Ultrasonic Enhanced Supercritical Carbon Dioxide Composite Cleaning Analysis

After more than a century of development,supercritical carbon dioxide fluid technology has been used in many fields,such as supercritical carbon dioxide cleaning,supercritical carbon dioxide extraction,and supercritical carbon dioxide power generation.Supercritical carbon dioxide has strong dissolving ability and good permeability to materials.Combined with the unique physical properties of supercritical carbon dioxide and the advantages of high efficiency and energy saving of ultrasonic cleaning,we independently designed the"ultrasonic enhanced supercritical carbon dioxide composite cleaning experimental platform"for research.Based on Rayleigh cavitation theory and the nature of supercritical carbon dioxide,this paper estimates that the threshold of cavitation in supercritical carbon dioxide fluid is about10~7Pa,and its pressure is equivalent to the static pressure of supercritical carbon dioxide.The high-pressure cleaning chamber in the"supersonic enhanced supercritical carbon dioxide composite cleaning experiment platform"can withstand 10 MPa high pressure,and the temperature in the high-pressure cleaning chamber can be controlled at 33?through the silicone rubber heating coil.The experiment ensures that carbon dioxide is in a supercritical state.It is designed and commissioned Sandwich piezoelectric ceramic ultrasonic transducers required for this experiment were processed.Using the designed"ultrasonic enhanced supercritical carbon dioxide composite cleaning experiment platform",the rust and oil stain removal experiment on the surface of CD03 carbon steel sheet was carried out.The rust removal experiment showed that the CD03 carbon steel sheet was subjected to ultrasonic cycles(supersonic power:1200W,working time:10s,pause time:20s,a working cycle of 30s)in the supercritical carbon dioxide fluid,and 1000 cycles of ultrasound Good cleaning effect can be achieved,the number of ultrasonic cycles can be extended to 1200 times,and obvious pit-like corrosion occurs.There is no obvious change in the sample without ultrasound.In the oil removal experiment,the concept of cleaning rate is introduced.The results show that the CD03 carbon steel sheet contaminated with oil stains in supercritical carbon dioxide fluid is subjected to ultrasonic cycles for 15 cycles,and the cleaning rate can reach 100%.It shows that the combination of supercritical carbon dioxide fluid and high-power ultrasound can achieve better cleaning results,and this technology can be applied to the cleaning of microelectronics,semiconductors,precision machinery and chips.The COMSOL Multiphysics 5.2a finite element software was used to simulate and analyze the sound field inside the high-pressure cleaning cavity to study the mechanism of supercritical carbon dioxide cleaning after the introduction of high-power ultrasonic waves.The sound pressure level inside the high-pressure cleaning chamber,the sound pressure of ZOX and ZOY sections,the sound pressure of the ultrasonic transducer axis,velocity and acceleration are analyzed.It is found that the maximum sound pressure inside the cleaning chamber is in the order of 10~6Pa,which can not reach the minimum sound pressure required for cavitation of the supercritical carbon dioxide fluid,but the acceleration of the particle at its central axis can reach30000g.Tens of thousands of impacts cause a huge impulse and can peel the dirt off the substrate.In the high-pressure cleaning chamber,the Z axis is 180mm to 190mm,and the sound pressure is the largest.The best cleaning effect can be obtained by placing the cleaning sample here.The three main mechanisms of ultrasonic cleaning,cavitation mechanism,thermal mechanism and mechanical mechanism are analyzed respectively.It is concluded that when the experimental platform is cleaned,the mechanical mechanism is the main driving force for ultrasonically enhanced supercritical carbon dioxide composite cleaning.