Showing papers on "Total pressure published in 1975"

Vapor‐liquid equilibrium: Part IV. Reduction of P‐x data for ternary systems

Abstract: Total pressure measurements taken for the ternay systems acetone-chloroform-methanol and chloroform-ethanol-n-heptane at 50°C are reduced by Barker's method and correlated by an equation similar to one proposed by Wohl (1953).

Freeze dehydration by microwave energy: Part I. Theoretical investigation

Abstract: A general unsteady state analysis is employed to derive a mathematical model of a freeze-drying process using microwave heating. The model takes into account the variations of the transport and dielectric properties in the sample with both time and location as a function of temperature and pressure. The variations of the properties are described by functionals which have been derived from literature data and are built into the model. The mathematical model is used to simulate the freeze drying of beef meat with microwave energy at 2450 MHz. The simulation shows that drying rates are essentially a function of the microwave power input. The model also shows that the total pressure and the partial pressure of water vapor in the vacuum chamber directly affect the sample temperature during dehydration. The simulation shows, in particular, that, an optimal microwave freeze-drying operation corresponds to an operation near corona and overheating/melting conditions.

A kinetics study of the reaction of OH radicals with two C2 hydrocarbons: C2H4 and C2H2

Abstract: The flash photolysis‐resonance fluorescence technique has been utilized to study the kinetics of hydroxyl radical reactions with ethylene and acetylene at 300 K over a wide range of experimental conditions. (1) OH+C2H4 →k1 Products (e.g., C2H5O), (2) OH+C2H2 →k1 Products (e.g.,C2H2O+H). The bimolecular rate constant for Reaction (1) was observed to increase from (2.24–5.33) × 10−12 cm3 molecule−1⋅ sec−1 as the total pressure varied from (3–300) torr of helium. The rate of Reaction (2) was invarient with total pressure, and the value obtained for k2 was (1.65±0.15) × 10−13 cm2 molecule⋅sec−1. The observed pressure dependency of Reaction (1) brings the existing literature values for k1 into close agreement. Reaction (2) has been shown to be particularly sensitive to secondary processes and this is discussed in some detail.

Isothermal vapor-liquid equilibrium data of isopropanol-water system

Abstract: Total pressure for the system of isopropanol and water was measured in a temperature range from 35 to 75°C by using a modified Othmer recirculation still. The vapor-liquid equilibrium was calculated from the total pressure-composition data by using the numerical method of Barker. Simultaneous fitting of the excess Gibbs energy and the excess enthalpy data was successfully done by using the Wilson equation.

Rate constants for the reaction of the OH radical with H2 and NO (M=Ar and N2)

Abstract: Absolute rate constants for the reaction of OH radicals with H2 and NO (M=Ar, N2) have been determined at 298±1 °K using a flash photolysis–resonance fluorescence technique. The rate constant for the reaction OH+H2 was determined to be (6.97±0.70) ×10−15 cm3 molecule−1 sec−1 in good agreement with recent literature values. Rate constants for the reaction OH + NO + M (M = Ar) were obtained over the pressure region 25–655 torr, while a rate constant for M = N2 was obtained at 25 torr total pressure. The low pressure third order rate constants for this reaction were determined to be (4.25±0.43) ×10−31 cm6 molecule−2 sec−1 (M=Ar) and (6.1±0.7) ×10−31 cm6 molecule−2 sec−1 (M = N2), in good agreement with the available literature values. The bimolecular rate constants at 760 torr total pressure were determined to be (5.2±0.8) ×10−12 cm3 molecule−1 sec−1 for M = Ar and (6.1±1.0) ×10−12 cm3 molecule−1 sec−1 for M = N2. A value of 8×10−12 cm3 molecule−1 sec−1 was obtained as a probable lower limit for the limiting high pressure second order rate constant from an extrapolation of the data.

Electronic fluid pipeline leak detector and method

Abstract: Disclosed is an instrument wherein the pressure or flow of a fluid in a pipeline is monitored with a voltage proportional thereto being electronically differentiated to determine whether any rate of change of pressure exists, which is often indicative of a leak in the pipeline. If a rate of pressure change of a predetermined extent exists for a predetermined period of time and if a total pressure change exceeds a predetermined value, an output signal can close a valve in the pipeline or can sound an alarm. In addition, in situations where a liquid is involved, a surge develops upon a line break, that is, a large rate of instantaneous pressure drop, and such surge can also be detected and appropriate remedial measures taken. The instrument is also capable of shutting down the pipeline in instances of inordinately low or high pressure conditions.

Behavior of Severely Asymmetric Flow in a Vaneless Diffuser

Abstract: There is controversy about the mechanism of decay of the asymmetric flow in the vaneless diffuser of centrifugal blowers. In order to clearly observe the behavior of asymmetric flow, every other flow passage of a centrifugal impeller is blocked with a punched plate so that a severely asymmetric flow is induced. The flow behavior in the vaneless diffuser is measured with unsteady flow measuring instruments as well as with conventional instruments for steady flow. The experimental results indicate that there are some flow phenomena which cannot be explained by the conception of mixing process. Such flow phenomena can be explained quantitatively as the isentropic energy exchange between relative streamlines due to the circumferential pressure variation. In addition, the wall roughness of the vaneless diffuser is changed, and the influence of the wall friction on the total pressure loss is compared with the predictions based on the two controversial hypothesis. While these data are handled, it is recognized that the time average total pressure is considerably larger than the mass average total pressure for a severely asymmetric flow. Therefore, if instruments for steady flow measurement are used near the impeller exit to measure the total pressure, the impeller efficiency may be overestimated and the diffuser efficiency may be underestimated.

Scaling of the helium‐nitrogen charge transfer laser

Abstract: The scaling to high powers of the nitrogen ion laser pumped by charge transfer from He+2 is reported. Intense emission has been found from three laser lines at 3914, 4278, and 4709 A upon discharge of a fast‐pulsed electron beam gun, APEX‐1, into several atmospheres of a mixture of helium and nitrogen. Excitation current densities were 1.4 kA/cm2 at 1 MV over a 1×10‐cm transverse geometry. The efficiency of the 4278‐A laser emission was found to be proportional to the total pressure raised to the 1.2 power. Outputs of 36 mJ have been obtained from the 16‐cm3 working volume at 30‐atm pressure and a peak efficiency of 1.6% relative to the energy lost by the electron beam in this radiating volume has been achieved.

Automatic digital microwave hygrometer

Abstract: This hygrometer is designed to measure the humidity of atmospheric air over the vapor pressure range 3–7400 Pa (0.03–74 mbar). The instrument is an adaptation of a microwave refractometer using two cavities operating at 12 GHz. One cavity is exposed to the moist test air and the other is exposed to the same air sample with all the water vapor removed. Both cavities are maintained at the same fixed temperature in a thermostated oven and at the same total pressure. The difference in frequency between the cavities is automatically nulled by a tuning probe in the sampling cavity. The instrument was calibrated by two independent methods. One involved the measurement of the resonance frequency of the sampling cavity as a function of probe penetration and using this in a theoretically derived equation for vapor pressure. The second involved the measurement of the probe penetration as an empirical function of known vapor pressure of a test gas. These two methods yielded results which agreed on the average to bett...

Apparatus and method for reducing flow disturbances in a flowing stream of compressible fluid

Abstract: Disclosed are methods and apparatus for reducing acoustic noise generated by high pressure ratio throttling of compressible fluids. High pressure gas is passed through a plurality of chokes, each adapted to cause an incremental pressure reduction and produce a normal shock at a Mach number between about 1.3 and 2.3, thereby reducing total pressure across the system without causing a high Mach number shock.

Membrane process for separating materials

Abstract: A process is disclosed for separating components, e.g., olefinically-unsaturated hydrocarbons, from mixtures with other materials by liquid barrier permeation and metal-complexing techniques using a semi-permeable membrane and a partial pressure differential across the membrane for the material being separated. The process is characterized by the use of elevated pressure on the feed side of the membrane, preferably at least about 200 psig, a low total pressure differential, if any, across the membrane, and preferably a partial pressure of the material being separated on the exit side of the membrane which is at least about 20 psi less than on the feed side. The separated material may be removed with advantage by the use of a liquid solvent in which the material is soluble, and preferably the concentration of the material in the solvent is up to about 25 weight percent of saturation when the solvent is charged to the exit side of the membrane. The separation of ethylene from its mixture with methane and ethane is of particular interest.

Wheel lock-up prevention apparatus

Abstract: A wheel lock-up prevention system for motor vehicles includes electromagnetic valves which decompress the main control chamber of the system when a wheel lock-up occurs and hence terminate the braking effort at the locked wheel. During re-compression, which takes place by cyclic actuation of one of the electromagnetic valves, excessively high pressure pulses are prevented by connecting the main control chamber with a surge chamber during part of the cycle so as to diminish the pressure in the main control chamber and to make the magnitude of the cyclic pressure increases inversely proportional to the total pressure in the control chamber.

TA5 - H 2 /F 2 flame propagation and repetitively pulsed hydrogen flouride (HF) chain-reaction chemical laser

Abstract: The burning velocity and the nature of the H 2 /F 2 flame at various gas compositions gas compositions have been experimentally determined. It was found that reactions induced by a diffusion-type flame proceed rather slowly, but reactions triggered by a compression wave proceed with supersonic speed. Based on the measurements of gas stability, repetetive pulse operation of H 2 /F 2 chemical lasers at atmospheric pressure has been achieved. The second and third explosion limits of H 2 + F 2 reactions in O 2 /He mixtures were also studied experimentally to improve our understanding of the nature of H 2 + F 2 explosion. The apparatus allowed the simultaneous time-resolved measurement of both gas pressure and temperature at the center of the spherical reaction vessel. It was found that, for fixed H 2 + F 2 total pressure and O 2 concentration, mixtures with higher F 2 /H 2 ratios are less stable and explode at a lower temperature. It appears quite certain that molecular O 2 plays an important role in the chain termination reaction. However, the addition of CF 4 , SF 6 , or N 2 showed no effect on the boundaries of the H 2 /F 2 explosion.

Intense laser emission at 3577 Å using N2‐SF6 mixtures in a TE nitrogen laser

Abstract: Intense laser emission at 3577 A (v′=0 of the C3πu state to v″=1 of the B3πg state of the nitrogen molecule) has been demonstrated to take place by an addition of a large quantity of SF6 as a foreign gas in a transversely excited nitrogen laser. The output at 3577 A is increased with increasing partial pressure of SF6, until a total pressure of up to 250 Torr. With sufficient SF6 added, the output at 3371 A is increased by a factor of 1.3 as compared with the case of N2 gas alone.

Novel method for measuring total pressure of fuel gas in hollow, glass Microshell pellets

Abstract: A sampling technique has been developed that permits direct, rapid, and accurate determination of the pressure inside gas‐filled, hollow, glass Microshell pellets.

An experimental and mechanistic study of the reactions of COF2 with H2 and with CO

Abstract: The decomposition of carbonyl fluoride (COF2), the reactions of carbonyl fluoride with carbon monoxide (CO), and the reactions of carbonyl fluoride with hydrogen (H2) in excess argon were studied behind reflected shock waves. Kinetic data were obtained in the temperature and total pressure ranges 2600–3300 °K and 2.5–9.0 atm, respectively, for the COF2 decompostion study, in the temperature and total pressure ranges 2400–3000 °K and 3.3–7.7 atm, respectively, for the COF2–CO study, and in the temperature and total pressure ranges 1900–2700 °K and 2–12 atm, respectively, for the COF2–H2 study. Under the experimental conditions, the bimolecular reaction between COF2 and CO was found to be negligible with respect to the decomposition of COF2. An empirical relationship for the over‐all kinetics of the COF2–H2 reaction was determined, and a combined analytical and experimental study was conducted to determine a plausible mechanism for the COF2–H2 reaction. Under the experimental conditions, the dominant reacti...

A Study on the Structure of Turbulent Jet Diffusion Flames

Abstract: The gross structure of turbulent jet diffusion flames developing in a coflowing high temperature vitiated air stream was examined experimentally and theoretically The observed radial profiles of total pressure within the flame were similar in all axial positions, while the temperature profile showed a sharp peak at the most luminous position The measured temperature profiles in the upstream region of flame were found to correlate satisfactory with those of a simplified analysis based on the flame surface approximation and the boundary layer similar solution for the velocity field

Investigation of the Stall Hammershock at the Engine Inlet

Abstract: The peak static pressures measured at the inlet to the engine during stall are presented for a turbojet and two turbofan engines. It is shown for one turbofan and the turbojet that the static pressure ratio across the hammershock does not exceed significantly the normal shock pressure ratio necessary to stop the flow. The second turbofan engine did not follow this rule. Possible reasons for the departure are discussed. For the two turbofan engines the influence of the stall method on the hammershock intensity has been investigated. Data related to the spatial distribution of pressure in the hammershock are also presented. Nomenclature a = speed of sound Cp = specific heat at constant pressure M = Mach number P - total pressure P = static pressure T = static temperature t = time

a Hydrophobic Membrane Probe for Total Pressure and Partial Pressure Measurements in the Soil Atmosphere

Abstract: For total air pressure and oxygen partial pressure measurements a hydrophobic membrane probe is used. The probe consists of a small membrane-covered chamber and two teflon capillaries. The probe represents an artificial, permanently air-filled pore which connects the soil atmosphere at a certain depth with a pressure transducer or an oxygen electrode placed on the soil surface. The soil water is excluded from the artificial gas phase by a water-repellent membrane highly permeable to air. The hydrophobic membrane makes the gaseous phase between soil and sensor continuous. This instrument was used in the field to follow changes in total air pressure and oxygen partial pressure in the soil atmosphere during water infiltration and drainage processes. The total pressure in the soil atmosphere and the partial pressure of its components strongly depend upon the continuity of the gaseous phase. This effect is shown in an undisturbed soil profile after a heavy artificial rainfall of 75 mm was applied within 2 hr.

Aerodynamic performance of a fully film cooled core turbine vane tested with cold air in a two-dimensional cascade

Abstract: The aerodynamic performance of a fully film cooled core turbine vane was investigated experimentally in a two-dimensional cascade of 10 vanes. Three of the 10 vanes were cooled; the others were solid (uncooled) vanes. Cold air was used for both the primary and coolant flows. The cascade test covered a range of pressure ratios corresponding to ideal exit critical velocity ratios of 0.6 to 0.95 and a range of coolant flow rates to 7.5 percent of the primary flow. The coolant flow was varied by changing the coolant supply pressure. The principal measurements were cross-channel surveys of exit total pressure, static pressure, and flow angle. The results presented include exit survey data and overall performance in terms of loss, flow angle, and weight flow for the range of exit velocity ratios and coolant flows investigated. The performance of the cooled vane is compared with the performance of an uncooled vane of the same profile and also with the performance obtained with a single cooled vane in the 10-vane cascade.

The Choking Pressure Ratio of a Critical Flow Venturi

Abstract: The critical flow venturi has many important applications in the measurement and control of gas flow. In many of these applications, it is desirable to minimize the pressure loss required to maintain critical flow conditions. The performance of the venturi may be characterized by the ratio of outlet static pressure to inlet total pressure just sufficiently small to produce critical flow. This ratio is called choking pressure ratio (CPR). The optimization of diffusers for critical flow Venturis is discussed and suggestions for designs practice are presented. Test results are given for six different diffuser configurations, and a comparison is made with data on 11 configurations from other investigators. This work was done under contract to the National Aeronautics and Space Administration—Marshall Space Flight Center. It is shown that, for the small divergence angles considered, a simply defined diffuser effectiveness parameter is approximately independent of flow conditions and may be used to predict choking pressure ratio. Even very short diffusers greatly improve performance, and, for longer diffusers, critical flow can be maintained at total pressure losses of 5 percent.

Experimental evaluation of a Mach 3.5 axisymmetric inlet

Abstract: Wind tunnel test results for a large scale inlet model designed for Mach 3.5 are presented and compared with analytical predictions. The inlet is an axisymmetric mixed-compression type with a lip diameter of 49.723 cm. The inlet design was developed using analytical procedures. Data are shown for freestream Mach numbers from 0.6 to 3.5. The test results indicate that boundary layer bleed requirements can be accurately predicted. Good agreement was obtained with analytical predictions of the flowfield structure and boundary layer development in the supersonic diffuser yielding high performance at the design Mach number. The highest engine face total pressure recovery at Mach 3.5 was 85.8%; this was obtained at 0.05 Mach tolerance with only 2.8% total pressure distortion and 13.4% bleed. In the started Mach number range from 1.6 to 3.5, the total pressure recovery in the throat, downstream of the terminal normal shock, ranged between 91% and 95%. Total pressure losses in the subsonic diffuser varied from 3% to 13%. The higher losses occuring between Mach 2.5 and 3.2 were believed to be caused by the rapid rate of increase in the area of the diffuser just downstream of the throat, possibly coupled with inadequate centerbody throat bleed. In the unstarted mode at transonic speeds, the maximum inlet flow was over 99% of the theoretical maximum capture mass-flow.