(Solved): a) Explain the meaning of the terms choked flow in relation to the flow of gas through a valve ...

a) Explain the meaning of the terms ‘choked flow’ in relation to the flow of gas through a valve. Explain also how choked flow for a gas differs from choked flow for a liquid.
b) Calculate the equivalent choked flow of propane through a particular valve if the choked flow of natural gas through it is 10 liters s–1.
The relative density* of propane is 1.45 and that of natural gas is 0.65.
[*with reference to air]
c) A valve is required to regulate the flow of natural gas. Details of the gas are given in table below. It can be assumed that the pipe size and the valve size are the same [i.e. piping geometry does not have to be allowed for].
The chosen valve type is the V250 rotary ball valve by Fisher Controls International [the V250 data sheet is available on Blackboard].
? Determine the required valve size in inches from the range of sizes given in the datasheet [the data sheet gives a range of nominal pipe sizes (NPS) in inches].
? Estimate the percentage the chosen valve would have to be open to carry the required flow

 

 

\begin{tabular}{|l|l|} \hline Natural Gas & \\ \hline Required volumetric flow rate [@, STP] & \( 2.8 \times 10^{6} \) litre per minute \\ \hline Density [@STP] & \( 0.752 \mathrm{~kg} \) per \( \mathrm{m}^{3} \) \\ \hline Specific heat ratio & \( 1.31 \) \\ \hline Inlet pressure & 20 bar gauge \\ \hline Outlet pressure & 6 bar gauge \\ \hline Inlet Temperature & \( 20{ }^{\circ} \mathrm{C} \) \\ \hline \end{tabular} Design V250 Rotary Control Valve The Design V250 Hi-Ball rotary control valve (figure 1) is designed for heavy-duty throttling and on-off applications. Depending on size, this valve installs between two CL600 or CL900 pipeline flanges. The Design V250 valve is available with a single ball seal, flow ring, or dual-seal construction. Single-seal constructions are used in tight shutoff applications; the flow ring construction can satisfy higher temperature requirements. The dual-seal construction, with a seal in the inlet and outlet openings, is used in bidirectional flow-shutoff applications. The Design V \( 250 \mathrm{Hi} \)-Ball valve is typically used for throttling and controlled flow applications in gas transmission lines, gas distribution, or liquid pipelines. of a maximum static pressure differential of \( 103 \mathrm{bar} \quad \) NACE MR0175-2002. \( (1500 \mathrm{psi}) \) at \( 82^{\circ} \mathrm{C}\left(180^{\circ} \mathrm{F}\right) \) for CL600, and 155 bar \begin{tabular}{ll} (2250 psi) for CL900 constructions at \( 38^{\circ} \mathrm{C}\left(100^{\circ} \mathrm{F}\right) \) & \multicolumn{1}{c}{ - Long Service Life-Pressure-balanced drive } \\ for LCC steel and CF8M (316 stainless steel). & shaft design with PTFE-lined bearings and pressure-assisted shaft sealing arrangement provides for a long life of reliable service. \\ \( \begin{array}{ll}\text { - Efficient Operation-Tapered-polygon } & \text { Minimum Maintenance-Two-piece ball and }\end{array} \) \\ splined actuator connection (see figure 6) removed & - Minnen (see figure 5) and clamped \end{tabular} lost motion or deadband from the drive train for shaft assembly allows for complete trim overhaul; throttling control applications. parts replacement is kept to a minimum. - Excellent Flow Control-Reduced ball port - Excellent Environmental Capabilities-The design provides a modified equal percentage flow optional live loaded packing system is designed with characteristic and an excellent response very smooth shaft surfaces and live loading to characteristic. provide excellent sealing. 1. 8oo tabla 1 for sour sarvice trim maierials. Figure 2. Sectional View of Design V250 Valve Product Bulletin V250 Valve 51.3:-V250 November 2007 Table 2. Approximate Weights Installation Install the Design V250 valve in any position, but the recommended orientation is in a horizontal pipeline with the shaft positioned horizontally and the ball closing in the downward direction (see figure 1). The actuator can be either right- or left-hand mounted as viewed from the valve inlet for forward-flow. For bidirectional flow, install the valve so that the highest pressure condition will flow as shown by the flow direction arrow on the valve body. Dimensions are shown in figure 8. Product Bulletin \[ \text { 51.3:V250 } \] November 2007 MMRTH DO NOT EXCEED THE LIMITS IN THIS CURVE OR THE BODY RATING, WHICHEVER IS LOWER. Figure 3. Maximum Allowable Shutoff Preseure Drop for Single and Dual POM Seal Construction Figure 4. Ball Seal and Flow Ring Constructions Product Bulletin 51.3:V250 November 2007 Tahle 2 Nimanoinno Figure 8. Dimensions (also see table 3) Coefficients Table 4. Design V250