hydraulic radius

English

Noun

hydraulic radius (plural hydraulic radii)

1. (hydraulics, surface science) For a porous material, the ratio of porosity (ratio of volume of interstitial space filled with fluid to volume of material) to specific surface area (ratio of surface area in contact with fluid to volume of material); for a pipe or channel, the ratio of cross-sectional area to wetted perimeter.
   • 1998, Robert Tijssen, “2: The Mechanisms and Importance of Zone-Spreading”, in Elena Katz, Roy Eksteen, Peter Schoenmakers, Neil Miller, editors, Handbook of HPLC, Marcel Decker, page 79:

     The hydraulic radius is found from the definition R_h = ([volume of (interstitial) pore space filled with fluid]/[surface area of (interstitial) pore apace in contact with fluid]) = (porosity (ε₀)/specific surface area (S_v)), where both ε₀ and S_v are practical and experimentally measurable characteristics of porous materials.

   • 2005, Jose Liria Montanes, Hydraulic Canals: Design, Construction, Regulation and Maintenance, Taylor & Francis, page 175:

     However, it is a better plan to use the tractive force formula, t = 1000·R·J, since this explicitly indicates the intervening factors, which are hydraulic radius and slope. In order to reduce the tractive force, it is necessary to reduce the hydraulic radius or the slope or both.
     It should be remembered that the hydraulic radius is the relationship between the useful area and the wet perimeter of the canal's section, but in a certain fashion this is also an index of the section's shape (Section 1.3). In a first approximation it can be said that the section is wider and shallower with a smaller hydraulic radius. […] On the other hand, canals which are deep and narrow, possess greater hydraulic radii and therefore corresponding tractive forces also tend to be greater.

   • 2006, Kalliopi K. Aligizaki, Pore Structure of Cement-Based Materials: Testing, Interpretation and Requirements, Taylor & Francis, page 18:

     The hydraulic radius of a single pore is defined as the cross-sectional area of the pore divided by the perimeter of the pore space, as it is given by Equation (1.2). […] Two cement pastes having the same hydraulic radius may have widely differing pore size distributions, but when two cement pastes are made from the same Portland cement, identity of hydraulic radii should imply at least a rough similarity in pore size distribution.

Usage notes

The hydraulic radius of a full pipe turns out to be half the radius of the pipe.

Further reading

• Hydraulic diameter on Wikipedia.Wikipedia
• Manning formula on Wikipedia.Wikipedia