Velocity probe

It is advisable in most of these cases to use accelerometers. Displacement probes will not give the high-frequency signals and velocity probes because their mechanical design is very directional and prone to deterioration. Figure 10-64 shows me signal from the various types of probes. 

There is also a standardized method based on the estimation of the flow rate on one measurement point only, In this method the velocity probe is placed in the duct so that the measured local velocity is equal to the mean axial velocity. In fully developed turbulent duct flow, this distance from the wall... 

The data presented in the chart are relative vibration levels (i.e., taken from a bearing pedestal using either an accelerometer or velocity probe) in inches per second (ips) peak. 

The measured pressure difference AP is the difference between the stagnation pressure in the velocity probe at the point where it connects to the DP cell and the static pressure at the corresponding point in the tube connected to the wall. Since there is no flow in the vertical direction, the difference in pressure between any two vertical elevations is strictly... 

In general, detonation test apparatus consists of a steel tube that is filled with the substance under investigation. One end of the tube is provided with a booster charge consisting of an electric detonator covered by detonative material. The other end is either closed or provided with a witness plate. One type of steel tube apparatus is provided with a velocity probe to record the shock wave velocity as shown in Figure 2.28. 

There will also be a temporal mean concentration. If there is a source or sink in the flow, or transport across the boundaries as in Figure 5.1, then the temporal mean concentration profile will eventually reach a value such as that given in Figure 5.1. This flux of compound seems to be from the bottom toward the top of the flow. Superimposed on this temporal mean concentration profile will be short-term variations in concentration caused by turbulent transport. The concentration profile is flatter in the middle of the flow because the large turbulent eddies that transport mass quickly are not as constrained by the flow boundaries in this region. Now, if we put a concentration-velocity probe into the flow at one location, the two traces of velocity and concentration versus time would look something like that shown in Figure 5.2. 

The probes get shorted on arrival of the detonation wave and the pulses generated by the event box are stored on the high speed oscilloscope. A hard copy can be obtained by using the plotter. A typical oscillogram obtained when detonation velocity is determined using two velocity probes is shown in Figure 3.19. The peaks on the oscillogram correspond to the arrival of the detonation wave at the probes. 

Unfortunately, the thinness of most liquid films makes it difficult to measure the velocity profiles experimentally, since it is practically impossible to introduce any of the usual fluid-velocity probes into a film which may be less than 1 mm. thick without grossly distorting the flow patterns. Nevertheless, film velocity profile measurements have been reported for a few special cases. 

FIGURE 9 Schematic representation of turbulent flow recorded from a velocity probe as a function of time, showing average velocity and fluctuating velocity. 

An attempt was made to measure the particle local velocity at 1.5 pipe diameters downstream of the elbow by using a particle velocity probe (56). However, the technique failed, presumably because the strong secondary fiow prevented the velocity probe from being aligned with the velocity vector. For this reason, velocities obtained at 22 pipe diameters downstream of the elbow had to be used to estimate the concentrations at this level (1.5 pipe diameters). Figure 20 shows the estimated solids concentration normalized by the discharge concentration CJC ) for fine and medium sand particles 1.5 pipe diameters downstream of the elbow. Most of the relative concentrations are lower than unity, and consequently the mean concentration based on these measurements would be lower than the true value. Similar findings were obtained by Sansone (57) in gas-solid systems downstream of a 90 elbow. This phenomenon occurs because the velocity vector and the probe axis are not colinear, so that the concentration results are only of qualitative value. 

Figure 20 illustrates flow pattern in the laminar flow region from a radial flat blade turbine. By using a velocity probe, the parabolic velocity distribution coming off the blades of the impeller is shown in Fig. 21. By taking the slope of the curve at any point, the shear rate may be calculated at that point. The maximum shear rate around the impeller periphery as well as the average shear rate around the impeller may also be calculated.

Figure 22 shows the flow pattern when there is sufficient power and low enough viscosity for turbulence to form. Now a velocity probe must be used that can pick up the high frequency response of these turbulent flow patterns, and a chart as shown in Fig. 23 is typical. The shear rate between the small scale velocity fluctuations is called microscale shear rate, while the shear rates between the average velocity at this point are called the macroscale rates. These macroscale shear rates still have the same general form and are determined the same way as shown in Fig. 21. 

VELOCITY PATTERNS AND VELOCITY GRADIENTS. More details of the flow patterns, the local velocities, and the total flow produced by an impeller have been obtained by use of small velocity probes or by photographic measurements of tracer particles. Some of Cutter s results for a 4-in. flat-blade turbine in an... 

G. Astarita and L. Nicodemo, Behavior of Velocity Probes in Viscoelastic Dilute Polymer Solutions, Ind. Eng. Chem. Fund. (8) 582,1969. 

The sampling procedure calls first of all for determination of the streaming gas velocity profile. For this purpose, a dynamic velocity probe is used (Prandtl or Pitot tube). This determines the dynamic pressure value at a particular measured point of the given profile. The gas flow rate at the i-the point, u, is directly proportional to the square root of the dynamic pressure at the same point according to the relationship ... 

Figure 25 Schematic diagram of room calorimeter test (ISO 7905). 1. Room. 2. Gas burner ignition source. 3. Room exit door. 4. Hood. 5. Fire gas mixing baffles. 6. Gas sampling, temperatures, and velocity probes, smoke measuring sensors. 7. Exhaust fan. Note Furniture calorimeter is similar but without room. Test. specimen is burned directly under hood (NT Fire 032).

The moving of the flame front may be followed using the ionisation probes (or other types of velocity probes)/electronic counter (or oscilloscope) technique. Optical and electrooptical methods may be used as well. 

SAMPLE HOLDER VELOCITY PROBE VESSEL BODY... 

Moreover, applying a special kind of velocity probe and an oscilloscope technique (Subsection 4.1.5) or an optical technique (Subsection 4.1.2), it is possible to obtain continuous viewing of the flame front vsdien it travels through the sample. That in turn enables the combustion rate in any part of the sample or at any moment during the combustion process to be obtained. 

Determination of the Detonation Velocity Using Electronic Counter and Velocity Probes Technique... 

A short time interval needed by the detonation wave to travel a known distance between two velocity probes (or pins) through the explosive is determined by an electronic counter. Thus, the detonation velocity is obtained as a ratio between the distance traveled and the corresponding time interval. 

The measuring system that uses an electronic counter/velocity probes technique is schematically represented in Figure 4.9. 

---