How To Measure The Flow Of Water From A Peristaltic Pump?

Really. You can't be serious. How do you think it should be done?

Do you see two tubes or hoses, or pipes?

And a pump between them.

Using your powers of deduction determine which pipes is in pipe and which is out.

Do you know how to determine the rotation of the pump?

Give the in pipe a water source and turn the pump on.

Put a bucket under the pipe you think the water will come out of.

Turn pump on. Fill bucket, time how long it takes.

So, you'll have some quantity of water in the bucket after so long.

That's the rate of flow.

I did that and I got a flow of 14L/day but I read a similar thread and someone wrote a theoretical way of calculating the flow would be multiplying the area of the pipe * the length of the pipe that is would in the pump* rpm. Using this formula I'm getting a massive number (about 450 L/day). So I thought maybe I was doing something wrong.

As you have discovered, there may be a large difference in "actual" and "theoretical" pump flow.

Now, it's up to you to figure out why this is.

that much difference, I would first look at your math

I did make a mistake. There is now a difference of about 100 L.

That's a big bucket!

I am sort of confused...

Are you looking for a way to increase the measured volume by 100 liters per day by conducting the test differently, so it is closer to your calculation?

Maybe the source at the highest point, the pump very near the source, and the outlet at the lowest point? That may do it.

No, I'm not trying to increase the measured volume. I wrote down pretty much what I am trying to do in my earlier post.

Why should it depend on the length of pipe in the pump? It varies with the tangential speed of the rollers, which is proportional to the radius at the roller centres, x rpm.

Did you record the details of each experiment, along with the results?

Length of inlet and outlet, elevation, etc. etc.

No I did not record the length of the tubes. The are both at the same level. This is the setting I have set up: I have a reservoir and an inlet tube in it followed by a peristaltic pump. The inlet tube after the pump is connected to another tube that connects to an ultrasound reactor (to a metallic chamber). There is another tube coming out of the chamber (which is the outlet). What I want to do is to create a recycled flow : So basically I have a reservoir with an inlet pipe and an outlet pipe in it as opposed to a simple flow through system. I want to find out the flow rate of such a system - inlet flow and recycled flow. I think that the experiment I conducted would give me the inlet flow. Also by mass balance, i think that the inlet flow should be equal to the recycled flow. However the pipe size is different for the recycled flow, so I'm stuck.

The pipe size that contacts the rollers inside the pump will determine flow rate.

This is a positive displacement pump.

So the experiment that I conducted earlier would give me the inlet flow, right? ( had an inlet and an outlet and measured time it took for a certain volume to pass) What about the recycled flow? Shouldn't it be the same as the inlet flow as per mass balance?

Correct.

However the thing that confusing me is that the pipe used for the recycled flow is not the same as the one used for the inlet flow, it is much bigger. So due to that the flow through the bigger pipe should be greater?

No, positive displacement pumps produce the same outflow as inflow. The pressure will be lower in a larger pipe, but the flow will be the same.

The relevant pipe dia is the one that's squeezed by the rollers.

bucket and stopwatch. You'll find the theoretical value is quite close, assuming no plugging and not too close to max or min of VFD or pump. At very slow set speeds, you'll find a floor pump rate (watch for motor overheating); at high, it may flatten a bit. Bigger bucket for more accuracy.

It's high time for the OP to go back to "Hydraulics 101" class and properly learn the Bernoulli Equation....

The answer was already given to you by others: Fixed measured volume divided by the time elapsed to pump that volume = flow rate. whatever you do don't recirculate that water volume that's been pumped to the receiving vessel! Also, keep a constant water level at the supply vessel + provide a free discharge above the water level in the receiving vessel. And make sure that any and all valves are fully open!

You're calculations apparently didn't take in account friction losses (ie, velocity head) along the suction pipe/tube, the friction losses along the discharge pip/tube, the static head, entrance and exit losses, any losses due to fittings and valves, and incorrect calculation of the energy input from the pump....

I think the OP is a student. (Grade or middle)

I think none of the losses you mention will come into play with a PD pump in this experiment.