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[15a-P3-2] Theoretical Analysis of Free Convection in the Drilled Hole in Supercritical Carbon Dioxide
Keywords:Supercritical fluid, carbon dioxide, laser drilling
Laser drilling in supercritical carbon dioxide has excellent ability to achieve micro holes, which have high aspect ratio of over 100.
To clarify the dominant machining mechanism, a thermo and fluid dynamics model was applied to explain the flow in the drilling holes. The supercritical carbon dioxide has extremely higher ability to circulate inside the hole by free convection, which promote the ejection of machining debris to the outside of the hole. The distribution of velocity and temperature in the holes were estimated by the Lighthill’s open-syphon model. It reveals that the effect is increased with the diameter of the holes.
For instance, when the diameter is 0.2 mm, the laminar convection flow is available in the depth of more than 50 mm (aspect ratio is >250). By contrast, 0.4 mm hole keeps convection even at more than 500 mm depth (aspect ratio is >1250). In the air and water, the effect of free convection is almost negligible due to the less expansion ratio and kinematic viscosity. If the theoretical limitation of depth of the hole is identical to the maximum depth at which free convection is available, our processing method is will be break the limitation of the depth of drilling including mechanical machining.
To clarify the dominant machining mechanism, a thermo and fluid dynamics model was applied to explain the flow in the drilling holes. The supercritical carbon dioxide has extremely higher ability to circulate inside the hole by free convection, which promote the ejection of machining debris to the outside of the hole. The distribution of velocity and temperature in the holes were estimated by the Lighthill’s open-syphon model. It reveals that the effect is increased with the diameter of the holes.
For instance, when the diameter is 0.2 mm, the laminar convection flow is available in the depth of more than 50 mm (aspect ratio is >250). By contrast, 0.4 mm hole keeps convection even at more than 500 mm depth (aspect ratio is >1250). In the air and water, the effect of free convection is almost negligible due to the less expansion ratio and kinematic viscosity. If the theoretical limitation of depth of the hole is identical to the maximum depth at which free convection is available, our processing method is will be break the limitation of the depth of drilling including mechanical machining.