6 replies to this topic

[pettypatel]

Hi everyone,

 

     I was learning calculating water velocity in fps for 5/8" copper tube of OD =0.75 inch. formula is

   fps= flowrate/area * number of tubes. but different coil manufacturer uses different formula. I am confused.

 

1) colmac coil: 5/8" tube fps =1.194xgpm/number of circuit

 

2) Modine coil   WATER VELOCITY FPS = (0.0022 x GPM) / (CS x # of circuits) CS = 0.785 x (D-2t)² (where D = tube outside diameter t = tube thickness)

 

3) daikinapplied coil manufacturer

 

         Water Velocity: 5/8" Tubes: Water Velocity FPS = 1.07 × GPM No. of Tubes Fed

 

 

        Can anyone explain why they are using different formula? how they come up with different formula.

 

I am really appreciate your time.

 

from 

Paresh

 

 

[Bobby Strain]

You should derive the formula for calculating tube velocity. Show it to us if you are still uncertain. If you can't do this, you should consider changing your course of study. It's simple arithmetic.

 

Bobby

[pettypatel]

Hi  there,

 

   Thanks for your reply. I can calculate tube water velocity using standard formula. i dont understand why different manufacturer are using  formula. If you know please describe.

 

Thanks,

 

Paresh

[Bobby Strain]

You should use your own formula. Formula 3 is obviously not correct. I give the same advice for spreadsheets. Don't use any that are not validated to your satisfaction. Even from what should be a reliable source.

 

Bobby

[pettypatel]

Hello bobby,

 

   The reason of putting this question here is, i want to figure it out why different manufacturer using different formula for same tube diameter to find water velocity. If any one know please tell. I don't understand why you are replying rudely. I was not able to understand their formula so i asked. If you know the answer then explain. As per your comments its just a simple arithmetic. Then please show so i can understand. 

 

Thanks,

 

Paresh patel

[breizh]

Hi ,

Let you use the Unit system you are comfortable with and develop your own calculation .

As you said : V=Q/S where  Q = Qtotal /Number of tubes fed  

Good luck.

Breizh 

[pettypatel]

Hi Breizh,

 

        Thanks for your reply. I figure it out imperial also.All three manufacturer are using correct formula. Difference is they are using different tube material thickness.

 

Here is my calculation

 

1) Copper Tube O.D = 0.625 inch

2) Copper Tube I.D = .555 inch (After tube expansion it becomes 0.565) so ID is 0.565. Tube expansion is required for proper tube to fin bonding

3) US GPM to Imperial GPM = 0.832674

4) GPM to Ft^3/sec = 0.00222800

5) 1 feet = 12 inch

 

Water velocity in Tube Ft/sec= GPM/Tube cross section area * No. of Circuit

                                              = GPM*0.00222800*0.832674*144/(pi/4 (.565)^2) * Number of circuit

                                              = 1.0655*GPM/No. of circuit

                                              = 1.07 * GPM/ No of circuit

 

Thanks,

 

Paresh Patel