3_Pumps_Gauges - Pumps and Gauges S Gupta Associate...

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Department of Metallurgical and Materials Engineering Pumps and Gauges S. Gupta Associate Professor Dept. of Metallurgical and Materials Engineering The University of Alabama
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Department of Metallurgical and Materials Engineering Contents Gas Flow Regimes Conductance Pumping Speed Vacuum Pumps Rotary Mechanical Pump Roots Pump Diffusion Pump Turbomolecular Pump Cryopump Sputter Ion Pumps Pumpdown Curves, Leak Rates Pressure gauges, Residual gas analyzers (RGAs)
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Department of Metallurgical and Materials Engineering Conductance Consider the molecular flow of gas through an orifice of area A that separates two chambers maintained at pressure P 1 and P 2 . A flow driven by the pressure difference can be expressed as Q = C (P 1 – P 2 ) where Q = throughput in torr-liters/sec, and C is the conductance of the orifice with units of liters/sec. When conductances are joined in series, the total system conductance is given by 1/C sys = 1/C 1 + 1/C 2 +1/C 3 ….. When conductances are joined in parallel, the total system conductance is given by C sys =C 1 + C 2 + C 3 + ….
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Department of Metallurgical and Materials Engineering Gas Flow Regimes Gas Flow => Net directed movement of gas in a system under the influence of attached pumps. Typical unit of gas flow is standard cubic cm per minute or sccm . The Knudsen number Kn is defined as the ratio of the gas mean free path to a characteristic dimension of the system (e.g. chamber or pipe diameter D p ). Kn = λ mfp / D p Molecular flow: Kn > 1 Intermediate flow: 1> Kn > 0.01 Viscous flow: Kn < 0.01
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Department of Metallurgical and Materials Engineering Pumping Speed ( 29 ) 20 2 ( exp ) ( / / ) ( / ) ( / / ) ( ) 19 2 ( / 1 / ) 18 2 ( 1 ) 17 2 ( / / 1 ) ( ) 16 2 ( / - - = - - = - - - = - - = - = - - = = - - = - = - = + = - = - = V t S P P P t P S Q P S Q t P Q P S dt t dP V dt dP V dt VP d Q P P S P Q S P S Q P S Q P S Q P Q S where C S S S P P C Q P Q S p o i o p p i p p p p o p p p p p p p p p p p
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Department of Metallurgical and Materials Engineering Vacuum Pumps Gas transfer pumps Remove gas molecules from the pumped volume and convey
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