and the jet grows thicker as a result of the exchange of momentum between stagnant air and a portion of the jet. In this study, jets of air ejected from square nozzles of large sizes and flowing into stagnant air are considered. Theoretical solutions based on two different turbulence theories are proposed with coefficients that should be measured experimentally. These coefficients are obtained for a wide range of Reynolds numbers and a correlation is also proposed. In different stations in the axial direction, the velocity distribution appears to have the same shape. This similarity is shown either by theoretical solutions or experimental measurements in this work

Today, the flow of gas-solid, solid-liquid and liquid-liquid mixtures is broadly used in many industries such as slurry transportation, propulsion, dredging and power generation equipment. In this paper, single solid particle motion through free and forced vortices is analytically studied. The equations are solved for cases in which the drag, pressure gradient, added mass, buoyancy and weight forces are considered individually and simultaneously. Verification has been done for the value of ReP, which confirms the solution for the first t=0.1 s. The results show that the most important force governing particle motion is the pressure gradient force.

In this paper, a new technique, namely, the New Homotopy Perturbation Method (NHPM) is applied for solving a non-linear two-dimensional wave equation. The two most important steps in application of the new homotopy perturbation method are to construct a suitable homotopy equation and to choose a suitable initial guess. Comparison between our solution with Homotopy perturbation method (HPM) shows that the NHPM is effective and accurate in solving these kinds of equation.

The Duffing oscillator is a common model for nonlinear phenomena in science and engineering. In this paper, we use the modified differential transform method to obtain the approximate solution of a nonlinear Duffing oscillator with a damping effect under different initial conditions. Moreover, the solutions of the nonlinear Duffing oscillator with the damping effect are obtained using the fourth-order Runge-Kutta numerical solution. A comparison of the results show that for the same number of terms the differential transform method (DTM) can only predict the solutions of a Duffing oscillator in a small range of time domains, whereas the MDTM can predict the results in a whole range of time domains accurately.

The authors regret that the author's name of Reference 12 has been misspelled as “Wang, X.W. “A new computational method for wrinkling analysis of gossamer space structures'', International Journal of Solids and Structures, 46, pp. 1516-1526 (2009)'', and should be corrected as “Wang, C.G.et al. “A new computational method for wrinkling analysis of gossamer space structures'', International Journal of Solids and Structures, 46, pp. 1516-1526 (2009)''. The authors would like to apologise for any inconvenience caused.