Venturi tube help needed in determining pressure difference

timothy1875

1. The problem statement, all variables and given/known data

Water flows through venturi tube at 0.3 litres/s. Diameter of venturi tube is 32mm to 20mm to 32mm and the water density is 1000kg/m^3.


2. Relevant equations

a) Assuming head loss is neglible, what is pressure difference between 1 and 2.

b) If pressure head difference between these is 45mm what is head loss.


3. The attempt at a solution


So far I have V2 = P1A1V1/P2A2 = 0.9548 and V1 (Q/A) = 0.3731

delta H 1/2 = H1 - H2 = 1/2g (V2^2-V1^2))
delta H 1/2 = 39.3mm

Where do I go from here, if this is even correct ?

Thanks a lot for your help.

tiny-tim

hi timothy1875! welcome to pf!

(try using the X² and X₂ icons just above the Reply box )

i don't follow you …

use the fact that the volume per time is constant, and Bernoulli's equation

timothy1875

Hi Tim,

Thanks for getting back to me.I am trying to answer the question but think I may be going about it the wrong way.

Using the Bernoulli equation do I need to transpose to find P ?

tiny-tim

show us what you have so far

timothy1875

V2 = P₁A₁V₁/P₂A₂ = 0.9548 and V1 (Q/A) = 0.3731

delta H 1/2 = H1 - H2 = 1/2g (V₂²-V₁²)
delta H 1/2 = 39.3mm

This where I have got to so far, :(

tiny-tim

what does this mean?

where does it come from?

timothy1875

Basically we have been set this question and there are numerous equations on the back that we have to pick from. I take it from your response I have selected the wrong equation initially. Should it be 1/2g (V₂² - V₁ ²) ??