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Thread: Flow Rate of water

19062011, 02:52 PM #1
Flow Rate of water
Dear Friends ,
Is there any standard formula to calculate the ideal flow rate of water in the condenser or chiller pipeline ? I have somewhat idea regarding the same but not sure.
I hope you will share your ideas.
Thanks for cooperation.

21062011, 02:55 AM #2
Re: Flow Rate of water
Hello sumit,
the majority of water chillers and water cooled condensers are based on 5.5'C temp rise.
Apply formula for water chilling ; Kw = 4.2 Kj/kg * temp rise [ 'C ] * flow rate in Litres per second.
Flow rate = Kwr / 4.2 / 5.5 'C example
160Kw r / 4.2 / 5.5 = 6.93 litres per sec.
Reduce the temp rise and flow rate will increase.

21062011, 05:10 PM #3
Re: Flow Rate of water
Dear Magoo ,
Thanks a lot for your reply. According to you , Flow Rate = KWr / 4.2 / Temp Rise. Can you please again explain me this formula , as i am not able to get the meaning of Kwr. I know what is temp rise , but please explain me other terms used in this formula. I will be thankful to you.

21062011, 10:31 PM #4
Re: Flow Rate of water
Kw refrigeration as opposed to Kw electrical

01072011, 10:43 PM #5
Re: Flow Rate of water
kw/ 4.2 x dt = kg/s or L/s for water
kw = energy absorbed through refrigeration
4.2 = specific heat capacity of water ( kj/kg )
dt = temp in and out ( k )fridge

02072011, 03:53 AM #6
Re: Flow Rate of water
Hi Fridge ,
Thanks for your reply.
According to you , flow rate (L/S) = KW / 4.2 * dt.
But Magoo's formula was different , he said Flow rate (L/S) = KW/4.2/DT
Which one is correct ?

02072011, 06:37 PM #7
Re: Flow Rate of water
well the formula is derived from:
Q = m x cp x dt hence m = Q/ cp x dt
where Q = capacity in (KW)
m = mass flow rate ( kg/s or L/s)
cp = specific heat capacity ( kj/kg)
dt = temp difference (k)
so its a simple transposing of the original formulafridge

16082011, 12:01 PM #8
Re: Flow Rate of water
Hi Fridge,
Thanks a lot for sharing the above formula about flow rate of water. I already have services to audit water leaks and techniques to detect them properly, but I want to know more about water audit services which can be helpful to save water and water bill. Can you tell me that this formula related with flow rate of water is useful or not to water audit services.
Please share your ideas and tell about other more water audit services to save water and cost money.
Thanks
Maire

16082011, 06:28 PM #9
Re: Flow Rate of water
Hello Sumit
The equipment specifications dictate which flow rates are necessary for the equipment normal functioning. Note that savings on water in this respect may lead to your lost of the equipment.

16082011, 07:10 PM #10
Re: Flow Rate of water
Hi Maire,
If by water audit you mean water treatment or rate of water lost, then this formula will not help. I have no experience in water treatment but regarding the leakage rate/ evaporation rate, i think it may be worth looking at the cooling tower drift eliminators. Over the years they deteriorate and allow more than the normal amount of water lost through evaporation and increase your water bill. Good water treatment can reduce this deterioration also.
I've heard of companies doing eliminators that can reduce the rate of water lost through evaporation in cooling tower. If you can reduce the rate of evaporation water loss without sacrificing the towers heat rejection capacity then you may make savings on your water bill.fridge

18082011, 02:20 PM #11

18082011, 06:25 PM #12
Re: Flow Rate of water
Hello
Water is supposed to evaporate in a cooling tower, and the more, the better. To achieve the same effect without evaporation, one need to move more volumes of water, but by that more energy is spent on pumps.
If ,for instance, to keep a condensation T at a T a water condenser is designed for there is need for a definite amount of the coolant, one cannot be happy with an economy he/she has achieved on water on expense of the equipment life.

19082011, 09:44 PM #13
Re: Flow Rate of water
Hello Yuri B,
Yes you are correct, but you can make water savings by combining sensible and evaporative heat transfer.
http://www.baltimoreaircoil.be/BAC/EU/axidownloads20.nsf/activedocuments/115FF044BDFE4B49C125709D00537C2F/$FILE/BAC%20Intelligent%20Water%20Saving%20Products.pdf
anyway dont worry, i think the person who asked the question is actually trying to sell something on herefridge

23082011, 03:26 AM #14
Re: Flow Rate of water
Hi sumit,
In order to get flow rate of chilled water or condenser water for centralized chiller plant, there are 3 ways to do it:
1) By using flow meter  result: very accurate reading
2) By using formula or calculation of Chiller Capacity (Q = m x Cp x delta T)  result: not much accurate
3) By using pump (either CHWP or CDWP) performance curve. Once u get the delta Pressure (Outlet Pressure  Inlet Pressure), use the pump OEM to plot the flowrate reading  result: accurate

23082011, 03:54 AM #15
Re: Flow Rate of water
HI,
Thanks Yuri, Fridge , Maire and schiZOprEni for your replies. schiZOprEni , can you please explain the third method to calculate flow rate.After getting the delta pressure of pump, how can one plot the flow rate reading ? What is OEM.
Thanks for your cooperation.

23082011, 11:35 AM #16
Re: Flow Rate of water
Btu/hr
flow rate (us gpm ) = 
500 x water temp out deg f  water temp in deg f

24082011, 05:51 PM #17
Re: Flow Rate of water
The more water flow is through the pump, the more work does its el. motor, the more ampers are consumed by it. You can look at what the pump (motor) maximal current is  by its maximal capacity, according to its specification  and what ampers the pump goes now with, then comparing you can see more or less what at this moment flow rate may be.
Last edited by Yuri B.; 24082011 at 06:03 PM.

25082011, 04:46 AM #18
Re: Flow Rate of water
OEM = original/official engineering/equipment manufacturer

05092011, 04:01 AM #19
Re: Flow Rate of water
Hi Sumit,
Pump performance chart/graph is given by the manufacturer (OEM) once a pump is tested at their lab. It is just like a birth certificate. On the graph, there are two parameters Total Head (or delta Pressure) at the Yaxis and Total Flow Rate (USGPM) at the Xaxis. As i said, once u get the value for delta Pressure across a Pump, then u can measure the liquid flow rate by plotting the point on the graph.

24102011, 09:06 PM #20
Re: Flow Rate of water
a easy way is by looking at your pumps info  min and max head. if it says e.g  4.2 min and 6.8 max you can take on the middle i.e about 5.5 bar. Or they may say 42 headmin 68 head max just remember they mean 4.2 not 42 bar. Head is up. bar is flow. to commission these you may need to slow the head pressure or increase which may require a bypass. Plus make sure pump amps are right. There are a lot of graphs that are easy to read per manufacturer