Natural Gas Processing

8.8. Calculating C_v for two phase flow

The method of C_v calculation for two phase flow assumes that the gas and liquid pass through the valve orifice at the same velocity. The required C_v is determined by using an equivalent density for the liquid gas mixture. This method is intended for use with mixtures of a liquid and a non-condensable gas. To size valves with liquids and their own vapor at the valve inlet will require good engineering judgment.

• Nomenclature:

A_v = flow area of body port (Table 8.9)

ΔP_a = allowable pressure drop

q_f = volumetric flow rate of liquid, ft³/h

q_g = volumetric flow rate of gas, ft³/h

w_f = liquid mass flow rate, lb/h

w_g = liquid mass flow rate, lb/h

G_f = liquid specific gravity at upstream conditions

G_g = gas specific gravity ...