# Flow rate and pressure drop relationship advice

The Hagen-Poiseuille equation is a relationship between the flow rate Q and the pressure drop?P for the laminar flow of a Newtonian fluid in a pipe. Here P is. Similarly, in unconfined convection over an external surface (imagine flow over a hot Both pressure drop and heat transfer are consequences of a velocity gradient. This relationship is simply and beautifully brought out by the simplest of all . Anyone is welcome for their opinions, advice or any info if in favor or not any. The relation between the flow rate through a pipeline of area A and the pressure drop∆p, across an orifice type flow meter inserted in that line (as shown in the.

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.

### fluid dynamics - Does pressure drop across pipe affect flow rate? - Physics Stack Exchange

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. 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.

Take a bucket and time how long it takes to fill it using an open end hose. Now time how long it takes to fill the same bucket with your thumb firmly pressed over the hose end. It will take longer to fill, because your thumb has reduced the flow!

The same thing would happen in your sprinkler system if you used smaller pipe to increase the pressure. The smaller pipe would restrict the flow of water. The reduced flow would reduce the pressure loss in the pipes, resulting in more pressure. Sprinklers require both flow and pressure. But there are also some much more complex scientific theory that I have been asked about in relation to this topic.

This is called the Venturi effect. By suddenly forcing the water through a narrow passage you can actually create enough of a pressure decrease that it creates suction. This is how many fertilizer injectors work. It also is another reason why using a smaller pipe would not increase the pressure— it would actually decrease it!

Another less common argument is the pipe size must be decreased because the flow is decreasing at each sprinkler head location along the pipe route. This is actually a good, scientifically based point, and accurate too! So the argument is that the pipe sizes must become smaller in order to keep the velocity constant and avoid an increase in water pressure.

The total energy of the fluid is the sum of the energy the fluid possesses due to its elevation elevation headvelocity velocity headand static pressure pressure head.

## Irrigation Tutorials

The energy loss, or head loss, is seen as some heat lost from the fluid, vibration of the piping, or noise generated by the fluid flow.

Between two points, the Bernoulli Equation can be expressed as: In other words, the upstream location can be at a lower or higher elevation than the downstream location. 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.