Wedge-shaped Air Research Articles

Static breakdown threshold modeling of quasi-uniform gas gaps with a focus on the PDIV of contacting enameled wire pairs

This paper provides a theoretical and conceptual framework for the determination of static breakdown inception thresholds in quasi-uniform gas gaps bounded by dielectric layers of thickness s and relative permittivity . The special case of uncoated metallic electrodes is included in the limit . Moreover, a review of breakdown mechanisms and the underlying physical processes in quasi-uniform gas gaps is provided, and the applicability of the associated breakdown criteria is discussed. The results include a parametrization of the partial discharge inception voltage of wedge-shaped air gaps at atmospheric pressure as a function of the reduced coating thickness . The predicted results for this prototypical insulation geometry agree well with a broad array of literature data and own measurements. Finally, a physically motivated parametrization of the ionization threshold K(d) is suggested for atmospheric pressure air in terms of secondary electron feedback by energetic photons and ion-enhanced field emission. This contrasts with the ad hoc introduction of modified ‘streamer constants’ often found in literature to explain breakdown voltages that deviate from the predictions of the classical Raether–Meek–Loeb criterion.

Performance analysis of a stand-alone thermal energy storage system based on CSM plates filled with phase change material

In this study, experimental investigations on a Phase Change Material (PCM) based thermal energy storage system (TES) were carried out. The TES system was designed and tested as a first step of developing a potential TES product which can be integrated with commercially available ventilation system (VEX308) to provide cold intake air for space cooling applications. The system consisted of wedge-shaped air flow regions before and after an array of Compact Storage Module (CSM) plates filled with PCM and arranged vertically with air gaps between the plates. Two design configurations of the TES system were investigated based on air gap size between PCM plates (1.5 mm and 3 mm) in order to compare them for pressure loss through the system and thermal performance of the PCM storage. Investigations were done at two air flow rates of 400 m3/h and 800 m3/h which were within the working range of VEX308 for fixed air inlet temperatures of 27 °C and 13 °C for heating and cooling cycles of the PCM storage, respectively. The temperatures ranges were chosen to investigate the application of the TES system during summer season in Denmark. Parameters investigated were: pressure loss through the TES system, pressure distribution from top to bottom in the TES system before and after the PCM stack, temperature distribution in the TES system from top to bottom, and melting and solidification rates of the PCM. Results showed that pressure drop through the system, for both configurations, was well within the desired limits (<180Pa) for a successful integration of the TES system with VEX308. Temperature distribution was relatively fair from top to bottom of the PCM stack indicating an adequate inlet manifold design. The 1.5 mm gap configuration (55 CSM plates and 110 kg PCM) showed faster heating and cooling rates at both flow rates as compared to 3 mm system (50 CSM plates and 100 kg PCM). Both systems showed almost same system efficiency (78.3%) for the utilization of the PCM. The 1.5 mm system provided approximately 8.7% more energy storage potential than the 3 mm system because of the presence of 10 kg of extra PCM.

Air curtain dust-collecting technology: Influence factors for air curtain performance

Air curtains are extensively used to isolate and control dust, heat, and smoke. Because of the high airflow velocity, columnar air curtains have several shortcomings, such as the nonuniform distribution of air, deviation from the axis, and the lack of a basis for determining the volume of the air curtain unit. Existing research cannot systematically explain the factors that directly influence these shortcomings. Therefore, this study employed a single factor design for investigating the effects of the spacing between guide vanes in the air curtain unit, cross sectionof the air curtain unit, and angle of the guide vanes on the air curtain uniformity, deviation, and volume of the air curtain unit, as well as the jet attenuation. The results show that the guide vanes can be used for shunting and diverting the airflow mechanically, the guide vanes with smaller spacing exhibit considerable mechanical diversion, which can lead the air flow out of the supply air slot in a timely manner, as well as reduce the downstream air flow and the overall static pressure difference of the air curtain unit to maintain a uniform air velocity. The cross section of the air curtain unit influences the uniformity of the air curtain. A wedge-shaped air curtain unit can ensure that the velocity of the internal airflow remains constant when the flow of air in the duct decreases gradually. This causes a drastic decrease in the pressure gradient in the air curtain unit, and an improvement in the overall uniformity of the air curtain unit. The deflection of the air curtain is affected directed by the angle of the guide vane, and the deflection is determined by the combined velocity direction of the mechanical deflection due to the guide vane and the non-mechanical air flow driven by the static pressure. The angle between the inside and outside of the symmetrically installed guide vane is 136°, and a jet of air curtain with a small inclination (≤8°) can be formed. The attenuation law of the air curtain jet may be approximately represented by a new correlation, and helps in the selection of air curtain velocity and range in different industrial applications.

Back-propagation suppression study based on intake configuration optimization for an air-breathing pulse detonation engine

In order to reduce the back-propagation of an air-breathing pulse detonation engine efficiently, a suppression method based on the optimization of the intake configuration with wedge-shaped angle and blockage ratio was proposed and studied in this paper. The 2-D numerical simulation based on propane/air combustible mixture was carried out to study the configuration, wedge-shaped angle and the blockage ratio effects of the air intake segment on the back-propagation in the air-breathing pulse detonation engine. The reliability of the numerical simulation was verified with the experimental results. The simulation results indicated that the wedge-shaped configuration was the most efficient geometry for back-propagation suppression in this paper. The back-propagation suppression performance in the case of wedge-shaped angle of 30° was better than that of wedge-shaped angle of 45° and 60°. In addition, based on the wedge-shaped air intake segment with a wedge-shaped angle of 30°, the back-propagation intensity and the arrival range of the burnt gas both decreased accordingly at the increased blockage ratio. When the blockage ratio was 0.8, the burnt gas could not flow into the inlet. In order to achieve the optimal performance of back-propagation suppression, the configuration and the blockage ratio of the air intake segment should both be optimized further according to the characteristics of the back-propagation pressure.

Effect of the Abdominal Aortic and Junctional Tourniquet on chest compressions in a swine model of ventricular fibrillation.

Mortality for out-of-hospital cardiac arrest is high when traditional chest compressions are used without adjuncts. The abdominal aortic and junctional tourniquet (AAJT) is a device with a wedge-shaped air bladder that occludes the aortic bifurcation, augmenting blood flow to the heart and brain. Previously, the addition of AAJT during chest compression led to an increase in rate of survival in a model of traumatic cardiac arrest. This study was designed to determine if application of the AAJT would lead to more effective chest compressions as measured by improved hemodynamic parameters and an increased rate of return of spontaneous circulation (ROSC). Yorkshire swine (n=6 per group) underwent general anesthesia and instrumentation. Ventricular fibrillation (Vfib) was electrically induced and animals were allocated into groups with or without the AAJT. The AAJT was inflated if selected after four minutes of compressions. Following a total of ten minutes of compressions, the animals entered into a ten-minute advanced cardiac life support phase. Hemodynamics and blood gas measurements were compared between groups. ROSC or cardioversion from Vfib was not achieved in either group. The AAJT group had improved hemodynamic parameters with significantly higher carotid diastolic pressure and higher blood flow in the carotid artery (p=0.016 and 0.028 respectively). However, no significant differences were observed with coronary perfusion pressure or end tidal CO2. The AAJT did not confer a survival advantage during chest compressions, but hemodynamic improvements were observed while the AAJT was in place.

Abstract 268: Evaluation of the Abdominal Aortic and Junctional Tourniquet as an Adjunct to Chest Compressions in a Swine Model of Out-Of-Hospital Cardiac Arrest

Introduction: Overall success in treating out-of-hospital cardiac arrest using traditional chest compressions is low. The abdominal aortic and junctional tourniquet (AAJT) is a device with a wedge-shaped air bladder that can be used to occlude the descending aorta at the level of bifurcation. In addition to shunting blood away from the lower extremities, this device may increase pleural pressures by inhibiting movement of the diaphragm during compressions. We have previously shown that the addition of an AAJT to mechanical chest compression leads to an increase in rate of survival in a model of traumatic cardiac arrest. Hypothesis: This study was designed to determine if application of the AAJT would lead to more effective chest compressions as measured by an increased rate of return of spontaneous circulation (ROSC) and hemodynamic parameters. Methods: Yorkshire swine (n=6 per group) underwent general anesthesia and instrumentation. Ventricular fibrillation was electrically induced using spinal needles placed in contact with the left ventricle. After eight minutes of arrest, chest compressions were initiated. Animals were then allocated into groups with or without the AAJT. Following a total of ten minutes of compressions, the animals entered into a ten-minute advanced cardiac life support phase. Results: A ROSC was not achieved in either group. No significant differences were observed with coronary perfusion pressure or end tidal CO 2 . However, the AAJT group had a significantly higher carotid diastolic pressure and higher blood flow in the carotid as compared with repeated-measures ANOVA (p = 0.016 and 0.028 respectively). Conclusion: The AAJT did not confer a survival advantage during chest compressions in our swine model of cardiac arrest. However, while the AAJT was in place, improvement was observed in some measures of CPR efficacy. Disclaimer: The views expressed are those of the authors and do not reflect the official views or policy of the Department of Defense or its Components. The experiments reported herein were conducted according to the principles set forth in the National Institute of Health Publication No. 80-23, Guide for the Care and Use of Laboratory Animals and the Animal Welfare Act of 1966, as amended.

Research on Taylor Vortices in the Wedge-Shaped Air Gap of Evaporation Cooling Turbo Generator

Cooling technique is one of the most important parts to improve the development of turbo generator. Turbo generator with evaporative cooling stator and water cooling rotor possesses many excellent qualities for mid unit. In this system the stator bars and core are immerged in evaporative coolant, which could be cooled fully. The rotor bars are cooled by water inner cooling mode. In this paper, we describe the Taylor Vortices in the Wedge-shaped air gap of Evaporation cooling Turbo Generator and present the research on gas-flow and heat-transfer with different features in the turbo generator. The CFD method is used to analyze this system, which has different features, including gap size, rotating speed, Apex angle. And the heat-transfer calculation proves the axial direction gas-flow can do well to the rotator heat-emitting.

Estimation of partial discharge inception voltage of magnet wires under inverter surge voltage by volume-time theory

This paper discusses a novel estimation method for partial discharge inception voltage (PDIV) of magnet wire under inverter surge voltage application. We focused on the generation probability of initial electrons, which induce PD under high electric field and short rise time of surge voltage, by means of Volume-Time theory. We applied the Volume-Time theory to PD inception phenomena in a wedge-shaped air gap of twisted pair samples composed of enameled wires, and estimated PDIV in consideration of initial electron generation probability with temporal and spatial change in electric field distribution. We could estimate PDIV under different waveforms of applied surge voltage for different specifications of enameled wires. PDIV estimated by the extended Volume-Time theory agreed well with the measured PDIV. The estimated PDIV decreased with the increase in the rise time of applied voltage waveform, which corresponded to the V-t characteristics in the time range of inverter surge voltage.

Colloid Transport and Retention in Unsaturated Porous Media: Effect of Colloid Input Concentration

Colloids play an important role in facilitating transport of adsorbed contaminants in soils. Recent studies showed that under saturated conditions colloid retention was a function of its concentration. It is unknown if this is the case under unsaturated conditions. In this study, the effect of colloid concentration on colloid retention was investigated in unsaturated columns by increasing concentrations of colloid influents with varying ionic strength. Colloid retention was observed in situ by bright field microscopy and quantified by measuring colloid breakthrough curves. In our unsaturated experiments, greater input concentrations resulted in increased colloid retention at ionic strength above 0.1 mM, but not in deionized water (i.e., 0 mM ionic strength). Bright field microscope images showed that colloid retention mainly occurred at the solid-water interface and wedge-shaped air-water-solid interfaces, whereas the retention at the grain-grain contacts was minor. Some colloids at the air-water-solid interfaces were rotating and oscillating and thus trapped. Computational hydrodynamic simulation confirmed that the wedge-shaped air-water-solid interface could form a "hydrodynamic trap" by retaining colloids in its low velocity vortices. Direct visualization also revealed that colloids once retained acted as new retention sites for other suspended colloids at ionic strength greater than 0.1 mM and thereby could explain the greater retention with increased input concentrations. Derjaguin-Landau-Verwey-Overbeek (DLVO) energy calculations support this concept. Finally, the results of unsaturated experiments were in agreement with limited saturated experiments under otherwise the same conditions.

A simple demonstration of frustrated total internal reflection

We describe a quantitative and inexpensive method of demonstrating frustrated total internal reflection based on the attenuation of a laser beam through a wedge-shaped air gap between two glass prisms. An advantage of this method is that the thickness of the air gap can be determined by observing interference effects with only a slight modification of the setup. The experiment avoids the need to employ high-precision translation stages as is often the case in standard demonstrations of frustrated total internal reflection.

Interferometric apodization of telescope apertures

Aims. We seek to produce apodized apertures for application in stellar coronagraphy to help in direct detections of exoplanets. We show that chromatic apodized apertures of any shape in transmission can be obtained with a specific MZI and we demonstrate this capability in two cases. Methods. The method takes advantage of the capabilities of the MZI, in which the two outputs correspond to the addition and subtraction of the two wave amplitudes in both arms. The result is obtained by re-imaging the entrance aperture of the telescope in the arms of the MZI where two complementary phase masks ± ϕ(x ,y ) are set. At the two outputs of the MZI, the re-imaged apertures interfere, and their transmissions are multiplied respectively by a factor of the form cos[ϕ(x ,y )] and i sin[ϕ(x ,y )]. They correspond to the apodized and anti-apodized complementary outputs. Results. We present the results obtained for two types of apodization. A 1D cosine apodization for a square aperture is obtained by introducing a thin wedge-shaped air film, slightly tilting one of the mirrors of the MZI. A 2D circular symmetric apodization of the form cos[x 2 + y 2 ] is obtained for a circular aperture using two complementary convergent and divergent lenses as phase masks. Aperture transmissions (in intensity) and corresponding point spread functions (PSFs) are given in each case and compared to the theoretical expectations. Conclusions. We have demonstrated the capability of the MZI to produce an apodized aperture. This result is obtained with no loss of photons, considering the fact that there are two complementary outputs. Considerations are given on the wavelength dependence of this technique.

A method for magnetic field determination inside magnetic fluids

The method is based on the phenomenon of levitation of a nonmagnetic spherical body immersed in a magnetic fluid situated in a magnetic field characterized by a vertical gradient oriented from top to bottom. This structure of the field has been obtained in a wedge-shaped air gap. Taking into account the levitation condition and the hyperbolic structure of the field, a theoretical formula for the z coordinate was used. The comparison between experimental and theoretical data allow to obtain the magnetic field intensity inside the magnetic fluids.

Model experiments on effectiveness of fracture plane control methods in blasting

Model experiments were carried out to demonstrate the effectiveness of two blasting methods for achieving fracture plane control. The methods used are the guide hole method utilizing a circular hole with notches and a charge holder method with two wedge-shaped air cavities. In these experiments, dynamic strains and the crack propagation velocity were measured by using strain gauges and velocity gauges, respectively. The dynamic behavior of cracks propagating along the control fracture plane was clarified by high-speed videography. The experimental results show that the two methods are effective in controlling the orientation of the fracture plane and in driving the controlled cracks to greater distances.

A214 レーザーシャドウグラフ法による爆破にともなう応力波の可視化観察

The stress wave propagation in blasting processes was observed by a shadowgraph method using a Q switched ruby laser as a light source. Model experiments were carried out with PMMA plates and electric detonators. In this report, the results of the following experiments for fracture control are presented. These include stress waves interacting with a circular hole, stress waves generated by a charge holder with two wedge-shaped air cavities and stress waves reflected at the free surface. It is shown from these experiments that utilization of the circular hole with notches and the charge holder is available for fracture control.

Discharges due to separation of a corona-charged insulating sheet from a grounded metal cylinder

An experimental study shows that when a corona-charged PMMA (polymethyl methacrylate) sheet, 0.5 mm thick, is separated from a grounded metal cylinder, discharges occur in the wedge-shaped air gap. These discharges serve as a model for discharges that occur between dielectric films and transferring rollers. Two modes of discharges are found: weak microdischarges and stronger major discharges. The microdischarges are very weak, consisting of small light spots, but it is possible to observe them through two cascaded image intensifiers. Charges are deposited on the PMMA sheet by the discharges; these charges are visualized by means of bipolar electrographic powder. The microdischarges occur at the position where the air gap length is approximately=100 mu m, and yield striped powder figures. The occurrence can be explained by means of the partial capacitance model and Paschen's law. At high electrification levels, both microdischarges and major discharges occur; the major discharges appear at longer gaps, since some part of the initial charge cannot be neutralized by the microdischarges. Powder figures of major discharges are tree-like with negative electrification, and round-moon-like with positive electrification. The major discharges with negative electrification are hazardous, since they yield large and clear tracks. >

STRUCTURE OF A COLD FRONT NEAR THE CENTER OF AN EXTRATROPICAL DEPRESSION

Hourly aerological soundings released at Bedford, Mass. in -4pril 1960, together with all :Lvailable convcntionnl synoptic observations, arc used for a detailed analysis of a cold front south of the center of :L northcnst~v-nrd-iiioving depression. It is shown that in this ease the dyii:imically important chmge from one air inas5 to another throughout the entire troposphere occurrcd several hours after the passage of R wcnk surface cold front. The major cooling over Bedford presented itself in a nearly vertical coliunn from about 500 in. :~IJOVC the ground to heights of around S kin., with the main decrease of temperatiire at the surface occurring during the following two hours. It is suggested that this case is not an esccptionnl one, but that it rather may reflect the typical structure of a strong cold air invasion near the center of a depression in which the horizontal ind componciit normal to the front increases with height. Under such conditions an analysis according to the classical Norwegian schcmc, with the wedge-shaped cold air iiinss, would be unrealistic.