Why is the calculated K Value different to the K Value I have defined for the K Node?
The difference arises from the change in density of the flowing fluid. Lets look at the example in the image below. The top model is a liquid flow system based on water at 15 degrees C. The defined K value is set to 0.99 and as we can see, the calculated K value in the result is also 0.99. The bottom model is identical to the top with the exception that the fluid is now set to steam at 205 degrees C. In this case, the defined K value is once again set to 0.99 however, the calculated K value in the results will change owing to the change in fluid density (K = 2 * DeltaP / rho * v^2). The calculated K value in the result therefore becomes 0.85 as shown.
As a cross-check, if we increase the temperature in the top water model from 15 to 205 degrees C (steam), the model now solves giving the exact same results for K value as that in the bottom model, i.e. 0.85.