height in Bernoulli's equation

[theonlytycrane]

Bernoulli's equation for the conservation of energy in fluids:

Does y1 and y2 refer to the height of the pipe above some reference point? If so, assuming that the pipe is horizontal, do we consider y1 and y2 to be equal even between two sections of pipe that have slightly different cross sectional areas?

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[studentdocftw]

y1 and y2 refer to depths...for instance..comparing a point in a tank at the top of the surface..and at a point leaving a spout....y1-y2 would be the change in depth from the top of the surface to the spout.

 

[basophilic]

Bernoulli's equation for the conservation of energy in fluids:
View attachment 194228

Does y1 and y2 refer to the height of the pipe above some reference point? If so, assuming that the pipe is horizontal, do we consider y1 and y2 to be equal even between two sections of pipe that have slightly different cross sectional areas?

The height is measured from the reference/ground level to the midpoint in the pipe cavity (this is by definition since the most ideal fluid flow happens in the center of the pipe). Hence as long as the midpoint doesn't change, the height in Bernoulli eqn doesn't change with changes in cross-sectional areas.