Streaming current

L is the pipe length (m), and r is the liquid relaxation time (seconds). 

The relaxation time is the time required for a charge to dissipate by leakage. It is determined using 

Britton, Avoiding Static Ignition Hazards in Chemical Operations (New York American Institute of Chemical Engineers, 1999). 

Chemical Engineers Handbook, 3d ed. (New York McGraw-Hill, 1950), p. 1734. Resistance = 1/conductivity = l/(raho/cra) = ohm cm. 

Specific conductivities and relative dielectric constants are listed in Table 7-2. 

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The presence of surface conductance behind the slip plane alters the relationships between the various electrokinetic phenomena [83, 84] further complications arise in solvent mixtures [85]. Surface conductance can have a profound effect on the streaming current and electrophoretic mobility of polymer latices [86, 87]. In order to obtain an accurate interpretation of the electrostatic properties of a suspension, one must perform more than one type of electrokinetic experiment. One novel approach is to measure electrophoretic mobility and dielectric spectroscopy in a single instrument [88]. 

Automated controls for flocciJating reagents can use a feedforward mode based on feed turbidity and feed volumetric rate, or a feed-back mode incorporating a streaming current detector on the flocculated feed. Attempts to control coagulant addition on the basis of overflow turbidity generally have been less successful. Control for pH has been accomplished by feed-forward modes on the feed pH and by feed-back modes on the basis of clarifier feedwell or external reaction tank pH. Control loops based on measurement of feedwell pH are useful for control in apphcations in which flocculated sohds are internaUy recirculated within the clarifier feedwell. 

Streaming Current Detectors These units produce a measurement closely related to the zeta potential of a suspension and are used successfully in optimizing the coagulant dose in clarification applications. 

Several devices are available commercially to measure mobihty. One of these (Zeta-Meter Inc., New York) allows direct microscopic measurement of individual particles. Another allows measurement in more concentrated suspensions (Numinco Instrument Corp., Monroeville, Pa.). The state of the charge can also be measured by a streaming-current detecdor (Waters Associates, Inc., Framingham, Mass.). For macromolecules, more elaborate devices such as the Tisehus moving-boundaiy apparatus are used. 

Of considerable usefulness in transporting heat toward the poles are the ocean currents. They are particularly effective because of the high heat content of water. Significant poleward-moving currents are the Brazil, Kuro-shio, and Gulf Stream currents. Currents returning cold water toward the equator are the Peru and California currents. 

The streaming current that is generated while transporting solids is a function of the solids processing method (see Table 7-3) and the flow rate, as shown by... 

Capacitances of various materials used in the chemical industry are given in Table 7-5. Charges can accumulate as a result of a streaming current dQldt = Is. Assuming a constant streaming current,... 

The streaming current is a function of the velocity and the pipe diameter. The average velocity in the pipe is... 

If the flows, streaming currents, and relaxation times are constant, Equation 7-35 is a linear differential equation that can be solved using standard techniques. The result is... 

Compute the accumulated charge and energy for a 100,000-gal vessel being filled with a fluid at a rate of 200 gpm and having a streaming current of 2 X 10-6 amp. Make the calculation for a fluid having a conductivity of 10-18 mho/cm and a dielectric constant of 2.0, Repeat the calculation for (a) a half full vessel, (b) a full vessel, and (c) a full vessel with an overflow line. 

There are actually no experimental measurements of protonic streaming currents (Lu) and coupled water and methanol transport (L23 = L32) however, the first may be related to the hydrodynamic component of the electro-osmotic drag L /Ln, Lis/Lu) (see discussion in Section 3.2.1.1). The second is expected to be qualitatively related to the ratio of the electro-osmotic drag coefficient of water and methanol (L12/Z.13). In the following, the directly accessible transport coefficients o (Do), FH2O, MvieOH,... 

An obvious idea arises now. If an electric field X can achieve what a pressure difference AP normally does, namely, produce a liquid flow, then perhaps a pressure difference will produce an electric current, which is normally the result of an electric field. Experiment (Fig. 6.135) once again yields an interesting answer an electric current known as a streaming current is in fact produced by a pressure difference. 

The streaming-current constant a3 is the streaming-current density produced by a unit pressure difference. 

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