Volumetric pumping behavior

Figure 32.27 shows how a centrifugal pump is affected, particularly at low flow rates, and the behavior is typical of conventional centrifugal pumps. Figures 32.28 and 32.29 present well-known information on the effects of dissolved and entrained gas on the volumetric efficiency of a positive displacement pump. 

The purity of the SCF is an important consideration in the planning of a synthesis. Low concentrations of impurities can have noticeable effects on the volumetric and phase behavior of SCFs. For example, helium can be present in commercial CO2 because it is sometimes added as a head-gas to ensure nearly-complete delivery of the cylinder contents and this has been found to affect the use of SCCO2 as a solvent for analytical and prepeu-ative purposes [51-53]. The He head-gas is unnecessary if a cooled pump is used for CO2 delivery. 

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