FluidFlow calculates the K Straight and K Branch values for Idelchik tees as follows:

Kb = Kt / (Vb / Vch)2

Kst = Kt / (Vst / Vch)2

Let’s consider the QA Example as follows:

Kb = Kt / (Vb / Vch)2

(Vb / Vch)2 = (3.141 / 6.131)2 = 0.262466.

Branch K = 0.4328, therefore Kt = 0.4328 / 0.262466 = 1.65 or 1.64897 to be more accurate.

Kst = Kt / (Vst / Vch)2

(Vst / Vch)2 = (2.99 / 6.131)2 = 0.237837.

Branch K = 0.5292, therefore Kt = 0.5292 / 0.237837 = 2.2244.

If we have a look at the models above, we can see a number of scenarios;

1. An Idelchik tee model developed based on design pressure inlets.
2. The same model developed using known flow inlets at the boundaries.
3. The same type of model developed using pressure loss coefficient nodes where the K values have been defined. The results are identical across all three models.

Note, the K values found in the Idelchik Handbook are based on volumetric flow in the “channel”.