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Pressure drop due to friction and condensation

by Meteorrain
Tags: condensation, friction, pressure
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Oct16-12, 06:33 AM
P: 1

I'm struggling with the following problem. We have a dryer in our plant which evaporates acetone and with a blower the vapour is driven to a scrubber. However the efficiency of the scrubber is not sufficient and that is why I want to place a plate heat exchanger in the vapour line to cool the gas (a portion of the vapour will be condensated).

The blower is almost at its limits and we don't want more pressure loss to prevent a too low flowrate. Now the company of the plate heat exchangers calculated a pressure drop of 50 mbar which is too much.

However a pressure drop due to condensation in the heat exchanger will increase the flowrate. But a pressure drop in the heat exchanger due to friction of the plates will decrease the flow. I tried to explain this to the contact person, but the pressure drop is calculated with their software and all he knows is that it is the pressure drop from inlet to outlet.

So I am wondering if this 50mbar pressure loss should be considered as total energy loss and thus the blower needs to deliver an additional 50mbar pressure to cover this. Or doesn't my point of view makes sense?
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Jan20-13, 06:48 PM
P: 51
Im not sure if I understand your problem fully but I have a bit of experience in condensation pressure drop. For your case, you are going to have pressure losses due to a combination of 3 effects; frictional losses, momentum losses and static/gravitational losses. If your hex is mounted horizontally, you can neglect the gravitational losses. In addition, as your flow is condensing, you will have momentum recovery (not loss) although if you say only a small amount of vapour is condensing, this may not matter much. It depends on your dryness fraction leaving the hex. My guess, is the 50mbar given to you is solely based on frictional losses, although to calculate this, it must be based on some flow rate of vapour? Obviously 50mbar is goning to seem excessive if the calculation was based on a high flow rate of vapour
Feb4-13, 04:22 PM
P: 71
I'm afraid condensation will even increase the pressure lost, due to droplets forming inside heat exchanger

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