Investigation of swirl injectors and supersonic nozzles for the development of a meso-scale thrust chamber / Ahmad Hussein Abdul Hamid

Issues of propellant atomizing, mixing and viscous loss become increasingly more important as the thrust chamber are reduced in size. Two main components in thrust chamber have been identified as critical since small differences in its design can result in dramatically different performance. They are injector and nozzle, which have been greatly studied by many researchers experimentally or numerically. Current research examines the performance of two solid cone and one hollow cone swirl injectors and 22 convergent-divergent nozzles for thrust chamber application. The spray characteristics of these injectors were investigated by means of cold flow test and the flow inside the nozzles were numerically analyzed by means of computational model that utilizes Spalart-AUmaras model as turbulence model, which was designed specifically for aerospace applications. In addition, optimization of the nozzle's performance was investigated, where nozzle divergence angle was reduced if flow separation occurs inside nozzle. Main objectives of injector cold flow test lay on the determination of flow discharge coefficients, spray cone angle and spray break up length of each injector at different injection pressure. Results show an approximate direct proportion between Reynolds number and discharge coefficient. However, introducing purely axial stream inside injector's swirl chamber does not necessarily increase the coefficient of discharge. Experiment also indicates that increase in injection pressure increased the spray angle. However, at higher injection pressure, both solid cone injectors experience slight decreases in spray angle as the liquid film at the nozzle outlet contracted. Further investigation leads to general conclusion that breakup length decreased with an increase in injection pressure where hollow cone spray produces the longest liquid film. From nozzles analysis, there was significant improvement in nozzle's performance as a result of optimization is foreseen. It is concluded that in order to operate the thrust chamber efficiently, the nozzle geometry must be contoured to prevent flow separation. Actual testing of thrust chamber was performed by means of combustion test utilizing a specially designed test stand and feed systems. Although the test did not provide quantitative performance data of thrust chamber, the functionality and reliability of the feed system had been proved

Development of composite panels for short span bridge construction using indigenous agro - based resources: Fabrication and mechanical testing / Ahmad Hussein Abdul Hamid

Bridges are mainly made of steel and concrete. Researchers have been working towards exploring the potential of such new natural fiber composite materials and their adequate application to structural engineering design. Oil palm empty fruit bunch (OPEFB) fiber, oil palm frond (OPF) fiber mat and sugar cane (SC) husk, which is rich in cellulose, relatively inexpensive and have fairly good possibilities in waste management due to their biodegradability has the potential for polymer-reinforced composite. Fiber reinforced plastics are used whenever there is the need for very high mechanical properties combined with low weight. In that respect natural fibers are of basic interest since they do not only have the functional capability to substitute the widely used manmade fibers but also possess advantages from the point of view of weight and fibermatrix adhesion. The composites were produced by pouring compounding into the mould and let it cured for at least one day. Two different values of fiber mass fraction, mf, namely 10% and 20% were studied for OPEFB fiber composite. Other composites samples were made from OPF fiber mat and 10% mass fraction SC husk. The matrix used in the experiments was epoxy with two to one epoxy-hardener ratio. The mechanical properties of each fiber-matrix combination have been investigated by conducting mechanical tests using ASTM standards. Results indicate that the most important factors for determining impact toughness were the interface behavior. This behavior determined the fiber debonding and pullout behavior. The impact strength of the composites was found to be increasing with fiber content. The tensile strength of the composites containing 10% mass fraction was found to be higher than that of homogeneous epoxy resin by 35%. Other composites had a lower tensile strength than the homogeneous epoxy resin. There are no improvement in flexural strength of epoxy composite. Increasing the density of fibers in the composite resulted in reduction of flexural strength, which OPF fiber mat composite has the lowest flexural strength compared to the other composites that being studied. Optical camera microscopic were used to examine the fiber-matrix adhesion and fiber breakage. The fiber pullout behavior and its effects on mechanical properties with different types of fiber as well as fiber mass fraction were investigated

Optimization of Co-Flow Jet Parameters for Ahmed Body Application

This study evaluates the drag reduction strategy of suction and blowing on idealize automotive vehicle,Ahmed Body. Optimization approach is adapted in order to analyse the effect of slot location, momentumcoefficient and slot angle on the vehicle which experiencing drag. Despite all the efforts that have been done toreduce the Ahmed body drag using various active flow control system, most of the drag reduction were only lessthan 15%. A 25° Ahmed body with build in co-flow jet is modelled using a CAD software. The flow around theAhmed body is simulated at Reynolds number based on length Re = 4.29 × 10 6 . The governing equation were solveusing an open source software package, which has been validated against experimental data. Pressure Implicit withSplitting of Operator (PISO) algorithm is applied to solve the equation. The outcome of the simulation are variesdepending on the variables. Some show a decrease in drag while there are also that actually increase the drag of thesystem. This are caused by the suction and blowing slots that effect the surrounding air flow whether it is reducingor increasing the wake size downstream of the body. The result shows the momentum coefficient and location ofboth suction and blowing jet played an important role of manipulating the flow around the body and reducing thedrag. The velocity contours indicated that the key to drag reduction is by using 40 m/s jet velocity, placement ofsuction and blowing away from each other. &nbsp

Optimization of Co-Flow Jet Parameters for Ahmed Body Application

This study evaluates the drag reduction strategy of suction and blowing on idealize automotive vehicle,Ahmed Body. Optimization approach is adapted in order to analyse the effect of slot location, momentumcoefficient and slot angle on the vehicle which experiencing drag. Despite all the efforts that have been done toreduce the Ahmed body drag using various active flow control system, most of the drag reduction were only lessthan 15%. A 25° Ahmed body with build in co-flow jet is modelled using a CAD software. The flow around theAhmed body is simulated at Reynolds number based on length Re = 4.29 × 10 6 . The governing equation were solveusing an open source software package, which has been validated against experimental data. Pressure Implicit withSplitting of Operator (PISO) algorithm is applied to solve the equation. The outcome of the simulation are variesdepending on the variables. Some show a decrease in drag while there are also that actually increase the drag of thesystem. This are caused by the suction and blowing slots that effect the surrounding air flow whether it is reducingor increasing the wake size downstream of the body. The result shows the momentum coefficient and location ofboth suction and blowing jet played an important role of manipulating the flow around the body and reducing thedrag. The velocity contours indicated that the key to drag reduction is by using 40 m/s jet velocity, placement ofsuction and blowing away from each other. &nbsp

Wake modifications in confined flows due to the presence of a downstream cylinder in staggered arrangement

In the present study, confined flows around two square cylinders in staggered arrangement were numerically investigated. Cross-flow and streamwise center-to-center spacings of one- and three-cylinder diameters, respectively, were considered. Simulations were carried out at Reynolds numbers Re = 50,100,150 and 180, where the resulting wakes are laminar and periodic. Results indicate that the presence of the downstream cylinder tends to reduce the Strouhal number, amplitude and the time-averaged lift coefficient of the upstream cylinder relative to the single cylinder cases. Furthermore, the time variations of upstream cylinder’s lift coefficient behave similar to that of a single cylinder

Preliminary Design of a Mini Hydroelectric System

AbstractRenewable energy is a common topic that has been discussed continuously since the past few decades. The process of generating and restoring energy needs to be developed, without neglecting the effect towards the environment itself. As for this research, the basis is to verify a concept; whether the fluid motion in normal pipeline; is able to be utilized and converted into sufficient electrical output or not. In this concept, each time the user runs the taps, the water flow shall initiate the system by moving the inner mini blades and convert rotational motion to the shaft, which links to the DC generator. The changes from kinetic energy shall then be converted to electrical energy, which shall be preserved for later use. As a result, this system is able to provide an economical way to produce electrical energy without affecting the environment

Study on flow structure behind multiple circular cylinders in a tandem arrangement under the effect of magnetic field

The fast-moving technologies and the increasing rate of growth population indicates that the demand for energy will continue to be spiking and prominent in the discussion of the upcoming future. Therefore, to cater to the need for sustainable and clean energy, the idea of nuclear fusion is proposed and studied. Because the nuclear fusion reaction happens at a high temperature, the concept of magnetic field is adapted to the nuclear or plasma fusion reaction. The energy will be harnessed inside a blanket module of the fusion reaction plant. However, the presence of the magnetic field affects the fluid flow inside the blanket module where it reduces the heat transfer efficiency in the channel. This research examines the flow structure behind multiple bluff bodies arranged in tandem in a channel under the influence of a magnetic field with the aim to increase the heat transfer efficiency inside the channel. The effect of gap ratio, G/h=[1-2.4] and Hartmann friction parameter, H=[0-800], were analysed to determine the critical Reynolds number and Nusselt number. It was found that the presence of the downstream cylinder with gap ratios, G/h= 1.2, 1.4 and 1.6, causes the flow to be unsteady at a lower Reynolds number compared to those of a single cylinder. The multiple cylinders proved to increase the Nusselt number. Increasing the Hartmann friction parameter increases the critical Reynolds number and decreases the Nusselt number

Electrocardiographic ECG characteristics among Malaysian athletes

The electrocardiogram (ECG) is a graphic representation of the heart’s electrical activity. Although it has some limitations as a diagnostic or prognostic tool, it contains a wealth of information necessary for the proper care of a patient with a potential cardiovascular disease. Understanding the ECG changes among athletes would allow medical practitioners to distinguish between normal physiological adaptations and abnormal changes. However, there is limited data on the ECG characteristics among multi-ethnic athletes such as in Malaysia. This study aimed to determine the ECG characteristics and its associated factors among Malaysian national athletes. Malaysian national athletes annual preparticipation medical records were retrieved. Information on sociodemographic, sports and medical history including the 12-lead resting ECG tracings were extracted. ECG were assessed and categorised into normal, physiological adaptation changes, and abnormal ECG using the standardised ‘Seattle criteria’. Differences in ECG characteristics between genders, ethnic background, and type of sports was investigated. Additionally, factors associated with the ECG characteristics were assessed using multiple logistic regression. Majority of Malaysian national athletes had physiological adaptation ECG changes (61%). The most frequent changes were early repolarization, sinus bradycardia and isolated left ventricular hypertrophy. We found significantly higher prevalence of physiological adaptation changes among men (χ2 (2,371) = 18.9; p = 0.001) and athletes of Chinese ethnicity (both genders) (χ2 (2,356) = 13.8; p = 0.002). Factors associated with physiological ECG changes were men (OR=2.67; 95% CI= 1.68, 4.27; p<0.001) and Chinese ethnicity (OR=2.92; 95% CI=1.68, 4.27; p=0.039). Most athletes had physiological adaptation ECG changes which were significantly associated with male gender and Chinese ethnicity. This information would facilitate the development of a specific guideline in interpreting ECG among Malaysian athletes

Electrocardiographic (ECG) characteristics among Malaysian athletes

The electrocardiogram (ECG) is a graphic representation of the heart’s electrical activity. Although it has some limitations as a diagnostic or prognostic tool, it contains a wealth of information necessary for the proper care of a patient with a potential cardiovascular disease. Understanding the ECG changes among athletes would allow medical practitioners to distinguish between normal physiological adaptations and abnormal changes. However, there is limited data on the ECG characteristics among multi-ethnic athletes such as in Malaysia. This study aimed to determine the ECG characteristics and its associated factors among Malaysian national athletes. Malaysian national athletes annual pre-participation medical records were retrieved. Information on sociodemographic, sports and medical history including the 12-lead resting ECG tracings were extracted. ECG were assessed and categorised into normal, physiological adaptation changes, and abnormal ECG using the standardised ‘Seattle criteria’. Differences in ECG characteristics between genders, ethnic background, and type of sports was investigated. Additionally, factors associated with the ECG characteristics were assessed using multiple logistic regression. Majority of Malaysian national athletes had physiological adaptation ECG changes (61%). The most frequent changes were early repolarization, sinus bradycardia and isolated left ventricular hypertrophy. We found significantly higher prevalence of physiological adaptation changes among men (χ2(2,371) = 18.9; p = 0.001) and athletes of Chinese ethnicity (both genders) (χ2(2,356) = 13.8; p = 0.002). Factors associated with physiological ECG changes were men (OR=2.67; 95% CI= 1.68, 4.27; p<0.001) and Chinese ethnicity (OR=2.92; 95% CI=1.68, 4.27; p=0.039). Most athletes had physiological adaptation ECG changes which were significantly associated with male gender and Chinese ethnicity. This information would facilitate the development of a specific guideline in interpreting ECG among Malaysian athletes

Study on Magnetohydrodynamic flow past two circular cylinders in staggered arrangement

The fusion reactor is anticipated to be a new source of clean energy. Magnetohydrodynamic flow in the fusion blanket is expected to cause the flow to be highly stable, causing the heat transfer to be poor. Passive vortex promoter such as bluff body is one of the methods found to be has a great potential in optimizing the heat transfer. In this study, two circular cylinders in a staggered arrangement are introduced to promote vortices to enhance heat convection from a heated wall using an electrically conducting fluid under a constant magnetic field. The effect of the Hartmann friction parameter and the height differential onto the Nusselt number were examined. Modified Navier—Stokes equations known as SM82 were used using OpenFOAM to simulate the confined, quasi-two-dimensional, incompressible and laminar MHD flow past the bluff bodies. It was found that the heat transfer is better when the height differential is small