A Simple Explanation of the Venturi Effect

The Venturi Effect was discovered by Italian physicist Giovanni Battista Venturi who lived between 1746 and 1822. In practice, there were a number of other physicists who were involved in the Venturi Effect but Giovanni Venturi is generally accepted as the first person to discover and explain the effect. So, what is the Venturi Effect, and how does it affect practical everyday living?

“A Venturi is a system for speeding the flow of the fluid by constricting it in a cone shape tube. In the restriction, the fluid increases its velocity, which reduces its pressure and produces a partial vacuum. As the fluid leaves the constriction, its pressure increases back to the ambient or pipe level.”

Any substance that flows is considered a fluid. This includes such things as water, shampoo, sunscreen, and even honey. Although not necessarily obvious, even gases, such as air, can be classified as fluids. So why would someone at EXAIR be talking about Venturi? Our E-Vacs use the Venturi Effect to create vacuum

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For most people the Venturi Effect is difficult to understand because you might expect the pressure to increase when a fluid is pushed through a restricted area. The fact that the increase in velocity is greater than any potential increase in pressure means that there is a net increase in velocity and a net reduction in pressure. The ability to mix-and-match certain fluids and gases via this process is relatively straightforward because the reduced pressure allows other substances to be sucked in through a connecting pipe at a rate of your choice.

EXAIR uses the Venturi Effect and other principles within the development of our engineered products. If you have questions or need a solution please call 800.903.9247 or visit us on www.EXAIR.com and let us help you.

Eric Kuhnash
Application Engineer
E-mail: EricKuhnash@exair.com
Twitter: @EXAIR_EK

 

Photo: Venturi Tube with labels by ComputerGeezer an Geof.  GNU Free Documentation License

Compressed Air Membrane Dryers: What are They? How do They Work?

A critical component on the supply side of your compressor system is the dryer. Atmospheric air contained within a compressed air system contains water vapor. The higher the temperature of the air, the more volume of moisture that air is capable of holding. As air is cooled, this water vapor can no longer be contained and this water falls out in the form of condensation. The temperature where this water will drop out is referred to as the dew point.

At a temperature of 75°F and 75% relative humidity, approximately 20 gallons of water will enter a 25HP compressor during a 24-hour period. As air is compressed, this water becomes concentrated. Since it’s heated during the compression process, this water stays in a vapor form. When this air cools further downstream, this vapor condenses into droplet form.

Moisture within the compressed air system can result in rust forming on the inside of the distribution piping, process failure due to clogged frozen lines in colder weather, false readings from instruments and controls, as well as issues with the point of use products installed within the system.

The solution to this problem is to install a dryer system. We’ve spent some time here on the EXAIR blog reviewing refrigerant dryers , desiccant dryersdeliquescent dryers, and heat of compression dryers. For the purposes of this blog, I’m going to focus on one of the newer styles on the market today: the membrane dryer.

Membrane Dryer

In a membrane dryer, compressed air is forced through a specially designed membrane that permits water vapor to pass through faster than the air. The water vapor is then purged along with a small amount of air while the rest of the compressed air passes through downstream. Generally, the dew point after the membrane dryer is reduced to about 40°F with even lower dew points also possible down to as low as -40°F!

With such low dew points possible, it makes a membrane dryer an optimal choice in outdoor applications that are susceptible to frost in colder climates. Membrane dryers also are able to be used in medical and dental applications where consistent reliability is critical.

A membrane dryer does not require a source of electricity in order to operate. The compact size makes it simple to install without requiring a lot of downtime and floor space. Since they have no moving parts, maintenance needed is minimal. Most often, this maintenance takes the form of checking/replacing filter elements just upstream of the membrane dryer. The membrane itself does need to be periodically replaced, an indicator on the membrane dryer will display when it needs to be changed. If particular instruments or processes in your facility are sensitive to moisture, a membrane dryer might be the best option.

However, there are some drawbacks to these types of dryers. They’re limited to low capacity installations, with models ranging from less than 1 SCFM up to 200 SCFM. This makes them more applicable for point-of-use installations than for an entire compressed air system. The nature in which the membrane dryer works necessitates some of the air to be purged out of the system along with the moisture. To achieve dew points as low as -40°F, this can equate to as much as 20% of the total airflow. When proper filtration isn’t installed upstream, oils and lubricants can ruin the dryer membrane and require premature replacement.

Make sure and ask plenty of questions of your compressor supplier during installation and maintenance of your system so you’re aware of the options out there. You’ll of course want to make sure that you’re using this air efficiently. For that, EXAIR’s wide range of engineered Intelligent Compressed Air Products fit the bill. With a variety of products available for same-day shipment from stock, we’ve got you covered.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@EXAIR.com
Twitter: @EXAIR_TD

Compressed Air Amplifiers Outperform Fans for Cooling Parts

When seeking a suitable solution for cooling or drying your parts, you may be tempted to try out a low-cost fan to get the job done. While fans do a great job of keeping you cool during the warmer months, they’re not the best choice for cooling or drying parts. Have you ever noticed that when standing in front of a fan the flow pattern is not consistent? This is due to the nature in which the fan blades create that air flow by “slapping” the air as they spin rapidly. The air flow that exits from the fan is turbulent and is not as effective as the laminar air flow pattern that is produced by EXAIR’s Super Air Amplifier. The Super Air Amplifier utilizes a patented shim design that maintains a critical position of the air gap and creates a laminar air flow pattern that will exit the outlet of the unit.

fan data2

In addition to providing laminar air flow more conducive for cooling and drying, the Super Air Amplifier provides much more air that can be directed at the target. A standard 2.36” x 2.36” DC operated fan provides anywhere from 12-27 CFM at the outlet, depending on the model. For comparison, a Model 120022 2” Super Air Amplifier will provide 341 SCFM at the outlet when operated at 80 psig. At just 6” away from the outlet, this value increases to 1,023 SCFM!! When compared to the fan outlet air flow, the Super Air Amplifier produces more than an 1,100% increase in air volume!

When replacing a fan with a Super Air Amplifier, the process time can be dramatically reduced. The increase in air volume significantly reduces the contact time that your part will need to be exposed to the air flow, allowing you to increase your line speed and decrease the overall production cost of the part. This is achieved due to the nature in which a Super Air Amplifier draws in air from the ambient environment. At amplification ratios as great as 25:1, the Super Air Amplifier is the best way to move a lot of air volume across the part with very little compressed air supplied to it. Check out the video

In addition to providing laminar airflow and increasing the volume of air, the Super Air Amplifier is also infinitely adjustable through one of two ways. Each size Super Air Amplifier has a shim set that can be purchased. Swapping out the stock shim for a thinner shim will reduce the compressed air consumption, force, and flow. Installing a thicker shim will increase it. Additionally, the force and flow can also be adjusted by regulating the input supply pressure through the use of a pressure regulator. With sizes ranges from ¾” up to 8”, there’s a Super Air Amplifier for all applications. Give us a call today to see how you can optimize your process by replacing your fans with one or more Super Air Amplifiers.

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@Exair.com
Twitter: @EXAIR_TD

Sliding Vane Compressors: How they Work

When it comes to air compressors there are many different types to choose from. Each compressor performs differently and have their own benefits and downfalls. In this case we will be taking a look a Sliding Vane Compressor which is a positive-displacement compressor. Positive-displacement type compressors have a given amount of air or gas that gets trapped in a compression chamber. From there the volume of that air is mechanically reduced causing an increase in the pressure. Sliding vane compressors use a circular stator that is housed in a cylindrical rotor; the rotor contains radially positioned slots where the vanes reside. These vanes are what create the compression in the “cells”.

Diagram of a sliding vane compressor

The inlet port on the system is positioned in a way that allows the air flow into each cell, optimizing the amount of air that each cell can hold. Once the air enters the system the cell size is reduced down farther and farther as rotation continues and each vane is pushed back into its original slot in the rotor. Compression will continue until each cell reaches the discharge port. One of the more common forms of a sliding vane compressor is the lubricant injected variety. These compressors inject a lubricant into the chamber to lubricate the walls and the vanes; this removes the heat of compression, as well as provide a seal on the cell. These air compressors are generally sold in a 10 – 200 HP range with capacities running between 40 – 800 acfm.

Advantages of a lubricant injected sliding-vane compressor include:

  • Compact size
  • Relatively low purchase cost
  • Vibration-free operation does not require special foundations
  • Routine maintenance includes lubricant and filter changes

Some of the disadvantages that come with this type of compressor:

  • Less efficient than the rotary screw type
  • Lubricant carryover into the delivered air will require proper maintenance of an oil-removal filtration system
  • Will require periodic lubricant changes

If you have any questions about compressed air systems or want more information on any of EXAIR’s products, give us a call, we have a team of Application Engineers ready to answer your questions and recommend a solution for your applications.

Cody Biehle
Application Engineer
EXAIR Corporation
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Photo Credit to Compressed Air Challenge Handbook