The Engineering Intern

Vortexes or Vortices often occurs in tanks when the velocity at the top of the fluid is much faster than the velocity at the bottom of the fluid. When this occurs, a swirling motion begins and a vortex is formed. There are various ways to mitigate the risk of a vortex forming such as installing a vortex breaker or completing calculations to ensure that the fluid level does not reach the point of vortexing. This post will describe the dangers of vortexes and the ways to avoid them as well as providing my experience with avoiding vortexes.

Vortexing is something engineers always wish to avoid. Vortexes can cause damage to equipment such as pumps, and can further reduce operation time and lead to further financial repercussions. Today, I will be explaining what vortexing is, how you can identify if your system is prone to vortexing, and how to prevent it from occurring within your system.

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What is a Vortex?

A vortex is created when there is a large difference in speed, which can occur in various fluid dynamics scenarios such as in pipes, rivers, or even during the aerodynamics of vehicles. This difference in speed is also coupled with a pressure difference between the top and bottom of the vortex, which is a fundamental aspect of fluid behavior. The top of the vortex has less pressure compared to the bottom, leading to a dynamic and often turbulent flow pattern.

Although it doesn’t seem like a big deal, it can damage equipment and reduce operating efficiency in industrial processes. This is largely due to air molecules being entrained with the fluid, which can cause pumps to cavitate, resulting in noise and vibration that may lead to mechanical failure. This also reduces the amount of fluid flowing efficiently through the system and can cause further issues such as a lack of flow, which can be detrimental to processes that rely on a consistent and adequate supply of fluid for optimal operation.

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The Dangers of Vortexing

Vortexing can damage equipment such as pumps. This is due to air being entrained within the fluid when a vortex occurs and can result in cavitation within the pumps. Cavitation can damage the pump’s impellers and may even require the purchase of a new pump. Vortexes can also create low pressure zones which can be hazardous for some processes. Due to these reasons, it becomes imperative that vortexes are controlled and prevented from forming in a system.

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Avoiding Vortexes Through Minimum Submergence

The difference in velocity forms when there is an insufficient level of fluid within the tank, causing the fluid to vortex. To prevent this, ANSI/HI 9.8 provides a formula to calculate the minimum level of submergence needed to avoid vortexing. Please see the formula below:

S = D + 0.574Q / D^1.5

Where:
D = Suction Bell Diameter or Diameter of the Drain in inches
Q = Flow rate in GPM
S = Submergence in inches

For a tank, the suction bell diameter will be the diameter of the discharge piping for the tank. The flow rate would be the flow rate of the fluid leaving the tank or the flow rate of the pump (if the pump is located along the discharge piping of the tank). By using this formula, the minimum fluid level needed within the tank to avoid vortexing can be determined.

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Utilizing Vortex Breakers to Prevent Vortexes

Another option to prevent vortexing is to purchase a vortex breaker. A vortex breaker is placed on the drainage or discharge of the piping and reduces the velocity of the fluid. By installing these devices, individuals can bring their minimum submergence level down even more if the extra working volume is required. It is a relatively cost effective way to prevent vortexes in a system and can yield promising results.

Vortex breakers are typically made of steel and usually come in two different styles. The most common style is the one shown below.

This style consists of two pieces of angle iron welded together to reduce the velocity of the fluid. Although this vortex breaker is relatively inexpensive and fairly straight forward to install, it also severely restricts the line. This can cause cavitation of pumps or prevent the fluid from flowing correctly. Before purchasing this equipment, ensure that all necessary calculations are completed and it has been determined that the vortex breaker will not affect the operation and integrity of the equipment.

Another design is the disk shaped vortex breaker. The disk vortex breaker is a disk shaped piece of steel place above the discharge of the tank. It prevents most of the horizontal movement of the fluid but still maintains horizontal motion for fluid that is about to leave the tank. However, this breaker can only be installed if the discharge is located at the bottom of the tank.

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My Personal Experience and Thoughts

In my work, the tank was owned by a different company but was operated by my organization. This resulted in an unusual scenario where my organization could not modify the tank but had control over the working volume and the level setpoints of the tank. To prevent vortexes from forming, I opted to use the minimum submergence formula provided from ANSI and determined the minimum amount of fluid needed within the tank before vortexing would form. Usually in industry, this scenario is unlikely and most organizations own the tanks they operate on so a vortex breaker is a great alternative; however, if there are economic considerations and the discharge piping or tank cannot be modified, then the minimum submergence formula may be your only option.

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Hello, I appreciate you taking the time out of your day to read my blog. If there was any inaccurate or incorrect information left or you require any additional information, be sure to leave it in the comments below or contact me on the About page.

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