Multichannel Square Tube Hydraulic Diameter

[chupacabras]

Hello, I am new to this forum.

I read the thread about the water flow in a rectangular tube because I wanted to correlate what was being said into my own problem.

My question I believe is very simple:

I have a rectangular tube that has inner dividers, let's say that my tube has 6 channels inside that are 7.15mm L X 3.54mm W, plus a 7th channel 7.15mm L X 5mm W.

Lets's say also that if I neglect the inner walls, the result is a bigger rectangle, roughly 29.3mm L x 7.15mm W.

I need to come up with the Hydraulic Diameter for the whole tube.

What is the approach I should take:

a) should I add the seven Hydraulic Diameters for each inner tube?

b) should I neglect the inner walls and calculate for the whole tube?

When I add up each channel's HDs, the results is 3 times higher than when I calculate for the whole tube, neglecting the inner walls.


I would really like your input on this subject, and I am sorry if this is so simple I had overlooked the answer.

Thanks,

[Q_Goest]

hi chup
a) should I add the seven Hydraulic Diameters for each inner tube?
That won't work, you'll get an enormous equivalent pipe diameter.

b) should I neglect the inner walls and calculate for the whole tube?
That won't work either. The inner walls create frictional pressure drop that you'd be neglecting.

The only way I know of to do this is to treat all seven diameters as independant flow paths.

[chupacabras]

Q_Goest: Thank you, that seems to be the most logical approach.