# Friction Loss Calculator

Created by Rahul Dhari
Reviewed by Hanna Pamuła, PhD candidate and Jack Bowater
Last updated: Mar 14, 2022

The friction loss calculator helps you to calculate the amount of pressure head loss due to friction for a given dimension of pipe and volumetric flow rate. The fluid flow inside a pipe or conduit is affected by friction, just like while pushing a heavy box on a rough surface. The friction force arising due to the due to interaction of fluids with the pipe walls causes loss in energy. The pipe friction calculator utilizes the Hazen-Williams formula to calculate friction loss.

Furthermore, you can estimate the loss in pressure due to friction using the specific weight of water in the advanced mode of our tool, meaning this pipe friction calculator can find the pressure drop in a water pipe system. Common examples of water pipe systems are the water supply to your kitchen, the sprinkler system on the roof, water in a fire hose and a piping system to fill your swimming pool. The water flow in the mentioned systems has varied efficiency and pressure output depending on factors like friction due to the pipe's material. Every material contributes differently to friction loss, e.g., friction loss in a fire hose will vary from friction loss in pipe fittings. We will find out in the subsequent sections about the variation in friction head loss pressure due to a change in material.

## What is friction loss?

When a fluid passes through a conduit or pipe, the roughness of the internal pipe walls and the fluid's viscosity affects the fluid flow, causing a loss in energy or pressure. This pressure loss affects the efficiency of pumping machines, as well as the output at the outlet. Engineers estimate this loss based on the pipes used in the system to get the desired water flow energy output.

## How to calculate friction loss?

There are several ways to calculate the friction loss in pipe fittings, such as the Darcy-Weisbach formula, Hagen-Poiseuille's law, and the Hazen-Williams friction loss formula. Each formulation has its merits and demerits. For instance, the Hagen-Poiseuille's Law utilises the dynamic viscosity and falls short in low fluid viscosity conditions and in wide pipes, due to turbulent water flow from the increase in Reynold's number.

This led researchers to move towards more complex models like the Darcy-Weisbach formula. However, despite being universally applicable and highly accurate, the friction factor term in the Darcy-Weisbach formula is difficult to estimate and has to be supplemented by the Moody diagram. The Moody diagram also relies on Reynold's number to estimate the friction factor. Lastly, the Hazen-Williams equation was pitched as a simpler version to estimate the pipe friction losses. The equation, however, is limited to water as the fluid medium.

## Hazen-Williams Equation

The friction head loss, HL, can be estimated by the empirical Hazen-Williams friction loss formula using the pipe dimensions - Length, L , diameter, D, volumetric flow rate, Q, and the roughness coefficient, C, as:

$H_L = \frac{10.67 \ L \ Q^{1.852}}{C^{1.852}D^{4.87}}$

Alternatively, the equation in its Imperial units form is:

$H_L = \frac{4.52 \ L \ Q^{1.852}}{C^{1.852}D^{4.87}}$

Furthermore, the pressure drop, Pd, can be estimated from head loss, HL, using the specific weight of water, W as:

$P_d = H_L \ W$

## Using the pipe friction loss calculator

1. Enter the dimensions of the pipe i.e. diameter, D, and length, L.

2. Input the volumetric flow rate, Q.

3. You can pick the pipe material, which will provide its respective roughness coefficient, C or tap on the advanced mode to directly input the roughness coefficient.

4. The pipe friction calculator will return friction loss for the pipe system.

You can also change the materials for the same dimensions and volumetric flow rates to note the difference between pressure loss and observe the performance of different pipe materials. See below for an example problem.

## Example: Using the friction loss calculator

Estimate the loss in pressure due to friction for a copper pipe with diameter 250 mm and length 10 m, if the volumetric flow rate is 0.5 m3/s. Take specific weight of water, W, as 9810 N/m3.

This gives D = 250 mm = 0.25 m, L = 10 m, and Q = 0.5 m3/s

For the material, a copper pipe, C = 135.

HL = 10.67 * 10 * (0.5 / 135)1.852 / 0.254.87

HL = 2.868 m of water.

The pressure drop, Pd, can be estimated as
Pd = 2.868 * 9810 = 28135.08 N/m2 = 0.28 bar.

This implies the pressure drop in the flow due to pipe friction is 0.28 bar. Now, let's compare this with a different pipe material, say a fiberglass (FRP) pipe.

For fiberglass, C = 150. Therefore,

HL = 10.67 * 10 * (0.5 / 150)1.852 / 0.254.87

HL = 2.3594 m of water.

The pressure drop, Pd, can be estimated as
Pd = 2.3594 * 9810 = 23145.714 N/m2 = 0.23 bar.

We observed that the pressure loss due to friction is higher in copper pipes compared to fiberglass pipes.

Rahul Dhari
Hazen-Williams equation
Pipe Diameter
ft
Pipe Length
ft
Volumetric Flow rate
ft³/s
Material
Select...
ft
of Water
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