Analytical Modeling of Particle Interference in Micro-abrasive Jets

Two existing analytical models of particle interference in non-divergent particle jets were modified to include radial symmetry of the particle jet across the nozzle axis, inter-particle spacing, and more complex rebound geometry. Two novel experimental techniques for obtaining the particle spatial and velocity distributions across a micro-abrasive jet were then devised and rigorously tested. One of the above mentioned analytical models was then chosen to be further modified to include the above-mentioned modifications along with the effect of a divergent jet, the ability to simulate high flux cases, and experimentally obtained particle spatial and velocity distributions. All of the models were tested at various jet conditions. The results of the models were quantitatively compared to a previously developed computer simulation and were found to qualitatively agree with previous experimental observations. The modified models allow the critical flux below which inter-particle interference is likely to occur to be determined.

Analytical Modeling of Particle Interference in Micro-abrasive Jets

Two existing analytical models of particle interference in non-divergent particle jets were modified to include radial symmetry of the particle jet across the nozzle axis, inter-particle spacing, and more complex rebound geometry. Two novel experimental techniques for obtaining the particle spatial and velocity distributions across a micro-abrasive jet were then devised and rigorously tested. One of the above mentioned analytical models was then chosen to be further modified to include the above-mentioned modifications along with the effect of a divergent jet, the ability to simulate high flux cases, and experimentally obtained particle spatial and velocity distributions. All of the models were tested at various jet conditions. The results of the models were quantitatively compared to a previously developed computer simulation and were found to qualitatively agree with previous experimental observations. The modified models allow the critical flux below which inter-particle interference is likely to occur to be determined.

Influence of Nozzle Geometry on Fluid Flow Parameters

The article discusses ways for optimization of a standard nozzle cup design to achieve a narrower paint flow. The analysis of a standard nozzle cup shows that distribution of air pressure is critically uneven both along the nozzle axis and in the radial direction. A decrease in pressure is about 45% at the distance of 2 mm from the front surface of the nozzle cup. Air pressure decreases about 40% at the distance of 2 mm from the nozzle axis in the radial direction. Air velocity decreases about 52% at the distance of 4 mm from nozzle surface but then the velocity stabilizes and decreases is about 59% at the distance of 10 mm from the nozzle surface in comparison to its magnitude on the nozzle surface.Six extra holes and a circular rim were added to the standard nozzle cup to obtain paint stream as narrow as possible. Also was modified inner surface of the nuzzle cup. Totally, four different components were analysed. The results show that with increasing the nozzle cone by fifteen or more degrees, the pressure distribution decreases. Most optimal solution has six small holes around the nozzle hole and a small rim covering all holes. In this case, pressure decreases only 3% in the axial direction and 4% in the radial direction at the distance of 2 mm from the front surface of the nozzle. Distribution of air velocity is still significant but its magnitude is about 35% … 45% less than at the standard nozzle cup.

Five-Axis Extrusion-Based Additive Manufacturing of Silicone 3D Contour Nonwoven Fabrics

This study investigates the extrusion-based additive manufacturing (AM) of silicone 3D contour nonwoven fabrics by liquid rope coiling. Customized contour fabrics are ideal for wearable devices for individualized fit and comfort in contact. The AM using silicone liquid rope coiling can fabricate the porous and 3D contour nonwoven fabrics with enhanced breathability and comfortability. The key challenge in the proposed fabrication is the inability to generate consistent coiling pattern because the nozzle orientation deviates from the surface normal vector. A five-axis machine for silicone extrusion AM of nonwoven fabrics was developed to continuously align the nozzle orientation continuously with the surface normal vector. Three cases of silicone printing by coiling were investigated: 1) 3-axis printing, 2) 4-axis printing with nozzle axis normal to the tangent of the toolpath, and 3) 5-axis printing with nozzle axis parallel to the base surface normal. The coiling pattern and geometrical accuracy of the contour fabrics are studied. Results show that the 5-axis AM can generate the consistent coiling pattern and the desired contour geometry to fabricate the silicone 3D contour nonwoven fabrics.

Numerical simulation of the air flow field in the foreign fiber separator

The air flow field of a foreign fiber separator is simulated numerically. Effects of design parameters such as the nozzle diameter and entrance width of the noil box on the air velocity along nozzle axis, turbulence intensity, and jet deflection distance are studied. Larger nozzle diameters and larger entrance widths of the noil box are advantageous to the elimination of foreign fibers. The results provide a theoretical basis for the design of foreign fiber separators.

Control Forces in Rocket Nozzles Produced by a Secondary Gas Stream Inclined at Various Angles to the Nozzle Axis

The side force produced by the injection of secondary gas into the supersonic regime of a main nozzle is investigated with particular reference to the effect of the angle between the secondary jet and the main nozzle axis. In the experiments, downstream and upstream injection angles at one secondary port location in the main nozzle were examined. It is shown that there is a definite advantage to be gained by injecting the secondary gas in an upstream direction. An analytical analysis of the results indicates that for moderate secondary mass flows maximum side force is produced when the angle between the axis of the secondary port and the normal to the axis of the main nozzle is in the range 40-50°. When injecting a given secondary mass flow at the angle for maximum side force the axial thrust augmentation is almost zero. As the angle of injection is reduced from upstream values to downstream values the side force reduces and the thrust augmentation increases, indicating that thrust augmentation can be used to determine how effectively a given mass flow of secondary fluid is being utilized in the production of side force.

Normal Shock Wave Phenomena in a Convergent-Divergent Nozzle

SummaryIn recent years, aerodynamics and thermodynamics have found common ground in the specialised field of gas dynamics. Developments in this subject have led to a much more complete and widespread knowledge of subsonic, sonic and supersonic flow of gases in the conventional type of convergent-divergent nozzle. When the back pressure is raised above the value against which the nozzle is designed to discharge, oblique and then normal shock waves are set up in the divergent cone at a position along the nozzle axis determined by the magnitude of that back pressure. The gas which has crossed the shock wave is subjected to a process of subsonic compression.In this paper a theoretical investigation is made of the changes in pressure, temperature, density and Mach number which occur across a normal shock wave, when the position of the wave varies along the nozzle axis. The investigation illustrates the effect of change of medium, for which the relevant property is the ratio of specific heats. This ratio for certain polyatomic gases may approach unity (e.g. for Dichlorodifluoromethane CCl2F2, in gaseous form, γ=1·06), and for the inert monatomic gases γ= 1·667. The analysis is made non-dimensional by expressing such quantities as gas pressure, temperature, and density at any given position along the nozzle axis relative to the values of the particular parameter at entry to the convergent section.