Agitation air sizing

A. I'm not sure what you mean by air "consumption". You do not "consume" air in acid copper plating, you are using air from a blower to agitate the bath (you are trying to rapidly replenish the copper concentration in the work/liquid boundary layer). As a rule of thumb, you would want to raise the solution layer about 3 cm (1") if you are looking for how much air you need.

There are also issues about sparger design and placement; you should consult with your supplier.

A. If your question is about how to size the blower, you need 1 pound/square inch/ 18 inches of solution depth, and 1 cubic foot/minute/linear foot of perforated pipe.

Perforated pipe: 3/32" diameter holes, spaced 3.75" apart. pipe diameter determined from cross sectional area of all drilled holes in the pipe. (3/4" schedule 80, .154" wall), this works out to no more than 10 feet long from the header.

Your supplier should be able to size the blower and pipes for you.

A. Hi Jon,

You worry too much, methinks.

Have a gander at # 9311, 7718 and 8345 .... they might give some insight, then again they might not!

You are right to assume that the area should be less than the blower outlet size ... one needs distribution even to the farthest hole.

If you are really worried, then test the motor output to ensure you are not overloading it.

I seem to remember that the farthest hole was a smidgen LARGER than the others to ensure that one achieved the right distribution. Most holes being, say, 1/8" and spaced at 6" to 12" apart.

You're probably right, I'm sure the system is a little more flexible than I have implied. I just want to get it right the first time if I can help it. Anyway, I think I found the missing piece that I needed in a technical bulletin from a regenerative blower company. It turns out that you want 1.0 in2 of total open hole area for each 62.5 SCFM in the system. That along with Ted's article in the Guidebook, gave me everything I needed to size the blower and agitation lines properly. Thanks.

A. Hi once again, Jon

Have a gander at # 7794, The Court Industries application.

Yes, I know that this was for air ... it's just that water is a heavier medium, that's all.

The crux is to place a larger hole at the very end of the pipe to aid distribution ... but your 62-1/2 CFM is insignificant, I feel ... what matters is the PRESSURE your pump generates.

Something else, before I forget ... if you are using plastics, sic. PVC pipe spargers, DON'T use an ultra small hole. Why? Because the drill bit will gum up and partially close those holes if, say, you use 1/16" dia.

A. A fairly common air agitation sizing is 5 ^^0.5 CFM per square foot of tank surface area (recalculate for metric). Use a throttling valve for adjustment and make sure your air supply is clean. High pressure blowers are commonly used in lieu of compressed air.

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Ed. note: We're quite sure that Rick's posting was missing a decimal point before the 5.

A. Hi Stephen,

This data won't help you determine the airflows BUT it sure could be, I think, of some assistance in getting a good distribution of the air along your longish tanks.

Please go to the archives and hit letter no. 7718 and # 9311.

A. Hi Stephen,
The volume of air required will be determined by three factors-
1. Depth of the tank will determine the pressure needed to ensure that the liquid does not enter the air line.
2. Diameter of the hole through which the air is to escape.
3. Number of holes in the piping.

Area of hole multiplied by number will give you the effective orifice size.

Head pressure(in Pascals )"p"= d x g x h (d=fluid density approx. 1000kg/m3 for water, g= gravitational force approx. 9.8, h= tank depth in meters)

>From a table you should be able to find the flow through the effective orifice at the calculated pressure.

I would suggest that the supply air be filtered and dried at the highest possible pressure to ensure that there is no contamination(oil water emulsions/ dirt) introduced into the tanks and there after reduce the pressure and add a flow control valve and non return valve just to be safe.

If I can assist further please let me know.

Regards,

A. Hi, Anand. To set the stage, we are talking about plating and metal finishing tanks here. It isn't clear what your topic is, but if it's not metal finishing, then this has no validity.

Rick Hall gave a figure of .5 CFM per square foot of tank surface. That means you multiply the width of the tank by its length, express that in square feet, and multiple by 0.5.

This is, of course, just one designer's approach. Others say use 1.0 CFM per linear foot of air agitation piping. Some tanks, like rinse tanks, might have one row of pipe from one corner of a tank to the diagonal corner. Other tanks like nickel plating tanks would probably have a row between each anode and cathode bar.

You need sufficient pressure to push the air down against the hydrostatic pressure of the solution in the tank, plus some more for dynamic losses. Some designers say that a good number is one ounce of pressure per inch of solution depth.

You might also consider that many new installations are moving from air agitation towards eductors. This is a system where venturi style eductors are put into the pipe, instead of holes, and the pipe is connected to a recirculating pump instead of an air supply. Good luck.

Regards,

A. It is off point a little bit, but a useful rule of thumb to consider is that air compressors will deliver only about 4 cfm per horsepower whereas properly sized low pressure blowers deliver about 28 cfm or more per horsepower. In dollars per year these differences are amazing. Please don't consider using a 100 psi air compressor to agitate tanks that only require 3-4 psi of air pressure. Instead invest in a low-pressure blower which will pay for itself very quickly.

Another rule of thumb for air agitation is that mild agitation is considered to be around 0.5 cfm per square foot of tank surface area and vigorous (such as for hard anodizing) is going to be around 1.5 cfm per square foot of tank surface area. 0.5 cfm/ft2 is plenty for most purposes and anything above that is is probably wasteful. Your hole sizing is probably not optimized for the air agitation that you need. If you have a Metal Finishing Guidebook, then you should definitely read Ted Mooney's article entitled "Solution Agitation and Mixing". It is excellent.

? Hi Ricyl. Sorry, I cannot decipher "30 lbs can"; please try to re-word it for me. And what kind of electroplating are you doing?

Regards,

A. Good day Ricyl.

Try a search for GAST BLOWERS. It will give you details on air sparger requirements.

Regards,

A. Hi Prakash. Wernick, Pinner & Sheasby references T. Turner's Aluminum Association Finishing Seminar 1968 mention of 0.22 - 0.45 m3 of air per m2 of tank surface for decorative anodizing. Certainly the high end of this would be appropriate for hard anodizing. 0.45 m3/m2 of surface is very close to Jon's 1.5 CFM/ft2.

Be careful of the word "compressor" though. High pressure blowers rather than general air compressors should be used for air agitation.

And remember that the reason for using air agitation in hard anodizing is a bit different than the reason for using it in electroplating! In electroplating, its roles include general solution equilibrium and stripping small hydrogen bubbles off the surfaces of the work; but its main function in hard anodizing is to make sure the temperature of the parts does not rise; this requires more air discharge holes, and below each piece, not just anywhere.

Regards,

A. Hi Cagin. We readers have no idea yet how big your tank is, or how deep it is, or how large the "water pump" is, or what kind of pump it is, or how big the hose is, or even what metal you are electroforming with :-)

But it sounds like you have a grossly oversized air pump. The way air agitation is supposed to work is the air bubbles simply rise through the solution because air is lighter than the solution. Consequently, a deeper tank does not absorb their energy and slow them down. In your case it sounds like the volume is so great that you are literally spraying air out of your hose rather than just allowing it to gently float up.

I think the right answer is not to try to fix everything else to match your greatly oversized pump, but to use a more practical agitation system:
- You could recirculate the electroforming solution through that pump instead of using it to pump air.
- You could use a simple mechanical agitation system instead of air agitation.
- You could (perhaps, depending on the type of pump) use a valve or smaller diameter tubing to lessen the air volume -- or at least try drilling larger holes in the hose so gravity propels the bubbles rather than pump pressure spraying it.

Good luck

Regards,

A. Hi. It does sound to me like you could put a tee in the hose and bleed off some of the air :-)

Regards,