A test procedure for water flow testing a 10 inch butterfly valve.  The application is 10000 GPM liquid hydrogen at 15 psig at the inlet.  In addition to pressure drop, I am trying to model the dynamic load (torque) to the blade/shaft assembly experienced at the application flow condition with a water flow test.  In order to have dynamic similitude, the Reynolds Number should be constant, but that results in a test flow rate 5 times that of the application.  Instead, I will be keeping the dynamic pressure constant to match pressure drop. Flow tests are done with water and the torque measured at the valve shaft is measured in both while opening and closing the valve.  Mathmatecally subtrascting the two results eliminates the effects of friction.  Knowing the valve Cv, flow rate,  and differential pressure at each measured position will allow you to calculate and factor known as the dynamic torque coefficient (Cd).  To predict the torque induced by flow around a butterfly valve disc, you multiply Cd by the valve port diameter^3 times the differential pressure.  This yields the dynamic torque.  To this you need to add back in friction depending upon the desired direction of rotation.  Note that the equation for dynamic torque does not include any media properties, just a dimensionless factor and differential pressure.  The media properies are included when calculating the differential pressure at each angle of opening.

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