subject: Ultrasonic Cleaning Solution: Control Heat for Maximum Cleaning Efficiency [print this page] Ultrasonic Cleaning Solution: Control Heat for Maximum Cleaning Efficiency
As we learnt in high school physics, heat plays a prominent role in many physical and chemical processes; and the ultrasonic cleaning process is no exception. An ultrasonic cleaner essentially works by generation of ultrasonic waves by means of a transducer. This ultrasound energy is transferred to a liquid medium (cleaning solution), where it produces a multitude of microscopic vacuum-filled bubbles that lifts off dirt, grime and other contaminants from any metal or plastic object placed in it. The process is known as cavitation.
Depending on the cleaning application, the cleaning solution, which is prepared by dissolving a specified concentration of cleaning liquid concentrate in distilled or de-ionized water, is generally heated to the required temperature before the start of the ultrasonic process. This has the effect of causing air bubbles trapped in the cleaning solution to rise to the surface and escape into the atmosphere. This increases the efficiency of the ultrasonic process. Some models have a built-in Degas mode, where entrained air is removed automatically.
We would be forgiven for assuming that once we set the temperature control to the correct value, the temperature of the cleaning solution will remain constant throughout the ultrasound operation. What we may not realize is that the ultrasound waves generate their own heat, which raises the temperature of the solution and the equipment itself. For most cleaning applications this is not a constraint. However, in the case of surgical instruments, for example, where protein and blood particles are required to be removed, it could be. This is because the recommended upper limit of temperature is 420 Celsius.
The point to remember is when you set the temperature knob to a particular value; it means that when the liquid in the tank reaches that temperature, the heating gets switched off. However, as mentioned earlier, the ultrasonic waves continue to generate heat in the liquid. To overcome this problem, some ultrasonic cleaning brands, like Elma, provide a cooling coil which is fastened into the ultrasonic cleaner tank and is connected to a cooling circulating system (tap water can be used for this). The cooling coil prevents overheating of the cleaning liquid.
Common sense dictates that the more uniformly the available heat is dispersed through the cleaning solution, the more uniform will be the final result. Uniform dispersion can be achieved by continuously revolving the liquid in the cleaning bath. Also, the cover provided as part of the equipment should always be kept on when the unit is operating. This will reduce the vaporization of the cleaning solution.
In the Medical, Research & Development Laboratories and Technology Industry, high cleaning performance is a must. Certain brands, like Elma's Transsonic Digital bench top series make this possible through the use of specially designed and manufactured spread beam sandwich transducers. It allows for power regulation from a low of 20%, suitable for soft material, to a peak of 140%. The Elmasonic S series ultrasonic cleaners achieve similar results with an ultrasound-controlled heating-up function. What this does is activate the ultrasound at regular intervals during the heating process.
