Micromanometers

There are certain limitations on the range of usefulness of pitot tubes. With gases, the differential is very small at low velocities e.g., at 4.6 m/s (15.1 ft/s) the differential is only about 1.30 mm (0.051 in) of water (20°C) for air at 1 atm (20°C), which represents a lower hmit for 1 percent error even when one uses a micromanometer with a precision of 0.0254 mm (0.001 in) of water. Equation does not apply for Mach numbers greater than 0.7 because of the interference of shock waves. For supersonic flow, local Mac-h numbers can be calculated from a knowledge of the dynamic and true static pressures. The free stream Mach number (MJ) is defined as the ratio of the speed of the stream (V ) to the speed of sound in the free stream ... 

Several micromanometers, based on the liquid-column principle and possessing extreme precision and sensitivity, have been developed for measuring minute gas-pressure differences and for cahbrating low-range gauges. Some of these micromanometers are available commercially. These micromanometers are free from errors due to capillarity and, aside from checking the micrometer scale, require no cahbration. See Doolittle, op. cit., p. 21. 

The sensitivity of the well manometer can be adjusted by changing the angle or and can be some 30 times that of the U-tube. This type is also often called a micromanometer due to its ability to measure very small pressure differences. Several other types of micromanometers and fluid manometers are also available. 

The Prosser was calibrated by measuring the air flows using a laminar flow meter (1% accuracy) for the odorous sample and a pitot tube with a micromanometer for the fan-blown air (3). The pitot pressures were converted to air velocities (4) and hence, from the cross sectional area of the tube, to volumetric flow rates. Since flow near the tube wall was slower than the centre, the tube was traversed by the pitot head and the average value calculated. A rotameter was also tried but it induced a back-pressure of 250 N/m2 and, as the manufacturer states that the maximum permissible back-pressure is 60 N/m for calibration to be accurate, its use was not pursued. 

Air flow volume electronic micromanometer with appropriate air flow hood, or equivalent... 

The excess pressure at a certain point z in the foam column which can be measured with a micromanometer [36] equals... 

The reduced pressure in foam Plateau borders can be measured with a capillary manometer, developed by Khristov et al. [31,32]. A number of modifications of such a micromanometer are available. 

The main element of any micromanometer is a capillary hermetically welded to a porous plate (usually a sintered glass filter) with a suitable size of pores. This filter ensures a contact between the liquid in the capillary and the foam Plateau borders. 

From the ratio between the air volume in the wider capillary part and the liquid in the capillary it is possible to calibrate the micromanometer for various ranges of pressure change. A disadvantage of these manometers is that a liquid flowing from the micromanometer can enter the foam. 

Fig. 4.3. Schematic presentation of the compensatory micromanometer 1 - capillary with a porous plate ...

An important condition which has to be fulfilled when using this method for foam dispersity determination is the absence of an excess hydrostatic pressure in the foam liquid phase. This pressure is equalized to a considerable extent when an equilibrium distribution the foam expansion ratio and the border pressure along the height of the foam column is established. This can be controlled by measuring the pressure in the Plateau borders at a certain level of the foam column by means of a micromanometer. However, if this condition is overlooked, the hydrostatic pressure can introduce a considerable error in the results of bubble size measurements, especially in low expansion ratio foams. Probably, it is the influence of the unrecorded hydrostatic pressure that can explain the lack of correspondence between the bubble size in the foam and the excess pressure in them, observed by Aleynikov[49]. The... 

A device for foam dispersity determination by measuring the local foam expansion ratio and the pressure in Plateau borders is illustrated in Fig. 4.4. It consists of a glass container equipped with platinum electrodes and a micromanometer. The container bottom is a porous plate (a sintered glass filter). The pressure Ap is measured with a capillary micromanometer and the expansion ratio is determined by the electrical conductivity of the foam. The manometer and the electrodes are positioned so that to ensure a distance of 1.0-1.5 cm between them and the porous plate. When the distance is small the liquid in the porous... 

I - foam container 2 - micromanometer 3 - electrodes 4 - porous plate 5 - stopcock. 

The accuracy of the discussed technique for measuring bubble size is influenced mainly by the degree of foam polyhedricity and by the precision of pressure measurement with the micromanometer. With the increase in Ap this precision increases. For dry foams the error... 

The radius of border curvature in a polyhedral foam which conforms the condition r/a 1 is the easiest to determine. If a micromanometer is used to measure the capillary pressure pa, then the radius of border curvature r can be calculated by combining Eqs. (1.40) and (1.45)... 

A mobile capillary micromanometer that can be set at various levels of the foam column, thus allowing pressure measurements at different points, can be used to evaluate the dependence of the radius of border curvature on the coordinates of either gravitational field or pressure gradient [51,68]. For a simultaneous determination of both the pressure and the radius of border curvature at non-steady state flow (for example, gravitational drainage) a system of a number of micromanometers can be used. 

As confirmed by the experimental studies, the border profile corresponds to the cylindrical model only at the final stage of the drainage process when the capillary pressure in borders is close to the equilibrium value. That is why Eq. (5.37) can be used to calculate Cexp reached at the final drainage stage. However, it must be kept in mind that the pressure should be measured with a micromanometer at the foam column top. 

The capillary pressure was measured by two independent methods by a compensatory and closed micromanometers and by an optical method for determination of the radius of border curvature [57,58], The data in Table 5.2 indicate that at Apo = 104 Pa the final capillary pressure is equal to the applied pressure drop in all cases studied. At Ap0 = 2104 Pa the capillary pressure reaches an equilibrium value only in foams from non-ionic surfactants. For... 

Fig. 8 Comparison of measured and calculated pressure drops. The measurements were carried out at the demonstration plant of Pori Forest Institute and the pilot plant at Nakkila Works, Terasmaki, The uncertainty of the micromanometer is + 1 Pa and of the volume rate measuring device 0.5%.

Isolated right ventricular tissues were used to measure the contribution of P-AR signaling to contractility. Cardiac inotropy was monitored in isolated, paced right ventricular muscle strips. Preparations from pr AR-KO mice failed to show any responsiveness to isoproterenol administration, while wild-type preparations showed robust inotropic responses (28). This lack of contractile response is not caused by generalized hyporesponsiveness of the contractile apparatus because prAR-KO ventricles responded normally to activators of adenylyl cyclase such as forskolin. Surprisingly, disruption of both pr and P2-ARs has only modest effects on resting left ventricular contractility in vivo. When contractility was assessed with a micromanometer-tipped catheter, -i-dP/dt was reduced by 20% and -dP/dt was reduced by 12% in p /prAR-KO mice compared to wild-type mice (30). 

Compression and Decompression Studies. Bovine serum albumin was spread on an isoelectric substrate (pH 5.3) and initially compressed to a pressure (tt) of 5 dynes/cm. The molecular weight of the protein, 66,590 g/mole (pH 5.35 at 26°C and co-surface of 12,000 A2/molecule) was determined with a surface micromanometer. The moving barrier compressed the monolayer at a constant rate of 1.96 X 10"2 cm/sec for 60... 

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