Measuring and Improving Cooling System Performance – Part 9: Duct Flow and Pressure Gradients
For the last several months, I've been trying to better understand duct flow as I've worked through this cooling system project. Ducts can be hard to wrap your head around, as I found in a propulsion class my last semester in school, and analysis of them sometimes reveals counterintuitive behavior. For this last post let's get into more of the theory of duct flows and compare to experimental results that illustrate some of their characteristics as well as the implications to car cooling system modification. We can consider the heat exchanger as a constant-area restriction or station in a longer cooling system duct (as in the Hoerner figure below), or as a collection of tiny ducts all stacked on top of each other. Either way, the physical behavior of the flow is the same; it's just a question of which is more convenient for analysis. Theory First, consider an ideal (inviscid airflow) duct with equal inlet and outlet area: with no friction, there is no resistance to ...