.Modelica.Fluid.Fittings.BaseClasses.QuadraticTurbulent.LossFactorData.wallFriction

Information

Friction in straight pipe with walls of nonuniform roughness (commercial pipes) in the region that does not depend on the Reynolds-number

The loss factors are given for mass flow rates from port_a to port_b as:

turbulent flow (Idelchik 1994, diagram 2-5, p. 117)
   zeta = (L/D)/(2*lg(3.7 / Δ))^2, for Re >= 560/Δ

   for Re ≥ 560/Δ the loss factor does not depend on the
   Reynolds number. For Re ≥ 4000, the flow is turbulent,
   but depends both on Δ and slightly on Re.

laminar flow (Idelchik 1994, diagram 2-1, p. 110):
   zeta = 64*(L/D)/Re

where

• D is the inner pipe diameter
• L is the length of the pipe
• Δ = δ/D is the relative roughness where δ is the absolute "roughness", i.e., the averaged height of asperities in the pipe. (δ may change over time due to growth of surface asperities during service, see [Idelchik 1994, p. 85, Tables 2-1, 2-2]).

Since the LossFactorData record can only describe loss factors that depend on geometry (but, e.g., not on the Reynolds number), only the region with Re ≥ 560/Δ is described by this data. Still, the turbulent region with the above zeta is defined to start at Re=4000, since otherwise the approximation for Re < 560/Δ is too bad.

The absolute roughness δ has usually to be estimated. In [Idelchik 1994, pp. 105-109, Table 2-5; Miller 1990, p. 190, Table 8-1] many examples are given. As a short summary:

Interface

encapsulated function wallFriction
  import Modelica.Units.SI;
  import Modelica.Fluid.Fittings.BaseClasses.QuadraticTurbulent.LossFactorData;
  import Modelica.Fluid.Types.Roughness;
  import lg = Modelica.Math.log10;
  input SI.Length length "Length of pipe" annotation(
    Dialog);
  input SI.Diameter diameter "Inner diameter of pipe" annotation(
    Dialog);
  input Roughness roughness(min = 1e-10) "Absolute roughness of pipe (> 0 required, details see info layer)" annotation(
    Dialog);
  output LossFactorData data "Pressure loss factors for both flow directions";
end wallFriction;