Particles conductivity probe measurements

Consider a ball probe of a conductive sphere such as a stainless steel ball bearing which is connected to an electrometer. When the ball probe is placed in a flow system, the electric current induced by charge transfer between the ball and the flowing charged particles can be measured. The amount of current measured will vary with the particle velocity and particle mass flux. 

Figure 31 shows the resistivity measured by the conductivity probe and the local concentration measured by the isokinetic sampling method. Measurements were made for slurries of polystyrene particles of 1.4-mm mean diameter at the pipe center and at radial positions of R = 0.8. Good agreement with calibration results is seen in these tests. Because the particles used in these experiments were large, no samples could be withdrawn from the center of the pipe at concentrations higher than 35%. Also, no voltage measurements could be taken closer to the pipe wall because particles tended to be trapped between the probe and the wall. 

Figure 23. A conductivity probe for measuring local particle velocity. (Reproduced with permission from reference 88. Copyright 1983.)...

To measure local particle velocity in slurry pipelines, Brown et al. (88) modified Beck et al. s (86, 87) conductivity method. They developed a new conductivity probe where four electrodes are mounted on an L-shaped probe. The probe has two field electrodes and two sets of sensor electrodes separated by a known distance (Figure 24). The probe is capable of measuring particle velocity in vertical and horizontal slurry... 

Optical probes are insensitive to changes in temperature and to impurities that do not absorb or scatter light. An optical probe will give an accurate and precise measure of the concentration of solids for which a prior calibration has been carried out. The probes are generally less susceptible to interference than conductivity probes. They should be used under laboratory conditions, although in some cases they may be used in industrial process plant. Optical probes can normally be used only to measure low solids concentrations (up to 2 to 3 vol %). Care should be taken to avoid errors due to changes in particle size distribution during measurement. 

Figure 3 Schematic diagram of the ambient particle concentrating system used to conduct animal exposures. The RH/T probe measures relative humidity and temperature. Specific honeycomb denuders can be used to remove varying gaseous aerosol components (14,15). (From Ref 14.)...

Microwave absorption and luminescence decay measurements have been independently carried out to monitor the charge injection from excited Ru(bpy)2-(dcbpy)2+ into Sn02, ZnO, and Ti02 nanocrystallites [245]. Since microwave conductivity arises as a result of mobile charge carriers within semiconductor particles it is possible to probe the charge injection process by monitoring the growth in the microwave absorption [178]. 

Experimental studies have been conducted by Bi et al. (1990) in a fast fluidized bed 186 mm in inside diameter at ambient temperature. FCC particles with a mean size of 48 fan were employed, and three cylindrical heat probes, 10 mm in diameter and 40,80 and 160 mm in length, respectively, were used. The probes, made of copper-sheathed inner heating elements, were instrumented with thermocouples 40 mm apart on the surface for the measurement of surface temperature. Located 2.9 m above the distributor, the probe was installed either upward or downward (see Fig. 5), and was moved along the radial direction by two connecting sticks for the measurement of heat transfer coefficients for different orientations and at different radial positions. 

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