flow coefficient and loss coefficient relationship???

[97S281]

Hello, I have searched all over and have not been able to find the answer to this question so I decided to post it here in hopes of getting some help.

First let me explain my situation. We are using an Engine Cycle and Gas Exchange Simulation program called BOOST that is made by AVL to model the effects of the intake manifolds for our 4 cylinder engine. This is a very rough sketch of what the plenum looks like.

The arrow shows the direction of air flow and the entrances enclosed in the red oval are sharp corners (NOT bellmouthed) for each of the 4 intake runners (round pipe). My problem is, the program is asking for a flow coefficient for those entrances and I have not been able to find any source that gives flow coefficients for something like this. I have a source that gives a loss coefficient of 0.5 for a sharp corner like this

but i'm not certain if it is acceptable to assume my situation is the same since the flow is entering the plenum and then turning (can I assume a loss coefficient of 0.5?)?

If it is ok to assume a loss coefficient of 0.5 (if not could you suggest some references to look at for appropriate K values?) is there a direct relationship between the loss coefficient and flow coefficient? I looked in my old fluids text books and found equations for both the loss and flow coefficients and I could manipulate those equations to get a relationship with the loss coefficient being equal to 1 over flow coefficient squared. This is the manipulations I performed to get this.

I am sorry for making such a long post especially since this is my first one here but I wanted to make sure I fully explained what it is i'm looking for. If anyone can give me some help or point me to a reference to look at that would answer this I would greatly appreciate it.


Thanks,

Nick

 

[Latexman]

Call AVL and ask for technical help.

Good luck,
Latexman

 

[97S281]

Latexman,
One of my advising professors for my thesis research is actually the person who is doing the AVL modeling since he is the only person with the software. I asked him last week if he had a phone number for AVL so I could talk to them about it but he said that the last time he tried calling them for help they were not very helpfull because they also sell tutorials and such. Thanks for the suggestion though.

If anyone else has any input i'd greatly appreciate hearing it.

Thanks

 

[MikeHalloran]

You need to get an ASHRAE Handbook.



Mike Halloran
Pembroke Pines, FL, USA

 

[97S281]

I will go to the library and see if I can find it in an ASHRAE handbook.

Thanks

 

[katmar]

Using a loss coefficient of 0.5 is probably a good start in the case. However, I do not recognise the equation you gave for the flow coefficient - the one using the alpha symbol. The more common flow coefficient is usually represented as C_v and the equation is

Q = C_v x sqrt( press drop / SG )
where
Q is in USgpm
press drop is in psi
SG is relative to water

If this is the flow coefficient that AVL are using then the relationship to the loss coefficient is given by

C_v = 29.9 x d^2 / sqrt(K)

where d is the inside diameter in inches.

A good reference to these conversions is the Crane Technical Publication 410, specifically Equation 3-16 on page 3-4. This is probably the most referenced book on fluid flow in the English language.

Harvey


Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[STYMIEDPIPER]

Right or wrong--I have previously modeled/calculated as two separate entities as per the following:
To account for the change of direction for flow I used loss coefficient of a tee with flow thru branch.
I also had to account for the sharp edge entrance. I used the sharp edge coefficient. I added the two pressure losses together.
I may have over compensated but I wanted to ensure that exhaust fan could handle the system pressure loss.

 

[Latexman]

While you are at the library, take a look at the Fluid Distribution section of the Fluid and Particle Dynamics chapter in Perry's Chemical Engineers' Handbook. In the 7th Edition, it starts on page 6-32.

Good luck,
Latexman

 

[97S281]

katmar, the equation I gave with alpha for the flow coefficient was taken from pages 417-418 of "Fluid Mechanics, 5th ed" by Frank M. White. They show the flow coefficient (alpha) as a function of the velocity-of-approach factor (E) times the discharge coefficient (Cd).

Thanks to everyone who gave references to look at. I'm going to try to make it to the library today to check these sources out and hopefully I can learn something today.