Gas flow through the installed control valve

The remarks made in Section 8.1 translate across to the gas flow cases more or less word for word, except that the methods of Chapter 9 must now be allied to those of Chapter 6 in order to calculate gas flow through line and valve. But the more complicated equations for both line flow and valve flow render explicit solutions to the full set of equations impossible. Two implicit methods, the Velocity-Head Implicit Method (VHIM) and the Smoothed Velocity-Head Implicit Method (SVHIM), will be presented, where the solution process has been reduced to iteration on a single variable. The SVHIM is judged to be more accurate because it deals with the compressible-flow valve equations at all times. 

An approximate meth, the Average Specific Volume Approximation Method (ASVAM), is also presented, based on the Long-Pipe Approximation described in Chapter 6. This approximate method retains much of the accuracy of the SVHIM, but has the advantage of yielding a direct estimate of flow. 

Examples will be given where the various methods are applied and results compared. 

2 Gas flow through an installed valve - Velocity-Head Implicit Method (VHIM) 

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