Showing papers on "Total pressure published in 2014"

Low GWP refrigerants R1234ze(E) and R1234ze(Z) for high temperature heat pumps

Abstract: Low global warming potential refrigerants R1234ze(E) and R1234ze(Z) are anticipated to be the refrigerants of choice for high-temperature heat pump systems in industrial applications. Their thermodynamic attributes are thermodynamically, experimentally, and numerically assessed in this study. The thermodynamic assessment indicates that the theoretical coefficients of performances (COP) are maximized at a condensation temperature approximately 20 K below the critical temperatures for each refrigerant. However, when the volumetric capacity is inadequate, the actual COP differs from the theoretical COP because of the large pressure drop. The breakdown of irreversible losses, which are experimentally quantified at a condensation temperature of 75 °C, results in the largest portion of the total pressure drop. The simulation results obtained at condensation temperatures of 105 and 125 °C indicate higher COPs than that at 75 °C for R1234ze(Z). The major factor is the reduction in the irreversible loss caused by the pressure drop. The above assessments demonstrate that R1234ze(Z) is suitable for high-temperature applications rather than in typical air conditioners.

Analytical model for non-thermal pressure in galaxy clusters

Abstract: Non-thermal pressure in the intracluster gas has been found ubiquitously in numerical simulations, and observed indirectly. In this paper we develop an analytical model for intracluster non-thermal pressure in the virial region of relaxed clusters. We write down and solve a firstorder di erential equation describing the evolution of non-thermal velocity dispersion. This equation is based on insights gained from observations, numerical simulations, and theory of turbulence. The non-thermal energy is sourced, in a self-similar fashion, by the mass growth of clusters via mergers and accretion, and dissipates with a time-scale determined by the turnover time of the largest turbulence eddies. Our model predicts a radial profile of nonthermal pressure for relaxed clusters. The non-thermal fraction increases with radius, redshift, and cluster mass, in agreement with numerical simulations. The radial dependence is due to a rapid increase of the dissipation time-scale with radii, and the mass and redshift dependence comes from the mass growth history. Combing our model for the non-thermal fraction with the Komatsu-Seljak model for the total pressure, we obtain thermal pressure profiles, and compute the hydrostatic mass bias. We find typically 10% bias for the hydrostatic mass enclosed within r500.

The role of pressure gradients in driving sunward magnetosheath flows and magnetopause motion

Abstract: While pressure balance can predict how far the magnetopause will move in response to an upstream pressure change, it cannot determine how fast the transient response will be. Using Time History of Events and Macroscale Interactions during Substorms (THEMIS), we present multipoint observations revealing, for the first time, strong (thermal + magnetic) pressure gradients in the magnetosheath due to a foreshock transient, most likely a hot flow anomaly, which decreased the total pressure upstream of the bow shock. By converting the spacecraft time series into a spatial picture, we quantitatively show that these pressure gradients caused the observed acceleration of the plasma, resulting in fast sunward magnetosheath flows ahead of a localized outward distortion of the magnetopause. The acceleration of the magnetosheath plasma was fast enough to keep the peak of the magnetopause bulge at approximately the equilibrium position, i.e., in pressure balance. Therefore, we show that pressure gradients in the magnetosheath due to transient changes in the total pressure upstream can directly drive anomalous flows and in turn are important in transmitting information from the bow shock to the magnetopause.

Theoretical and Experimental Study of Factors Affecting the Suction Force of a Bernoulli Gripper

Abstract: A Bernoulli noncontact gripper can generate suction force to achieve noncontact handling by use of axisymmetric radial airflow. An experimental and theoretical study of the factors that affect the suction force and its variation is conducted. First, a theoretical model of the pressure distribution is developed, taking into consideration the inertial effect of airflow deceleration, viscous effect, total pressure of the central air-supply hole, and gap height between the gripper and the workpiece. Based on the model, the suction force is calculated. Then, the pressure distribution and suction force are measured experimentally. The theoretical calculation and experimental results reveal that the inertial effect causes a negative pressure distribution and resulting suction force, while the viscous effect and the total pressure of the central air supply give rise to positive distributions and a resulting repulsive force. Because the repulsive force is inversely proportional to the gap height to a highe...

Numerical Investigation of the Stability of Rotating Detonation Engines

Abstract: As the injection total pressure increases, the flow field in the combustion chamber of rotating detonation engine (RDE) becomes complicated and the detonation wave becomes unstable. When the total pressure is high enough, the detonation oscillates periodically and alternates between strong and weak. Under the same injection conditions, no oscillation is observed in two-wave RDE, and the two detonation waves propagate stably in the combustion chamber. The choking ratio of the injection Laval nozzle along the head end is not influenced by the total pressure, the mode of propagation, or the number of detonation waves. And thus the mass flux of RDE can be estimated using the maximum mass flux of the injection Laval nozzle. The specific impulse and thrust of RDE show overall growth as total pressure increases. However, they oscillate with the unstable detonation wave in one-wave RDE at high total pressure.

Corner Separation Control by Boundary Layer Suction Applied to a Highly Loaded Axial Compressor Cascade

Abstract: Control of corner separation has attracted much interest due to its improvement of performance and energy utilization in turbomachinery. Numerical studies have been performed under both design and off-design flow conditions to investigate the effects of boundary layer suction (BLS) on corner separation in a highly loaded compressor cascade. Two new BLS slot configurations are proposed and a total of five suction slot configurations were studied and compared. Averaged static pressure rise, exit loss coefficient, passage blockage and flow turning angle have been given and compared systematically over a range of operation incidence angles. Distributions of significant loss removal, blade loading, exit deviation and total pressure loss at 3 degree and 7 degree incidence have also been studied. Under the same suction mass flows of 0.7% of the inlet mass flows, the pitchwise suction slot on the endwall shows a better optimal performance over the whole operation incidence among single suction slots. By using of the new proposed compound slot configuration with one spanwise slot on the blade suction side and one pitchwise slot on the endwall, the maximum reduction of total pressure loss at 7 degree incidence can be 39.4%.

Experimental study of the hydrodynamic behaviour of slug flow in a vertical riser

Abstract: High throughput spatial atomic layer deposition (ALD) often uses higher reactor pressure than typical batch processes, but the specific effects of pressure on species transport and reaction rates are not fully understood. For aluminum oxide (Al2O3) ALD, water or ozone can be used as oxygen sources, but how reaction pressure influences deposition using ozone has not previously been reported. This work describes the effect of deposition pressure, between ∼2 and 760 Torr, on ALD Al2O3 using TMA and ozone. Similar to reports for pressure dependence during TMA/water ALD, surface reaction saturation studies show self-limiting growth at low and high pressure across a reasonable temperature range. Higher pressure tends to increase the growth per cycle, especially at lower gas velocities and temperatures. However, growth saturation at high pressure requires longer O3 dose times per cycle. Results are consistent with a model of ozone decomposition kinetics versus pressure and temperature. Quartz crystal microbalance (QCM) results confirm the trends in growth rate and indicate that the surface reaction mechanisms for Al2O3 growth using ozone are similar under low and high total pressure, including expected trends in the reaction mechanism at different temperatures.

Atmospheric Pressure Atomic Layer Deposition of Al2O3 Using Trimethyl Aluminum and Ozone

Abstract: High throughput spatial atomic layer deposition (ALD) often uses higher reactor pressure than typical batch processes, but the specific effects of pressure on species transport and reaction rates are not fully understood. For aluminum oxide (Al2O3) ALD, water or ozone can be used as oxygen sources, but how reaction pressure influences deposition using ozone has not previously been reported. This work describes the effect of deposition pressure, between ∼2 and 760 Torr, on ALD Al2O3 using TMA and ozone. Similar to reports for pressure dependence during TMA/water ALD, surface reaction saturation studies show self-limiting growth at low and high pressure across a reasonable temperature range. Higher pressure tends to increase the growth per cycle, especially at lower gas velocities and temperatures. However, growth saturation at high pressure requires longer O3 dose times per cycle. Results are consistent with a model of ozone decomposition kinetics versus pressure and temperature. Quartz crystal microbalance (QCM) results confirm the trends in growth rate and indicate that the surface reaction mechanisms for Al2O3 growth using ozone are similar under low and high total pressure, including expected trends in the reaction mechanism at different temperatures.

Effect of total pressure on the absorption line blackbody distribution function and radiative transfer in H2O, CO2, and CO

Abstract: The absorption spectrum has been generated for H2O, CO2, and CO at total pressures varying from 0.1 to 50 atm using the HITEMP 2010 spectroscopic database. From these spectra the absorption line blackbody distribution function (ALBDF) has been calculated at variable total pressure in order to understand the importance of accounting for pressure changes on this parameter. The ALBDF is used in the SLW solution method to the radiative transfer equation. ALBDF data for H2O, CO2, and CO are presented, revealing a shift in the ALBDF to lower values as total pressure increases. This shift is weaker at high temperature. The shift due to increase in mole fraction of H2O and CO2 was shown to be modest, and similar at different pressures. The ALBDF was shown to become less smooth as pressure increases. Total emissivity calculations are presented for variable total pressure, and it is seen that pressure changes account for a significant change in total emissivity. Total radiative flux and radiative flux divergence were calculated from line-by-line spectral integrations for one-dimensional layers of constant length and constant mass cases, showing that total pressure changes result in a significant impact on radiative transfer in a layer of gas. Radiative flux exiting a layer of gas can change by more than a factor of four over the pressure range investigated when the pressure change is the only variable considered.

Simulation of the Evolution of Pressure in a Lignite Particle during Pyrolysis

Abstract: The evolution of pressure in a lignite particle during pyrolysis was simulated on the basis of the gas motion equation in porous media and considering the Klinkenberg effect. The chemical percolation devolatilization (CPD) model was used to describe pyrolysis. The pore diameter in the particle is close to the average free path of volatile gas molecules; therefore, the solid phase restrains the movement of gas. Because flow out of the particle is restricted, the internal pressure rises. The internal pressure first increases and then decreases during pyrolysis, and the evolution is influenced by heating conditions. The pressure rise is larger at a higher heating rate, but the duration of the pressure peak is shorter. The total pressure in the particle is larger at a higher ambient pressure, but the pressure difference between the inside and the surroundings decreases with the increasing ambient pressure. A growing internal pressure can restrain tar gasification, which can lead to the increase of the Metapla...

Total pressure fluctuations and two-phase flow turbulence in hydraulic jumps

Abstract: The large-scale turbulence and high air content in a hydraulic jump restrict the application of many traditional flow measurement techniques. This paper presents a physical modelling of hydraulic jump, where the total pressure and air–water flow properties were measured simultaneously with intrusive probes, namely a miniature pressure transducer and a dual-tip phase-detection probe, in the jump roller. The total pressure data were compared to theoretical values calculated based upon void fraction, water depth and flow velocity measured by the phase-detection probe. The successful comparison showed valid pressure measurement results in the turbulent shear region with constant flow direction. The roller region was characterised by hydrostatic pressure distributions, taking into account the void fraction distributions. The total pressure fluctuations were related to both velocity fluctuations in the air–water flow and free-surface dynamics above the roller, though the time scales of these motions differed substantially.

Parametric Optimization of Unsteady End Wall Blowing on a Highly Loaded Low-Pressure Turbine

Abstract: Efforts to reduce blade count and avoid boundary layer separation have led to lowpressure turbine airfoils with significant increases in loading as well as front-loaded pressure distributions. These features have been independently shown to increase losses within the secondary flow field at the end wall. Compound angle blowing from discrete jets on the blade suction surface near the end wall has been shown to be effective in reducing these increased losses and enabling the efficient use of highly loaded blade designs. In this study, experiments are performed on the front loaded L2F low-pressure turbine airfoil in a linear cascade. The required mass flow is reduced by decreasing the hole count from previous configurations and from the introduction of unsteady blowing. The effects of pulsing frequency and duty cycle are investigated using phase-locked stereo particle image velocimetry to demonstrate the large scale movement and hysteresis behavior of the passage vortex interacting with the pulsed jets. Total pressure loss contours at the cascade outlet demonstrate that the efficiency benefit is maintained with the use of unsteady forcing. [DOI: 10.1115/1.4026127]

Determining of the hydrodynamic forces on the multi-hull tunnel vessel in steady motion

Abstract: The research described in this paper was carried out to determine the hydrodynamic forces on the multi-hull tunnel vessel in steady motion. The hull form of vessel is fairly generated by the tunnel hull form generator code using the non-uniform rational B-Spline method. Then, the hydrodynamics simulation is carried out based on finite volume discretization method using volume of fluid model to consider free surface between water and air phases around the vessel. A dynamic mesh restructuring method is applied for grid generation regarding to the heave and pitch motions of vessel in each time step. The calculations of the center of gravity arising, trim angle, pressure, resistance and effective power are studied at various vessel’s speeds. The resistance plot versus velocity has an increasing trend having a hump velocity while the power curve shows a linear-like changes respect to speed increasing. Pressure calculations show that the ratio of hydrostatic pressure to total pressure is decreased at the end point of keel from 100 to 1 % as velocity increases from 5 to 20 m/s. The proposed numerical algorithm is a promising method for hydrodynamic analyses of wide-ranging high speed vessel types, particularly tunnel vessels.

Relationship between the structure and electrical characteristics of diamond-like carbon films

Abstract: To elucidate the relationship between the structure and the electrical characteristics of diamond-like carbon (DLC) films, DLC films were synthesized in a well-controlled glow discharge with the aid of photoelectrons in an argon/methane atmosphere. The dielectric constant and breakdown strength of the films exhibited opposite behaviors, depending on the total pressure during the synthesis. The product of these two values decreased monotonically as the pressure increased. The Raman spectra were analyzed with a Voigt-type formula. Based on the results, the authors propose the “sp2 cluster model” for the DLC structure. This model consists of conductive clusters of sp2 carbons surrounded by a dielectric matrix sea of sp2 carbon, sp3 carbon, and hydrogen, and indicates that the dielectric constant of the whole DLC film is determined by the balance between the dielectric constant of the matrix and the total size of the clusters, while the breakdown strength is determined by the reciprocal of the cluster size. T...

Transverse Injection Into a Supersonic Cross Flow Through a Circular Injector With Chevrons

Abstract: Results from 3D, compressible, unsteady Favre-averaged calculations of transverse injection into a supersonic cross flow are reported. Four injector geometries, namely, circular, wedge, diamond, and chevron, have been investigated. The effectiveness of the chevron injector is demonstrated by comparing performance metrics, such as degree of mixing and total pressure loss, against those of the other injectors. The results show that the chevron injector provides better mixing and spreading compared to other injectors, with almost the same total pressure loss. Furthermore, for the operating conditions studied, the chevron-penetration angle is shown to have a minimal impact on the mixing and the total pressure loss.

Off-Design Performance of a Highly Loaded Low Pressure Turbine Cascade Under Steady and Unsteady Incoming Flow Conditions

Abstract: The off-design performance of a highly loaded low pressure (LP) turbine cascade has been experimentally investigated, at the Aerodynamics and Turbomachinery Laboratory of Genova University, under steady and unsteady incoming flow conditions. Tests have been performed for different Reynolds numbers (Re = 70,000 and Re = 300,000), in order to cover the typical LP turbine working range. The incidence angle has been varied between i = −9 deg and +9 deg, in order to test off-design conditions characterizing the engine. For the unsteady case, upstream wake periodic perturbations have been generated by means of a tangential wheel of radial rods. The cascade and the moving bars system have been located over a common bearing in order to make them rigidly rotating. This solution allows a proper comparison of the cascade robustness at the incidence angle variation under steady and unsteady incoming flows, since all the other operating parameters have been kept the same. In order to survey the variation of the unsteady boundary conditions characterizing the off-design operation of the downstream cascade, time-mean and time-resolved wake structures have been analyzed in detail. For what concerns the cascade performance, profile aerodynamic loadings and total pressure loss coefficients at the cascade exit have been surveyed for the different incidence angles under both steady and unsteady inflows. Different total pressure loss sensitivity at the incidence angle variation has been observed for the steady and the unsteady inflow conditions. Hot-wire anemometer has been employed to obtain the time-mean pressure and suction side boundary layer velocity profiles at the blade trailing edge for the different conditions. The integral parameters at the cascade exit plane help to justify the different loss trend versus incidence angle found for the steady and the unsteady cases, explaining the different sensibility of the blade profile when this operates under realistic unsteady inflow condition.

Dynamic Store Release of Ice Models from a Cavity into Mach 2.9 Flow

Abstract: An investigation was conducted into store separation from a cavity in a Mach 2.94 freestream using both experimental and computational methods. Both approaches used an open cavity with a length-to-depth ratio of 4.5, and for the sake of simplicity, release of a spherical model was analyzed. The experimental process used a piezoresistive pressure transducer to collect the time-varying content of the pressure signal, while schlieren visualization and high-speed photography capture the dynamic response of a store released from the cavity. Computationally, the OVERFLOW solver was applied with higher-order numerical methods, Chimera grids, and the delayed detached-eddy simulation/shear-stress transport hybrid turbulence model. Tests were performed in a blowdown tunnel exhausting to a vacuum, which enabled robust control of the total pressure, and computational conditions were selected to match the experiment. The studies demonstrated that the shock wave formed on the bottom surface of the sphere led to the los...