Ahmad Hussein Abdul Hamid

Spatial evolution of a quasi-two-dimensional Kármán vortex street subjected to a strong uniform magnetic field

A vortex decay model for predicting spatial evolution of peak vorticity in a wake behind a cylinder is presented. For wake vortices in the stable region behind the formation region, results have shown that the presented model has a good capability of predicting spatial evolution of peak vorticity within an advecting vortex across 0.1 ≤ β ≤ 0.4, 500 ≤ H ≤ 5000, and 1500 ≤ ReL ≤ 8250. The model is also generalized to predict the decay behaviour of wake vortices in a class of quasi-two-dimensional magnetohydrodynamic duct flows. Comparison with published data demonstrates remarkable consistency.

An Experimental Investigation on the Effect of Various Swirl Atomizer Orifice Geometries on the Air Core Diameter

Liquid atomization is a process of changing the liquid into small droplets. There are many applications which are related to liquid atomization including fuel injection in combustion systems and also in agricultural sprays. In pressure swirl atomizer, the liquid is injected into the atomizer through tangential port and a swirling motion is formed inside the swirl chamber. In high strength of swirling motion, an air core will be visible inside the atomizer. The liquid is then discharged from the orifice to form a spray which breaks up the liquid into small droplets. The objective of this research is to investigate the effect of various orifice geometries on the air core diameter. The injection pressure was varied in the range of 2 to 8 bar and water was used as the working fluid. Experiment data shows that the air core diameter increases as the injection pressure increased, regardless the discharge orifice diameter and discharge orifice length. It also found that the air core diameter increases as the discharge orifice length decreases and the discharge orifice diameter increases.

Characteristics of swirl effervescent atomizer spray angle

In the application of sprays produced by an atomizer, spray angle is one of key performance parameters. A larger spray angle is often required in providing a better spray dispersion. Swirl effervescent atomizer is one of the existing atomizers with the capability to produce a large spray angle. The formation of spray angle from this atomizer however is hardly understood. A newly-designed swirl effervescent atomizer was developed and tested with different swirl-generating vane angle in order to understand the swirl intensity effect on the spray angle. Experiments were carried out based on a cold flow test approach using water as the working fluid and nitrogen gas as the atomizing agent. High-speed shadowgraph technique was deployed to record the resultant sprays produced. Video recordings, acquired using a high-speed video camera, were converted to a sequence of images for further analysis using an image processing software. It was found that the spray angle increases with the swirl-generating vane angle. Specifically, the spray angle shows an abrupt increase for the case of swirl-generating vane angle changing from 30° to 45° but visualizes only a gradual increase in the case of swirl-generating vane angle changing from 45° to 60°.

Heat transfer augmentation of a quasi-two-dimensional MHD duct flow via electrically driven vortices

ABSTRACT The fluid dynamics and heat transfer characteristics of magnetohydrodynamic duct flow often degrade the laminarization caused by the magnetic field. The present work evaluates the performance of a system featuring alternating current injection from a point electrode as a vortex promoter for enhancement of the thermal-hydraulic characteristics. It is found that the vortices generated by the current injection alone generally induce a greater thermal-hydraulic performance with a significantly smaller additional pressure loss than configurations featuring a physical obstacle. A maximum overall efficiency index of 1.83 was recorded within the parameter space investigated.

A review on spray characteristics of effervescent atomizer under various geometrical parameters and operating condition

Effervescent atomizer is one of the most innovative atomizers and has been used in various applications such as gas turbine combustors, consumer products, and incinerators due to their advantages such as good atomization and insensitive to liquid viscosity. Spray characteristics of any atomizers is very crucial parameter since it will determine the performance of the atomizers. This paper discussed the previous studies related to the influence of independent parameters towards the spray characteristics of an effervescent atomizer. Independent parameters covers in this paper include gas-to-liquid ratio (GLR), injection pressure, and atomizers geometries including aerator tube diameter, aeration holes diameter and exit orifice diameter.

Spray Characteristics of Swirl Effervescent Injector in Rocket Application: A Review

Injector is one of the vital devices in liquid rocket engine (LRE) as small changes in its configurations and design can result in significantly different LRE performance. Characteristics of spray such as spray cone angle, breakup length and Sauter mean diameter (SMD) are examples of crucial parameters that play the important role in the performance of liquid propellant rocket engine. Wider spray cone angle is beneficial for widespread of fuel in the combustion chamber for fast quiet ignition and a shorter breakup length provides shorter combustion chamber to be utilized and small SMD will result in fast and clean combustion. There are several mechanisms of liquid atomization such as swirling, e.g. jet swirl atomization or introducing bubbles into the liquid and effervescent atomization. Introducing a swirl component in the flow can enhance the propellant atomization and mixing whereas introducing bubbling gas directly into the liquid stream inside the injector leads to finer sprays even at lower injection pressures. This paper reviews the influence of both operating conditions and injector internal geometries towards the spray characteristics of swirl effervescent injectors. Operating conditions reviewed are injection pressure and gas-to-liquid ratio (GLR), while the injector internal geometries reviewed are limited to swirler geometry, mixing chamber diameter (dc), mixing chamber length (lc), aeration hole diameter (da), discharge orifice diameter (do) and discharge orifice length (lo).

Current injection vortex promoter for heat transfer enhancement in a magnetohydrodynamic duct flow

The quest for cleaner, cheaper and reliable energy has motivated the development of magnetic confinement fusion reactor technology as a possible means of harnessing the energy produced by nuclear fusion for power generation. However, the magnetohydrodynamic effects act to reduce the thermal-hydraulic performance of the duct flows within the cooling blankets. The present paper reports the investigation of the duct flow with current injection as a vortex promoter for the enhancement of the convection heat transfer. The results indicate a maximum enhancement of approximately 70% over the duct flow without current injection for the highest current amplitude investigated. The competing effects of the Lorentz force and Hartmann damping result in a non-monotonic trend of Nusselt number with respect to friction parameter, while increasing Reynolds number results in a monotonic increase of Nusselt number. Keywords—MHD, quasi-2-d, heat transfer, vortex promoter

An experimental investigation on spray characteristics emanating from liquid–liquid coaxial swirl atomizer

Liquid fuel/oxidizer atomization is extensively used in rocket engines for exploiting their high mixing efficiency. An experimental investigation is performed to explore the characteristics of sprays produced by a liquid–liquid coaxial swirl atomizer in a non-combusting environment. Investigation data will be used to correlate between liquid properties, atomizer geometric dimension, and atomization spray characterization. The idea is design the atomizer, fabricate, cold flow test and analyze the result. This atomizer is divided into two parts which is the inner atomizer and the outer atomizer. There also has two liquid inlet points where one inlet is meant for inner nozzle while the other inlet is meant for the outer nozzle. Two water supplies of the same kind will be supplied into the atomizer. As compared to basic conventional atomizer design, this atomizer sprays two liquid simultaneously at different angles and different swirl directions, but at the same axis. In this paper, it described the character...

Thermal and Coolant Flow Computational Analysis of Cooling Channels for an Air-Cooled PEM Fuel Cell

Polymer Electrolyte Membrane (PEM) fuel cells are clean electrical power generators for applications normally up to 100 kW power requirements. It has the advantage of fast start-up due to its low operating temperatures of 60oC to 100oC. However, the low temperature requirement has to be addressed with an efficient thermal management system. For an air-cooled PEM fuel cell, cooling channels with a straight rectangular configuration are widely applied. This work establishes a computational methodology for the analysis of coolant flow mechanics related to the channel geometry for a specific bipolar plate size. The velocity and thermal gradient, average velocity rise factor (AVRF) and total cooling rates were determined from Computational Fluid Dynamics simulation based on initial coolant Reynolds number of approximately 250 to 750 with a steady heat flow of 82W. All geometries showed nearly 100% cooling capability respective to the heat load, but differ in the aspects of average plate temperature achieved, its temperature profile as well as existing gradient. From the analytical perspective of thermo fluids engineering, the selection criteria of suitable micro cooling channel configurations, depending on operating priority, was established.

Study on the possible defects in plastic injection molding for different designs of studs for football boot sole using CAD and CAE technologies and applications

Computer aided design (CAD) and computer aided engineering (CAE) technologies are extensively utilized nowadays to assist engineers and mold designers in the engineering world. These technologies and applications serves as vital tools to generate better, safer and more reliable products. Beside it saves a lot of time in the design process that includes modeling and drafting through the use of CAD technology, engineers and designers may also simulate their design to determine and predict the performance of the final product that will be manufactured through CAE technology. This research study outlines the utilization of these technologies in designing a football boot sole that will be used for plastic injection molding. In plastic injection molding, it is highly aimed to produce plastic products with no defects or at least less imperfection. Therefore, utilizing CAD and CAE technologies may contribute a high impact to the plastic injection molding industry whereby through simulation and analysis using CAD and CAE technologies, predictions of the possible defects on the final product can be made. ProE,GI,EER 2000i2 and MOLDFLOW Plastics Advisers (MPA) were the CAD and CAE technology applications that were widely used in this research study. Apart from that, the predicted defects on the final product managed to give a clear view to the research and design team about what defects may occur on the football boot sole design.