hydraulic calculation to find velocity in heat exchanger

[mzstar]

I need to do a hydraulic calculation on cooling water from one tower going to several heat exchangers. I have the total flowrate from the tower, but the pipe branches heading to heat exchangers in three different units. I need to find the velocity through each of the heat exchangers. Can anyone give me some clues on how to get started on this calculation? I have the pipe lengths, diameters, etc. Also, how would I calculate the pressure drop across each of the heat exchangers? Any help is greatly appreciated. Thanks.

 

[Montemayor]

mzstar:

If I understand correctly what you are trying to say: You have a Cooling Water Tower producing CWS (cooling water supply) to 3 separate units in parallel circuits.

All you need to know as basic data is the individual CWS in each circuit and the size, and number of tubes in each pass (if the CWS in in the tube side). The CWS velocity is equal to the flowrate divided by the flow cross-sectional area.

If you have the CWS flowing in the shell side, you have a more complex problem; the cross-sectional area varies across the tube banks and through the baffles. See your friendly heat transfer or heat exchanger text book for the conventional equations. The pressure drop calculations will also be found in the text books.

Art Montemayor
Spring, TX

 

[mzstar]

Art:

Thank you for the reply. The CWS is on the tube side of the heat exchanger. I understand that the velocity is Q/A, however there are several heat exchangers involved. Each unit has about 10-15. Do I need to calculate the flowrate going off at each split to a heat exchanger? Also, where does the pressure drop come in if I am only concerned with flowrate and area. Thanks again.

 

[Montemayor]

mzstar:

You have an easier problem, with the CWS in the tube side. However, you lost me when you say "Each unit has about 10-15." 10-15 what? -- tubes, exchangers, gpms?

You originally asked how to "calculate the pressure drop across each of the heat exchangers". If you are trying to figure out the pressure drop across each exchanger, it stands to reason that you would have to identify the CWS flow rate in each exchanger.

The pressure drop across the exchanger is related to the velocity (which you acknowledge "is Q/A&quot, the mass flow rate, the viscosity, and the friction the CWS sees as it traverses the exchanger. As I said before, this is detailed and explained in your friendly heat transfer text book.

Art Montemayor
Spring, TX

 

[CRG]

If the system is already built, have you considered using a ultrasonic strap on flow meter?