Advancing the Art of Professional Airless Spraying
Hydraulic Diameter Calculation
Flow Rate Analysis A key parameter of an airless spray orifice is its Hydraulic Diameter, dh.Once the geometry is determined it can be used to calculate the dh.There is a close correlation between dh and flow rate.Therefore, it is possible to predict with reasonable accuracy the flow rate of similarly constructed spray orifices during the design stage.This can greatly reduce the number of iterations required to dial-in the geometry needed to produce a given flow rate.
Below is how to calculate Hydraulic Diameter.The edge highlighted in red is the wetted perimeter of the orifice. dh = 4 A / p where, dh = hydraulic diameter A = area of orifice opening p = wetted perimeter of orifice opening
Additionally, it is helpful to generate pressure vs. flow curves for spray orifices. These are accurate over a wide range of flows and can be correlated to dh which yields a three dimensional relation of flow, pressure and dh. This is the relationship that allows the prediction of pressure at a given flow rate for a given dh.
