O. M. Haddad

Mechanisms and Responses of a Dielectric Barrier Plasma Actuator: Geometric Effects

The single dielectric barrier discharge plasma, a plasma sustainable at atmospheric pressure, has shown considerable promise as a flow control device operating at modest (tens of watts) power levels. Measurements are presented of the development of the plasma during the course of the discharge cycle, and the relevance of these measurements to the modeling of the actuators electrical properties is discussed. Experimental evidence is presented strongly pointing to the electric field enhancement near the leading edge of the actuator as a dominant factor determining the effectiveness of momentum coupling into the surrounding air

The effect of alcohol fumigation on diesel engine performance and emissions

Abstract The effects of ethanol fumigation (i.e. the addition of ethanol to the intake air manifold) and ethanol–diesel fuel blends on the performance and emissions of a single cylinder diesel engine have been investigated experimentally and compared. An attempt was made to determine the optimum percentage of ethanol that gives lower emissions and better performance at the same time. This was done by using a simple fumigation technique. The results show that both the fumigation and blends methods have the same behavior in affecting performance and emissions, but the improvement in using the fumigation method was better than when using blends. The optimum percentage for ethanol fumigation is 20%. This percentage produces an increase of 7.5% in brake thermal efficiency, 55% in CO emissions, 36% in HC emissions and reduction of 51% in soot mass concentration. The optimum percentage for ethanol–diesel fuel blends is 15%. This produces an increase of 3.6% in brake thermal efficiency, 43.3% in CO emissions, 34% in HC and a reduction of 32% in soot mass concentration.

Developing Free-Convection Gas Flow in a Vertical Open-Ended Microchannel Filled with Porous Media

Abstract The developing hydrodynamic and thermal behaviors of free convection gas flow in a vertical open-ended parallel-plate microchannel filled with porous media are investigated numerically. The extended Darcy-Brinkman-Forchheimer model is used to model the flow in porous medium and the solid and fluid media are not assumed in local thermal equilibrium. The microflow regime considered is the slip flow regime. The slip in velocity and jump in temperature are found to decrease in the axial direction of the flow. The friction factor is found to decrease as Knudsen number, Forchheimer number and Grashof number are increased. However, the friction factor is found to increase as Darcy number increased. On the other hand, Nusselt number is found to decrease as Knudsen number, Darcy number and thermal conductivity ratio are increased, whereas it increased as Forchheimer number, Grashof number and Biot number are increased.

Entropy Generation Due to Laminar Incompressible Forced Convection Flow Through Parallel-Plates Microchannel

The entropy generation due to steady laminar forced convection fluid flow through parallel plates microchannel is investigated numerically. The effect of Knudsen, Reynolds, Prandtl, Eckert numbers and the nondimensional temperature difference on entropy generation within the microchannel is discussed. The fraction of the entropy generation due to heat transfer to the total entropy generation within the microchannel is studied in terms of Bejan number. The entropy generation within the microchannel is found to decrease as Knudsen number increases, and it is found to increase as Reynolds, Prandtl, Eckert numbers and the nondimensional temperature difference increase. The contribution of the viscous dissipation in the total entropy generation increases as Knudsen number increases over wide ranges of the flow controlling parameters.

Boundary layer receptivity to free-stream sound on parabolic bodies

We use a numerical approach to study the receptivity of the boundary layer flow over a slender body with a leading edge of finite radius of curvature to small streamwise velocity fluctuations of a given frequency. The body of interest is a parabola in order to exclude jumps in curvature, which are known sites of receptivity and which occur on elliptic leading edges matched to finite-thickness at plates. The infinitesimally thin flat plate is the limiting solution for the parabola as the nose radius of curvature goes to zero. The formulation of the problem allows the two-dimensional unsteady Navier–Stokes equations in stream function and vorticity form to be converted to two steady systems of equations describing the basic (nonlinear) flow and the perturbation (linear) flow. The results for the basic flow are in excellent agreement with those in the literature. As expected, the perturbation flow was found to be a combination of an unsteady Stokes flow and Orr–Sommerfeld modes. To separate these, the unsteady Stokes flow was solved separately and subtracted from the total perturbation flow. We found agreement with the streamwise wavelengths and locations of Branches I and II of the linear stability neutral growth curve for Tollmien–Schlichting waves. The results showed an increase in the leading-edge receptivity with decreasing nose radius, with the maximum occurring for an infinitely sharp flat plate. The receptivity coefficient was also found to increase with angle of attack. These results were in qualitative agreement with the asymptotic analysis of Hammerton & Kerschen (1992). Good quantitative agreement was also found with the recent numerical results of Fuciarelli (1997), and the experimental results of Saric, Wei & Rasmussen (1994).

Entropy generation due to laminar forced convection in the entrance region of a concentric annulus

This study is focused on the entropy production due to laminar forced convection in the entrance region of a concentric cylindrical annulus. The present hydrodynamic and temperature fields are obtained numerically. Local entropy generation distributions are obtained based on the resulting velocity and temperature fields by solving the entropy generation equation. The effect of different flow parameters on thermal, viscous, and total entropy generation is studied for different thermal boundary conditions. Moreover, the effect of radius ratio on the entropy generation is investigated. Entropy generation was found to be inversely proportional to both Reynolds number and the dimensionless entrance temperature. The results also show that increasing Eckert number and/or the radius ratio will increase the entropy generation. Finally, it is found that thermal entropy generation is relatively dominant over viscous entropy generation.

Enhanced solar still performance using a radiative cooling system

A basin type solar still is integrated with a packed bed storage tank which is used as an external condenser for the still. The packed bed condenser is cooled during the night using a radiative cooling panel by circulating pure water into the packed bed condenser and the radiative cooling panel. At the end of the cooling process, the packed bed tank attains low temperature, which is very close to the effective sky temperature. At the begining of daylight, the vapor produced by the solar still is sucked naturally by the packed bed condenser and condenses within it. A mathematical model describing the behavior of the modified still is proposed. The effects of different designs, climate and operating parameters on the still performance are investigated.

Acoustic receptivity of the boundary layer over parabolic bodies at angles of attack

The effect of angle of attack on the acoustic receptivity of the boundary layer over two-dimensional parabolic bodies is investigated using a spatial solution of the Navier–Stokes equations. The free stream is decomposed into a uniform flow with a superposed periodic velocity fluctuation of small amplitude. The method follows that of Haddad & Corke (1998) and Erturk & Corke (2001) in which the solution for the basic flow and linearized perturbation flow are solved separately. Different angles of incidence of the body are investigated for three leading-edge radii Reynolds numbers. For each, the angle of attack ranges from

Entropy generation due to laminar forced convection flow past a parabolic cylinder

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Laminar Incompressible Flow Past Parabolic Bodies at Angles of Attack

to past the angle where the mean flow separates. The results then document the effect of the angle of incidence on the leading-edge receptivity coefficient (