Vacuum rough

The majority of industrial chemical and petrochemical plants vacuum operations are in the range of 100 microns to 760 torn This is practically speaking the rough vacuum range noted above. For reference ... 

Assume a velocity, v, ft/sec consistent with Figure 2-46. Use Table 2-21 for short, direct connected connections to the vacuum pump. Base the final specifications for the line on pump specifications. Also the diameter of the line should match the inlet connection for the pump. General good practice indicates that velocities of 100 to 200 ft/sec are used, w ith 300 to 400 ft/sec being the upper limit for the rough vacuum classification. 

Rough vacuum Medium vacuum High vacuum Ultra-high vacuum... 

Specific Air Inleakage Rates for Rough Vacuum, for Use with Equations... 

Rough vacuum Medium vacuum High vacuum Ultra high vacuum 760 torr to 1 torr 1 to 10-3 torr 10-3 to 10 torr 10 7 torr and below... 

Based on rough vacuum process pumps. Use 25 ft/s for high vacuum pumps. 

Materials. Methylene 4,4 -diphenyldiisocyanate (MDI, Mobay) was recrystallized from cyclohexane. Toluenediisocyanate (TDI— represents mixture of 2,4- and 2,6-isomers in 80/20 ratio), p-toluidine (Aldrich) and aniline (Aldrich) were purified by vacuum distillation before use. Diphenylmethane, tert-butyl peroxide (TBP), 4-bromoaniline, butyl lithium in hexane, and ethyl chloroformate, were obtained from Aldrich and used as received. Spectrograde tetrahydrofuran (THF) and benzene from Burdick and Jackson were used as received. Poly(tetramethylene ether glycol) with MW 1000 was obtained from polysciences and dehydrated under a rough vacuum at 50 °C for 24 h. 

Important note Particularly in rough vacuum technology, partial pressure in a mix of gas and vapor is often understood to be the sum of the partial pressures for all the non-condensable components present in the mix - in case of the partial ultimate pressure at a rotary vane pump, for example. 

Rough vacuum (RV) Medium vacuum (MV) Fligh vacuum (FIV) Ultrahigh vacuum (UFIV)... 

This will be found almost exclusively in the rough vacuum range. The character of this type of flow is determined by the interaction of the molecules. Consequently Internal friction, the viscosity of the flowing substance. Is a major factor. If vortex motion appears In the streaming process, one speaks of turbulent flow. If various layers of the flowing medium slide one over the other, then the term laminar flow or layer flux may be applied. 

Normally a Roots pump will be operated in connection with a dovmstream rough vacuum pump having a nominal pumping speed Sy. The continuity equation gives ... 

Fig. 2.41 Condenser (I) with downstream gas ballast pump (II) for pumping of large quantities of water vapor in the rough vacuum mnge (III) - adjustable throUle...

The gas ballast pump has the function of pumping the fraction of air, which is often only a small part of the water-vapor mixture concerned, without simultaneously pumping much water vapor. It is, therefore, understandable that, within the combination of condenser and gas ballast pump in the stationary condition, the ratios of flow, which occur in the region of rough vacuum, are not easily assessed without further consideration. The simple application of the continuity equation is not adequate because one is no longer concerned with a source or sink-free field of flow (the condenser is, on the basis of condensation processes, a sink). This is emphasized especially at this point. In a practical case of non-functioning of the condenser - gas ballast pump combination, it might be unjustifiable to blame the condenser for the failure. 

Because of the factors described above, an assessment of the pump-down time must be basically different for the evacuation of a container in the rough vacuum region from evacuation in the medium- and high vacuum regions. 

In the rough vacuum region, the volume of the vessel is decisive for the time involved in the pumping process. In the high and ultrahigh vacuum regions, however, the gas evolution from the walls plays a significant role. 

Measurement of pressures in the rough vacuum range can be carried out relatively precisely by means of vacuum gauges with direct pressure measurement. Measurement of lower pressures, on the other hand, is almost always subject to a number of fundamental errors that limit the measuring accuracy right from the start so that it is not comparable at all to... 

U-tube vacuum gauges fiiied with mercury are the simpiest and most exact instruments for measuring pressure in the rough vacuum range (1013 to a... 

Fig. 9.7 Nomogram for determination of pump-down time tp of a vessei in the rough vacuum pressure range...

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