International Journal of Engineering
Volume:16 Issue: 2, Jun 2003

New equations have been developed to predict the effect of geometrical dimensions of tangential cyclones on their operational performances. To check the validity of the derived equations, an experimental apparatus was set up and some experimental work was performed. It was observed that the experimental results confirm properly the theoretical predictions.

A complete series of potential functions for solving the wave equations in an almost transversely isotropic media is presented. The potential functions are reduced to only one potential function particularly for axisymmetric wave propagation problems. The potential functions presented in this paper can be reduced to Lekhnitskii-Hu-Nowacki solution for elastostatics problems.

A scale-up design procedure, based on a new physical mass transfer (PMT) model, whichdescribes the performance, for aerobic rotating biological contactors (RBC’s) is developed. This scale-up procedure can be used to determine the disc surface area needed to prevent an oxygen limitation or to obtain a specific degree of treatment. In contrast to the empirical, and most previous RBC performance model, a major advantage of the PMT model in design is that it can predict the onset of oxygen limiting conditions since it accounts for the fact that low dissolved oxygen concentrations can limit the growth rate of the attached microorganisms. The PMT model can be used to predict the oxygen limiting loading rate so that this loading rate is not exceeded in practice. The proposed procedure has been successfully applied to design and install two relatively small full-scale domestic RBC units in parallel treating a cement plant wastewater efficiently.

In this study, a limit equilibrium method has been developed that satisfies all conditions of equilibrium and assumes circular slip surfaces. All force and moment equilibrium equations are employed without using simplification assumptions. A non-linear optimization technique is used to solve the system of equations with the corresponding constraints. The proposed method is capable to determine the interslice forces, factor of safety, and the coordinates of the critical slip surface center and the length of its radius. Examples for various unknown slope stability parameters are presented and compared to other conventional methods. The concept of the proposed method can be simply extended to multi-layered soil problems with circular and non-circular slip surfaces.

Problem of knowledge analysis for decision support system is the most difficult task of information systems. This paper presents a new approach based on notions of mathematical theory of Rough Sets to solve this problem. Using these concepts a systematic approach has been developed to reduce the size of decision database and extract reduced rules set from vague and uncertain data. The method has been applied to an imprical medical database with large scale data size and the final reduced and core rules has been extracted using concepts of this theory.

An unsteady two-dimensional finite-volume solver was developed based on Van Leer’s flux splitting algorithm in conjunction with “Monotonic Upstream Scheme for Conservation Laws (MUSCL)” limiters to improve the order of accuracy and the two-layer Baldwin-Lomax turbulence model was also implemented. Two test cases were prepared to validate the solver. The computed results were compared with the experimental data and a good agreement validated the solver. Finally, the solver was used for the flow through a multi-blade stage of an axial compressor in its off-design condition. The computed results showed a rotating stall-like instability with a periodic behavior. To investigate the flow properties during the instability condition, the flow pattern, Vortex properties and the axial velocity were studied. It was concluded that the instability vortices in the multi-blade cascade do not have the same generation history of the separated vortices over a single body.

Direct numerical simulation of the wake flow around and behind a planar ellipse using a random vortex method is presented. Fluid is considered incompressible and the aspect ratios of ellipse and the angles of attacks are varied. This geometry can be a logical prelude to the more complex geometries, but less time dependent experimental measurements are available to validate the numerical results. Therefore, the key figures of the averaged values of selected cases are chosen to check the accuracy of the results. Based on the results, the general behavior of the flow around an ellipse at the zero angle of attack is almost similar to that around a circle. But, at the other angle of attacks, the asymmetry of the flow is dominant and pronounced clearly.

In this paper, the effect of cold air on the fluid flow inside the cylindrical combustion chamber and its wall temperature distribution have been studied computationally, taking into account the effect of radiative heat transfer from hot gases. The results have been compared with the case that radiative heat transfer was neglected. It is observed that the reattachment length increases when increasing the expansion ratio, and mixing of two fluid flows are not affected by temperature. As mixing is directly related to turbulence, higher turbulence will cause uniform mixture in a shorter length and sudden expansion is helpful for faster mixing. The results show that the combustion chamber wall temperature due to gas radiation will increase very quickly at the entrance and will then decrease rapidly, while neglecting the radiation effect, the wall temperature will increase monotonically.

Industrial demands for more compact heat exchangers are a motivation to find new technology features. Electrohydrodynamics (EHD) is introduced as a promising phenomenon for heat transfer enhancement mechanisms. Similar to any new technology, EHD has not been understood completely yet and requires more fundamental studies. In boiling phase change phenomena, nucleation is the dominant mechanism in heat transfer. Because of higher performance in heat transfer, nucleate boiling is considered as the main regime in thermal components. Hence, bubble dynamic investigation is a means to evaluate heat transfer. This study investigates bubble formation, including homogeneous and heterogeneous nucleation, from a thermodynamic point of view. Change in availability due to bubble embryo nucleation is discussed. Stability criteria for these systems are theoretically studied and results are discussed considering experimental data. In addition, a conceptual discussion on entropy generation in a thermodynamic system under electric field is presented.

This paper provides steady state queue-size distribution for a G/G/1 queue by using principle of maximum entropy. For this purpose we have used average queue length and normalizing condition as constraints to derive queue-size distribution. Our results give good approximation as demonstrated by taking a numerical illustration. In particular case when square coefficient of variation of inter-arrival time is equal to one, the average queue length provided tallies with the results for M/G/1 model. Other particulars cases have also been deduced which match with already existing results.