Natural Gas and LNG Flow and Pressure Drop Calculator

Description

q - volumetric flow rate at standard conditions

Volumetric flow rate of gas referred to specified standard pressure and temperature conditions, expressed as volume per unit time.

q₁ - volumetric flow rate at the start of pipeline

Volumetric flow rate of gas at inlet pressure and temperature conditions.

q₂ - volumetric flow rate at the end of pipeline

Volumetric flow rate of gas at outlet pressure and temperature conditions.

ṁ - mass flow rate

Rate of gas flow expressed as mass per unit time, constant along the pipeline under steady-state conditions.

V₁ - velocity at the start of pipeline

Average gas velocity at the pipeline inlet cross-section.

V₂ - velocity at the end of pipeline

Average gas velocity at the pipeline outlet cross-section.

p₁ - pressure at the start of pipeline

Gas pressure at the pipeline inlet, expressed as absolute pressure.

p₂ - pressure at the end of pipeline

Gas pressure at the pipeline outlet, expressed as absolute pressure.

Δp - pressure drop

Total pressure loss between the inlet and outlet of the pipeline.

Δp/L - pressure drop per unit of length

Pressure loss per unit length of pipeline, representing the pressure gradient along the flow direction.

Δp friction - pressure drop due to friction

Pressure loss caused by wall friction along straight sections of the pipeline, calculated using the Darcy–Weisbach equation.

Δp local - pressure drop due to local resistance

Pressure loss caused by fittings, valves, bends, entrances, exits, and other local disturbances.

L - pipe length

Total developed length of the pipeline section under consideration.

D - pipeline internal diameter

Internal diameter of the pipe used for flow area and velocity calculations.

kr - pipe internal surface roughness

Absolute roughness of the internal pipe surface, used in friction factor determination.

K - minor losses coefficient

Dimensionless loss coefficient used to quantify pressure losses due to local resistances.

Leq - equivalent length

Equivalent length of straight pipe that produces the same pressure loss as a local resistance.

f - friction factor

Dimensionless Darcy friction factor dependent on Reynolds number and relative roughness.

Re - Reynolds number

Dimensionless parameter used to characterize the flow regime of the gas.

T - gas temperature

Absolute gas temperature used in density and thermodynamic property calculations.

ρ₁ - gas density at the pipeline start

Gas density at inlet pressure and temperature conditions.

ρ₂ - gas density at the pipeline end

Gas density at outlet pressure and temperature conditions.

μ - dynamic viscosity

Dynamic viscosity of the gas used in Reynolds number and friction calculations.

cₚ - specific heat (heat capacity) at constant pressure

Specific heat capacity of the gas at constant pressure.

R - gas constant

Specific gas constant used in the ideal gas equation of state.

How to Use the Calculator

Using the calculator is straightforward. First, select the type of calculation required, then choose the flow parameters that should be entered as known values. The remaining flow parameters will be calculated automatically and displayed in the results.

Start by selecting whether you want to calculate:

• Pressure drop
• Flow rate
• Pipeline diameter

Next, select the flow parameters that are known and need to be entered into the calculator.

Available input parameters include:

• q – Volumetric flow rate
• ṁ – Mass flow rate
• P₁ – Pressure at the pipeline inlet
• P₂ – Pressure at the pipeline outlet

Pressure can be entered either as absolute pressure or gauge pressure, depending on the selected option.

The calculator can determine pressure drop by treating natural gas as either a compressible or an incompressible fluid.

If the gas is treated as compressible, two compressibility factor models are available:

• Redlich-Kwong
• Van der Waals

All of these options can be selected before performing the calculation.

When Is the Natural Gas Flow Calculator Applicable?

The calculator can be used to calculate pressure drop, flow rate, or pipeline diameter. It is intended for circular pipes and natural gas in the gaseous state.

The calculator applies only to single pipelines and is not suitable for pipeline network systems. For pipeline networks, the Pipe Network Calculator should be used.

How Does the Natural Gas Calculator Work?

Based on the selected calculation type and the entered input values, the calculator uses formulas that relate pressure drop to flow rate and pipeline diameter.

The applied formulas correspond to either:

• isothermal compressible flow, or
• incompressible flow

depending on the selected calculation method.

If the goal is to calculate pressure drop or flow rate through a pipeline, the pipeline diameter must be entered. The calculator allows selection of standard pipes from three available pipe standards.

If the goal is to calculate pipeline diameter or pressure drop, the gas flow rate must be entered. The calculator allows input of either:

• volumetric flow rate at standard conditions, or
• mass flow rate.

If pressure drop is to be calculated, both the flow rate and the pipeline diameter must be entered, along with one of the two known pressures:

• pressure at the beginning of the pipeline, or
• pressure at the end of the pipeline.

In all cases, additional pipeline parameters must also be entered, including:

• pipeline length
• internal pipe roughness
• local resistance coefficient
• gas temperature

After performing the calculation, the calculator also provides additional flow parameters, including:

• friction factor
• Reynolds number
• gas density at the pipeline inlet and outlet
• gas velocity at the pipeline inlet and outlet
• specific heat and gas constant
• pressure drop per unit pipeline length

When Is This Calculator Not Applicable?

The calculator does not account for elevation differences along the pipeline. It also does not support calculations for pipeline networks.

Since the compressible flow calculation is based on an isothermal flow model, the calculator is not applicable to short pipelines with large pressure drops, where adiabatic flow effects are significant.