Ultrasonic Agitation, mixing solution

A. That should not be a problem. You might have a problem with the amount of acid in a micromist that is entrained in the air and carried out of the tank. You can always go to manual mixing or powered mechanical mixing prior to using the ultrasonics.

Phil,
If you are using air agitation just for mixing for a brief time, then shutting it down, then I don't see any problem. There are some acid based plating solutions that use continuous air agitation with no adverse affects other than a slight increase in evaporation rates.

Phil,

The negative effect you will find using that sequence of operations is potentially longer processing times. The use of air agitation will cause gases to dissolve in solution. Some of the energy of the ultrasonics will be transferred to these gases versus directly to the part. This could cause longer time in the acid to obtain the necessary cleaning action. If your parts are susceptible to hydrogen embrittlement, I would recommend holding in a rinse and allowing the ultrasonics to operate for 5-7 minutes to remove the dissolved gases.

Best of luck!

A. Ultrasonic agitation cleans largely by cavitation. I would not expect it to need any additional mixing except perhaps a gentle stir when making additions.
If you pass air through the solution you disrupt the ultrasonic path at every air bubble/solution interface and I would expect it to significantly decrease the efficiency of the bath.
Acids are rarely used for cleaning. If your actual use is removal of surface oxides, etc., I would not expect US to greatly improve the process. Simple immersion usually does the job as well, cheaper and a great deal quieter.