Flow measurements isentropic

Significantly lower temperatures have been achieved by Rowe and co-workers [23, 24] using the CRESU (Cinetique de Reaction en Ecoulement Supersonique Uniforme) technique, in which the gas is expanded through a Laval nozzle and the flow parameters, density, temperature, pressure and velocity in the central 10-20 mm of the resulting uniform supersonic jet are invariant in both axial and radial directions, since the flow is isentropic over a flow distance of tens of centimetres. The jet crosses an electron beam to provide the ions and into a mass spectrometer, which is movable so that the reaction times can be varied. Measurements have been made down to 8 K. Measurements on He + N2 gave... 

This formula gives good results for low-velocity gas flow (less than about 200ft/s), hut for high-velocity gas flows Bernoulli s equation is no longer applicable. For all velocities between zero and sonic velocities, we can assume that the part of the mainstream which is stopped by the impact tube is stopped practically isentropically. If that is correct, then the pressure measured at F, is the reservoir pressure for the flow. Thus, we can use Eq. 8.17, solved for... 

The liquid-nitrogen flow rate was measured with a turbine flowmeter. The total pressure of the jet exhaust Ptj was measured at an orifice in the model plenum chamber by a Precision Pressure Balance transducer. The total temperature of the CO2 exhaust was measured by a thermocouple in the line leading into the vacuum chamber. This thermocouple was downstream of the pressure-regulating valve and therefore measured the total temperature of the CO2 after the expansion to near the jet total pressure. The total temperature and the total pressure of the jet were used in a one-dimensional isentropic flow equation for choked nozzles to calculate the mass flow of CO2. The specific heat ratio used was that corresponding to the total temperature and pressure of the jet. 

The addition of condensation enthalpy to the supersonic flow causes an increase in static pressure, in temperature and in vapour density and a decrease in the flow velocity, compared to the non-condensing isentropic flow. Since deviations of the static pressure can be determined reliably, the onset and the progress of condensation were observed from precise measurement of the static pressure along the nozzle axis. 

The gas temperature at the atomizer exit calculated under the hypothesis of an isentropic expansion of the gas (7 expanded,isentropic(7 o = 400 °C)= 183 °C) is much lower than the measured values further away from the nozzle. That shows the strongly dissipative effects of the gas flow during expansion and the effective mixing with the (warm) recirculating gas. In [1, 39], these effects have been investigated experimentally and numerically. This viscous heating effect may be beneficial since more thermal energy is introduced into the breakup zone. 

Flow-stream pressures. Static pressure is pressing measured perpendicularly to the direction of flow. This is the pressiu-e that one would sense when moving downstream with the fluid. Total pressure is pressiue in the direction of flow, where pressure as a function of direction is at a maximum. Total pressure would be sensed if the stream were brought to rest isentropically. Velocity pressure is the difference between static and total pressure measured at a specific region in the direction of flow. It is called velocity head when measured in height of fluid. Velocity pressure is equal to V2pV, where p is the fluid density and V is the fluid velocity. 

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