if water from a 6 inch pipe is discharged into a 4 inch pipe,what will the velocity be?

Question

lets see, will it increase by 2 or 4

would the velocity increase by 2 or 4 times?

Answer 1

Really it depends ... you are making an assuption that the pipe is full and moving at a given rate, right? If it was just trickling, you could not tell ... it would just trickle at the same rate.

Since the volume is just the opening of the pipe times the legnth of pipe, the volume and surface area are proportional, so the velocity of the water is inversely proportional to the width of the pipe ... meaning that the thinner the pipe the faster the water has to flow to have a given volume flow per time, right.

So since the pipe is thinner, create a ratio of the opening of the larger pipe over the opening of the smaller pipe since for a given volume of flow the flow must be faster is the thinner pipe... that is

pipe 1 opening = pi * r1^2
pipe 2 opening = pi * r2^2

a ratio is going to cancel everything but the radius part giving
you

r1^2 / r2^2 .... times velocity in r1.

or the velocity in pipe 2 = velocity in pipe 1 * ( r1 / r2 )^2

Answer 2

If the velocity of the 6 inch pipe is V then the velocity in the 4in pipe will be the ratio of the cross section areas, so the velocity in the 4in pipe will be V * 36/16

Answer 3

Due to the change in size, the pressure in the 4" pipe would decrease and the velocity would increase ... similar effect as in an eductor or a venturi tube.

Answer 4

do you know the velocity or flow rate in the 6 inch pipe? if you know the velocity, then A(1)V(1)=A(2)V(2) since the flow rate will be continuous despite different pipe diameters. if you're given the flow rate, find the velocity for the 6 inch pipe by V=Q/A.

Answer 5

Host consciousness:

The above are all good answers.

Clearly law of conservation of mas applies. However on the microscopic level we could further complicate matters by discussing the velocity gradient across the radius. This will be effected by the nature of the pipe join and laminar versus turbulent flow.

Answer 6

Well you dont give enough information to give a specific answer, however in order for the same amount of water per second to flow through the 4in as it did the 6, its velocity will have to increase.

Answer 7

six squared divived by four squared. two & a quarter times