# Understanding Concepts & Types of Gas Flow

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Gas flow meters are used to measure and control gas flow. To be able to use the right gas flow meter, it is important to understand how gases flow. This understanding and subsequent calculations help us control the various factors that contribute to the flow within an application. Regulating the flow of the gas or liquid will assist in increasing application efficiency.

Different Types of Gas Flow
Below are mentioned three main types of flow. These are common for both gases and liquids.

1. Turbulent Flow
This type of flow is characteristic of high flow rates or higher mass. It is generally seen in pipes or containers with large inner volumes. Flow disturbing phenomena like eddies, vortexes, and wakes are commonly seen in turbulent flows. The point velocity vectors are located in all various directions within a unidirectional flow. This makes it difficult to measure the flow rate accurately. This flow can be helpful when the gas or liquid consists of large solids. Turbulent flow ensures the solids stay afloat, thus preventing them from blocking the pipes, or settling on the floor.
2. Laminar (Smooth) Flow
This flow does not display any turbulence. The flow can be imagined to move in cylinders. The outermost layer/ cylinder is highest in density, and hence moves at a slow pace. The layer adjacent to it moves at a faster velocity. The innermost layer/ cylinder will move at the fastest speed.
3. Transitional Flow
Transitional flow exhibits characteristics of both turbulent as well as laminar flow. The middle portion of the medium is turbulent while the edges are smooth.

Gas Flow Concepts
The formula called Reynold’s Number is used to understand the type of gas flow and predict any changes that might occur in the flow. This measurement doesn’t have any dimensions. Hence, no units are used to denote the findings.

Calculation of Reynold’s Number in Pipes and Circular Conduits
It is calculated using the following formula, Reynold’s Number (Re) =
{(Fluid Density) × (Velocity of Fluid) × (Length Travelled/ Diameter of Pipe)} ÷ (Fluid Viscosity)
*This formula differs for non-circular conduits.

Value of Reynold’s Number for Different Flow Types
The distinct types of flow rates are differentiated according to the following values of Reynold’s number:

• For Turbulent flow, Reynold’s number (Re) is greater than 4000.
• For Transitional flow, Re measures between 2000 – 4000.
• For Laminar flow, Re is less than 2000.

Manipulating Flow Type
With the help of the variables used in Re, one can manipulate the flow type. For example, to make the flow more laminar or smooth, we will need to lower the value of Re to below 2000. This can be accomplished by increasing the viscosity of the fluid or reducing the values of the following parameters:

1. Fluid Density
2. Mean velocity
3. Diameter/ Length Travelled

Using Reynold’s number to predict flow patterns and control the flow is extremely useful in practical applications. It can be used in water treatment plants, pulp and paper industry, and other industries where pipe flow needs to be controlled. With the help of this formula, one can determine the size and type of pipe to be used in a particular application

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