Pipe flow question, finding diameter

[raoulduke1]

Homework Statement

Water pumped to a cooling plant through a 4km long cast iron pipeline.
power available is 30kW.
what pipe diameter is required to ensure a mass flow rate of 100kg/s.

Homework Equations

The Attempt at a Solution

I know you have to guess a value and find it through trial and error. But is it the velocity you guess?
And what equations do you use to get the diameter

 

[LawrenceC]

You do guess a value and it does not matter which because based on the mass flow the other parameter is defined. Your iterations would be based on diameter because that is what is sought.

 

[rude man]

Two equations:
1. amount of water/sec. leaving pipe = ?
2. Kinetic energy of water being expelled from the pipe/sec. = ?

2 equations, 2 unknowns: velocity v and and pipe diameter D.