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A Look At Cooling Tower Fan Efficiency Pt. 2

Cooling Tower Fan Efficiency Requires Careful Analysis

Hello, and welcome back to the Industrial Cooling Solutions, Inc. blog! If you are just now joining us, we are in the middle of a multi-part blog series that is dedicated to detailing the factors that influence the efficiency levels of industrial cooling tower fans. If you have not read our previous post, we highly suggest that you go do so now. While you may find the information in this second post useful, it is build upon important ideas that are presented in the first post and, as such, will make more sense if you read the posts in sequential order. Now that we have that small disclaimer out of the way, we are going to use today’s post to continue where we left off last time and discuss some of the factors that influence the overall efficiency of a cooling tower fan system. While each factor may seem small when isolated, together they can greatly decrease the efficiency of a cooling tower, effectively rendering the tower useless for its intended application. Keep reading below to learn more.

Potential Losses in System Efficiency Can Occur in Several Separate Areas

When it comes to overall system efficiency in cooling tower fan assemblies, there are three main areas that need to be considered by researchers and engineers alike.

  1. Losses caused by the system design of the fan rather than by variable physical properties.
  2. Losses caused by variable environmental properties.
  3. Performance losses caused by the recirculation of hot air.

Of these three main areas of potential loss, only the second category is easily fixable. Below, we have listed out the details surrounding the first category that affects the efficiency of a cooling tower fan system.

Losses Caused by System Designs

While the variables that might potentially decrease the efficiency of a cooling tower fan system are sometimes easy to identify, most of the time they are not. One factor that can greatly affect the overall efficiency of the system is the design of the fan blade. For the most part, modern axial fans found in industrial cooling towers are made from either FRP materials or aluminum. Aluminum fan blades, by their very nature, are always of a uniform design, whereas FRP fan blades can be molded into pretty much any shape that an engineer may want. No matter which type of fan blade material is used, the main purpose of the fan assembly is to produce uniform airflow over the entire plane of the fan. Uniform airflow ensures that the optimal amount of force is produced to adequately dissipate the heat that is introduced into the cooling tower. To determine that a fan blade design is able to produce the amount of airflow that is needed, the work done at any radius along the fan blade is a function of blade width (angle of attack and tangential velocity squared).

The Shape of Fan Blades Plays an Important Role in Efficiency

With the above information in mind, it can be concluded that as a point on the fan blade decreases from the tip toward the hub of the fan assembly, the tangential velocity decreases sharply. To compensate for this and produce uniform airflow, the twist of the blade along with its width must also increase. This becomes an issue when dealing with aluminum fan blades because if the blade width cannot be increased, the twist of the blade must be increased to compensate. Due to the elasticity limits of aluminum, this twist can only be taken to a certain level before the fan blades break. Luckily, FRP fan blades have no such limitation because they are molded into a single piece, allowing the most ideal shape to be more closely achieved.
Another factor that is affected by the design, shape, and twist of the fan blade is the fan operating point, or the point where the system resistance line meets the fan performance line. In laymen’s terms. The operating point is the blade pitch angle that produces the necessary air flow against the required system resistance of the cooling tower. Depending upon the fan speed, only a single pitch angle will be able to satisfy the system design operating condition. To put all of this together, within certain limits, the speed of a cooling tower fan can be adjusted so that the most optimal pitch angle can be selected that will satisfy the required system resistance.

Faulty Design Leads to Faulty Performance

When considering the above two points, it is easy to see how poor fan blade design, as well as a poor selection in the operating point of the fan system, can contribute to a loss in efficiency of a particular cooling tower fan system. Once in place, these two factors are not always the easiest things to fix, meaning that it is always in the best interest of the engineer and designer to make sure that their initial system design is as efficient as possible. If these considerations are not taken into account, valuable time, energy, and money will have to be spent rectifying the issue.

Thank you for reading part two of our blog series on the factors that should be taken into consideration in relation to cooling tower fan efficiency. If you would like to learn more about our selection of FRP fan blade designs and the applications in which they can be used, please contact us today at Industrial Cooling Solutions, Inc. We have completed dozens of cooling tower projects around the world and we are certain that we can handle any and all needs you may have when it comes to optimizing your fan system.

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The Importance Of A Stable Fan

A Wobbly Fan is Bad for Business

Here at Industrial Cooling Solutions Inc., we have a lot of experience when it comes to cooling tower fans. For the vast majority of industrial cooling towers, fans are used as a way to ensure that as much heat as possible is mitigated while also helping to reduce the rate of evaporation present within the tower itself. Unfortunately, because these fans are in a near constant state of rotation, issues can pop up. Although the average person doesn’t put too much thought into it, circular rotation is not as easy to accomplish as one might think. Centrifugal force can place a large amount of stress on these fan assemblies and, if left to their own devices, these fans can and will spin themselves into oblivion. In today’s post, we are going to go over some of the ways that you can make sure that your cooling towers fan is set up for success and ways you can reduce the amount of wobble present in your fan assembly. Continue reading below to learn more.

Why Does the Wobble Matter?

First things first, we think it is important to explain exactly what we mean when we use the term “wobble.” If you have every had an unbalanced ceiling fan, you probably already realize how bad a fan can start to wobble when it is not setup correctly or it is damaged. This same idea can be applied to fans in industrial cooling towers, however, with these particular types of fans, we aren’t so much worried about the wobbling so much as we are worried about the vibrations that cause the fan to wobble. Vibrations, even small ones, can cause fans in industrial cooling towers to perform poorly and, in some extreme cases, they can even cause damage to additional components within the tower. So, what should you do to help mitigate vibrations and ensure that your fan is working as well as possible? Read below to find out.

  • Balance: Like The Force, fans in industrial cooling towers are all about balance. These fans rotate at such high speeds that even a slight variation in the balancing of the fan blades can have tremendous effects on the fan assembly as a whole. If one fan blade is unbalanced, it will place stress on the other fan blades through vibrational forces which, over time, can compromise the entire system including the motor that drives the fan and the drive shaft that transforms mechanical energy into rotational force. If you’ve noticed that a fan in one of your cooling towers is underperforming, take the time to make sure that the blades are balanced. A small adjustment now could save a lot of time and energy in the future.  
  • Damage: In industrial cooling tower applications, fans are used to push large quantities of air through the top of the tower or, in some cases, are used to pull large amounts of air into the tower. If a fan blade becomes damaged, it can affect the way that the air flows over the entire fan assembly and, if not caught quickly, can lead to quite a bit of damage. Even a small knick in a single fan blade can be enough to disrupt the airflow to the point that it starts to cause vibrations to occur. As we stated earlier, vibrations are never a good thing when it comes to fan assemblies. To help reduce the chances that this will happen, we suggest that you inspect the blades of your cooling towers fans on a regular basis to ensure that they have not become damaged in some way.

We hope that this blog has been informative and that you have gained a little more knowledge about the importance of a stable fan in your industrial cooling tower. If one of your fans has become damaged beyond repair or you would simply like the advice of some experts, contact us at Industrial Cooling Solutions Inc. today. We have years of experience dealing with cooling tower fans and we feel that our past projects give us the knowledge, tools, and experience needed to handle any issues that you may have in relation to your tower.

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