Vacuum techniques Vacuum Ideal Vacuum A space totally
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Vacuum techniques
Vacuum • Ideal Vacuum A space totally devoid of all matter. Does not exist, even in outer space! Actual Vacuum (Partial Vacuum) A space containing gas at a pressure below the surrounding atmosphere or atmospheric pressure <760 T @ sea level and 00 C with no humidity
Important areas of applications Ø In electron tube used in wireless tele communication vacuum tubes are used Ø In the developments of thin films, solid state circuit components , LCD etc vacuum techniques are used Ø In manufacture of electric bulb , electric motors Ø Metal properties Ø Medical instruments Ø Food preservation Ø Particle accelerators
Brief history • 16 Th century Galileo. • 1643 Torricelli-space above the mercury in the nanometer tube was came to known as Torricellian vacuum • 1650 Otto von Guericke invented first mechanical vacuum pump • Modern high-vacuum technology is considered to start in 1905 with the German physicist Wolfgang Gaede (1878– 1945) and his invention of the rotating vacuum pump
1 Atmospheric pressure is 760 mm Hg = 1 Bar = 105 Pa 1 Torr = 1 mm Hg 1 Torr = 1/760 of an atmosphere = 132 Pa 1 milli. Torr = 0. 13 Pa = 1 μm. Hg 1 mbar = 1/1000 Atm = 0. 76 Torr = 100 Pa 1 Pa = 7. 6 milli. Torr = 7. 6 μm. Hg
Why is a Vacuum Needed? To move a particle in a (straight) line over a large distance Atmosphere (High)Vacuum Contamination (usually water) Clean surface To provide a clean surface
FLOW REGIMES Viscous Flow: Distance between molecules is small; collisions between molecules dominate; flow through momentum transfer; generally P greater than 0. 1 mbar Transition Flow: Region between viscous and molecular flow Molecular Flow: Distance between molecules is large; collisions between molecules and wall dominate; flow through random motion; generally P smaller than 10 mbar
Vacuum regions •
Vacuum pump classification
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