Enjoy the Holidays everyone!
EXAIR will be closed December 23, 24, 30 & 31 so every EXAIR employee can enjoy their family and friends over the holidays.
EXAIR has been manufacturing Intelligent Compressed Air Products since 1983. They are engineered with the highest of quality, efficiency, safety, and effectiveness in mind. Since compressed air is the source for operation, the performance limitations can be defined by its supply. With EXAIR products and pneumatic equipment, you will need a way to transfer the compressed air from the source to the point-of-use. There are three main ways; pipes, hoses and tubes. In this blog, I will compare the difference between compressed air hoses and compressed air tubes.
The basic difference between a compressed air hose and a compressed air tube is the way the diameter is defined. A hose is measured by the inner diameter while a tube is measured by the outer diameter. As an example, a 3/8” compressed air hose has an inner diameter of 3/8”. While a 3/8” compressed air tube has an outer diameter that measures 3/8”. Thus, the inner diameter of the tube will be smaller than the hose.
Why do I bring this up? Pressure drop… Pressure Drop is a waste of energy, and it reduces the ability of your compressed air system to do work. To cut waste, we need to reduce pressure drop. If we look at the equation for pressure drop, we can find the factors that play an important role. Equation 1 shows an equation for pressure drop.
From Equation 1, differential pressure is controlled by the flow of compressed air, the length of the pipe, the diameter of the pipe, and the inlet pressure. As you can see, the pressure drop is inversely affected by the inner diameter to the fifth power. So, if the inner diameter of the pipe is twice as small, the pressure drop will increase by 25, or 32 times.
As an example, we have a 1/2″ black schedule 40 pipe which has an I.D. of 0.622″. We use this pipe to flow 40 SCFM of compressed air at 100 PSIG through 100 feet. What would be the pressure drop? With Equation 1, imperial units, we get a pressure drop of 1.28 * (40 SCFM/60) ^1.85 * 100 feet / ((0.622″)^5 * 100 PSIG) = 6.5 PSID. Thus, you started with 100 PSIG, and at the end of the pipe, you will only have (100 PSI – 6.5 PSI) = 93.5 PSIG to use. Sizing pipe is very important when supplying compressed air to your system as pressure drop is a waste of energy.
Let’s revisit the 3/8” hose and 3/8” tube. The 3/8” hose has an inner diameter of 0.375”, and the 3/8” tube has an inner diameter of 0.25”. In keeping the same variables except for the diameter, we can make a pressure drop comparison in Equation 2.
As you can see, by using a 3/8” tube in the process instead of the 3/8” hose, the pressure drop will be 7.6 times higher. As an example, if the pressure drop through a 3/8″ hose is 1 PSID, and you decide to switch out to a 3/8″ tube. The pressure drop will then be 7.6 PSID, and a big loss of pressure.
At EXAIR, we want to make sure that our customers are able to get the most from our products. To do this, we need to properly size the compressed air lines. Within our installation sheets for our Super Air Knives, we recommend the infeed pipe sizes for each air knife at different lengths. (You will have to sign into the website to download). We also have an excerpt about replacing schedule 40 pipe with a compressed air hose. We state; “If compressed air hose is used, always go one size larger than the recommended pipe size due to the smaller I.D. of hose”. Here is the reason. The 1/4” NPT Schedule 40 pipe has an inner diameter of 0.364” (9.2mm). Since the 3/8” compressed air hose has an inner diameter of 0.375” (9.5mm), the diameter will not create any additional pressure drop. Some industrial facilities like to use compressed air tubing instead of hoses. This is fine as long as the inner diameters match appropriately with the recommended pipe in the installation sheets. Then you can reduce waste from pressure drop and get the most from your EXAIR products.
With the diameter being such a significant role in creating pressure drop, it is very important to understand the type of connections to your pneumatic devices; i.e. hoses, pipes, or tubes. In most cases, this could be the reason for under performance of your pneumatic products, as well as wasting money within your compressed air system. If you would like to discuss further the ways to save energy and reduce pressure drops, an Application Engineer at EXAIR will be happy to help you.
Fluid mechanics is the field that studies the properties of fluids in various states. There are two areas, fluid statics and fluid dynamics. Fluid dynamics studies the forces on a fluid, either as a liquid or a gas, during motion. Osborne Reynolds, an Irish innovator, popularized this dynamic with a dimensionless number, Re. This number determines the state in which the fluid is moving; either laminar flow or turbulent flow. Equation 1 shows the relationship between the inertial forces of the fluid as compared to the viscous forces.
Equation 1: Re = V * Dh/u
Re – Reynolds Number (no dimensions)
V – Velocity (feet/sec or meters/sec)
Dh – hydraulic diameter (feet or meters)
u – Kinematic Viscosity (feet^2/sec or meter^2/sec)
The value of Re will mark the region in which the fluid (liquid or gas) is moving. If the Reynolds number, Re, is below 2300, then it is considered to be laminar (streamline and predictable). If Re is greater than 4000, then it is considered to be turbulent (chaotic and violent). The area between these two numbers is the transitional area where you can have eddy currents and some non-linear velocities. To better show the differences between each state, I have a picture below that shows water flowing from a drain pipe into a channel. The water is loud and disorderly; traveling in different directions, even upstream. With the high velocity of water coming out of the drain pipe, the inertial forces are greater than the viscosity of the water. This indicates turbulent flow with a Reynolds number larger than 4000. As the water flows into the mouth of the river after the channel, the waves transform from a disorderly mess into a more uniform stream. This is the transitional region. A bit further downstream, the stream becomes calm and quiet, flowing in the same direction. This is laminar flow. Air is also a fluid, and it will behave in a similar way depending on the Reynolds number.
Why is this important to know? In certain applications, one state may be better suited than the other. For mixing, suspension and heat transfer; turbulent flows are better. But, when it comes to effective blowing, lower pressure drops and reduced noise levels; laminar flows are better. In many compressed air applications, the laminar region is the best method to generate a strong force efficiently and quietly. EXAIR offers a large line of products, including the Super Air Knives and Super Air Nozzles that utilizes that laminar flow for compressed air applications. If you would like to discuss further how laminar flows could benefit your process, an EXAIR Application Engineer will be happy to help you.
Desiccant dryers come in different forms. They are designed for water sensitive areas as they can reach a dew point to -40oF (-40oC) and below. That means that water will not condense in the compressed air lines until the temperature is below the dew point. The desiccant inside these units will adsorb the water vapor as compressed air passes through a bed. Once the desiccant bed is full of water vapor, it will have to be regenerated.
A typical system will use two towers that will switch back and forth. One tower is used to remove the water from the compressed air system, and the other is used to regenerate the desiccant. In this blog, I will cover how the desiccant can be regenerated with a Heat of Compression (HOC) type of desiccant dryer.
An air compressor is not an efficient device. For every eight horsepower of energy to make compressed air, only one horsepower is used as work. And for compressed air drying, the type of desiccant dryer is important. Regeneration of desiccant beads can be done either with non-heated or heated means. The non-heated, or heatless version will use 15% of your compressed air to purge through the regeneration tank. The air escapes into the atmosphere with the water vapor and is wasted.
With the heated type desiccant dryers, they come in three different categories. One type uses a heater to increase the temperature of the compressed air. At the elevated temperature, the purge requirement can be reduced to 7% for the regeneration of desiccant. But, still compressed air is wasted. To cut the purge to zero, a blower-type heated desiccant dryer can be used. Instead of heating the compressed air, the blower will push ambient air through a heater to regenerate the desiccant bed. But can you get more efficient than that?
Well, what if you can remove the heater and the blower? The heat of compression type of desiccant dryers can do that. Remember above when I mentioned that “for every eight horsepower of energy to make compressed air, only one horsepower is used as work”. The seven horsepower of energy that is lost is given off as heat. The HOC dryer uses that heat to regenerate the desiccant bed. So, the overall energy is reduced even further. There is a restriction when using this type of dryer. The air compressor will have to be oil-free because oil will coat the desiccant beads and stop the adsorption rate.
When the air is compressed, heat is generated. This heated air can reach around 200oF (93oC). With the higher temperature, air can hold more water vapor. As the heated air passes through the desiccant bed that needs to be regenerated, the water vapor is picked up from the desiccant beads. The saturated air would then pass through an aftercooler. The aftercooler reduces the air temperature below 100oF (38oC) which will cause the water to drop out. From the aftercooler, the air will then pass through the desiccant bed in the drying tower. When the cycle time is reached, the towers will switch to regenerate the second tower.
With these types of dryers, the desiccant beads will start to degrade from regeneration. To help replace them, EXAIR offers a Line Vac. Instead of climbing a ladder with many bags of desiccant, the Line Vac can do this safely and ergonomically. EXAIR Line Vacs use a small amount of compressed air to generate a powerful vacuum by a Venturi effect. The unique design of the generators creates a high velocity of air to create a low pressure on one side and a powerful thrust on the other. The Line Vac can pick up and move solid material vertically up to 20 feet (6 meters). You can watch a video on the operation of a Line Vac HERE. The EXAIR Line Vacs are very quiet, compact, rugged, and powerful. To replace the desiccant, it can do it quickly and safely.
If you need to convey solid materials in a quick and easy way, an EXAIR Line Vac could be a solution for you. We have them in a variety of materials and designs to match your application. Ergonomically, they can save the back-wrenching labor of picking up bags, climbing stairs, and dumping material into towers. If you want to know if the EXAIR Line Vac could work for you, an Application Engineer at EXAIR can help to recommend the best unit for you.