Muhanad Hajjawi
@hct.ac.ae
Higher colleges of technology
Scopus Publications
Scholar Citations
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Scopus Publications
Muhanad Hajjawi
IEEE
Pressure loss in mini duct bends did not receive a lot of researcher's attention, yet with the recent industry interest in mini and micro flow applications, it is necessary to address viscous flows in mini scale bends. This study numerically investigates the effect of curvature radius and Reynolds number on pressure drop in mini duct bends. The study addresses laminar flow in fixed cross-sectional area 180°duct bends with varying bend curvature radiuses and Reynold numbers. The results show that pressure drop is linearly related to bend curvature radius, while it has a nonlinear relation with Reynolds number. A pressure drop equation is proposed which introduces a curvature factor as a function of Reynold number and bend radius in the well-known Darcy-Weisbach equation. The results show less than 5% error in pressure drop using the presented curvature factor equation compared with the simulation results. On the other hand, the flow characteristics in the 180 bends are presented and discussed.
Sufian Shaker, Muhanad Hajjawi, Altaf Khan, and Mohammad Kilani
Informa UK Limited
Abstract The paper presents a CFD investigation of the effect of the inlet and outlet angles on the flow performance of the ferrolfuidic magnetic mircropump. The methodology employed is based on treating the overall flow path in the inlet or outlet chambers as a series connected network, and calculating the pressure loss in the inlet and outlet at various angles by subtracting the total pressure loss in the flow path from the known pressure losses in the other items in the path. CFD simulations employed in this study include first-order and second-order momentum schemes as well as simple and couple momentum schemes. The simulation shows that a gentler inlet and outlet angles reduce the inlet and outlet pressure loss coefficients, leading to a significant drop in the torque and power needed to drive the pump, and a significant improvement in its mechanical efficiency. For a pump with typical geometric and operating conditions, reducing the inlet angle from 90° to 0° causes the inlet pressure loss coefficient to drop by 80%, while a similar reduction in the outlet angle would drop the outlet pressure loss coefficient by almost 50%. This leads to a 5.4% rise in the mechanical efficiency of the pump. Further, an increased pressure loss coefficient at sharp inlet and outlet angles compromises pump’s applicability to higher pressure application as it causes the loss of magnetic coupling between the external drivers and the driven pistons.
Yo Nakamura and Muhanad Hajjawi
Avestia Publishing
Smoke management systems design is very important as it affect saving human lives in case of fire. The majority of firerelated deaths are caused by smoke inhalation of toxic gases, only 30% of deaths are due to fire burns. Recently, a great attention has been given to smoke management systems design validation using CFD simulations to ensure its effectiveness and compliance with fire codes regulations. CFD smoke simulation usually conducted using the inert fire species transport model, in which the fire source values specified at the fire inlet are assumed to be equivalent to an actual car fire products generation rates. Nonetheless, with the lack of a comprehensive conclusion on actual car fire products generation rates in literature, fire codes usually specify a certain fuel to represent a car fire, such as polyurethane as per UAE fire code. Considering the aforementioned, this work reviews literature on both polyurethane and actual car fires products generation rates, in an effort to conclude a proper fire products generation rates for CFD smoke simulations. Furthermore, this study demonstrates the use of the concluded fire source values to validate an underground car park smoke management systems design of a residential tower in UAE. The design is validated in compliance with the UAE fire code regulations considering both fire products concentrations and visibility analysis. The simulation results shows considerable difference in smoke generation between actual car fire and polyurethane fire. Mainly due to polyurethane higher fire growth rate and soot generation rates. On the other hand, the results illustrate that the smoke management system design satisfies the fire code CO and CO2 concentrations limits, yet it failed to comply with the fire code visibility requirements when polyurethane was used as fire source.
Muhanad Hajjawi, Lafe Taylor, and Stephen Nichols
American Institute of Aeronautics and Astronautics
M.K. Hajjawi and A. Shirkhodaie
IEEE
The problem of visual coordination and target tracking mobile robots cooperating in an unstructured environment is addressed. In this paper, we consider a team of semi-autonomous robots controlled by a remote supervisory control system. We present an algorithm for visual position tracking of individual cooperative robots within their working environment. Initially, we present a technique suitable for visual servoing of a robot toward its landmark targets. Then, we present an image-processing technique that utilizes images from a remote surveillance camera for localization of the robots within the operational environment. In this algorithm, the surveillance camera can be either stationary or mobile. The supervisor control system keeps tracks of relative locations of individual robots and utilizes relative coordinates information of the robots to coordinate their cooperative activities. We present some results of this research effort that illustrates the effectiveness of the proposed algorithms for cooperative robotic systems visual team working and target tracking.