Calculating volume required for a pressure value ( for duct design)

In summary, the person is calculating the sizes of ducts and the fan flow rate for a given pressure. They are stuck at calculating the volume of section4 using the ideal gas law due to not knowing the value of 'n' for air. They have assumed laminar flow, incompressible fluid, and inviscid conditions for simplicity and plan to optimize the design later with a CFD solver. They are looking for help and have been recommended to refer to SAE AIR1168-1 for guidance.
  • #1
kirankanimetl
2
0
I am calculating sizes of duct ( section1= constant area pipe, section2= transition to a rectangular cross section , section3= constant rectangular cross section upto 0.5m, section4= similar to section3, section5= similar to section1) and fan flow rate for a given pressure(minimum of 12 psi at section4) which is required to be maintained. for which I have started calculating from section4 and working through to the inlet by adding losses and pressure changes( bernoullis principle) and finally obtaining volume flow rate required.

I am stuck at calculating volume of section4 from ideal gas (PV=nRT)for the given pressure as I do not know 'n' value for air. Also I have considered fluid to be inviscid, incompressible and the flow regime to be laminar for simplifcation.

Can some body help me with this?
 
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  • #2
If you have the velocity (guessing obtained from Bernoulli's equation) and the area, then
[tex] Q = AV[/tex]
 
  • #3
Hi,

Thanks for your initiation, but I guess you havn't understood my question,
To start calculations, I am working from rectangular section of the duct where there is a minimum pressure requirment of 12psi is nessecary. But to start calculations assuming the pressure to be 12psi gauge ( static+dynmic pressure) and without having duct sizes(which has to be calculated), i need to evaluate volume of the rectangular duct from ideal gas law (PxV= nxRxT)for a static pressure of maximum 12psi. After which velocities and flow rates can be calculated for each sucessive duct sections from bernoullis and continuty eq.

But I need to know number of moles i.e. 'n' value for air at STP or appropriate conditions.

And as I have previously specified I have assumed Flow to be laminar, incompressible and inviscid for simplification and I will later optimize this design through CFD solver.

Thanks again
Kiran
 
  • #4
I would highly recommend that you get a copy of SAE AIR1168-1, specifically sections 1A and 1B. It is very applicable to what you are designing for.
 

1. How do I determine the volume required for a specific pressure value?

The volume required for a pressure value can be calculated using the ideal gas law, which states that the volume of a gas is directly proportional to its pressure and inversely proportional to its temperature. Therefore, to determine the volume, you will need to know the pressure and temperature of the gas.

2. What units should I use when calculating volume for duct design?

The most common units used for calculating volume in duct design are cubic feet (ft3) or cubic meters (m3). It is important to use consistent units throughout your calculations to ensure accurate results.

3. Can I use a general formula to calculate the volume required for any pressure value?

Yes, the general formula to calculate volume for a given pressure is V = nRT/P, where V is the volume, n is the number of moles of the gas, R is the ideal gas constant, T is the temperature, and P is the pressure. However, keep in mind that this formula assumes ideal gas behavior, so it may not be accurate for all types of gases.

4. What factors can affect the volume required for a certain pressure value?

The volume required for a specific pressure value can be affected by various factors, such as the type of gas, temperature, and altitude. The type of duct material and the shape and size of the duct can also impact the required volume.

5. Is there a specific method for calculating volume required for a pressure value in duct design?

Yes, there are several methods for calculating volume required for a pressure value in duct design, such as the equal friction method, the static regain method, and the T-Method. Each method has its own advantages and limitations, so it is important to choose the most appropriate one based on your specific duct design requirements.

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