Total pressure

About: Total pressure is a research topic. Over the lifetime, 5199 publications have been published within this topic receiving 66658 citations.

A High Temperature High Bandwidth Fast Response Total Pressure Probe for Measurements in a Multistage Axial Compressor

Abstract: Over the last decades, fast response aerodynamic probes have been recognized as a robust measurement technique to provide time-resolved flow field data in turbomachinery environments. Still, most of the existing probe designs are restricted to low temperature applications (< 120 °C) either because of sensor temperature range limitations or packaging issues. Measurements in turbomachines also require a small probe size often with a very high bandwidth which are conflictual constraints difficult to satisfy simultaneously. This contribution therefore presents the development of a novel miniature (O 2.5 mm) high temperature single sensor total pressure probe, designed for operation up to 250 °C with a very high bandwidth of 250 kHz. The probe main element is a 1.7 mm diameter commercial piezoresistive transducer placed in a Pitot type arrangement with a flush mounted sensor to provide the highest bandwidth. The details of the probe design are presented as well as the probe calibrations in pressure and in temperature. The effects of using a thermal compensation module or a sense resistor to monitor the temperature drift are described in the context of measurement uncertainty. The probes were characterized in terms of aerodynamic characteristics versus flow angle and Mach number. Shock tube tests have shown a dynamic response of the probe with sensor resonance frequencies well over 300 kHz, with a flat frequency range up to 250 kHz. Two probe prototypes were manufactured and first used in the 3 1/2-stage high speed axial compressor CREATE of the LMFA at Ecole Centrale de Lyon in France. The probes were traversed at each inter blade row plane up to temperatures of 180 °C and absolute pressure of 3 bar. The probe was able to resolve the high blade passing frequencies (∼16 kHz) and several harmonics including rotor-stator interaction frequencies up to 200 kHz. Besides the average total pressure distributions from the radial traverses, phase-locked averages and random unsteadiness are presented. The probe spatial and temporal resolutions are discussed in the context of those results.Copyright © 2011 by ASME

Vacuum chamber pressure effects on thrust measurements of low Reynolds number nozzles

Abstract: Tests were conducted to investigate the effect of vacuum facility pressure on the performance of small thruster nozzles. Thrust measurements of two converging-diverging nozzles with an area ratio of 140 and an orifice plate flowing unheated nitrogen and hydrogen were taken over a wide range of vacuum facility pressures and nozzle throat Reynolds numbers. In the Reynolds number range of 2200 to 12 000 there was no discernable viscous effect on thrust below an ambient to total pressure ratio of 1000. In nearly all cases, flow separation occurred at a pressure ratio of about 1000. This was the upper limit for obtaining an accurate thrust measurement for a conical nozzle with an area ratio of 140.

The influence of hydrogen pressure on the heterogeneous hydrogenation of β-myrcene in a CO2-expanded liquid

Abstract: This paper presents the second part of work on the effect of hydrogen partial pressure on the hydrogenation of a terpene in a CO 2 -expanded liquid. The effect of hydrogen partial pressure on the hydrogenation of β-myrcene possessing three C C bonds catalysed by alumina-supported ruthenium and rhodium was studied. Experiments were performed at various hydrogen pressures in the range from 2.0 up to 4.5 MPa at a fixed total pressure of 12.5 MPa. In all the conditions the reaction proceeded in two phases (liquid + gas), that is, the total pressure was below the critical pressure of the CO 2 + β-myrcene + H 2 system. The liquid phase volume is expanded in relation to the initial volume of β-myrcene in a fashion that is strongly dependent on the hydrogen and carbon dioxide pressures. An increase of H 2 pressure concomitantly diminishes carbon dioxide pressure, which leads to the enhancement of the liquid phase in hydrogen and a terpene. It does not direct to straightforward higher reaction rate, but surprisingly the effect of higher concentrations either hydrogen or β-myrcene is opposite. It is attributed to the fact that the hydrogenation of β-myrcene rate-controlling factor turns out to be the hydrogen to β-myrcene ratio which decreases as the hydrogen pressure increases. These unexpected appealing results present that lower pressures of hydrogen guide to higher hydrogen/β-myrcene ratios in the liquid phase, but on the other hand they also amplify the initial reaction rate constant. The obtained results are opposite to the results achieved for effect of hydrogen pressure on the Pd-catalysed hydrogenation of limonene consisting of two C C double bonds.

Total pressure measurements below 10-10 torr with non-magnetic ionization gauges

Abstract: The modulation method has been applied to (i) the Bayard-Alpert gauge and (ii) the suppressor gauge to reduce their lower pressure limits and measurements made with these two gauges to pressures as low as 10-14 torr. It is shown that the modulated Bayard-Alpert gauge can measure pressure to 3 × 10-11 torr (10% error) without correction for the residual-current modulation effect, and measurements can be extended to 3 × 10-13 torr if corrections for the residual-current modulation are made. The residual limit of the suppressor gauge has been measured (approximately 2 × 10-13 torr). With modulation applied to the suppressor gauge the lowest measureable pressure, set by amplifier noise, is about 10-13 torr for a 10: 1 signal-to-noise ratio. Electronic desorption of chemisorbed material from the grid of a gauge and/or a molecular flux in the gauge are shown to cause a limitation to the lowest measurable pressure; these limits may be higher than the x-ray limit under certain conditions.