Pressure measurement, point

Reciprocating Reciprocating pumps are more difficult to monitor because of the combined rotational and linear motions that are required to increase the discharge pressure. Measurement-point location and orientation should be based on the same logic as that of reciprocating compressors. 

If the outflow downstream from the venous catheter is suddenly occluded, the venous pressure increases, and its rate of increase is measured. The rate of inflow is also measured so that the compliance can be estimated as the ratio flow to rate of pressure rise Compliance in ml/mmHg = (flow in ml/min)/(rate of venous pressure rise in mmHg/min). The method is predicated on the assumption that the inflow continues at a constant rate and that there is no pressure gradient between the pressure measuring point and the site of compliance for the first few seconds of occlusion when the rate of pressure rise is measured. 

The model is three-dimensional. In order to comprehensively analyze the distribution of flow field, 260 sampling points for 4 levels in goaf are sampled in a short time, and then the gas concentration of samples was analyzed and tested by GC-4000 A gas chromatograph. The sampling points are also used as pressure measurement points. The static pressure of points are absorbed by the YJB-1500-type compensator micro-manometer, and the wind speed and static pressure of intake and return airway were measured by electronic wind instrument and U-type differential pressure meter. 

For micromixers for which experimental pressure drop data are available, it is possible to estimate the specific power dissipation from Equation (6.4) between the inlet and the outlet pressure measurement points. It is assumed here that the estimated specific power contributes to mixing, which is a rough estimation because of the pressure drop induced by the micromixer pipe connections. In Figure 6.9 is plotted the mixing time with respect to the specific power dissipation for several mixers. The experimental mixing times scale fairly well as a power law of the... 

Some of the factors that should be considered in locating the pressure measuring point are ... 

The calibration curve of each rosetta strain gauge was so obtained and ftg.5 shows the sum of the principal stresses at the measuring points versus pressure inside the vessel. Further tests were carried out to obtain the calibration factor and to check that it remained constant on the whole scan area of the test surface. This was achieved through additional measurements using the SPATE system on fixed points on the surface located very close to the applied rosetta strain gauges. This procedure gave the following results ... 

Fig.5 Sum of the principal stresses at the measuring points versus pressure inside the vessel.

The activity coefficients of sulfuric acid have been deterrnined independentiy by measuring three types of physical phenomena cell potentials, vapor pressure, and freeting point. A consistent set of activity coefficients has been reported from 0.1 to 8 at 25°C (14), from 0.1 to 4 and 5 to 55°C (18), and from 0.001 to 0.02 m at 25°C (19). These values are all based on cell potential measurements. The activity coefficients based on vapor pressure measurements (20) agree with those from potential measurements when they are corrected to the same reference activity coefficient. 

Liquid Column Density may be determined by measuring the gauge pressure at the base of a fixed-height hquid column open to the atmosphere. If the process system is closed, then a differential pressure measurement is made between the bottom of the fixed height liquid column and the vapor over the column. If vapor space is not always present, the differential-pressure measurement is made between the bottom and top of a fixed-height column with the top measurement being made at a point below the liquid surface. 

Instrumentation Calibration may be required for the instruments installed in the field. This is typically the job of an instrument mechanic. Orifice plates should be inspected for physical condition and suitabihty. Where necessary, they should be replaced. Pressure and flow instruments should be zeroed. A prehminary material balance developed as part of the prehminary test will assist in identifying flow meters that provide erroneous measurements and indicating missing flow-measurement points. 

Measurement versus Equipment Performance Pumps that are in reasonable condition typically operate within 5 percent of their pump curve. Consequently, pressures and flows that are inconsistent with the pump curve imply that the indicated flow and/or pressure are incorrecl . Figure 30-16 shows a single impeller curve plotted as head versus flow. The point shown is inconsistent with the pump operation. Therefore, that pair of flow and pressure measurements is not validated and should not be used in the subsequent steps. 

I he origins of the above two errors are chfferent in cause and nature. A sim ple example is, when the mass of a weight is less than its nominal value, a systematic error occurs, which is constant in absolute value and sign. This is a pure systematic error. A ventilation-related example is, when the instrument faaor of a Pitot-static tube, which defines the relationship between the measured pressure difference and the velocity, is incorrect, a systematic error occurs. On the other hand, if a Pitot-static tube is positioned manually in a duct in such a way that the tube tip is randomly on either side of the intended measurement point, a random error occurs. This way, different phenomena create different ty pes of error. I he (total) error of measurement usually is a combination of the above two types. 

With the single-channel method, data are acquired in series or one channel at a time. Normally, a series of data points are established for each machine-train and data are acquired from each point in a measurement route. While this approach is more than adequate for routine monitoring of relatively simple machines, it is based on the assumption that the machine s dynamics and the resultant vibration profile are constant throughout the entire data acquisition process. This approach hinders the ability to evaluate real-time relationships between measurement points on the machine-train and variations in process parameters such as speed, load, pressure, etc. 

Restrictions or other causes of back-pressure in the discharge piping deflect the shaft in the opposite direction. Referring back to the illustration, the shaft would be deflected toward the front of the picture. If the discharge were vertical and in the downward direction, the primary radial measurement point would be at the top of the pump s bearing cap looking downward. 

A second radial (Y-axis) measurement point should be positioned at 90° to the primary in a plane that captures secondary shaft deflection. For the pump illustrated in Figure 44.21, the secondary (Y-axis) radial measurement point is located on top of the pump s bearing cap and oriented downward. Since the pump has a clockwise rotation, back-pressure in the discharge piping forces the shaft both downward and horizontally toward the front of the picture. 

A visual inspection of the blower indicated that the discharge is horizontal and opposite the measurement point location. By checking the process parameters recorded concurrent with the vibration measurements, we found that the motor was in a no-load or run-out condition and that the discharge pressure was abnormally low. In addition, the visual inspection showed that the blower sits... 

Two additional points near 17.0 and 20.3 K are required. These may be determined by using either ihe constant volume gas thermometer or by vapor pressure measurements of H . 

In Equation 5.2.2, it is assumed that acoustic wavelengths A are large when compared with any of the characteristic scales of the flow (A L) and that the measurement point r is far from the source region (r /l). The previous expression provides the sormd pressure in the far-field for a compact source, but it can be used indifferently for premixed or nonpremixed flames [30]. 

The depression of the activity may be measured in various ways. The most obvious would involve a measurement of the vapor pressure lowering, but this method is superseded by others both in accuracy and in simplicity of execution. The boiling point elevation and freezing point depression methods relegated vapor pressure measurement... 

The pitot tube is a device for measuring v(r), the local velocity at a given position in the conduit, as illustrated in Fig. 10-1. The measured velocity is then used in Eq. (10-2) to determine the flow rate. It consists of a differential pressure measuring device (e.g., a manometer, transducer, or DP cell) that measures the pressure difference between two tubes. One tube is attached to a hollow probe that can be positioned at any radial location in the conduit, and the other is attached to the wall of the conduit in the same axial plane as the end of the probe. The local velocity of the streamline that impinges on the end of the probe is v(r). The fluid element that impacts the open end of the probe must come to rest at that point, because there is no flow through the probe or the DP cell this is known as the stagnation point. The Bernoulli equation can be applied to the fluid streamline that impacts the probe tip ... 

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