The Saltation Velocity in Horizontal Transport

In the region E and F some solids may move in dense phase flow along the bottom of the pipe whilst others travel in dilute phase flow in the gas in the upper part of the pipe. The saltation velocity marks the boundary between dilute phase flow and dense phase flow in horizontal pneumatic transport. 

Once again, it is not possible to theoretically predict the conditions under which saltation will occur. However, many correlations for predicting saltation velocity are available in the literature. The correlation by Zenz (1964) is frequently used but is entirely empirical and requires the use of a graph. It is reported by Leung and Jones (1978) to have an average error of 54 %. The correlation of Rizk (1973), based on a semi-theoretical approach, is considerably simpler to use, and has a similar error range. It is most unambiguously expressed as  

Hsait is the superficial gas velocity (see Section 8.1.4 for the definition of superficial velocity) at saltation when the mass flow rate of solids is Mp, the pipe diameter is D and the particle size is x. (The units are SI.) 

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