I and a friend have made a venturi tube trough which water flows at a low speed. The flow is therefore laminar. We measured the static pressure using some piëzometers at the points 1,2 and 3. We know the average velocity with which the water flows at the end of reservoir 3.
My friend suggests calculating the speeds at other resvoirs(1,2) of the venturi-tube by using the volumetric flow rate. We namely know the cross-sectional area of the venturi tube at all places.
I however don't think this volumetric flow rate will stay the same because of frictional losses, and so prefer to calculating the speed by using a bernoulli equation with a head loss incorporated in it. What's best to calculate the other speeds in this situation? Or are we both completely wrong?!
Diameter of the venturi tube at different points:
- Point 1: 17 mm
- Point 2: 13 mm
- Point 3: 10 mm
Measured static pressure at points:
- Point 1: 106503 Pa
- Point 2: 105375 Pa
- Point 3: 102903 Pa
Measured velocity at the end of reservoir 3:
Differences between methods:
Calculated head loss between the end of reservoir 2 and the end of reservoir 3 : 0.1208901666 Pa
Calculated velocity at the end of reservoir 2 using bermoulli with head loss: 0.81 m/s
Calculated velocity at the end of reservoir 2 using constant volumetric flow rate and area changes: 1.06 m/s