# How to calculate a circulation pump size?

I would like to get some help regarding sizing a pump.

I'm working on a project in which we want to select a pump to generate a flow through a rectangular channel whose two ends (the inlet and outlet) are connected by a pipe. We want to place this pump at (near) the inlet port of this channel.

We will be filling this pipe with water of a volume around 1 liter. And we want to circulate this water through the rectangular channel (Imagine the 1 liter volume of water just entering the inlet port of the channel and exiting from the outlet port and doing this action for say 24 hours). There will not be any extra volume added or removed, just the set volume of water requires to be circulated.

The inlet and outlet ports and the pipe connecting them are at the same elevation (they are all in a horizonal plane/imagine them to be placed on a bench top). The pipe diameter would be around 3/8", the pipe length is lets assume 14 feet. (Please note that the numbers are only for me to learn the technique to solve for my actual system).

So, I would like to request if someone can help me decide how to find the pump size? or do you recommend any pump which you may have used/come across?

• Does the 1 liter of water is replenished by a constant inflow, or the water is circulating in a closed-loop? If it is the former case, what is the flow rate of the makeup water? Your description is quite confusing, try explain better, please.
– r13
Commented Sep 15, 2021 at 21:02
• That is a small pump. There are many aquarium small water submersible pumps. I presume you could restrict flow with a valve if necessary. Commented Sep 16, 2021 at 0:05
• The aquarium pumps are available with only several watts power consumption but that may be enough to warm your small system. Commented Sep 16, 2021 at 0:08
• A picture or sketch of your system will save everyone a lot of time. Commented Sep 16, 2021 at 21:27
• Thank you for your responses, I will update the question with a sketch/diagram soon. Commented Sep 17, 2021 at 16:10

Calculate the flow rate desired, the head loss, then the pump size to get your desired flow.

1. What flow rate do you want? This should be your base specification

2. What is the head (pressure) loss based on the flow rate you want. You'll have to find a Civil to tell you about flows in open channels, I can't help here.

3. What is the pump to give you the flow at the appropriate head (pressure). Find a pump manufacturer and consult the charts or their app.

I don't quite follow what you are trying to do, but if the desired flow rate is 1/24/60 liters per minute, your flow is so low as to practically eliminate head loss, so you may just want a tiny positive displacement pump.

• I guess he has two reservoirs and wanted to add a pump near the inlet to help the flow.
– r13
Commented Sep 15, 2021 at 21:07

The critical question is dimensions and design of the open channel. Because you will have a high hydrolic jump on the open channel due to sudden drop of flow velocity.

You need to start from the open channel flow model, and see how high the hydolic jump range you get . one restiction is your open channel should not be flooded spilling the water out.

That gives you the head feeding into the outlet of the loop and sets the flow and speed. Now you have enough info to select a pump for that flow with that head.