I am writing up a report on Orifice jet flow experiment in which I am required to find coefficient of flow velocity, $C_v$, and the Coefficient of discharge, $C_d$.

There are couple of things that I can't really figure out.

  1. Would you expect the flow coefficient to change depending on the head height of the system?
  2. I've used two different diameter orifices so have two data sets. Should I average all coefficient values from both diameters, or should I do averaging for each orifice separately? Which would mean that in the end I'd have two different values for the coefficients.

1 Answer 1


To answer both parts of your question:

  1. In general the flow coefficient will not change with the head height of the system. The head height will only impact on the static pressure and hence the flow rate through the nozzle. This will be true provided the liquid level is not so low that it is influencing the flow pattern near the orifice, in which case the results you are using to calculate the coefficient of discharge may have been influenced by the changing flow pattern near the nozzle.

  2. The coefficient of discharge is related to the geometry of your nozzle. It is very unlikely that your nozzles have the same coefficeint of discharge unless you carefully planned the sizes. So to answer your question, no, you should not average the results for both nozzles together.


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