Pressure into Flow

You cannot convert a pressure directly into a flow measurement. As the two are totally different characteristics. Pressure is force / unit area (ie kPa, PSI) were flow is volume / unit time (ie GPM, cubic metres/s). You only get flow if there is a pressure differential. That is if you open the tap on a tank.The tank holds a fliud under pressure or head (height of liquid) you open the tap the fluid flows out to a lower pressure (atmospheric). The amout of flow depends on the size of the tap openning. The bigger the openning the higher the flow. Look in a fluid dynamics book for more info. rgds Dave

In an open end system the pressure must be canceled by the friction.

You therefore have to divide by the remaining distance to obtain a friction/unit distance. The flow can be looked up on a friction curve for that specific pipe.

It can be calculated but i will have to find my notes to supply formula. Note that the smoothness of the pipe features in the equation.

Agreeing with guest's response that pressure and flow are different things, I think I've read into your question and understand what you're looking for.

I'm assuming your talking about a piping system where the ID and length of the pipe produce a pressure drop. Additionally each fitting and valve also creates a pressure drop. And since the pressure drop in the piping system affects flow, I'm assuming the intent of your questions could be reworded as: How do I calculate the pressure drop of a piping system?

Am I correct? If not, can you be a little more specific? Once we know exactly what your desired end result is we'll probably be able to help you out a little better.

As for your question related to a "photodetector," I have no clue but the manufacture of the detector should.

Here is a link to a discussion already started about pressure vs. flow. If you already know how convert between column height and pressure you have a good start.

http://cr4.globalspec.com/thread/6501/Fluid-flow-velocity-and-Pressure-calculation

HI

If you mean flow in pipes ,

The flow of liquid depend on , area and velocity and we add pressure to accomodate the minor or maigor losses in the pipes .

from charactersic curve of the centrifugal pumps you can notice the relation between the flow and head (pressure)

thanks

nelson

Assuming you are speaking about a centrifugal pump flow versus pressure (head), the pump will operate at the intersection of the system curve (the resistance of the system proposed) and the head capacity curve of the pump. There will be no flow without pressure differential, in any system. For a positive displacement pump it is a bit easier as each 'stoke' or revolution of the pump produces theoretical infinite pressure, only limited by mechanical limits of the pump design. Thus, flow will occur when the pressure producing mechanism (pump) overcomes the pressure required (resistance of the system) to create a pressure differential in the direction of desired flow.

This may not help, but it points out what others are posting here.

George

Regarding the question of how to convert the intensity of light into power received by a photodetector, I think the power received by the photodetector should be proportional to the square root of the intensity, but the output voltage of the photodetector is just proportional to the received intensity.