Talk:Venturi tube

This is a new article

This articles was written from scratch. Milton Beychok 15:30, 20 March 2010 (UTC)

Bernoulli equation

I have a (small) problem with the height h in the Bernoulli equation. Now height is defined of a point, which implies that there may a difference in gravitational attraction over the cross section (as opposed to the length) of a tube. Later h₁ is canceled against h₂ for the gravitational terms in a horizontal tube, which implies that h is assumed constant over the cross-sectional dimension. It seems to me that h is (approximated as) a function of one dimension. In cylinder coordinates with the axis of the tube as z-axis, my guess is that h is a function of z only and not of r and θ. This is physically reasonable and allows cancellation of the gravitational terms in a horizontal tube. --Paul Wormer 07:49, 29 March 2010 (UTC)

Paul, if you believe that the Bernoulli equation should use z rather than h, feel free to change it. Milton Beychok 15:04, 29 March 2010 (UTC)

My problem is not with notation h versus z, but with the dependence of gravitational force on position. The Bernoulli equation as you give it is correct but it seems to me that when you cancel ρgh₁ against ρgh₂ you make an extra approximation (on top of assuming that ρ₁=ρ₂). --Paul Wormer 15:16, 29 March 2010 (UTC)

Beta

I added another definition for β, but on second thought it seems that the first definition (d/D) is superfluous. By referring to diameters it is assumed that tubes are cylindrical and then d and D do not need to be introduced in addition to the respective cross sections A₁ and A₂. For non-cylindrical ducts one needs more dimensions, e.g., width and height for rectangular shaped ones.--Paul Wormer 08:01, 29 March 2010 (UTC)

I will revise the the definition of beta to use the areas as you suggest, and thanks for your comments. Milton Beychok 15:04, 29 March 2010 (UTC)