Total Exit Research Articles

Numerical design study on a high-powered segmented-type arc plasma torch for a high-enthalpy supersonic plasma wind tunnel

As a high-powered plasma source to produce a specific enthalpy higher than 20 MJ/kg at an air flow rate of 50 g/s for a supersonic plasma wind tunnel, a segmented-type arc plasma torch with an input power level of MW class is characterized in this paper. For this purpose, a numerical parametric study was carried out to determine the main design parameters, such as, the constrictor length LC, the diameter of segmented disk DC, and the diameter of the electrode DE, under the requirements of specific enthalpy and air flow rate. From the results of the numerical study, firstly the plasma power and specific enthalpy are found to increase with increasing LC at the expense of the torch efficiency, which is defined as the ratio of the total exit enthalpy to the plasma power. On the other hand, an increase in DC is observed to improve the torch efficiency by reducing the plasma power at a fixed arc current and gas flow rate. Moreover, an increase in DE is also found to contribute to improvements in the torch efficiency and the specific enthalpy by expanding the high-temperature region of the arc plasma and decreasing plasma velocities at the torch exit. Accordingly, a scale up to MW class for obtaining a high specific enthalpy can be achieved efficiently by inserting segmented disks with relatively large diameters between enlarged electrodes and then increasing the arc currents. For example, if the length of a constrictor consisting of segmented disks with a diameter of DC = 25 mm is extended to LC = 900 mm and then the arc current is increased up to 800 A, it is predicted that a specific enthalpy of 21.2 MJ/kg can be achieved at a plasma power of 2.89 MW and an air flow rate of 50 g/s, which corresponds to a torch efficiency of 36.6%. Based on these numerical parametric study results, we expect that a segmented arc plasma torch can be designed to meet the requirements of a supersonic plasma wind tunnel, such as a specific enthalpy, air flow rate and plasma power.

Study of Staircase Design Effects on Evacuation in Architectural Plane Design

As the flat form of a return shape building for example, the effects of staircase design on evacuation in architectural plane design was studied using Pathfinder numerical simulation method. The staircase layout effects on evacuation time was the mainly research content. The results indicate that in addition to considering the distance between two adjacent stairs, the distribution of occupants in building plane is also an important factor which needs to be considered on the layout of staircase. The changes of staircase plane positions have a great impact on the total evacuation time in the case of the same total stair exit width. It is favored for evacuation when the evacuation time differences of staircase exits are small. The study results have some guidance on the plane design of staircases and evacuation.

Computing the Exit Complexity of Knowledge in Distributed Quantum Computers

Distributed Quantum computers abide from the exit complexity of the knowledge. The exit complexity is the accrue of the nodal information needed to clarify the total egress system with deference to a distinguished exit node. The core objective of this paper is to compile an arrogant methodology for assessing the exit complexity of the knowledge in distributed quantum computers. The proposed methodology is based on contouring the knowledge using the unlabeled binary trees, hence building an benchmarked and a computer based model. The proposed methodology dramatizes knowledge autocratically calculates the exit complexity. The methodology consists of several amphitheaters, starting with detecting the baron aspect of the tree of others entitled express knowledge and then measure the volume of information and the complexity of behavior destining from the bargain of information. Then calculate egress resulting from episodes that do not lead to the withdrawal of the information. In the end is calculated total egress complexity and then appraised total exit complexity of the system. Given the complexity of the operations within the Distributed Computing Quantity, this research addresses effective transactions that could affect the three-dimensional behavior of knowledge. The results materialized that the best affair where total exit complexity as minimal as possible is a picture of a binary tree is entitled at the rate of positive and negative cardinal points medium value. It could be argued that these cardinal points should not amass the upper bound apex or minimum.

Effect of Exit Spacing in a Multiple-Jet Nozzle on Noise Levels at Audible Frequencies

This work investigated the effect of exit spacing on audible noise levels generated by a multiple-jet nozzle, which replaces the single exit in a common nozzle with multiple smaller exits to reduce the risk of hearing damage. Sound measurements and 1/3-octave band analyses were performed for multiple-jet nozzles with varying exit diameters and exit spacings. Results show that the effect of exit spacing is evident below a certain frequency range, which falls in the relatively low frequency part of the sound spectrum. The frequency range affected by exit spacing was found to extend to higher frequencies if the exits were more closely distributed. It was found that decreasing the exit spacing will shift the sound spectrum toward the low frequency side, which has been shifted toward the high frequency side by the use of smaller exits, and will increase the sound pressure levels at lower frequencies. When the exits were confined in a limited area, to maintain a constant total exit area, decreasing the exit diameters will increase the number of exits and reduce the exit spacing. Smaller exit diameters will increase the sound frequency and shift the sound spectrum toward the high frequency side, while decreased exit spacing has the opposite effect of shifting the spectrum toward the low frequency side. Due to these two opposing effects, for a multiple-jet nozzle with a limited size, there is an optimum exit diameter that, depending on the method used to evaluate the overall sound pressure level, generates the lowest sound pressure levels in the audible frequency range. If there is no limit to its physical size, a multiple-jet nozzle should avoid using an exit spacing that is too small. The minimum exit spacing required to avoid the adverse effects of a small exit spacing requires more extensive studies.

Dose energy dependence in proton imaging

Abstract In the earliest works dedicated to proton radiography and proton computed tomography it was shown that the advantage of image creation using proton beams appears when the energy is chosen as small as possible, but enough to pass the object. This phenomenon is based on the great sensitivity of the energy flux of the proton beam in relation to the length and density of the object at the end of the proton range. However, this fact was proved experimentally only with thin detectors, such as photographic films, which detect only part of the exit energy of protons. Another method which is based on the measurement of total exit energy of protons contains two effects that act in opposite ways: the necessary irradiation dose increases when the energy of the proton is reduced. In this work, the dependence of the irradiation dose on proton initial energy was studied using analytical formulas and computer simulations. The investigation shows that the irradiation dose depends slightly on the proton energy beyond the region at the end of the proton range and increases sharply in it.

Disincentive Effects of Unemployment Insurance Benefits: Maximum Benefit Duration Versus Benefit Level

This paper uses a unique dataset about unemployment insurance recipients and their exits to employment in Estonia to investigate the effects of benefits on unemployment duration. The administrative data used clearly pinpoints total unemployment spells and exits to employment. Both nonparametric and parametric estimations show that unemployment benefits have a strong and significant disincentive effect on hazard rates to exit into employment, just as search theory predicts. The effects of benefits are stronger and more homogeneous when the maximum duration of unemployment insurance benefit is longer. Unemployed people eligible for shorter unemployment insurance benefits are influenced more by the size of benefits and changes in the benefit replacement rate. Also, for both groups there is a rise in hazard rates during the benefit period and a sharp drop straight after.

Natural convection heat transfer augmentation in a partially heated and partially cooled square cavity utilizing nanofluids

PurposeThe purpose of this paper is to investigate the behaviour of nanofluids numerically inside a partially heated and partially cooled square cavity to gain insight into heat transfer and flow processes induced by a nanofluid.Design/methodology/approachA model is developed to analyze the behaviour of nanofluids taking into account the solid volume fraction χ. The transport equations are solved numerically with finite volume approach using SIMPLEC algorithm.FindingsComparisons with previously published work on the basis of special cases are performed and found to be in excellent agreement. Five different relative positions of the active zones are considered.While circulation depend strongly on the total exit length. Governing parameters were 103 < Gr < 107 but due to space constraints the results for 104 < Gr <107 are presented. It is found that both the Grashof number and solid volume fraction χ affect the fluid flow and heat transfer in the cavity. CopperWater nanofluid is used with Pr = 6.2 and solid volume fraction is varied as 0, 4, 8, 12, 16 and 20 per cent. Detailed results are presented for flow pattern and heat transfer curves.Originality/valueThe present study focusses on the analysis of several parameters on the heat transfer characteristics of nanofluids within the enclosure.

Migration of Combustor Exit Profiles Through High Pressure Turbine Vanes

The high pressure turbine stage within gas turbine engines is exposed to combustor exit flows that are nonuniform in both stagnation pressure and temperature. These highly turbulent flows typically enter the first stage vanes with significant spatial gradients near the inner and outer diameter endwalls. These gradients can result in secondary flow development within the vane passage that is different than what classical secondary flow models predict. The heat transfer between the working fluid and the turbine vane surface and endwalls is directly related to the secondary flows. The goal of the current study was to examine the migration of different inlet radial temperature and pressure profiles through the high turbine vane of a modern turbine engine. The tests were performed using an inlet profile generator located in the Turbine Research Facility at the Air Force Research Laboratory. Comparisons of area-averaged radial exit profiles are reported as well as profiles at three vane pitch locations to document the circumferential variation in the profiles. The results show that the shape of the total pressure profile near the endwalls at the inlet of the vane can alter the redistribution of stagnation enthalpy through the airfoil passage significantly. Total pressure loss and exit flow angle variations are also examined for the different inlet profiles.

Effect of exit-port geometry on the performance of a flow distribution manifold

A significant issue of manifold design, not heretofore considered, is the geometric shape of the exit ports as a means for tailoring manifold performance. To investigate the efficacy of this strategy, three candidate exit-port geometries were considered: (a) an array of discrete slots, (b) an array of discrete circular apertures, and (c) a single, continuous longitudinal slot. In order to have a valid comparison of the impacts of these individual geometries, the total exit areas of all three were made identical. Numerical simulations of the turbulent flow within and exiting from these manifolds were performed using a turbulence model that had been previously established by comparison studies involving both simulations and experiments for situations related to that considered here. The numerical results indicated that the continuous single-slot geometry yielded the most uniform outflow from among those considered. With regard to practice the simplicity of manufacture of single-slot-equipped manifold has clear advantages.

On Using Multiple-Jet Nozzles to Suppress Industrial Jet Noise

This work investigates the efficacy of multiple-jet nozzles in reducing exposure to noise radiated from high-speed jet flows that are frequently used for cleaning and other purposes. A single-jet nozzle is replaced by one with multiple and smaller outlets with the same combined exit area. Noise generated by multiple-jet nozzles will shift to higher frequencies due to the smaller openings; thus, a portion of the sound energy is moved to the ultrasonic range and the audible noise levels will be reduced. In this study, nozzle outlet sizes of 2.2 mm, 2 mm, 1 mm, and 0.7 mm are tested at various flow rates. Results show that the noise-abating effect of using smaller outlets is significant. Although industrial jet flows, in general, have multiple noise-generating mechanisms, the multiple-jet approach is effective for flows ranging from the subsonic to the highly choked. Noise spectra show that the reduction of noise level in the audible range is related to frequency shifting. The comparison of overall sound pressure levels generated by 1-mm and 0.7-mm outlets shows that even a raise of frequency by 40% can have a notable effect. As for the concern that the multiple-jet nozzles may suffer a drop in thrust, as long as the total exit area is fixed, thrust loss generally is not serious. One potential hazard of the multiple-jet nozzle is that posed by noise at frequencies higher than 10 kHz or ultrasound. More investigations in this field are suggested.

A Comparison of Mirtazapine and Nortriptyline Following Two Consecutive Failed Medication Treatments for Depressed Outpatients: A STAR*D Report

Few controlled studies have addressed the issue of which antidepressant medications should be recommended for outpatients who have not responded to multiple treatment trials. This study compared the efficacy of switching to mirtazapine to that of switching to a tricyclic antidepressant (nortriptyline) following two prospective, consecutive, unsuccessful medication treatments for nonpsychotic major depressive disorder. Following lack of remission or an inability to tolerate an initial trial of citalopram for up to 12 weeks (first step) and a second trial with either monotherapy involving another antidepressant or augmentation of citalopram with bupropion or buspirone (second step), adult outpatients (N=235) with nonpsychotic major depressive disorder were randomly assigned to 14 weeks of treatment with mirtazapine (up to 60 mg/day) (N=114) or nortriptyline (up to 200 mg/day) (N=121). The primary outcome, symptom remission, was defined a priori as a total exit score of </=7 on the 17-item Hamilton Rating Scale for Depression. The 16-item Quick Inventory of Depressive Symptomatology-Self-Report (QIDS-SR(16)), obtained at treatment visits, provided secondary outcomes of remission (score </=5 at exit) and response (>/=50% reduction in score from baseline). For mirtazapine, remission rates were 12.3% and 8.0% per the Hamilton and QIDS-SR(16) scores, respectively. For nortriptyline, remission rates were 19.8% and 12.4%, respectively. QIDS-SR(16) response rates were 13.4% for mirtazapine and 16.5% for nortriptyline. Neither response nor remission rates statistically differed by treatment, nor did these two treatments differ in tolerability or adverse events. Switching to a third antidepressant monotherapy regimen after two consecutive unsuccessful antidepressant trials resulted in low remission rates (<20%) among patients with major depressive disorder.

A Comparison of Mirtazapine and Nortriptyline Following Two Consecutive Failed Medication Treatments for Depressed Outpatients: A STAR*D Report

Few controlled studies have addressed the issue of which antidepressant medications should be recommended for outpatients who have not responded to multiple treatment trials. This study compared the efficacy of switching to mirtazapine to that of switching to a tricyclic antidepressant (nortriptyline) following two prospective, consecutive, unsuccessful medication treatments for nonpsychotic major depressive disorder. Following lack of remission or an inability to tolerate an initial trial of citalopram for up to 12 weeks (first step) and a second trial with either monotherapy involving another antidepressant or augmentation of citalopram with bupropion or buspirone (second step), adult outpatients (N=235) with nonpsychotic major depressive disorder were randomly assigned to 14 weeks of treatment with mirtazapine (up to 60 mg/day) (N=114) or nortriptyline (up to 200 mg/day) (N=121). The primary outcome, symptom remission, was defined a priori as a total exit score of </=7 on the 17-item Hamilton Rating Scale for Depression. The 16-item Quick Inventory of Depressive Symptomatology-Self-Report (QIDS-SR(16)), obtained at treatment visits, provided secondary outcomes of remission (score </=5 at exit) and response (>/=50% reduction in score from baseline). For mirtazapine, remission rates were 12.3% and 8.0% per the Hamilton and QIDS-SR(16) scores, respectively. For nortriptyline, remission rates were 19.8% and 12.4%, respectively. QIDS-SR(16) response rates were 13.4% for mirtazapine and 16.5% for nortriptyline. Neither response nor remission rates statistically differed by treatment, nor did these two treatments differ in tolerability or adverse events. Switching to a third antidepressant monotherapy regimen after two consecutive unsuccessful antidepressant trials resulted in low remission rates (<20%) among patients with major depressive disorder.

Village Chicken Flock Dynamics and the Contribution of Chickens to Household Livelihoods in a Smallholder Farming Area in Zimbabwe

The development of successful production strategies for poultry rearing depends on an accurate description of village chicken production systems. In Rushinga District of Zimbabwe, participatory rural appraisals (PRAs) followed by checklists and intensive case studies were carried out in three villages. The role of chickens in the livelihoods of households was evaluated. Flock dynamics were monitored monthly for 24 months. Women who were resident on the farm headed 19% of the households. A household comprised 4.8 +/- 2.5 members with arable land of approximately 2.6 ha. In addition to chickens, households grew maize, cotton and sunflower and kept large animals. Flocks ranging from 1 to 50 village chickens per household were reared under a scavenging system of management with suboptimal housing, inadequate feeding and poor health care. The use of ethno-veterinary medicine was common in treating sick chickens. The largest flock sizes were observed in the hot-wet season. Over 90% of an average of 5.4 entries/household per month were from hatched chicks. Mortality claimed an average of 80% of the total exits. Chicken production potential (CPP), which defined the proportion of chickens that could be utilized by a household, averaged 50%. Chicken production efficiency (CPE) was approximately 15% of the CPP. Egg consumption patterns were low and similar across seasons.

Experimental study of a tunable fiber ring laser stability

We have experimentally studied the mid-term (1–1000 s) stability of a traveling-wave unidirectional Erbium-doped fiber (EDF) ring laser as a function of the pump power, doped fiber length and type, total laser cavity length, polarization control and exit coupler ratio. The laser operated in a multi-wavelength regime with the central wavelength defined by a 1.12 GHz-band tunable Fabry–Pérot filter (FPF) with a 3.1 THz free spectral range (FSR). We have found that the key parameters defining the laser stability are the cavity length and the out-coupling ratio, while the polarization control has little influence on the multi-wavelength regime. In the optimal configuration, we obtained output power variations below 0.02 dB of a total power of about 1.5 mW in a 10 min interval.

Atomization characteristics of intermittent multi-hole diesel spray using time-resolved PDPA data

The intermittent spray characteristics of a multi-hole diesel nozzle with a 2-spring nozzle holder were investigated experimentally. Without changing the total orifice exit area, the hole number of the multi-hole nozzle varied from 3 (dn=O.42 mm) to 5 (dn=O.32 mm). The timeresolved droplet diameters of the spray including the SMD (Sauter mean diameter) and the AMD (arithmetic mean diameter), injected intermittently from the multi-hole nozzles into still ambient air, were measured by using a 2-D PDP A (phase Doppler particle analyzer). The 5hole nozzle spray shows the smaller spray cone angle, the decreased SMD distributions and the small difference between the SMD and the AMD, compared with that of the 3-hole nozzle spray. From the SMD distributions with the radial distance, the spray structure can be classified into the three regions: (a) the inner region showing the high SMD distribution; (b) the mixing flow region where the shear flow structure would be constructed; and (c) the outer region formed through the disintegration processes of the spray inner region and composed of fine droplets. Through the SMD distributions along the spray centerline, it reveals that the SMD decreases rapidly after showing the maximum value in the vicinity of the nozzle tip. The SMD remains the constant value near the Z/dn= 166 and 156.3 for the 3-hole and 5-hole nozzles, which illustrate that the disintegration processes of the 5-hole nozzle spray proceed more rapidly than that of the 3-hole nozzle spray.

Comparing and Modeling the Dehydrogenation of Ethanol in a Plug-Flow Reactor and a Pd−Ag Membrane Reactor

In this study the performance of a membrane reactor was compared to that of a plug-flow reactor for the dehydrogenation of ethanol. The membrane consisted of a 2.2 μm Pd-Ag film (23 wt% Ag) deposited on the inside of an asymmetric α-alumina membrane tube (SCT). The membrane tube was packed with a 14.5 wt% Cu on SiO 2 catalyst. The effects of the sweep gas flow rate, the ethanol feed flow rate, and the temperature on acetaldehyde yield and selectivity were investigated. A model was developed using measured kinetic data and membrane permeance data to predict the performance of the membrane reactor. The membrane reactor performed significantly better than the plug-flow reactor at all temperatures tested. The best results were obtained at 275°C, where the total ethanol exit conversion increased from 45% (plug-flow reactor) to 60% at low feed flow rates and from 36% to 46% at high feed flow rates. The acetaldehyde selectivity for the membrane reactor increased from the lower 80% range to above 90% at 275°C. The model underpredicted the total ethanol conversion, indicating that the measured reaction rate parameters for a differential reactor were lower than those for the membrane reactor.

Catalytic dehydrogenation of hydrocarbons in palladium composite membrane reactors

Different methods for the preparation of hydrogen permselective palladium composite membranes on asymmetric ceramic and porous stainless-steel tubes were tested. Electroless plating, electroplating, chemical and physical vapor deposition, as well as high velocity oxy-fuel spraying were investigated. Electroless plating was confirmed to be a suitable method for coating ceramic supports. Promising methods for the preparation of composite palladium–steel membranes are high velocity oxy-fuel spraying and a combined method of electroplating and electroless plating. Successfully coated membranes were employed for hydrogen separation in lab-scale membrane reactors during the dehydrogenation of ethylbenzene to styrene and propane to propylene. In both cases, the removal of hydrogen significantly increased the olefin yield, as compared to the corresponding conventional packed-bed reactor results. A relative increase of styrene yield above 15% was observed using a palladium–ceramic membrane. The relative increase of propylene yield was close to 18% for the same type of membrane. Employing a stainless steel-based membrane even further increased the yield of propylene. However, in contrast to the virtually defect-free ceramic-based membranes, a certain amount of other components passed the palladium–steel membrane along with hydrogen, amounting to roughly 20% of the total exit gas flow.

Effect of Nommiform Nozzle Flow on Scramjet Performance

Introduction H YDROCARBON-FUELED scramjet propulsion appears to offer promising performance at hypersonic speeds. For example, Fig. 1 shows performance, measured by thrust coefficient and specific impulse, as functions of nozzle efficiency based on one-dimensional calculations provided in Ref. 1. However, up to the present time, the potential performance indicated by these predictions has not been demonstrated experimentally. Perhaps the sensitivity to nozzle efficiency provides a clue to the difficulty in actually achieving high propulsive efficiency. Possible sources of loss in nozzle efficiency include errors in nozzle design or manufacture, nonuniform entrance flow, shear in nonuniform streams, wall friction, separation, nonequilibrium flow, incomplete expansion, and shock waves. Some of these potential losses, such as errors in design or manufacture, can be avoided or minimized. The question addressed in this note is, to what extent might nonuniform flow entering a scramjet nozzle result in unavoidable loss of exit momentum? To answer this question, the following procedure has been adopted: 1) Specify a form of inlet nonuniformity. In this investigation, a so-called fictitious or average uniform axial entrance flow is subdivided into two adjacent streams having the same pressure, the same total momentum, and the same total energy as the average uniform stream, but different initial Mach numbers. 2) Approximate the nozzle flow by a model that will exhibit the effects of the entrance nonuniformity isolated from other flow parameters. To this end, the two streams, depicted in Fig. 2, are assumed to be nonmixing and inviscid. Then the unrecoverable loss will be measured by the difference between the exit momentum achieved when the average stream is expanded isentropically to exit pressure and the total combined exit momenta of the two adjacent streams when they are isentropically expanded to the same exit pressure. 3) Calculate the exit momenta by one-dimensional isentropic ideal gas formulas. This approximation would be inappropriate for the design of a scramjet nozzle, or the accurate analysis of the nozzle flow, but by treating each of the streams on the same approximate basis, the unrecoverable loss resulting from the specified entrance nonuniformity can be estimated as a function of chosen inlet parameters. Effects of nonuniform flow in convergent-divergent nozzles have been examined, using a one-dimensional model. The one-dimensional predictions show surprisingly good agreement with a three-dimensional analysis and with wind-tunnel tests. Decher also estimated the effects of flow nonuniformities on nozzle exit momentum for convergent-divergent nozzles. Initial conditions are prescribed in the subsonic part of the flow, and the analysis is linearized by assuming relatively small variations in initial profiles. In Ref. 4, the theory is applied to nozzle performance calculations and includes mixing effects.

Symmetrical Cylindrical Model for TAP Pulse Response Experiments and Validity of the One-Dimensional TAP Model

A two-dimensional symmetrical cylindrical transport model for TAP pulse response experiments is analyzed and compared with the one-dimensional TAP model. It is shown that both models give the same total exit flow for experimentally realistic boundary conditions. The uniformity of the flux distribution at the outlet face of the cylindrical model is also analyzed. It is shown that after time greater than tpeak/60, the flux distribution on the radial coordinate of the outlet face can be considered uniform.

NOISE FROM SUPERSONIC COAXIAL JETS, PART 2: NORMAL VELOCITY PROFILE

Instability waves have been established as noise generators in supersonic jets. Recent analysis of these slowly diverging jets has shown that these instability waves radiate noise to the far field when the waves have components with phase velocities that are supersonic relative to the ambient speed of sound. This instability wave noise generation model has been applied to supersonic jets with a single shear layer and is now applied to supersonic coaxial jets with two initial shear layers. In this paper the case of coaxial jets with normal velocity profiles is considered, where the inner jet stream velocity is higher than the outer jet stream velocity. To provide mean flow profiles at all axial locations, a numerical scheme is used to calculate the mean flow properties. Calculations are made for the stability characteristics in the coaxial jet shear layers and the noise radiated from the instability waves for different operating conditions with the same total thrust, mass flow and exit area as a single reference jet. The effects of changes in the velocity ratio, the density ratios and the area ratio are each considered independently.