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Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

(OP)
Hi All,

I continuation to the discussion in the thread below, I wanted to ask a few questions. I am sizing a Cooling Tower pump for a Counter Flow Induced Draft Cooling Tower. I am trying to calculate the pressure at the inlet of the spray distribution piping as shown below.

https://www.eng-tips.com/viewthread.cfm?qid=500845




As you can see the spray distribution consists of a 8" Header pipe to which three rows of 4" branch pipes are connected. To each branch pipe there are three equally spaced 2" spray nozzles.
I am using the AXA sprinkler hydraulics document shared by Mr. Pierre in the last thread ( attached for your reference). Since spray distribution system is a Tree type of system, I am using the methodology discussed in the sample example in Pages 5- 12. My question is how do I know or calculate K-factor for my 2" spray nozzle.


Thanks and Regards,
Pavan Kumar





RE: Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

You look it up in the data from the manufacturer.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

Hi,
It depends on the type of nozzle, drop an email or call the vendor of cooling tower to get support.
Good luck
Pierre

RE: Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

(OP)
Hi EdStainless, pierreick,

The company which sold the Cooling Tower(Waltco Systems,ON) is no longer existing, hence cannot contact the vendor. I can contact another vendor SPX Cooling Technologies and try to get information if possible. Also from the attached document PRC 12.0.1 of AXA there is a derivation and formula given for "K" on page 6/16 in terms Cd, Pipe Dia D, and fluid density. However the value I am getting is very low. I want to know if I am correct in using this formula. If yes why is the so low.

The formula is

K= Cd*(PI D^2/4)*SQRT(2gc/Rho)

Cd = 0.62
D = 2.157 inches = 2.157 /12 = 0.17975 ft ( for 2" Sch 10 Nozzle)
Rho = 62.4 lbm/ft3

K = 0.62*(22/7/4)*(0.17975^2)*SQRT(2*32.174/62.4)
= 0.62*0.785*0.0323*1.015 = 0.0159 ft3sec-1/(lbf/ft2)^0.5
= 0.0159*448.8311*12 US gpm/(psi^0.5)
= 86.016 US gpm/(psi^0.5)

From the AXA paper the value of K for 1/2" sprinkler head is 5.6 so for 2" nozzle t should be higher than 5.6 gpm/psi^0.5. I want to understand what is wrong. I will contact SPX Technologies tomorrow and try parallelly.

Thanks and Regards,
Pavan Kumar


RE: Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

Quote (Pavan Kumar)

I can contact another vendor SPX Cooling Technologies and try to get information if possible.

Yes, or an OEM Manufacturer Cooling Tower Parts Supplier like Cyrco, Inc. There are others. Ask them the make and model of spray nozzle Waltco bought/used.

Good Luck,
Latexman

RE: Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

With a bit of luck the nozzle part number will be stamped on the nozzle itself - but surely covered with years of gunk build-up.

Katmar Software - AioFlo Pipe Hydraulics
http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

RE: Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

(OP)
Hi All,

I found that I did a mistake in my calculation in the conversion from ft3sec-1/[(lbf/ft2)^0.5] to US gpm/(psi^0.5). Instead of multiplying by 12 I divided. I have now corrected the calculation(shown in red in thread above). The value now I calculate for K is 86.016 gpm/(psi^0.5). Does this number look reasonable?.

I also called SPX and they said they will get back to after some time. What system design density should I use?. Can I adjust the design density in gpm/ft2 that gives me a reasonable water demand and pressure?. NFPA 13 gives some guidelines but the numbers apply to large areas of application and my cooling tower area is only 120 ft2. Your suggestions will be very helpful to complete my calculations. How are calculations for Spray pipe pressure calculation for Counter flow Cooling Towers, is it by the Tree Calculation Method. In that case what design density should be used?.

Thanks and Regards,
Pavan Kumar

RE: Cooling Tower Spray Pipe Pressure Drop Calculation (Contd)

(OP)
Hi pierreick ,

I checked the website for Chalmers group but it seems they are in Cooling Tower business.

Thanks and Regards,
Pavan Kumar

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