Darby 3K Fittings
Darby 3K fittings use a three-constant (K1, Ki and Kd) loss model that provides an improved representation of the how head-loss coefficients change across different flow conditions. Instead of relying on a single K value, the Darby method applies three empirical constants that define the fittings behaviour for laminar flow through to fully turbulent flow. Darby 3K fittings are particularly important for fittings where losses vary significantly for different fluid viscosities, in particular laminar flow with high viscosities where additional losses occur (in excess of the predicted loss found using standard K factors for the same fitting).
The Darby 3K library includes a broad range of fittings catering for flow geometries commonly used in engineering applications. For each fitting, the Pipe Flow Expert database defines the appropriate Darby constants.
When a Darby 3K Fitting is added to a pipe, the software automatically calculates and applies the loss coefficient.
See Section: Calculation Theory and Method of Solution > Darby 3K for the formula and further information.
