The Effect Of Tangential Velocity Component In Abrasive Jet Micro-Machining Of Borosilicate Glass

Generally two types of erosion testers are used in solid particle erosion testing: air blast erosion testers and mechanically powered erosion testers. In the first portion of this thesis, the feasibility of implementing a mechanically powered erosion tester for abrasive jet micro-machining applications using very small particles was studied. It was found that, due to the ultrahigh vacuum requirement, such a device would not be practical. Therefore, in the second part of the thesis, the designed rotary mechanism was utilized as a rotary disc target holder apparatus and blasted with a typical air blast system. The apparatus could add or deduct a tangential velocity component into the system, allowing for detailed studies of the effect that the tangential velocity component has on the erosion of borosilicate glass using 25-150 μm aluminum oxide particles. Although the tangential velocity effect has been ignored for brittle materials by most researchers, the present results show that it can have an important role in erosion rate.Generally two types of erosion testers are used in solid particle erosion testing: air blast erosion testers and mechanically powered erosion testers. In the first portion of this thesis, the feasibility of implementing a mechanically powered erosion tester for abrasive jet micro-machining applications using very small particles was studied. It was found that, due to the ultrahigh vacuum requirement, such a device would not be practical. Therefore, in the second part of the thesis, the designed rotary mechanism was utilized as a rotary disc target holder apparatus and blasted with a typical air blast system. The apparatus could add or deduct a tangential velocity component into the system, allowing for detailed studies of the effect that the tangential velocity component has on the erosion of borosilicate glass using 25-150 μm aluminum oxide particles. Although the tangential velocity effect has been ignored for brittle materials by most researchers, the present results show that it can have an important role in erosion rate.

The Effect Of Tangential Velocity Component In Abrasive Jet Micro-Machining Of Borosilicate Glass

Generally two types of erosion testers are used in solid particle erosion testing: air blast erosion testers and mechanically powered erosion testers. In the first portion of this thesis, the feasibility of implementing a mechanically powered erosion tester for abrasive jet micro-machining applications using very small particles was studied. It was found that, due to the ultrahigh vacuum requirement, such a device would not be practical. Therefore, in the second part of the thesis, the designed rotary mechanism was utilized as a rotary disc target holder apparatus and blasted with a typical air blast system. The apparatus could add or deduct a tangential velocity component into the system, allowing for detailed studies of the effect that the tangential velocity component has on the erosion of borosilicate glass using 25-150 μm aluminum oxide particles. Although the tangential velocity effect has been ignored for brittle materials by most researchers, the present results show that it can have an important role in erosion rate.Generally two types of erosion testers are used in solid particle erosion testing: air blast erosion testers and mechanically powered erosion testers. In the first portion of this thesis, the feasibility of implementing a mechanically powered erosion tester for abrasive jet micro-machining applications using very small particles was studied. It was found that, due to the ultrahigh vacuum requirement, such a device would not be practical. Therefore, in the second part of the thesis, the designed rotary mechanism was utilized as a rotary disc target holder apparatus and blasted with a typical air blast system. The apparatus could add or deduct a tangential velocity component into the system, allowing for detailed studies of the effect that the tangential velocity component has on the erosion of borosilicate glass using 25-150 μm aluminum oxide particles. Although the tangential velocity effect has been ignored for brittle materials by most researchers, the present results show that it can have an important role in erosion rate.

New Design Method for Spiral Casings Considering the Properties of the Impeller and Spiral Casing at Design and Off-Design Conditions and Numerical Verification With CFD

Radial fans for industrial applications are very commonly operated with a spiral casing, also called volute. The function of the volute is to collect the air from the impellers outlet and to transport it to the fans outlet. In the volute the tangential velocity component of the impeller is transformed in a straight velocity component at the volute’s outlet. In the volute the static pressure is increased according to the cross sectional area of the volute. When the flow exits the impeller the flow rate is given basically by the radial velocity component times the outlet area of the impeller. In the volute, however, the flow rate is basically given by the tangential velocity component at the impeller exit and in the volute considering the conservation of angular momentum. Hence, there is only one operating point, i.e. the design point of the volute, where the flow rate in the impeller matches the flow rate in the volute. In the literature the design of the volute is performed at the design point only and the cross sectional area of the volute is usually computed distributing the flow rate linearly from the tongue to the exit of the volute. In this work an extended theoretical approach was developed considering the design point flow rate and off design flow rates. At the design point, the properties of the specific impeller, i.e. it’s radial and its tangential velocity components at the impeller’s exit are considered to design the volute. Furthermore, also the off-design characteristics of the impeller, i.e. its radial and tangential velocity components are considered in the design process of the volute. The flow rates in the impeller and in the volute match only at the design point, at off-design points the flow rates in the impeller and in the volute are different. This has an important impact on the design process of impeller – volute units. Each volute has also to be matched to the specific impeller. In the numerical part a usual volute was designed considering the properties of a particular impeller. The performance of the volute and of complete fan was investigated with the commercial Navier–Stokes Solver ANSYS CFX. A detailed analysis of the results and the flow conditions in volute as well as in the impeller-volute unit and a comparison with the results predicted by the new volute theory is given.

COMPUTATIONAL STUDY OF CYCLONE FLOW FLUID DYNAMICS USING A DIFFERENT INLET SECTION ANGLE

The conventional design of the cyclone model has been used without significant modifications for about a century. Recently, some studies were carried out to improve equipment performance by evaluating the geometric influence of the tangential inlet section and scroll inlet duct design. In this work, the influence of cyclone inlet section geometry was studied using an angle of 45 degrees in relation to the cyclone body. The study was conducted for the gas and gas-particle phases, based on an experimental study available in the literature, where a conventional inlet section was used. Numerical experiments were carried out with the CFX computational code. The fluid dynamics profiles and tangential velocity component were evaluated for three inlet velocities (2.75, 7.75 and 15.2 m/s) using the Reynolds Stress model. The results showed that this proposal is useful for improving the cyclone performance.

Performance of a Trapped Vortex Spray Combustor

The performance of a liquid-fueled trapped vortex (TV) combustor is analyzed both experimentally and computationally. The TV cavity, formed between a forebody and an afterbody, is placed coaxially inside a combustor shell. Fuel and primary air are injected from the inside face of the afterbody. The flame holding capability of this trapped vortex configuration is evaluated for different primary equivalence ratios. Very low overall lean-blow-out (LBO) equivalence ratios are obtained for the TV combustor over a wide range of annular and primary airflow rates. It is found that by injecting the primary air with a tangential velocity component the circumferential mixing is improved without disrupting the vortex trapped in the cavity. The performance of the TV combustor is also evaluated through emissions measurements at the exit of the combustor and temperature distribution inside the cavity. Numerical simulations are performed for the TV configuration with a k-ε turbulence model coupled with a PDF combustion chemistry model for simulating liquid spray combustion. The predicted results are in reasonable agreement with the measurements and provide an assessment of the flow distribution in the cavity region.

Effect of wire separation on X-probe measurements in a turbulent flow

The effect of the separation between hot wires in a crossed wire or X-probe on Reynolds stress measurements has been studied analytically and experimentally. Wyn-gaard's (1968) spectral analysis, which assumes isotropic turbulence, has been modified to include the effect of the tangential velocity component and possible asymmetries of the probe. The relaxation of the assumption of isotropy to one of homogeneity allows corrections to be made to Reynolds stress measurements obtained when the separation between the wires is in the spanwise direction. Measurements with two inclined hot wires in the central region of a fully developed turbulent channel flow provide reasonable support for the modified analysis. In the anisotropic wall region, the measurements provide reasonable support for the correction ratios which have been derived by assuming that turbulence is homogeneous in a plane parallel to the wall.

Water Quality Effects on Cavitation Inception in a Trailing Vortex

Tip vortex cavitation studies were made with a hydrofoil that was elliptical in planform, with an aspect ratio of 3, and having a modified NACA 662-415 profile. LDV measurements of the tangential velocity component in the vortex were used to determine that the minimum pressure in the vortex varies with lift coefficient squared, i.e., that the incipient cavitation number σi should follow a Cl2 relation (σi ≈ Cl2). This is in contradiction to previous observations (Arndt et al. 1991) that the tip vortex cavitation index varied approximately with lift coefficient to the power 1.4. By carefully monitoring the tensile strength of the water, i.e., its susceptibility to cavitation, the discrepancy was traced to the capability of the test water to sustain a tensile stress. Cavitation in “weak” water (no tensile strength) does follow the Cl2 relationship, whereas observations in “strong” water (rupture considerably below vapor pressure) more closely followed the previously observed variation, i.e., σi ≈ Cl1.4. Since the structure of the vortex cannot be affected by changes in the water quality, the discrepancy can be explained only by the amount of tension that can be sustained by the test water before inception occurs. Apparently a relatively larger value of tension can be sustained in the vortex is the strength of the vortex is increased (i.e., increasing Cl). This would explain the observed deviation from the expected Cl2 law for water with measurable tensile strength.

A Study on Unstable S-Shape Characteristic Curves of Pump Turbines at No-Flow

A small model of a Francis-type pump turbine was tested without the rotating shroud and the radial distribution of pressure in the rotor was measured using pressure taps on the stationary shroud. The mean tangential velocity component in the rotor was measured with a laser velocimeter, and the flow pattern was visualized using a camera which rotated with the rotor. Comparing data at the no-flow condition in the turbine mode with those in the pump mode, the effect of semi-open spaces at the inlet and at the exit of blade rows on the difference of pressure rise between the two modes was recognized, and the flow patterns and the distributions of tangential velocity component in these zones were utilized to understand the phenomena. Furthermore, some discussion is included on the relationship between the design head coefficient in the turbine mode and the S-shape characteristics.

Wechselwirkung kondensierter Molekularstrahlen mit festen Oberflächen

The reflection of a beam of nitrogen clusters from a polished stainless steel surface is investigated. The scattered flux shows a strong maximum at an angle of reflection almost 90°, independent of angle of incidence. The mean velocity of the reflected beam is about equal to the tangential velocity component of the incident beam. Measurements with increased background pressure demonstrate that the reflected beam still consists essentially of clusters.