Microelectronics

Fundamentals of Vacuum Technology by W. Umrath

By W. Umrath

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Moreover, the surface through which the diffusion occurs is much smaller because of the special construction of the nozzles. The specific pumping speed of the vapor ejector pumps is, therefore, smaller than that of the diffusion pumps. As the pumped gas in the neighborhood of the jet under the essentially higher inlet pressure decisively influences the course of the flow lines, optimum conditions are obtained only at certain inlet pressures. Therefore, the pumping speed does Intake pressure pa Fig.

43), even when no throttle is present. The higher air partial pressure pp2 at the condenser exit is produced by an accumulation of air, which, as long as it is present at the exit, results in a stationary flow equilibrium. From this accumulation of air, the (eventually throttled) gas ballast pump in equilibrium removes just so much as streams from the entrance (1) through the condenser. 23a) for which, however, information on the quantity of pumped vapors and permanent gases, the composition, and the pressure should be available.

Shown in Fig. 39 is the pumping speed characteristic of an ÒALLáexÓ 250. This pump has a nominal pumping speed of 250 m3/h and an ultimate pressure of < 10 mbar. At 10 mbar it still has a pumping speed of 100 m3/h. 5 kW of electric power. Vacuum generation 1000 m Saugvermˆgen Pumping speed Cooling gas Exhaust gas 3 . h-1 100 10 8 6 4 2 1 1 2 4 6 8 10 100 Ansaugdruck Intake pressure Fig. 37 Circulation of the cold gas in the ÒALLáexÓ with cooler / condenser mbar 1000 Fig. 39 Pumping speed characteristic of an ALLáex 250 Vmax Exhaust slot 1 Volume of the pump chamber starts to increase Intake slot Suction Cold gas inlet Vmin 100 (10) 1000 Pmbar (100) 100 (10) 1000 Pmbar (100) Vmax 2 Volume of the pump chamber at maximum End of suction Vmin Cold gas inlet Vmax 3 Volume of the pump chamber stars to decrease (without compression).

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