I'm working on a research project dealing with cooling an electrical component in an air duct with a fan. I'm experimenting with different shrouds and directional vanes around the component to see which offers the best cooling. Obviously this has to be judged against the pressure drop caused by any constriction in the duct. I've seen the equation K = ΔPt/0.5ρv^2 used to compute minor losses. How does this differ from all the equations that use ratios of the cross-sectional areas of sudden expansions/contractions to calculate K? sudden contraction would be K=0.5*(1-A1/A2)^0.75 If I have a sudden contraction in my air duct caused by some type of shroud, would it be wrong to use K = ΔPt/0.5ρv^2 where the v is the velocity through the constriction? How would this differ from using the ratio of cross sectional areas?