TERRITORIALIDAD, SOBERANÍA Y CONSTITUCIÓN: LAS BASES
3. LA TERRITORIALIDAD COMO UNIDAD ESTRUCTURANTE DEL
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Input Field Description Properties
Group VLE Method
(Overall) The options for the Vapor-Liquid Equilibrium calculations are as follows:
Compressible Gas - Real Gas relationship.
Peng Robinson - Peng Robinson Equation of State.
Soave Redlich Kwong - Soave Redlich Kwong Equation of State.
Vapor Pressure - Vapor Pressure method as described in API Technical Data Book - Volume 113.
Enthalpy Method (Overall)
The following calculation method for the determination of fluid enthalpies are available:
Ideal Gas - This method uses the specified downstream temperature of a source to calculate the heat balance within the network.
Peng Robinson - The Peng Robinson enthalpy is determined rigorously.
Soave Redlich Kwong - The Soave Redlich Kwong enthalpy is determined rigorously.
Lee-Kesler - This method uses the specified upstream temperature and pressure of a source to calculate the heat balance within the network. The Lee Kesler enthalpies may be more accurate than the Property Package enthalpies, but they require solution of a separate model.
8 Calculations 109 Input Field Description
VLE Method (Source Outlet Temperature Estimation)
The VLE method that will be used for the estimation of the
temperature at the downstream flange for source nodes. The options are the same as for the Overall VLE Method.
Enthalpy
The enthalpy method that will be used for the estimation of the temperature at the downstream flange for source nodes. The options are the same as for the Overall enthalpy Method.
Pressure
Isothermal Gas - This is a compressible gas method that assumes isothermal expansion of the gas as it passes along the pipe. Flare System Analyzer uses averaged properties of the fluid over the length of the pipe. The outlet temperature from the pipe is calculated by adiabatic heat balance either with or without heat transfer. Pressure losses due to change in elevation are ignored.
Adiabatic Gas - This is a compressible gas method that assumes adiabatic expansion of the gas as it passes along the pipe. As with the Isothermal Gas method, pressure losses due to changes in elevation are ignored.
Beggs & Brill - The Beggs and Brill method is based on work done with an air-water mixture at many different conditions, and is applicable for inclined flow. For more details, see Appendix A - Theoretical Basis.
Dukler - Dukler breaks the pressure drop in two-phase systems into three components - friction, elevation and acceleration. Each component is evaluated independently and added algebraically to determine the overall pressure drop. For more details, see Appendix A - Theoretical Basis.
Lockhart Martinelli – Lockhart Martinelli correlations models the two phase pressure drop in terms of a single phase pressure drop multiplied by a correction factor. Acceleration changes are not included.
Beggs and Brill (No Acc.) – The Beggs and Brill methods without the acceleration term.
Beggs and Brill (Homog.) – The Beggs and Brill methods with a homogeneous acceleration term.
Model Default - If this is selected, the Default method for the Horizontal/Inclined method (as defined on the Calculation Options Editor view) will be used.
Vertical
Pipes The options are:
Isothermal Gas - This is a compressible gas method that assumes isothermal expansion of the gas as it passes along the pipe. Flare System Analyzer uses averaged properties of the fluid over the length of the pipe. The outlet temperature from the pipe is calculated by adiabatic heat balance either with or without heat transfer. Pressure losses due to change in elevation are ignored.
Adiabatic Gas - This is a compressible gas method that assumes
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adiabatic expansion of the gas as it passes along the pipe. As with the Isothermal Gas method, pressure losses due to changes in elevation are ignored.
Beggs & Brill - Although the Beggs and Brill method was not originally intended for use with vertical pipes, it is nevertheless commonly used for this purpose, and is therefore included as an option for vertical pressure drop methods. For more details, see Appendix A - Theoretical Basis.
Dukler - Although the Dukler method is not generally applicable to vertical pipes, it is included here to allow comparison with the other methods.
8 Calculations 111 Input Field Description
Orkiszewski - This is a pressure drop correlation for vertical, two-phase flow for four different flow regimes - bubble, slug, annular-slug transition and annular mist. For more details, see Appendix A - Theoretical Basis.
Lockhart Martinelli – Lockhart Martinelli correlations models the two phase pressure drop in terms of a single phase pressure drop multiplied by a correction factor. Acceleration changes are not included.
Beggs and Brill (No Acc.) – The Beggs and Brill methods without the acceleration term.
Beggs and Brill (Homog.) – The Beggs and Brill methods with a homogeneous acceleration term.
Model Default - If this is selected, the Default method for the Vertical method (as defined on the Calculation Options Editor view) will be used.
Two Phase
Elements For two-phase calculations, the pipe segment is divided into a
specified number of elements. On each element, energy and material balances are solved along with the pressure drop correlation. In simulations involving high heat transfer rates, many increments may be necessary, due to the non-linearity of the temperature profile.
Obviously, as the number of increments increases, so does the calculation time; therefore, you should try to select a number of increments which reflects the required accuracy.
Friction Factor Method
The Friction Factor Method applies only when you have entered a value for friction factor. The options are:
Round - This method has been maintained primarily for historical purposes in order for older Flare System Analyzer calculations to be matched. It tends to over predict the friction factor by up to 10% in the fully turbulent region.
Chen - It should always be the method of preference since it gives better predictions at the fully turbulent flow conditions normally found within flare systems.