This article discusses about slug flow in pipe. Slug flow is a pattern of two phase flow, more specifically a liquid-gas flow. In this pattern, the lighter fluid moves faster continuously which also contains gas bubbles.

**A slug flow can cause pressure oscillations inside a pipe flow. Usually the heavier fluid is termed as slug that moves slower. But we can refer the bubbles of lighter fast moving fluid also as slug. In this article we shall study about the slug flow in detail.**

**What is a slug flow?**

A slug flow is a pattern made in a two phase flow where the lighter fluid moves faster pushing along disperse gas bubble.

**The term slug refers to heavier fluid that moves slowly. But we can be using this term for lighter fluid also that moves quickly. Slug flow happens inside a two phase flow, specifically a liquid-gas flow. The pressure oscillations in the pipe are caused by this slug flow. Let us study more about this flow in further sections of this article.**

**Image credits: MichaelFYP, Slug flow, CC BY-SA 4.0**

**What is slug load in piping?**

Slug load in piping refers to the load applied by slug flow inside the pipe. The slug flow is characterized by intermittent sequence of liquid slugs which are then followed by longer gas bubbles flowing through the pipe.

**As discussed in the above section, slug usually refers to heavy liquid that flows very slowly. But here we can refer to lighter fluid that has a swift movement. We can experience pressure oscillations inside pipe due to slug flow taking place.**

**Slug flow in horizontal pipeline**

When the fluid dlow is taking place in a horizontal pipeline, then the resulting slug flow can be referred to as slug flow in horizontal pipeline.

**To calculate the load applied by the slug flow in a horizontal pipeline we need to understand that it depends on few factors. These factors are Diameter of the pipe, cross section area of the pipe, resultant force, angle of bend (in case of horizontal pipe the angle is zero) and the length of the pipe. We shall study about the formula for calculating slug loads in next section.**

**Slug load formula in horizontal pipeline**

We have discussed about the slug flow in horizontal pipeline and the factors on which the load depend. In the section below we shall discuss about the formula required to find slug load in horizontal direction.

**The formula for slug load in horizontal pipeline is given below-**

Where,

D is the diameter of the pipe

A is the cross section area of the pipe

L is the length of the pipe

Theta is the angle of bend

F is the resultant force

**Slug flow in vertical pipes**

When the pipe in which the slug flow is taking place is vertical, then the resulting flow is called as slug flow in vertical pipes.

**The slug load in vertical pipes depends on various factors. These factors are diameter of the pipe, cross section area of the pipe, length of pipe, angle of bend (in case of vertical pipe the angle is ninety degrees), resultant force. In the next section we shall discuss about the formula for calculating slug loads in vertical pipe.**

**Slug load formula for vertical pipe**

The factors on which the slug load depends is discussed in the above section. Now we shall discuss the formula used to calculate the slug load.

**The formula for slug load in vertical pipe is discussed in the section given below-**

Where,

D is the diameter of the pipe

A is the cross section of the pipe

L is the length of pipe

Theta is the angle of bend

**Slug flow in inclined pipes**

When the pipe through which the slug flow is taking place then the resulting flow is reffered as slug flow in inclined pipes. We shall see the factors on which the slug load in inclined pipe depends.

**The slug load depends on the same factors as that of vertical and horizontal pipes. These factors are diameter of the pipe, cross section area of the pipe, length of the pipe and angle of inclination or bend. In the next section we shall discuss about the formula used for calculating slug load in inclined pipe.**

**Slug load formula for inclined pipe**

The slug load formula depends on some factors and these factors are discussed in the above section already. In this section we shall use these factors and come up with a formula to calculate the slug load in inclined pipe.

**The slug load formula is given in the section given below-**

Where,

D is the diameter of the pipe

A is the cross section of the pipe

L is the length of pipe

Theta is the angle of bend

**How to avoid slug flow in pipes?**

Slug flow can create pressure oscillations inside the pipe. Although slug flow can be avoided by taking certain measures. These measures are discussed in the next section.

**The following methods can be used to avoid slug flow in pipings-**

- Usage of low point effluent drain or bypass
- Reducing line sizes to the minimum point permitted by the pressure drop
- Keeping the arrangement of pipe flow in such a way that it protects against the pipe flow.

**Plug flow vs slug flow**

The difference between the two is not too big that we equire a table of differentiation for it. Both the flows are actually very similar and hold similar meanings.

**The only difference between a plug flow and a slug flow is that in plug flow the bubbles move at a slower rate than the bubbles in slug flow. Also, the size of bubbles are smaller in plug flow as compared to the size of bubbles in slug flow.**

**Examples of Slug flow**

**The list below shows the different places where slug flow is used. **

- To produce hydrocarbons in wells and their transportation through pipelines.
- In geothermal power plants, to produce steam and water.
- Boiling and condensing of liquid vapour systems of thermal power plants.
- To cool core of nuclear reactors in emergency situations.
- In chemical reactors, to transfer heat and mass between gas and liquid.

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