The effectiveness of an ultrasonic cleaning system is greatly reduced or eliminated when the cleaning fluid is in motion, or circulating.  This is the primary reason why filtration systems which are installed on an ultrasonic cleaning tank are typically operated intermittently, or with significantly reduced flow rates.

When ultrasonic cleaning fluid is in motion, cavitation is difficult to achieve, since cavities are created when sound waves separate fluid molecules.  When fluids are in motion, the ultrasonic energy is never working on the exact same location in the fluid at any time, which prevents ultrasonic cavitation from occurring.

The amount of circulation that can exist before ultrasonic cleaning action is diminished, and how fast the system can recover from fluid circulation once the circulation source has stopped, will depend upon the size and shape of the tank being considered.  This is called the Circulation Recovery Period.  Small ultrasonic tanks tend to have greater watt densities than larger tanks, and circulating fluids do not remain in motion for long after the circulation source has stopped.  However, large tanks over 100 gallons in size may require several minutes before circulation has stopped to a degree where full ultrasonic power is restored.  Not only do fluids remain in motion longer in larger tanks, but watt densities are also less in larger systems, which exacerbates the problem.  Also, square or round tanks will require more time for ultrasonic recovery after the circulation source has been stopped since these tanks require more time to reduce fluid circulation.

The state of ultrasonic degassing will also play a role in the circulation recovery period as well.  When fluids are not fully degassed, the recovery period is extended since the dissolved gasses are circulating as well, thereby creating a moving wall of entrapped air which further reduces the effectiveness of the system.  However, there is a positive side to this property.  By circulating the fluid during the degassing period, the rate of degassing is increased.  Fluids can be degassed much faster if fluids are in motion or lightly circulating since the moving air entrapped within the fluid is allowed to join with other smaller air bubbles which can float to the surface.  More information on ultrasonic degassing can be found in the Ultrasonic College drop down menu above under "Degassing of Fluids."

Fluids which are circulating in deionized water rinse tanks are subject to complete elimination of ultrasonic activity.  Deionized water is very difficult to cavitate for any ultrasonic cleaning system since the tensile strength of the liquid is very high, making molecular separation of water difficult to achieve.  Circulating deionized water is highly detrimental to the ultrasonic cleaning action in these tanks.

Circulating Fluids:

• Should be Reduced in Flow if Constant Circulation is Required.
• Can be Performed during Times when Ultrasonics are Not in Use.
• Will Greatly Reduce Ultrasonic Effectiveness in Deionized Water Rinse Tanks.
• Will Require a Circulation Recover Period when Fluid Slows Enough to Permit Full Ultrasonic Cleaning Action.
• Greatly Reduce Ultrasonic Power when Fluids are Not Degassed

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Zenith Mfg. & Chemical Corp.
85 Oak St.
Norwood, NJ  07648-0412
800-432-SONIC (7664)
201-768-6999
sales@zenith-ultrasonics.com