Electrostatic precipitator diffusion charging

According to this approximation, the drift velocity is proportional to the square of the electric field. This is a clear indication of the importance of the electric field inside an electrostatic precipitator. Equation (13.60) is a valid approximation for large particles [dp > 0.5 m), provided that particle charge is close to the saturation level. In the case of small particles, the effect of diffusion charging must be taken into account. 

Gaseous ion diffusion A method of charging particles in an electrostatic precipitator. 

For particles smaller than about 0.05 rm, the diffusion charging theory discussed above breaks down the calculated number of charges per particle decreases to a value less than unity which is physically unacceptable. Instead, only a fraction of such particles acquire unit charge for values of the product in the range usually of interest in such applications as electrostatic precipitation and aerosol instrumentation (< 10 ions sec cin - ). 

IKelectroNtiitic forces fail for uncharged ultrafine particles, there are at least two Ollier possible removal mechanisms. Ultrafine parlieics can diffuse to tlic collecting plates or cun coagulate with charged courser panicles that then deposit. Coagulation is discussed in Chapter 7. The other mechanism, difftisional transport, appears with electrostatic precipitation in the combined (lux expression (3.91), which, for u,/ > c, reduces to l7 = u,/iioc. 

Electrostatic charger—with diffusion charging upper Umit is about 2 pm senses both nuclei and accumulation modes 0.007-0.02 2-25 1 pg/m Charging and precipitation n S ... 

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