How do you estimate pressure drop in pipelines?

1 Basic concepts

Before you start estimating pressure drop, you need to understand some basic concepts and definitions. Pressure drop is usually expressed as the difference between the inlet and outlet pressures of a pipeline segment, or as the pressure gradient per unit length. The pressure drop depends on the flow rate, fluid properties, pipe geometry, and flow regime. The flow regime is the pattern of fluid distribution and motion in the pipe, which can be classified as single-phase or multiphase, and as laminar or turbulent. The flow regime affects the friction factor, which is a dimensionless coefficient that measures the resistance to flow.

2 Empirical correlations

One way to estimate pressure drop in pipelines is to use empirical correlations, which are mathematical formulas derived from experimental data and simplified assumptions. Empirical correlations are easy to apply and require only a few input parameters, such as flow rate, fluid density, viscosity, pipe diameter, and roughness. However, they have some limitations and uncertainties, such as being valid only for certain ranges of conditions, being sensitive to errors in input data, and ignoring some factors like elevation changes and fittings. Some examples of empirical correlations for single-phase flow are the Darcy-Weisbach equation, the Hazen-Williams equation, and the Moody chart. For multiphase flow, some examples are the Beggs and Brill correlation, the Duns and Ros correlation, and the Mukherjee and Brill correlation.

3 Mechanistic models

Another way to estimate pressure drop in pipelines is to use mechanistic models, which are based on physical principles and conservation laws. Mechanistic models are more complex and rigorous than empirical correlations, and require more input parameters, such as fluid composition, phase behavior, interfacial tension, slip ratio, and holdup. However, they have some advantages, such as being able to account for different flow regimes, elevation changes, fittings, and heat transfer. They can also provide more information about the fluid distribution and properties along the pipeline. Some examples of mechanistic models for multiphase flow are the TUFFP model, the OLGA model, and the LedaFlow model.

4 Computational methods

A third way to estimate pressure drop in pipelines is to use computational methods, which are numerical solutions of the governing equations of fluid dynamics. Computational methods are the most advanced and accurate way to estimate pressure drop, but they are also the most time-consuming and resource-intensive. They require a lot of input data, such as fluid properties, pipe geometry, boundary conditions, and initial conditions. They also require a high-performance computer and a specialized software to perform the calculations and simulations. Some examples of computational methods for multiphase flow are the finite difference method, the finite element method, and the computational fluid dynamics method.

5 Experimental methods

A fourth way to estimate pressure drop in pipelines is to use experimental methods, which are direct measurements of the pressure drop in a laboratory or a field setting. Experimental methods are the most reliable and realistic way to estimate pressure drop, but they are also the most costly and challenging. They require a lot of equipment, such as pumps, pipes, sensors, meters, and valves. They also require a lot of safety precautions, such as avoiding leaks, explosions, and environmental hazards. Experimental methods are usually used to validate and calibrate the other methods, or to investigate specific cases that are not well covered by the existing methods.

6 Software tools

To make the estimation of pressure drop in pipelines easier and faster, you can use software tools that implement the different methods and models mentioned above. Software tools can help you perform the calculations, simulations, and analyses of pressure drop in pipelines, and provide you with graphical and tabular outputs. They can also help you compare different scenarios, optimize the pipeline design, and troubleshoot the pipeline performance. Some examples of software tools for pressure drop estimation are PIPE-FLO, AFT Fathom, PIPESIM, and HYSYS.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?