Preferential Flow in Aerial Cooler Configuration
Preferential Flow in Aerial Cooler Configuration
(OP)
Ok I have never been asked this question before so I need some help.
Currently I have 8 aerial coolers in a first in last out configuration (also called "U" configuration I believe) and people i.e my boss is concerned that the first cooler will have more flow due to its smaller pressure drop. He wants me to quantify "more flow". Ideally he wants a number like x kg/h into cooler 1, y kg/h into cooler 2 but Im not sure how to give him what he wants. Thanks to the goodness of 3-D models I know all my lengths and elevations (The gas is clean and single phase)
I had one idea of treating it like a electrc ciruit and using pressure loss like a resistance. Any suggestions are welcomed.
Currently I have 8 aerial coolers in a first in last out configuration (also called "U" configuration I believe) and people i.e my boss is concerned that the first cooler will have more flow due to its smaller pressure drop. He wants me to quantify "more flow". Ideally he wants a number like x kg/h into cooler 1, y kg/h into cooler 2 but Im not sure how to give him what he wants. Thanks to the goodness of 3-D models I know all my lengths and elevations (The gas is clean and single phase)
I had one idea of treating it like a electrc ciruit and using pressure loss like a resistance. Any suggestions are welcomed.





RE: Preferential Flow in Aerial Cooler Configuration
As the first step to determining whether there will be a significant difference in flow between the coolers, you need to check to see how much pressure drop is expected in the common inlet and outlet headers using the total flow. If the common headers are large enough then each cooler and it's associated piping will have the same overall pressure drop. Using your circuit analogy, an equal pressure drop does not mean that the flows are the same unless the resistances are also the same for each cooler branch. Checking the headers first will greatly simplify your calculations, especially if you are doing them by hand.
best wishes, sshep
RE: Preferential Flow in Aerial Cooler Configuration
RE: Preferential Flow in Aerial Cooler Configuration
Ideally, you should employ reversed return piping in this case(first in first out).
If you can provide balancing valves for each cooler, you can check and correct the flowrate by means of a manometer and valve performance curve.
Regards,
RE: Preferential Flow in Aerial Cooler Configuration
I would be cautious about extending the circuit analogy to actual calculations of resistences in parallel, etc. For example in a circuit V=IR, in piping dP=KQ^2.
On the otherhand your calculation is simple if pressure drop in the common headers can be neglected as per the initial check I suggested above. Once you have calculated your K values for each branch (from Crane if that is your method), you merely need to trial and error dP values until the sum of the flows through all branches equals the total flow.
If you have to account for the common headers then it is not so simple because you will have 14 other pipe segment resistances to consider, i.e. 2*(8coolers-1). This is where some pipe network software comes in handy. You can still use a similar approach as per above by guessing an overall dP, but now you have to back calculate up the piping (using the total flow) to get a dP and flow through each branch- easy enough with a spreadsheet. You system is converged when you find a dP such that the flow through the last branch (as calculated by your flow equation) also satisfies the total flow constraint.
With respect to balancing the flows, the shortcut way is to try and adjust any individual exchanger butterfly valves that are avialable so as to get all the outlet temperatures the same.
best wishes, sshep
RE: Preferential Flow in Aerial Cooler Configuration
RE: Preferential Flow in Aerial Cooler Configuration
Doug