Maximum Flow in a Piping System

What pipe size is the regulator?

I think I had stated it in the question:

Pipe size: 1/4"

Regulator: 0-50 psi

9.5e-5 m³/sec for 1/4" Ø at 3 m/sec liquid max velocity, or about twice the rate a human can send urine. Is this in the right tennis court or is there something wrong with the question data?

and how do you get to this result with the pressure of 50 psi?

Does the fact that the gas is CO2 changes something?

I don't really understand why the limit is 10m/s.

For example if I have:

Pressure = 0.5*(density*v^2)

for 50 psi, and the density for the gas (let's say methane which is 0.68 kg/m^3) then I get v=1006 m/s

Is the flow speed limited because of the size of the pipe (1/4")?

Flow speed is limited because of the economic limit in the pipe. If the fluid is doing more than 3m/s for a liquid and 10m/s for a gas, then the pipe is too small. If the flow is sonic, then the valve is too small.

What is the process? First it was liquid, then it was carbon dioxide, now it's methane....

What is it doing - gas reservoir boost equipment or something? If so, then why only 1/4in Ø? Very confusing......

well sorry for the mix.

In fact I have a tank of methane and another one of CO2. Both merge to a a single pipe going to a diesel engine (to simulate biogas injection). (all the pipes in the setup are 1/4")

The biogas flow rate I am looking to obtain is around 40 L/min. I wanted 100 psi regulators but I could only get 50 psi regulators. So I want to make sure I can get that flow rate of 40 l/min (about 30 l/min of methane and 10 l/min of CO2) to the engine

How big is the engine?

Why are pressure regulators being used?

Well biogas has a composition of:

60% CH4 and 40% CO2. Injecting biogaz in the air inlet of the diesel engine reduces the consumption of diesel. The goal of the project is to study the effect on performance in a diesel engine functionning with dual fuel (biogas-diesel).

Thats why it's interesting to inject CO2 in the engine.

Right, so now the gas is going into the air intake instead of the fuel injection system. That wasn't clear. It is now. OK. Next question.

Instead of expensive pressure regulators, why not use a simple needle valve instead?

Well at the university we don't have much methane and CO2 available so we took high pressurized tanks and we found some 0-50 psi pressure regulators, so the price isn't much important.

The question now is to know is the pipe of 1/4" can prevent a flow of 40L/min or if the pressure of 50 psi isn't sufficient to delivre the required flow rate.

PS:

I am using a needle valve to make precise adjustements of the flow rate of biogaz (in order to have a stoechiometric combustion).

OK. Arrival at last.

Use the Weisbach-Darcy generalised pipe flow equation on the pipe to determine the pressure drop along its length for a flow of 40l/min. If the answer exceeds 50psi, then the pipe is too small, and either a larger pipe or a higher pressure regulator will be needed.

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CH4 tank----- 1 meter pipe

CO2 tank----- 1 meter pipe merging of the 2 pipes ------- 2 meters pipe ----- engine

Hope it's clear enough

the engine is a 3.3 kW engine. Pressure regulators are used to place on the pressurized tanks of CO2 and CH4.

Does that make sense now?

I would first determine the acceptable velocity of the fluid down the pipework,in theory you could push what you want down it but may need some pretty good ear defenders to live with it.

Unfortunately my tables only go down to 3/8",but as a rule of thumb I would use 1.8 to 2 m/sec for wateR.

GA. Good to have. The OP should be happy with that, Ky.

Thanks your spreadsheet is really well done.

Another useful link might be this:

http://www.engineeringtoolbox.com/darcy-weisbach-equation-d_646.html

On a quick glance, it appears that your desired flow through the given pipe size would be way supersonic, so it won't work. Also, Cv's differ for liquids (essentially incompressible) versus gases. To echo another question, why not use needle valves and flowmeters, rather than pressure regulators, so that you could make comparisons between different flow rates and mixtures?

Thanks for your link. I tried it to get a flow of 30 L/min for methane (0.68 kg/m^3) and everything seemed to work fine.

As a result I think it's a really small amount of flow so I don't really understand why would it be supersonic?

I was just looking to get the flow rate of 30L/min and the pressure regulator can go to 50 psi, but I can adjust it to just a couple psi to get the flow I want. Then make precise adjustements with a needle valve.

In low-pressure drop flow—when outlet pressure (p2) is greater than half of inlet pressure (p1)—outlet pressure restricts flow through the orifice: as outlet pressure decreases, flow increases, and so does the velocity of the gas leaving the orifice.

When outlet pressure decreases to half of inlet pressure, the gas leaves the orifice at the velocity of sound. The gas cannot exceed the velocity of sound and—therefore—this becomes the maximum flow rate. The maximum flow rate is also known as choked flow or critical flow.

It seems that your required flow rate will be well below this maximum.

Regards Woody