## Appendix 3. Friction Losses and the Reynolds Number

The frictional head loss for fluids flowing in pipes is calculated by the following equation: (27) Where: f is the friction factor (see below for calculation) L is the pipe length (m) v is the average fluid velocity (m/s) D is the pipe diameter (m) g is the acceleration due to gravity (9.81 m/s/s) The only variable not available to us immediately is the frictional factor (f). This is dependent on the type of flow occurring in the pipe. There are basically two types of flow (although there is a transition state between them ), these are: Laminar flow. Example: This is similar to the stream of smoke from a cigarette in still air. Close to the cigarette the stream of smoke is very uniform and flowing evenly. This is laminar flow. Turbulent flow. Example: This is when the stream of smoke from the cigarette becomes unstable, with whorls and eddies. This state occurs in the stream of smoke after the laminar flow. These two states of flow can be described by a dimensionless quantity (just a number) known as the Reynolds Number (NRE). This number is calculated by the following formula: (28) Where: v is the average fluid velocity (m/s) D is the pipe diameter (m) μk is the kinematic viscosity of the fluid (m2/s), which is a measure of how ‘thick’ the fluid is If the Reynolds Number is less than 2000 then the fluid flow is laminar. In this case the friction factor (f) can be calculated by the following equation: (29) If the Reynolds Number is greater than 2000 then the fluid flow is turbulent. In this case the friction factor (f) can be calculated by use of a Moody...

Read More## Appendix 6: Frictional Head Loss Chart

Polyethylene (PE) SDR-Pressure Rated Tube [(2306, 3206, 3306) SDR 7, 9, 11.5, 15 C=150]

Read More## Fluid Mechanics For Gravity – Flow Water Systems and Pumps

A text detailing the design of water systems including the design parameters recommended for a successful and long lasting water supply. Issue 2 May 2003.

Read More## Friction Loss Tables

Data for frictional losses in plastic pipe Diameter: 13-75mm, Flow rates: 0.06-3.15LPS, Frictional coefficient: C=150 This table is available as a PDF.

Read More## Gravity Flow Water Supply

By Santiago Arnalich Castañeda. This book intends to provide you with the tools needed to complete a sucessful gravity flow water project in a short amount of time. You may well already be dealing with a real life project, but without the time to do intensive study to get up to scratch. This book is meant to be: 99% Fat Free – Only what you really need is included. Simple – One of the most common causes of failure is that the complexity and excessive rigour become very intimidating, and things get left half done. Chronological – It more or less follows the logical order in which you’d undertake the project. Practical – With calculation examples. For a generous step by step exercises collection see “How to design a Gravity Flow Water System Through Worked Example“, a book from the same author. Self contained – It is assumed that you are in a remote area with not access to information, so all the essential information is included. Never the less links to other sources of information are provided. You can read the whole of Gravity Flow Water Supply on Google...

Read More## Head Loss Calculator Spreadsheet

This spreadsheet allows the user to calculate the frictional head loss (m) for a given flow rate (LPS) and pipe length (m), for a series of different diameter pipes (in). The user can also find the optimum combination of 100m sections of two pipes of different diameters (in) to “burn off” a given frictional head (m). Microsoft Excel...

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