Chamber pressure

About: Chamber pressure is a research topic. Over the lifetime, 2988 publications have been published within this topic receiving 30725 citations.

On maintaining pressure equilibrium between a soil CO2 flux chamber and the ambient air

Abstract: [1] Pressure equilibrium between inside a soil CO2 flux chamber and the surrounding air outside the chamber must be maintained during a measurement if measured soil CO2 flux (FCO2) is to accurately represent the rate occurring naturally outside the chamber. In previous studies a simple vent tube connecting to the chamber has often been used to maintain pressure equilibrium. This approach, however, can be effective only under calm conditions. Under windy conditions, negative pressure excursions will occur inside the chamber that are artifacts resulting from wind passing over the vent tube's external open end, a phenomenon known as the Venturi effect. This causes anomalous mass flow of CO2-rich air from the soil into the chamber, leading to a significant overestimation of FCO2. In this present study, we found that negative chamber pressure excursions due to the Venturi effect cannot be observed unless the differential pressure measurement is made with the chamber resting on an impermeable base. Making pressure measurements with a chamber resting on porous soil can lead to the erroneous conclusion that an anomalous mass flow is not a problem precisely when it is causing serious artifacts. We also present a new vent design for a soil CO2 flux chamber capable of maintaining pressure equilibrium between inside the chamber and the ambient air outside the chamber under both calm and windy conditions. Differential pressure measurements from field experiments show that the pressures inside our newly designed vented chamber equal those outside the chamber when wind speed at a height of 0.5 m is up to 7 m s−1, thus virtually eliminating artifacts due to the Venturi effect. Our field data show that the problem of overestimation in measured FCO2 by a chamber with older vent designs under windy conditions can be avoided with our newly designed vented chamber.

An improved open chamber system for measuring soil CO2 effluxes in the field

Abstract: An “open” chamber for the measurement of soil CO2 efflux has been designed which utilizes an air seal to maintain chamber pressure within 0.004 Pa of atmospheric pressure, eliminating any mass flow and ensuring that atmospheric pressure fluctuations are transferred through to the soil surface. The system was used at the Boreal Ecosystem-Atmosphere Study (BOREAS) southern study area old black spruce site through the 1994 and 1996 field campaigns and was found to be robust and simple to use. Consistency was found between soil CO2 effluxes measured with this system and a closed dynamic chamber system.

Injection and Mixing Processes in High-Pressure Liquid Oxygen/Gaseous Hydrogen Rocket Combustors

Abstract: The injection, mixing combustion processes in a liquid oxygen (LOX)/gaseous hydrogen (GH2) rocket engine combustor at high chamber pressures (10 MPa) are studied and modeled. An experimental LOX/GH2 rocket motor consisting of a single coaxial shear injector element and a cylindrical chamber with optical access has been used for flow visualizations and measurements. Cold-flow injection test utilizing liquid nitrogen and gaseous helium at elevated pressures have been done for flowfield characterization by different diagnostic methods such as flash-ligth photography and high-speed cinematography using a shadowgraph setup. The injection visualizations and studies under cold-flow and combusting conditions revealed a remarkable difference between subcritical spray formation and evaporation and the supercritical injection and mixing process. The study shows that aproaching supercritical chamber pressures injection can no longer be regarded as a spray formation but rather as a fluid/fluid mixing process. As the flow visualizations indicate, the effect of the coaxial atomizer gas is less effective as previously expected. The flame is attached to the LOX post and develops in the LOX post wake. The observed flame holding mechanism is discussed. An evaluation of the radiation spectrum of the flame inside the combustion chamber revealed that radiation in the visible range is mainly due to water vapor.

Method and apparatus for substrate temperature control

Abstract: A method and apparatus for gas control is provided. The apparatus may be used for controlling gases delivered to a chamber, controlling the chamber pressure, controlling the delivery of backside gas between a substrate and substrate support and the like. In one embodiment, an apparatus for controlling gas control includes at least a first flow sensor having a control valve, a first pressure sensor and at least a second pressure sensor. An inlet of the first flow sensor is adapted for coupling to a gas supply. A control valve is coupled to an outlet of the flow sensor. The first pressure sensor is adapted to sense a metric indicative of the pressure upstream of the first flow sensor. The second pressure sensor is adapted to sense a metric indicative of the pressure downstream of the control valve.

Wafer tray and ceramic blade for semiconductor processing apparatus

Abstract: A semiconductor wafer processing system for processing wafers from a wafer storage cassette includes a wafer transfer chamber; a wafer storage elevator within the transfer chamber; one or more wafer processing chambers; and a wafer transfer apparatus for transferring a wafer between a standard storage cassette adjacent and outside the transfer chamber and the elevator, and between the elevator and the processing chamber. The storage chamber pressure varies between atmospheric when accepting wafers from outside, and a subatmospheric pressure when transferring wafers to or from a processing chamber. The transfer apparatus includes a robot arm; a thin flat wafer carrying blade at the leading end of the robot arm configured for engaging a wafer from the storage cassette or the elevator; and a wafer support tray configured for removable engagement with the blade and for engaging and positively positioning a wafer from the elevator, or a support pedestal within a processing chamber. When the transfer apparatus moves a wafer between the elevator and a processing chamber in an evacuated environment, the tray is engaged with the blade and helps retain the wafer during transit. When wafers are transferred between the cassette and the elevator at atmospheric pressure the tray is disengaged from the blade and placed in a rest position on the elevator, and the wafer transfer is performed by means of the blade alone with a vacuum pick integral to the blade. The blade includes upper and lower halves together defining vacuum channels and capacitive position sensors.