water flow through a coil

[Teto]

Hi all,
I'm in a plant were circuit setters on air handlers were not always used (hand valves instead throttled down). THe problem I have , aside from balancing, I can't tell how much flow is running through a coil. I can contact the coil manufacturer and give him the Delta P and he can run through a software program and give me the answer. However, that is not always an option or available. Has anyone tried using the coil manufacturer's coil spec sheet to calculate the C sub v. Then use the derived Cv to calculate the flow using the Delta P across the coil? Will this work? I have 1.09 x SCFM x (Delta T airside) = 500 x GPM x (Delta T Water Side)
Thanks,
Teto

 

[quark]

the Cv method will not work. You can check the pressure drops if you have manufacturers chart of flowrate vs pressure drop. You can very well calculate it by doing the heat balance of air and water sides, as you mentioned.

Cheaper and reliable method is to collect water in a bucket(don't blame me if you have slab cutouts).

 

[Teto]

Quark,
Please explain the catch the water in the bucket method.
Thanks,
Teto

 

[BigInch]

I think he means Flowrate = get your stop watch out and find out how many buckets you can fill in 1 minute.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[25362]

Professor Lydersen (Fluid flow and heat transfer-Wiley) states that you may use the usual friction drop formula with its [±]10-15% accuracy. He says that the friction factors can be obtained from Srinivasan, Nandapurkar and Holland: Friction factors for coils, Trans. Instn. Chem. Engrs., 48, T156-T161 (1970).

 

[quark]

BigInch got it but my idea is slightly different.

I was toungue in cheek, initially, but here is the explanation. What time it takes to fill a bucket is what you should check. (PS:If you take a standard bucket of 14 liters(it is standard here), you can't fill it faster than 15seconds if your AHU capacity is 6TR or less, theoretically. So, one bucket should be enough.) Filling a drum(200 liter) may be a better method.

However, you should take care to maintain the exact pressure drop that generally occurs when the AHU return is connected to pipe return header. Connect a gauge and valve arrangement (gauge-->valve--->hose) to the draining hose and simulate the original pressure drop.

25362,

Crane gives the procedure to check single inlet coil pressure drops. AHUs coils are multiple inlet type. Are you referring to same type of coils? If yes, how about a copy to +912066207920? (If I am not asking too much)

 

[25362]

To quark,

Sorry, only for single inlet helical coils. The only equation I have for the friction factor f, given the tube inner diameter d and the coil diameter D (measured from the centers of the tube), is:

f = 0.076 Re[sup]-0.25[/sup] + 0.0073(d/D)[sup]0.5[/sup] [±] 10%​

where 0.34 < Re(d/D)[sup]2[/sup] < 300; Re = Reynolds No.

to be used in the estimation of the pressure drop [&Delta;]P[sub]f[/sub] in:

[&Delta;]P[sub]f[/sub] ~ 4 f [&rho;] (L/d) V[sup]2[/sup]/2​

[&rho;] is density; L is coil length; V is linear velocity.

Is this equation similar to Crane's ?

 

[quark]

Yes, I know that equation from Perry's. There is a good discussion at 6-18 & 6-19 Chapter 6, Fluid and Particle Dynamics. The Dean's number is an interesting topic.

Crane discusses about flat coils and not helical coils.

 

[lilliput1]

Quark,
Because a standard hose is 5/8" and usually water coils are 5/8" (some are 1/2") isn't the resulting bucket flow measured be typical only for (1) of the coil? So the total flow through the coils should = estimated flow by bucket method x the number of coils connected to each coil bank supply header x the number of coil banks.