Particle Technology

gas cleaning

Problems 14.6

Question 2.vi

Having assumed steady settling of the 50 micron particle in air (at the same rate as if the air was static) we had now better check to see if this conceptual model makes sense. We will do this by calculating the flow Reynolds number. However, we need to account for the rectangular cross-section of the flow channel, see below.

The characteristic linear dimension to use in a flow Reynolds number calculation is the hydraulic mean diameter which is 4 times the area open to flow divided by the wetted perimeter. Note, for gases the wetted perimeter is simply the actual perimeter. The hydraulic mean diameter of the above settling chamber system is 0.3 m.

	a) 440000 b) 180000 c) 99000 d) 89000
Note, OK these are all turbulent, but which one is correct?