J. Phil Thien's Projects

Quote from: Schreck on March 15, 2021, 09:22:16 PM
In each case the flanged pipe showed higher velocity and lower static pressure than the raw pipe end.  When the reducer was tested, it showed a further increase in velocity and reduction of static pressure. 

Note how little the motor amperage changes.  Measuring changes in motor amperage is often cited as a way to determine whether more work is being done by the blower, which generally means it is moving more air.  The changes I measured are very small, which would (incorrectly) indicate small changes in airflow.  As motors become more loaded, the amperage increases but so does the power factor and it is the product of the amperage and power factor that reflects the change in work being done.

The table below summarizes the data behind the charts and it includes watts and power factor.  My blower motor is showing a very low power factor: 0.65 when loaded versus 0.80 or higher for good quality modern motors.
[quote ] The load current of an induction motor shafted to a fan inside of a housing is purely based upon how much the output flow is restricted.  A completely open output causes the motor to draw maximum current, maybe even exceeds the rated load stamped on the tag.  Always restricted the output of the fan housing slightly to prevent burning the windings to toast. When the fan housing output is restricted, the shaft spins slightly faster (less load) and load current declines.  Should the intake be restricted, there is less air mass available to the fan blade to draw upon, motor rpm is increased and load current will reduce (slightly).  Measurements should use pressure deltas inlet vs outlet and mass flow volume (ft^3/min?).  This type of problem is a mass flow and finding the solution on the curve is a differential equation.  Set up the parameters and Excel has Goal seeker app to solve differential equations for these particular problems.