Thanks for info RC Al
I have previously read that slot spacing should be 4mm - 5mm, with no explanation to why so thanks for explaining the reasoning.
4mm slot spacing leaves very little room left for the slots on DN25 1"/25.4mm tube (circumference 79.8mm).
Trying to get maximum spacing and still adequate slot area without flow restriction requires a bit of a compromise.
3mm to 3.5 mm slot spacing is about the maximum can go without flow restriction.
The best I could come up with using DN25 tube:
A: 18 x 1.5mm (5mm high) Slots with a spacing of close to 3mm
B: 16 x 1.5mm (5.5mm hight) Slots with a spacing of close to 3.5mm
C: 16 x 1.6mm (5.5mm high) Slots with a spacing of close to 3.4mm
Made a bit of a spread sheet that shows many combinations.
Bubble Cap Slots.xlsx
Last column shows the 4" plate area (minus dowmcommer area) to total slot open area (5 x Caps) as a percentage, have read (theory) that for bubble plates this should be 9 to 10%. Sieve plates are less, 7 to 8%. This 9 - 10% seems to match a cap slot area between 132 - 146 sqmm.
5/8 riser area (ID 13.86mm) of 150sqmm is slightly more than cap slot area. Slot area is the limiting function with this design.
The next size up is to use a DN25 coupling or cap with 25.4mm ID & approx 28mm OD. Or I could expand out the many meters of DN25 tube that I already have lying around.
Can get a few more slots than DN50 tube and still maintain 3 to 3.5mm spacing.
If I go to 4mm spacing, 16 slots of 1.5mm (5mm High) reduced slot area to 120 sqmm, perhaps this is still ok?
Commercial bubble caps (most common I have seen) are 28mm OD, they have 16 slots, guestimate around 2mm wide/ 4.5 mm high and spacing calculated around 3.5mm. These seem to flow well. The 2mm slot seems to be on the large side however they must be ok as many use them.
Cap2.PNG
Cap1.PNG
I will probably make the riser height a bit less than the downcomer height, doesn't seem to have much of an effect.
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