P2

Thus, for choked flow, Eq. (l0-5l) becomes

3.78 x l05A2Pl SGffiT

The quantity in square brackets which is a function only of k [fn (k)], represents the dependence of the flow rate on the gas property. Hence it can be used to define a correction factor C2 that can be used as a multiplier to correct the flow rate for air to that for any other gas:

fn(k)air 0.4839

A plot of C2 vs. k as given by Eq. (10-54) is shown in Fig. 10-22.

D. Viscosity Correction

A correction for fluid viscosity must be applied to the flow coefficient (Cv) for liquids other than water. This viscosity correction factor (Fv) is obtained from Fig. 10-23 by the following procedure, depending upon whether the objective is to find the valve size for a given Q and AP, to find Q for a given valve and AP, or to find AP for a given valve and Q.

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