Determination of the KL for Laminar Flow in Square and circular Pipe Fittings

Ha Dinh and Lisa Dahl

The pressure drop coefficient KL is a parameter used for scaling the contribution of a non-standard geometry in a pipe.  When combined with the Hagen Pouiseuille law, the total pressure drop in a pipe can be calculated for a non-standard geometry.  The goal of this research was to determine these coefficients for the following pipe fittings:

1. Square pipe, 45° ell
2. Square pipe, 180° bend (close and long return)
3. Circular pipe, 45° bend (standard and long radius)
4. Circular pipe, 90° bend (standard and long radius)
5. Circular pipe, 180° bend (close and long return)

All coefficients were evaluated at fully developed laminar flow and under non-dimensional parameters.  The geometries were modeled in COMSOL Multiphysics, which solved for the overall fully-developed pressure drop in the model.  Values of KL were found for all geometries under the condition of the Reynolds number equal to 1.  The results account for the pressure drop seen in straight sections of the pipe such that the report KL can describe the pressure drop in solely the fitting.  In addition, the variation in KL over varying Reynolds numbers from 1 to 100 was examined for all geometries.  The results demonstrate that the KL increases in value as the Reynolds number increases when only the straight sections of the pipe are subtracted from the system. 

report

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