Pumping speed area-related

Surface area related pumping speed (area related impact rate according to equations 1.17 and 1.20, proportional to the mean velocity of the gas molecules in the direction of the cryopanel) a Probability of condensation (pumping)... 

The gas molecules entering the pump produce the area related theoretical pumping speed according the equation 2.29a with T = 293 K. The different pumping speeds have been combined for three representative gases H2, N2 and H2O taken from each of the aforementioned groups. Since water vapor is pumped on the entire entry area of the cryopump, the pumping speed... 

The equation of state for a perfect gas is presented and expressions arising from this for pure gases and gas mixtures are given. The kinetic theory of gases, which is a useful model of perfect gases, is introduced and two particularly useful results are emphasised. These are the mean free path (/) and the mean or thermal velocity (c). Of particular importance is Z74, which is numerically equal to the volume rate of flow per unit area and which can be used to determine quantities such as area-related pumping speeds, conductances, etc. 

The LN2-cooled trap will only condense water vapour. The area-related pumping speed of the trap for water is (from Equation (1.13)) ... 

Pumping speed. So far, the maximum area-related pumping speed (collision rate, SA) has been used in calculations. For a cryopanel built into a chamber with Acryo < Achdmber, the pumping speed is given by ... 

SA = the maximum area-related pumping speed a = the probability of condensation (at sufficiently low temperatures, a = 1 for all gases) pult = ultimate pressure (see below) p = pressure in the chamber... 

The area-related pumping speed achieved by a cryopanel can be calculated from Equation (3.19) ... 

P is the pressure increase, V is the volume of the chamber, S is Che pumping speed of the pumping system, and C is a constant depending on sample area, gas constant and gas phase temperature. If the desorption rate is small compared with the pumping speed, it will be proportional to the pressure P. The desorption rate is related Co desorption parameters through the following Polanyi-Wigner equation ... 

Effects of performance changes, 201-203 Head curve for single pump, 198 Relations between head, horsepower, capacity and speed, 200 Temperature rise 207-209 Viscosity corrections, 203-207 Purging, flare stack systems, 535 Reciprocating pumps, 215—219 Flow patterns, 219 Specification form, 219 Relief areas, 437 External fires, 451, 453 Sizing, 434, 436... 

Determine the pump efficiency and impeller shape. Figure 6.12 shows the general relation between impeller shape, specific speed, pump capacity, efficiency, and characteristic curves. At Ns — 2000, efficiency = 87 percent. The impeller, as shown in Fig. 6.12, is moderately short and has a relatively large discharge area. A cross section of the impeller appears directly under the Ns = 2000 ordinate. 

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