The flow rate K v is the volumetric flow rate of water in m³ / h at a density of 1000 kg / m³ passing through the valve at a pressure drop of 100,000 Pa or 1 bar. Measured in (m³ / h) / bar 0.5 . In the literature, you can find units of measure cubic meter per hour or square meter , but this does not quite correspond to the hydraulic essence.
To determine the pressure loss ΔP in bars at a water flow rate of V, m³ / h, the formula is applied:
- ,
where from:
- .
For connection with the local resistance coefficient ζ, it is necessary to take the calculated passage area F, m², or the calculated diameter d, m, with F = πd² / 4; then it follows from the definition of ζ = ΔP / (ρv² / 2) = (V / K v ) ² / (ρV² / (2F²)) that
- ζ = (2 · F²) / (10³ kg / m³ · K v ² / (3600 s / h) ² / 10 5 Pa / bar) = [ Pa = kg / (s² · m)] = 2,592 · 10 9 m² / (m² · bar) · F² / K v ² ≈ 1.6 · 10 9 m² / (m² · bar) · d 4 / K v ²,
that is, if K v is expressed in (m³ / h) / bar 0.5 , F in cm² and d in mm,
- ζ = 25.9 F² / K v ²,
- ζ = 0.0016 d 4 / K v ².
Literature
Pyrkov V.V. Hydraulic regulation of heating and cooling systems. Theory and practice . - II. - K .: Taki Help, 2005 .-- 304 p. - 2000 copies.