Author Topic: A Simplified Pipeline Calculations Program: Isothermal Gas Flow (2)  (Read 3061 times)

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Author : Tonye K. Jack
International Journal of Scientific & Engineering Research Volume 3, Issue 1, January-2012
ISSN 2229-5518
Download Full Paper : PDF

Abstract — and Program Objective -The familiarity and user friendliness of the Microsoft Excel TM spreadsheet environment allows the practicing engineer to develop engineering desktop companion tools to carry out routine calculations. A Multitask single screen gas pipeline sizing calculation program is developed in Microsoft Excel TM. Required equations, and data sources for such development is provided.

Index Terms— Isothermal pipeline design, pipe sizing, piping program, gas pipelines, engineering on spreadsheet, spreadsheet solutions.

1   INTRODUCTION                                                                     
Gas pipelines are employed for meeting various energy needs. Calculations for the design of such gas piping can often involve repetitive calculations whether for simple horizontal straight pipelines or pipelines for complex terrains. Advances in computer applications for piping design have created several off-the-shelf can programs, for which cost might be a limitation to their uses for certain, quick-check calculations. Microsoft Excel TM with its Visual Basic for Applications (VBA) automation   tool   can   be   used   to   develop   a   multi - functional   single   screen   desktop tool   to   carry   out   such   calculations.

2 REQUIRED GENERAL EQUATIONS FOR ISOTHERMAL FLOW
Pipe cross-sections are of Circular types for which the applicable relations are:

Reynolds Number:                (1)

Velocity:                            (2)

Area:                       (3)

Friction factor:

For Laminar Flow,                   (4)

For Turbulent Flow, f, is obtained by the Colebrook-White equation. Method of solution described in [1], uses the goal seek option in Microsoft ExcelTM.
   
    (5)

Flow rate:
G = γAV      (6)
      Where,
γ = P/RT = ρg       (6a)

The General Relation for evaluating such gas lines is given by equation (7).
   
          (7)      
   
3   FLUID PROPERTIES FUNCTIONS
A database of physical properties of typical piped gases can be developed using Microsoft Excel TM Functions category. The developed functions are then available as drop down lists in the Functions option of the Toolbar INSERT menu. Yaws, [2], [3], [4] provides density, and viscosity data as functions of temperature.

As an example, the [5], derived curve-fitted gas viscosity relationship for Methane (CH4), as a function of temperature is:
 
         (9)

Where, A= 15.96, B= 0.3439, C=-8.14 E-05
The unit of viscosity is in micro-poise, which can be converted to Ns/m2 by multiplying by 1E-6:

Thus, the revised equation is:

               (9a)

The temperature, T, in “(9),” is in Kelvin (K). The program can be developed to handle temperature data in Centigrade (oC) with a built-in conversion option.
The ALIGNAgraphics [6], structured naming convention for the fluid properties functions described in [1], is applied, i.e.

Name of property_ (temperature)

For Methane:    rhoMethane (temperature)
      viscoMethane (temperature)

Where rhoMethane, and viscoMethane are the function names for Methane gas density and gas viscosity respectively. The program developer could also adopt the chemical formula of the fluid type, particularly in cases of long fluid property names as in some hydrocarbons. Thus, using Methane as example, the following gas density function name will apply:

   rhoCH4(temperature).

4   APPLICATION EXAMPLE
Carbon Dioxide flows isothermally at 30oC through a horizontal 250 mm diameter pipe at the rate of 0.12kN/s. If the pressure at a section 1 is 250 kPa, find the pressure at a section 2, which is 150 m downstream?  Take that: Pipe Roughness = 6 x 10-4 m.

Nomenclature

P1   Upstream pressure (kPa).
P2   Downstream pressure (kPa ).
G    Mass Flowrate  (KN/s).
g    Gravity constant  (m/s2).
A   Area (m2).
f     Friction factor
D    Pipe internal diameter (m)
L    Pipe section length  (m).
M   Molecular Weight
γ    Specific weight  (kN/m3).
ρ     Gas density  (kN-s2/m4).
V     Velocity of flow  (m/s).
R     Gas constant  (m/degK ).
T   Temperature, (oC) or (K)

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