3 replies to this topic

[deltaChe]

Dear members:

The cooling water network consist of hundreds of supply and return line
and our boss design a PG and butterfly valve located on the return line.
He said this PG is to indicate any vacuum may happen on the return line
and butterfly valve can open and close to control the cooling water flow rate.

It is common to see the TT and butterfly valve located on the return line
as the temperature too high the valve to be opened and vise versa.

Could any master help me to explain this complex issue (seems to me) and
suggest any excel spreadsheet to calculated this hydraulic network?


Thank you so much.

Best regards,

[Steve Hall]

Depending on the specific design of your system, especially the method for controlling flow to the users, it might be feasible to use Excel to model it. I've created a simple demonstration. You'll see that with hundreds of users the model could be very complex and might be difficult to follow.

I've also created distribution models such as the one described at my website: http://www.pipesizin...m_project1.html

Note that to use the attached demonstration spreadsheet you must enable VBA macros.

Attached Files

•  Cooling Water Model.xls   104.5KB   298 downloads

[Dacs]

Just to explain your boss' insights on the matter:

Not all heat exchangers are placed near grade. Some of them are located way high above grade (normally the case with overhead condensers).

It's feasible that the CW lines going to those exchangers may experience vacuum conditions (due to too high elevation and not high enough CWS header pressure which is normally at 3-5 barG). Those PGs will serve as a function to monitor the pressure.

Butterfly valve will serve to throttle the flow. Normally you'd modulate this and monitor the process fluid outlet temperature to match to your desired setpoint. Remember, there are no flow controllers in your CW network and they will flow in accordance to your piping layout. So you need to have a way to control the CW flow going to your exchanger.

In design, you'd normally consider the piping layout and the your CW inlet and outlet header pressure. If you have AFT Fathom in your software suite, you can use this to estimate your CW flows in your network.

Hope this helps.

[Theomnivorous]

I have observed that once when HE was located at higher elevation than cooling tower top distribution header and if pressure drop of HE (and for overall system) was lower than designed for cooling water pump,following phenomena was observed.Recovered head was very high causing high velocity in HE outlet to CT top.This lowered pressure inside the piping header to the extent that PG showed vacuum,GRP pipe developed cracks due to ext.pressure and pipe rack started vibrating.For instant relief I provided high vent pipe on return line and than trimmed impeller to reduce head.By controlling butterfly valve also one can add to pressure drop and control this vacuum phenomena.