Pressure Drop in Heat Exchanger and flow at outlet 2

[santoshdada]

Dear all can any one tell me the what will be the effect on delta P and flow if nos of plate incraeses in a plate type heat exchanger keeping same flow at inlet of the heat exchanger

is there any formula to calculate the exact pressure drop/flow

thx in advance

 

[MintJulep]

If you increase the number of plates the pressure drop will increase for the same flow.

If you "keep the same flow at the inlet" then the flow at the outlet will be the same. Flow in = flow out.

 

[willard3]

snip
If you "keep the same flow at the inlet" then the flow at the outlet will be the same. Flow in = flow out.
snip
Called conservation of mass.....must have been sleepin' in Thermo



Heat transfer will increase and pressure drop will increase for the same flow (GPM) through more plates.

 

[jcazenave]

I disagree if you keep the same number of passes and increases the number of plates (channels) the pressure drop will decrease and the local heat transfer will decrease. However the overall surface will increase and the overall heat transfer is likely to increase.

the pressure drop is the sum of the pressure drop in the inlet and the plates. You would need know the distribution of the pressure drop to be able to hand calculate the increase by adding more plates.

hope it helps

 

[jmiles]

jcazenave is correct, if you add more plates (assuming you do not also reduce the space between plates) then your total flow area will increase, this will result in a drop in pressure loss, but your heat exchanger will also be larger. He is also correct in that your heat flux will decrease, however with a much larger area to consider now the overall rate should increase.

 

[MintJulep]

I stand corrected and plead that I was only half-way through my morning coffee.

Adding plates will increase the number of parallel flow paths, reducing pressure drop.

 

[rmw]

That makes me feel better, Mint. And, not only that, increasing the number of plates DOES increase the potential for fouling as the velocity in each individual plate pass decreases and a P&F's ability to stay clean depends on the velocity through the passes, over under around and through the convolutions. This assumes that the fluid has anything in it that would tend to come out of suspension upon a decrease in velocity and that describes most fluids in the end, even some of the 'clean' ones.

rmw

 

[santoshdada]

ok finally it mean pressure drop will reduce as nos of channel incraeses(flow path increases) for same flow rate . i think as pressure drop reduced so flow rate should be incraese at the outlet as compared to previous condition

 

[rmw]

Get a patent.

rmw

 

[wimple]

santoshdada

conservation of mass apply. or are u talking about a compressible fluid???

 

[SNORGY]

I think what santoshdada means is that for a given supply pressure and a fixed constraint on the allowable pressure drop, more flow can be accommodated through the exchanger by increasing (adding to) the plate pack. There will be some optimization of this with heat transfer depending on the ratio of the "before and after" plate count. If the number of plates to be added is significant relative to the original plate count, I suspect the heat transfer will be compromised to a greater degree.

Regards,

SNORGY.

 

[wimple]

I agree snorgy.
what was confusing is :
quoted/
i think as pressure drop reduced so flow rate should be incraese at the outlet as compared to previous condition
unquoted/

 

[wimple]

I would add that In any case, it cannot be related to some compressibility aspect..
For a compressible flow, reducing pressure drop, means lower outlet volume flow.
So Again I agree with Snorgy.

 

[25362]

I've seen somewhere that the [Δ]P is (on the average) an inverse function of Np[sup]1.7[/sup] where Np is the number of plates.

 

[santoshdada]

many many thanks to all of you