Cloud of charge

An AC corona discharge in the throat leads to a cloud of charged droplets whose large momentum allows very long travel distances. Multiple devices for eliminating static discharges in powder silos have been tested [41] but the tests did not address typical flow rates for large capacity, dense phase pneumatic transfer operations. 

A molecule may be viewed as a number N of nuclear charges, Z e, of a certain arrangement given by their position vectors, Rt for i = 1... JV, surrounded by an electronic cloud of charge density p(r) of finite dimensions. The potential of the electrostatic field at the point R outside the electronic cloud is given by... 

Figure 8-2 An ionic atmosphere, shown as a spherical cloud of charge 8+ or S-, surrounds ions in solution. The charge of the atmosphere is less than the charge of the central ion. The greater the ionic strength of the solution, the greater the charge in each ionic atmosphere.

Jj( 1) is the potential energy of interaction between the point charge of electron 1 and electron 2 considered to be smeared out into a hypothetical charge cloud of charge density (charge per unit volume) - e)Hartree-Fock method considers average interelectronic interactions, rather than instantaneous inter-... 

In the case of a cloud of charged particles, let the totality of charge be i , and k the specific inductive capacity, then... 

A. 19.8 The Gouy-Chapman model replaces the double layer of the Helmholtz-Perrin model with the diffuse cloud of charge that was more concentrated near the electrode. One of its fundamental problems is that it ignores the effect of the dielectric constant of high-potential fields present at the interface. See Fig. 20.4... 

One other crucial featme of the model is that aU the ions in the ionic atmosphere which would normally be thought of as a set of discrete charges are to be replaced by a smeared out cloud of charge which varies continuously from point to point, with the charge density... 

This smeared out cloud of charge density is the ionic atmosphere of the centraly-ion, and... 

Step 3 involved smearing out of the discrete ions of the ionic atmosphere into a continuous cloud of charge so that the Poisson equation could be used. The problem in this step, however, is to find the actual distribution of the discrete ions of the ionic atmosphere around the central y -ion. Statistical mechanics in the form of the Maxwell-Boltzmann distribution is used. The derivation of the Maxwell-Boltzmann distribution automatically involves an implicit averaging process, but this statistical mechanical averaging is different from that used for the Poisson equation when smearing out has been done. 

The physical restriction arises from the concept of the ionic atmosphere which is the basic postulate of the Debye-Hiickel theory. The ions in the ionic atmosphere are not treated as discrete charges, but are described in terms of a smeared out cloud of charge density. Such a description is only valid if 1/k is significantly greater then the diameter of an ion, a. The model of a continuous charge fails when 1/k becomes of the order of the distance of closest approach, a (see Table 12.4). 

The same expression also means the interaction energy (in a.u.) of two charges 1 (pointlike elementary charge —1) and 2, represented by a diffiised cloud of charge density distribution P(2) = IZf °2p/(2) carrying N elementary charges —1 because — / p(2)dV2 = —2 1 =... 

These diagrams are also called electron cloud depictions because, if we could take a time-exposure photograph of the electron in wavelike motion around the nucleus, it would appear as a cloud of positions. The electron cloud is an imaginary picture of the electron changing its position rapidly over time it does not mean that an electron is a diffuse cloud of charge. 

In the case of the electrostatic fluidised bed, a combination of the electrostatic spray technique and the fluidised bed technique is used. The apparatus consists of an array of electrostatic elements on the bottom of a shallow bed. A small quantity of powder is placed on the elements and fluidised by the normal method. The elements impart a negative charge to the powder with the result that a cloud of charged powder is obtained. An earthed object held in the cloud collects a layer of powder by electrostatic rather than fluidised bed principles. Unfortunately, the density of the cloud varies considerably from top to bottom and is sensibly uniform over only 4 in. This is offset somewhat by the fact that an electrostatic fluidised bed requires only one-tenth of the raw material compared with an equal sized conventional fluidised bed and this helps considerably as far as stock holding of colours is concerned. 

In the continuous powder coating of wire—most often for fencing, but occasionally for insulated cable components — it is advantageous to use electrostatic fluidized bed devices. In these, electrodes arc embedded in the fluidized compound and a ground plate is mounted above the bed. This produces a cloud of charged compound particles above the actual bed, permitting the wire (also grounded) to be mn... 

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