Chapter 10M

10M. Diameter (Two-Phase-Modified Flanagan Calculations For Flow Lines) Back to Main

This page is used to determine gas flow rate of a two-phase flow. The relationship between gas flow rate, diameter and pressure drop is represented by the Panhandle A equation (Table 10.1). Two corrections are made for two-phase flow.

1. The value of outlet pressure () is adjusted for the pressure loss due to uphill and downhill flow of two phases, including the effect of holdups.

2. The efficiency term (E) is correlated to reflect measured system performance based on gas velocity and liquid-gas ratio.

As thus, the modified Panhandle A equation becomes

(Equation 10.61)

Where: = gas rate at

P = absolute pressure

= mean absolute temperature of line

= temperature, standard conditions

d = inside diameter of pipe

L = pipe length

g = gas relative density

= mean compressibility factor

= two-phase efficiency, can be found in Figure 10.11

K = constant Metric , English 435.87

= (10.62)

Where: = additive correction to Panhandle A

A = constant Metric 0.00981, English 0.0069

= liquid density

= gas density

H = head

= uphill heads

= downhill heads

= empirical head factor (Figure 10.10)

(Equation 10.63, used with Figure 10.10 to find Eh)

To solve for the diameter the flow rate and pressure drop must be known. Assume a diameter to start a trial-and-error process. For this assumed value calculate and and solve Equation 10.61 for "d." When value calculated checks the assumed value (within even pipe sizes), the correct diameter is known.

To solve for the outlet pressure drop the flow rate and diameter must be known. This is a straightforward solution. Solve Equation 10.61 for . is the desired outlet pressure.

To carry out the calculation the method of calculation must be decided. Choose A. Pipe inside diameter calculations or B. Pipe outlet pressure calculations by clicking on and shading the circle provided for that selection. Once the method of calculation has been decided the Inlet pressure, Pipe length, Uphill heads, Gas relative density, Liquid density, Mean line temperature, Gas flow rate, Downhill heads, Mean line compressibility, Liquid gas ratio and Inside diameter or Outlet pressure must be entered into their entry space. To do so use the mouse to click the curser in the entry spaces and input the data. Once this has been done, select Run to execute the solution.

Inlet pressure is the gas pressure as the gas enters the pipe.

Pipe length

L

Y

X

Where: Y = distance from the bottom of the pipeline to the top of the pipeline in the vertical direction.

X = distance from the beginning of the pipeline to the end of the pipeline in the horizontal direction.

L = pipe length

Uphill heads is the sum of the changes in elevation in the uphill direction.

Downhill heads is the sum of the changes in elevation in the downhill direction. (Page 262, Volume 1)

Gas relative density is the molecular weight of the gas divided by the molecular weight of air or the density of the gas divided by the density of air at atmospheric pressure.

(1.2)

Mean line temperature is defined in Equation 10.41:

Outlet pressure is the pressure of the solution as it leaves the system.

The inside diameter of the pipe is the length from one inner edge of the pipe to another inner edge of the pipe on the exact opposite side.

Mean line compressibility is a measure of the average deviation of the actual relation from the ideal-gas equation state (PV = nRT.) If the gas compositions are known, Compressibility Factor can be calculated using screen 3C.

Liquid to gas ratio is the amount of liquid within the mixture in respect to the gas.

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