Papers by Keyword: Cavity

Abstract: In this study, the experimental measurement of the pressure distribution in a cylindrical die cavity for squeeze casting of magnesium alloy AM50A was carried out. Piezo-electric quartz pressure transducers were integrated into a die cavity for real-time pressure measurements. The experimental results revealed that local cavity pressures at various locations changed with time in the duration of squeeze casting solidification and cooling. The pressure transfer rate varied considerably within the casting geometry. The distribution of local cavity pressures was inhomogeneous in the cavity.

Abstract: One of the important phenomena which is important in equipment when they are under high voltage stress is Partial discharge (PD). Partial discharge measurement is commonly used to evaluate the performance of the insulation in high voltage system. Modeling of the discharge in insulation can give a better understanding of this important phenomenon. A cavity within a dielectric material is a highly stressed area and the ideal place for starting partial discharge and breakdown. The applied voltage is one of the important factors that PD activity is influenced by that. Previous studies have considered the behavior of PD activity in a spherical cavity at 50Hz of sinusoidal applied voltage. However, still not so much work on the simulation of the PD activity in the cavity under different condition. Also, there is little data are available on the effect of parameters on the PD activity. This paper describes the behavior of PD activity as a function of applied voltage in a cylindrical cavity within a homogeneous dielectric. COMSOL and MATLAB software were used to carry out the simulation based on the finite element method (FEM). The number of PDs per cycle changed with different applied voltage so the highest number of PD at 20kV and the lowest value at 8kV. The maximum PD magnitude is raised from 1200pC at 8kV to 2400pC at 20kV applied voltage. The number of PD is most prevalent for sinusoidal followed by triangular waveform and then sawtooth. Comparison of the simulation results and experimental results are in good agreement. The result can help the researcher to understand more about the characteristics and behavior of partial discharge. Which may help the insulation diagnostic testing or condition monitoring.

Abstract: Molecular imprinting is a technique to produce a polymer called as molecularly imprinted polymer (MIP) that provides cavities to form a particular space generated by removing the template when the polymer has been formed. It will recognize a target that has the shape and physico-chemical properties similar or identical with those of template molecule. In this study, MIPs using atrazine as template have been made via the cooling-heating method. Initially the pre-polymer solution was cooled at a refrigerator for 1 h. Next, the polymerization was carried out at 70 °C for heating times of 90, 120, and 150 min. without nitrogen flow which is generally done for polymerization process. Characterizations were performed by employing a reversed-phase high performance liquid chromatograph (HPLC) and scanning electron microscope (SEM). From Scatchard plots, it was found that the equilibrium dissociation constant K_D and the apparent maximum number of binding sites B_max, which are written as (K_D, B_max), are (4.69 μM, 9.87 mmol/g), (4.54 μM, 9.56 mmol/g) and (3.52 μM, 7.44 mmol/g) for the heating times of 150, 120, and 90 min., respectively. This is verified by their SEM images showing that the broadest pore size distribution with the highest number of pores is in the MIP prepared under the heating time of 150 min. The MIPs therefore could be applied as an atrazine sensor and the MIP prepared under the heating time of 150 min. would give its best characteristics compared to the others.

Abstract: Distributions of the electrode information within cavities are much more complex than simulation results. In this paper, a novel set of experiments scanning real potential variations inside cavities under current control were employed to characterize local electrochemical information. Wide variation-fluctuations of electrode potentials have been experimentally revealed. Furthermore, combined with the theoretical analysis and measurement results, kinetic parameters range inside cavities can be indirectly derived.

Abstract: The effect of the cavity design parameters on the integrated performance parameter net thrust of hypersonic vehicle was investigated by computer numerical simulation methods in this paper. The cavity design parameters include position value XL and length-to-depth ratio L/D. The research purpose of the paper is to develop ideas for the integrated design of hypersonic vehicle. The studied results show that the effect curve charts of the ratio L/D on net thrust are similar at variable cavity positions. The extreme value of net thrust is obtained at some value of L/D. The fuel mixture touch underside step of the combustor easily to cause eddy loss which make against combustion and lead to net thrust descend while the cavity locates down step in the combustor. While the position of cavity on more combustor back, the combustion process is not built completely and the gas is exhausted quickly, which induces the more net thrust loss.

Abstract: To explore the noise suppression effect of mesh on cavity, the wind tunnel experiment is carried out based on the analysis of clean cavity flow characteristics. The meshes are arranged both in the cavity and at the leading edge of the cavity. Through the analysis of pressure distribution on the cavity bottom and the noise spectrum monitored at front and rear walls respectively, noise suppression effects of mesh programs relative to the clean cavity and changes in the flow field are studied, the results show that the mesh inside the cavity has a better noise reduction effect. The work in this paper provides an effective way for cavity noise reduction.

Abstract: Super plastic behavior of the commonly as-extruded Mg-3Zn-1Al (ZA31) magnesium alloy is investigated at temperatures ranging from 593 to 623K and strain rates ranging from 8×10^-5 to 10^-3s^-1. The results show that the alloy exhibits excellent super plasticity and the maximum elongation-to-failure reaches 220.4%. The alloy also shows a high strain rate sensitivity exponent of 0.38. Microstructure observations suggest that grain boundary sliding (GBS) with cavity coordination makes a substantial contribution to the super plastic deformation.

Abstract: This investigation is concerned with the elastohydrodynamic lubrication of the piston skirt / cylinder link of an internal combustion engine. In such compliant structures, the thickness of the lubricant film depends not only on the elastic deformation elements of the mechanism but also on their profiles. We have developed a computer program to study the effect of the profile of the piston skirt on the lubricant film. This program is based on a two-dimensional description of the lubricant film flow and a three-dimensional deformation of solids. The Reynolds equation defines the behavior of hydrodynamic film of oil in the liaison piston skirt / cylinder, and the equations of static and elastic equilibrium quantify the behavior of the structure. These Equations are solved numerically by using the finite differences method.

Abstract: The microstructures and properties of 2024 aeronautical aluminum alloy subjected to thermal cycling were investigated in simulated Low Earth Orbit space environment. The experimental results demonstrate that the microhardness of aluminum alloys changed with the increasing of thermal cycles. The results of X-ray diffraction (XRD) and transmission electron microscopy (TEM) show that the property changes of the 2024 aluminum alloys during the thermal cycling period are closely related to the microstructural evolution. The relationship between the microstructural evolution and the thermal fatigue was also discussed.

Abstract: Experimental study of an integrated aerodynamic-ramp-injector /gas-portfire (aero-ramp/G-P) has been conducted in a hydrogen-fueled scramjet combustor. The aero-ramp injectors consisted of four flush-walled holes, arranged to induce vorticular motion and enhance mixing. For comparison, a recessed cavity with four low downstream-angled circular injector holes was also examined. The combustor models were investigated experimentally using the scramjet direct connected test facility at the Beihang University. The facility can deliver a continuous supersonic flow of Mach number 2 with a total temperature of 1200K. The hot experimental results showed that the combustion efficiency and air specific impulse of aero-ramp/G-P are 85% and 35s while the corresponding values of cavity are 92% and 34s. These results justify the feasibility of aero-ramp/G-P flame holder.