Static Pressure Differences Research Articles

Steady pressure-flow relationship in a cast of the upper and central human airways

Pressure drops across the upper (larynx) and central airways of a human lung cast were measured at steady state inspiratory and expiratory flows. Air, HeO 2 and SF6-O 1 gas mixtures were used at tracheal Reynolds' numbers ranging from 145 to 30 000. The pressure-flow characteristics of the model were analysed using standard pressure-flow diagrams and Moody plots. We found that the asymmetry between inspiratory and expiratory resistances, observed in the central airways (larynx excluded), was markedly reduced in the presence of the larynx. However, static pressure differences were greater across the entire model of the upper and central airways than across the model of the five generations of the tracheo-bronchial tree (without larynx) at the same flow-rates. In addition, our results showed that the presence of the larynx tended to reduce the zone of fully developed laminar flow in the Moody diagram with the higher density gas, while extending the zone of turbulent flow even for the low density gas at low Reynold's numbers.

Flow and Pressure Balancing in a Fluid Interface Impactor

Fluid interface impactors, such as virtual and opposing jet impactors, require particular attention to flow and pressure balance in the incoming and outgoing airstreams. The relationship of flow rate to pressure drop has been studied in an opposing jet aerosol classifier of rectangular design. In tests of the sensitivity of classifier operation, changes in pressure differences across the inlets and the outlets were associated with changes in the flow balances of 0.5 and -1.0%/mm w.g., respectively. These flow sensitivities may be used in conjunction with cut size sensitivities to conclude that the appropriate measurements to use for classifier control are the static pressure differences between the two inlets and between the two outlets, rather than the mass flow rates of the four jets. For aerosol size classification tests, a nebulizer-virtual impactor polydisperse aerosol generator was designed to reduce the concentration of small particles and make the generator compatible with dynamic optical particle...

Steady expiratory flow-pressure relationship in a model of the human bronchial tree.

Static pressure differences across a human bronchial tree model were obtained for steady expiratory flows of several gases producing Reynolds numbers (Re1) in the bronchus carrying the entire flow (first bronchus) between 150 and 50,000. The model was constructed from an air-dried lung and was complete to bronchi about 2 mm in diameter. Dimensionless static pressure plotted against Re1 consolidated the data on a single curve, phenomenologically described by an equation of the form: delta Ps/delta Pd1 = A + B Re1 where delta P d1 is a pressure drop for Poiseuille flow, Velocity profile measurements at two sites along the first bronchus for laminar and turbulent flows indicate a dependence on the latter and distance from the first junction. Loss in total pressure was computed and may result from both frictional dissipation and changes in momentum flux associated with development of velocity profiles near the junctions. An average loss in total pressure within a single bronchus was calculated after making several simplifying assumptions, and this result may be useful in modeling both the resistance of the entire bronchial tree and the more complex phenomenon of maximal expiratory flow.

Steady pressure-flow relationship of a model of the canine bronchial tree.

Static pressure differences (deltaP) across the entire length and portions of a latex reproduction of a canine bronchial tree were measured during steady inspiratory or expiratory flow (V). The reproduction consists of a 10-cm length of trachea through bronchi of about 2 mm in diameter. The airflow was simulated by a water flow with tracheal Renolds number (Re0) in the range from 1,500 to 10,000. Loss in total pressure (deltaPt) was computed by summing deltaPt and V were well described (r greater than 0.98) by a dimensionless Rohrer equation deltaPt/deltaPd0 = A + B Re0 applicable to gas flow, in which deltaPd0 is a Poiseuille pressure drop. For expiratory deltaPt, A was about twice that for inspiration, while the values for B were nearly equal. Differences in kinetic energy between sites of static pressure measurement are important in determining loss in total pressure. Rohrer's equation is a good approximation to the phenomenological laws of steady inspiratory and expiratory flow-pressure relations in the canine bronchial tree for the range of Reynolds number investigated.

Patency of the Eustachian Tube in Different Body Positions

The Eustachian tube function was studied during simulated descents and ascents in 5 experienced divers, all known to have a good capacity for equilibrating static pressure differences across the ear-drum. Their ability to equilibrate by deglutitions during descents was greatly reduced in the recumbent as compared with the sitting position, and when tilted with the head downwards no one could equilibrate completely. The pressure level required to passively force the Eustachian tubes open during ascent was recorded higher in recumbency and still higher when the subject was tilted as compared with the sitting position. The pressure level in the rhinopharynx required to force the Eustachian tubes open during Valsalva’s manoeuvre was also higher in the recumbent and tilted positions. It was also observed that a higher speed of pressure increase in the rhinopharynx resulted in a higher pressure level for passive opening of the tubes.

参照静圧管を利用した静圧平衡形等速吸引装置の開発に関する研究

In the case of the measuring dust content in the flue gas, the gas sample should be drawn into the suction nozzle of the dust collector at the same velocity as that of the flue gas. That is well known isokinetic sampling.Presently, there are some isokinetic samplers with the null balance type nozzles by which the isokinetic suction can be very easily performed. One of those is the static pressures balance type isokinetic sampler. It has, however, a few problems, e. g., that the construction is of a greatest complexity and a big form. Therefore, we have studied for developing a new isokinetic sampler with the reference static pressure tube according to a new principle of measuring.The first step in the experiment was to measure inside static pressures of the suction nozzle in the isokinetic conditions.We designed the reference static pressure tubes which had the same frontal shapes and showed the same static pressures as those of the suction nozzles.Using the dust sampler equipped with the suction nozzle and the reference static pressure tube, the suction errors have been measured in relation to the static pressure differences and the excellent characteristics have been experimentally confirmed.

Analysis of Flow Separation in an Annular Expansion—Contraction With Inner Cylinder Rotating

A three-dimensional incompressible isothermal laminar separation of a Newtonian fluid in transient and steady flow was investigated. The geometry chosen for this study was an annular expansion-contraction chamber with a rotating inner cylinder. It was found that an adaptation of a numerical solution first proposed by Fromm gave converged solutions for all Reynolds numbers in the laminar range. Theoretical computer plotted streamline patterns were superimposed on time exposure photographs of air bubbles in transparent oil. Measured static pressure differentials were compared with laminar theory. Turbulent flow was studied experimentally.

Importance of Superimposed Acoustic, Static, and Dynamic Loadings and Their Application to Aerospace Structural Testing

The effects of interactions between acoustic, static, and dynamic loadings during design and analysis of structures have received relatively little attention. Now, the importance of combined-loads reliability testing has been documented by an aerospace survey. Numerous premature acoustic-fatigue failures were uncovered—indicating the necessity for time-mission-history simulation during testing to ensure realistic environmental loading. In this study, the importance of combined acoustic, static, and dynamic loadings is discussed in terms of (1) general principles that must be considered, and (2) testing arrangements that are applicable to difficult and costly vehicle-reliability problems. Methods are presented for selected combined-loading situations, which are graphically illustrated to show appropriate means of load application when test articles are simultaneously subjected to high-energy acoustic environments. Several new approaches are presented to the load-superposition challenge requiring accurate simulation and noninterference with structural response during sonic excitation. Typical of the proposed combined-load arrangements is that of an engine-intake airduct that is subjected during service life to considerable fatigue-induced damage contributed by high-frequency compressor whine, static differential pressure, and dynamic unbalance. An unconventional solution to this problem is suggested whereby the fatigue-producing parameters are simultaneously introduced without utilizing an operating engine.

Control of blast furnace operation according to static pressure differences

Control of blast furnace operation according to static pressure differences

Calibration of Sensitive Differential Pressure Devices

A new technique for the calibration of static, differential pressure sensing devices is described. The system of calibration is explained and the necessary equations are developed in detail. The basis of this technique for producing known values of very small static pressure differences is that of the air centrifuge. This method has been employed for developing pressure differences as small as 10−6 psi.