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Old Jul 4th 2018, 03:40 AM   #1
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Gas flow direction in chamber with holes


I built a chamber for oxidation testing and I was trying to come up with a way to direct the flow preferentially to the specimens.

A top view of the chamber:

The chamber is inside a big furnace under vacuum: there is one entry for air on the right (blue) and two Exits on the left (red). Each hole is in correspondence of the two test specimens.

My thinking was that when I open the valve, the air will be redirected homogeneously on the two specimens as depicted in the Picture. I assume the vacuum will produce a current that will drag the air flow through the two openings.

Recently we also had to make a hole in the frontal wall, did a test and saw a different behaviour on the sample closer to the frontal hole (it was less oxidized). This got me thinking that maybe that 3rd hole deviated the gas flow, like in the Picture below.

I'm not much knowledgeable in fluid dynamics so I'm just going by intuition: do you think this configuration would result in a sort of Oxygen-free zone in the middle where nothing happens? Do you have some source or text I can consult for this kind of problem or does it require a too high level of understanding of the subject?

Thank you
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Old Jul 5th 2018, 06:02 AM   #2
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For a simple situation like the one shown you can probably make a sensible estimate using a "source sink" model.
In your picture you have 1 source and either 2 or 3 sinks.

The influence of a source/sink at any position is given by S/d
where S is the strength of the source and d is the distance from the source.
S is (by convention) negative for sinks (a sink is a negative source).

Using this simple idea I think you can already start to build an impression of how different inlet and outlet pressures and positions will affect the flow within the box.

In your top illustration the flow will be symmetrical (much as you indicate).
However in your second illustration, I would expect the lowest flow area in the top part of the box (in particular the to right corner of the box)
The flow will be higher toward the bottom of the box.
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chamber, direction, flow, gas, holes

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