### Flow in pipe - Bernoulli equation

Pipe cross-sectional area and flow vary with the diameter (of the pipe) squared. As we have previously calculated, this means that twice the pipe diameter yields . Flow in pipe - diameter, velocity, Reynolds number, Bernoulli equation, friction factor. pressure drop, flow rate, pipe diameter . where is: M - Mach number M=v/ c - relation between local fluid and local sound velocity; γ - isentropic coefficient;. Pipe diameter calculation for known flow rate and velocity, in closed round pipe, applicable for liquids and gases. absolute pressure of gas (p). Pa, kPa, MPa.

Keep in mind that the stated size of a pipe is a measure of its diameter, and you need the radius to apply Poiseuille's law.

## Pipe diameter calculator

The radius is half the diameter. Suppose you have a length of 2-inch water pipe, and you want to know how much the flow rate will increase if you replace it with 6-inch pipe.

That's a change in radius of 2 inches. Assume the length of the pipe and the pressure are constant. The temperature of the water should also be constant, because the viscosity of water increases as the temperature decreases. That would seem to prove that decreasing the opening size is increasing the water pressure. So logically, using a smaller pipe would also increase the water pressure.

- 2.3 Relationship Between Pipe Size and Friction
- You've found the web's mother lode of irrigation information!
- The Hagen-Poiseuille Law

As water moves through a hose or pipe there is a lot of resistance caused by the hose or pipe surfaces. The water moves through the hose at the maximum speed it can while still overcoming this friction. When the water reaches the end of the hose it has close to zero pressure left as it exits.

### Relationship Between Pipe Size and Friction: 5. Basic Irrigation Concepts

If there were 60 PSI of pressure, the water would just move a little faster through the hose so that it used up almost all 60 PSI by the time it exits.

So basically regardless of the pressure, almost all the water pressure is used up by the time the water flows through the hose. The nature of water is that it will reach the most efficient balance between flow rate and pressure loss that it can. Note, I am oversimplifying this to make it digestible for the average person.

If you have a degree in hydraulics you already know all the other related stuff about open vs. When you put your thumb over the end of the hose you change the flow dynamics in the hose. Your thumb restricts the flow of water through the hose. With your thumb over the end, the water is flowing much slower through the hose, and as a result, there is a lot less pressure loss due to friction.

## Flow in pipe - diameter, velocity, Reynolds number, Bernoulli equation, friction factor

So with less pressure being lost in the hose, the pressure at the end of the hose where your thumb is increases. The tighter you squeeze your thumb, the more the flow is reduced, and the greater the pressure you feel will be.

You have simply traded reduced flow for increased pressure.

You can easily test this yourself. If the fluid is flowing up to a higher elevation, this energy conversion will act to decrease the static pressure. If the fluid flows down to a lower elevation, the change in elevation head will act to increase the static pressure. Conversely, if the fluid is flowing down hill from an elevation of 75 ft to 25 ft, the result would be negative and there will be a Pressure Change due to Velocity Change Fluid velocity will change if the internal flow area changes.

For example, if the pipe size is reduced, the velocity will increase and act to decrease the static pressure. If the flow area increases through an expansion or diffuser, the velocity will decrease and result in an increase in the static pressure. If the pipe diameter is constant, the velocity will be constant and there will be no change in pressure due to a change in velocity.

As an example, if an expansion fitting increases a 4 inch schedule 40 pipe to a 6 inch schedule 40 pipe, the inside diameter increases from 4.