CTI Bibliography of Technical Papers - Fans

Revised 2017

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Order NumberTitleAuthorDate
Blade Dynamics Nicola Romano, Cofimco Srl 2017
Abstract: The usual way of designing large fans is with wide and stiff blades rigidly connected to the hub. This way leads, often, to high time-dependent load variations causing high vibration amplitude and high stress. Both stress and vibrations are strictly related to the blade's dynamic response to the aerodynamic force's pulses. A proper choice of the blades' mechanical and physical characteristics (stiffness and mass distribution, aerodynamic features, energy dissipation capability) can resolve in a substantial reduction of the blades' dynamic response. Cofimco, established in 1975, has since then continuously studied blades' mechanics, with regard to both fiberglass and aluminum blades.
FRP Cooling Tower Fan Blades - Inspection, Repair and Maintenance Jim Witt, Choice Industrial Solutions, Inc. 2017
Abstract: Best practices for inspection: known hazards and causes, difference between repairable and unrepairable deterioration. Best practices for remediation: proper preparation, products and process choices, address individual environments. Best practices for developing a maintenance program: time table, individual needs.
Design Considerations for Axial Flow Fans Bhumik Modi and David Tran, Hudson Products Corporation 2017
Abstract: Mechanical & Aerospace Engineering from Syracuse University. Low Pressure Axial flow fans, sometimes referred to as Propeller fans, are used in a variety of industries such as oil and gas, power plants, HVAC, et cetera for cooling purposes. The size of such fans vary from as small as 6 inches, typically used in data center cooling, up to 50 feet, used in Cooling Towers and Air-cooled Condensers. With the concern about energy savings becoming grave and the government imposed standards and subsidies, designing an optimum efficiency fan has become very valuable. Research engineers have been striving hard to strike a balance between airflow produced and power consumed that will make the fan of optimum efficiency. Hence, it is very valuable for everyone dealing with axial fans to understand the various parameters involved in designing an efficient axial fan. This paper is focused on delineating the few fundamental design considerations and methodology that can be adopted for development of axial flow fans which are used in Air-cooled Heat Exchangers, Cooling Towers and Air-cooled Condensers, the size of which range from 5 feet to 50 feet. The author's intention is to direct attention to the aerodynamic sizing and optimization and only briefly cover the structural design of the fan.
Using Direct Drive Technology for Improved Reliability and Efficiency in Wet Cooling Towers Thomas Weinandy, Baldor/ABB 2017
Abstract: This paper discusses the development of low speed, permanent magnet motors and how they can be used in direct-drive applications to eliminate the gearbox, NEMA motor, driveshaft, and disc couplings from field erect cooling tower designs. Improved reliability of cooling tower fan drives is now possible due to advancements in motor technology as evidenced over the last 9 years. Case studies are presented where cooling towers have been retrofitted. Design considerations, best practices, performance data, maintenance, air flow considerations and efficiency comparisons will be discussed.
Innovative FRP-Carbon Pultruded Shaft for Axial Fan Blades Carlo Gallina, Cofimco S.r.l. 2015
Abstract: Cofimco extensive research and laboratory tests pointed out in the development of an innovative shank to connect the blade airfoils to the hub of large axial fans used on Cooling Towers and Air Cooled Condensers: the new pultruded FRP shank reinforced with carbon rovings. The innovative shank material gives to the blade a suitable elasticity, midway between flexible and rigid links, resulting in a noticeable reduction of the vibration level introduced by the fan in the supporting structure; simultaneously, high strength of carbon rovings and innovative "damped" shaft design let fan blades to withstand the most severe duty points and limit blade deformation.
Leveling the Playing Field for Axial Impeller Comparisons and Regulatory Compliance Sham Morten Gabr, Multi-Wing 2015
Abstract: Axial Impellers are integrated as driven impellers in multiple non-fan products, including cooling towers. However, there is no common rating standard for axial impellers. That means that a level playing field for axial impeller performance comparisons is absent. No commonly accepted standard for comparing axial impeller data on an apple-to-apple basis exists. There is no commonly accepted guide for compliance officers to follow to support the implementation of regulatory minimum efficiency requirements. Perhaps therefore, some traditional fan manufacturers lobby for having axial impellers integrated into cooling towers tested as complete assembled fans. That means with the specific fan housing geometry section of the cooling tower! In those cases where the cooling tower section and impeller is too big for testing it’s suggested to test a scaled down replica or do in situ testing. To avoid that “not very meaningful” situation and to help create an even playing field, an initiative is pursued to ensure the development of a standard set of fan parameters to be set for testing of axial impellers. This may then be accepted by regulators in lieu of fan performance compliance verification, when the testing of the fan is impractical, represents an undue burden to the customer and may be technically unjustifiable.
Innovative Tandem Blade Fans for High Efficiency Heat Exchangers Carlo Gallina of Cofimco S.R.L. 2014
Abstract: Cofimco extensive research and the application of aerodynamic concepts to fan blades trough computational fluid dynamic analysis (i.e. CFD simulation) and laboratory tests pointed out in the development of a new innovative patented design: the Tandem Blade. Scope of the present study is to examine the aerodynamic basis which determinates the fan blade efficiency, and then shows how the new design can lead to an increase in the fan performances by increasing lift and reducing vortexes generated by the blade.
Understanding Vibrations Switches David Corelli, IMI Sensors 2014
Abstract: This paper will present the basics of both mechanical and electronic vibration switches, explain how they are designed, how they work, and show where they are effective and where they are not. It will show their frequency responses along with the major differences in the responses of mechanical and electronic switches. Finally, it will show how the various switches meet or do not meet the new CTI Vibration Standard. A video will also be included in the presentation to show switch response using vibration shakers.
Low-Speed Motor Experience Martin Kubicek, FANS, A.s. and Jan Holl, DAC Motors, A.s. 2013
Abstract: Most of the cooling towers used all around the world are operating by using of standard fan unit solution such as fan impeller, gear box, driving shaft and motor. As presented in the previous paper, later fan unit development in the cooling tower industry can be slow-running motor, which is directly coupled with fan impeller. This paper discusses slow-running motor experiences of one of the European cooling tower manufacturer.
Direct Drive Motor Design - Improving Product Availability by Rationalizing Design Considerations Robbie McElveen and Bill Martin, Baldor Electric Company 2013
Abstract: The horsepower and speed required for a given fan depends on many factors, including maximum tip speed, blade design, blade pitch, and required CFM. There are an infinite number of HP/RPM/shaft combinations that could be requested from a direct drive motor manufacturer. With careful design, it is possible to create a "universal" motor that covers a wide range of requirements. This paper discusses characteristics that must be considered when designing a universal direct drive motor. Pros and cons of this approach will be discussed. Comparisons between a universal motor design and a more traditional motor design concept will be made.
Effect Of Air Flow On Size And Weight Of Direct Drive Permanent Magnet Motors Robbie McElveen and Bill Martin, Baldor Electric Company 2011
Abstract: The usage of direct drive fan motors is increasing. One concern about using the direct drive solution is the weight difference between this type of motor and the gearbox it replaces. The motors are located in the center of the fan hub where there is typically only a nominal amount of air movement. More air flow over the motor frame results in better heat dissipation and smaller, lighter motors. This paper investigates the effect of air flow on size and weight of direct drive motors of various diameters. A simple method to direct more air flow over the motor is presented.
Retrofit Of Cooling Fans In Hybrid Cooling Tower With Energy Savings, Airflow & Vibration Improvement Regina Wong Chin Pau, Genting Sanyen Power and Jos Oude Luttikhuis, Howden Cooling Fans 2011
Abstract: This paper summarizes the Cooling Tower Fan Upgrade Project undertaken at Kuala Langat Power Plant (Malaysia) and the results of performance verification tests in a full scale, practical industrial application. The primary objective of the improvement project is to overcome the existing problem of overload stress failures in operating gear reducer, by replacing the high efficiency and light weight construction ELF6 Fan in the hybrid cooling tower cells. In addition to reduction in input energy to fan drives and improved vibration level, the reduction in gearbox mechanical load and fan drive power closer to its rated limit is expected to bring about fewer number of gear failures and therefore higher reliability of the cooling tower fans.
Electric Motors 101: What You Need To Know Bill Martin and Robbie McElveen, Baldor Electric Company 2011
Abstract: Electric motors are used extensively on cooling towers. The most obvious application is the fan drive motor, but multiple pump motors are used on every tower as well. Tower manufacturers or end users are tasked with selecting the proper motor, but may not have the understanding they need of different motor types, features, etc. This paper offers an introduction to motors including: terminology often used by motor manufacturers, operating motors on adjustable speed drives, performance characteristics of various motor types, bearing sizing, insulation materials and vibration.
Recent Development in Motor Technology Allow Direct Drive of Low Speed Cooling Tower Fans Robbie McElveen and Bill Martin, Baldor Electric 2009
Abstract: Improved reliability of cooling tower systems is now possible due to a new development in motor technology. This paper will discuss the development of low speed, permanent magnet motors and how they can be used in direct-drive applications to eliminate the gearbox, NEMA motor, driveshaft, and disc couplings from cooling tower designs. A case study will be presented where an existing tower was refurbished using a direct drive motor which fit the exact footprint and height of the existing gearbox. Design considerations, performance data, maintenance history and efficiency comparisons will be presented.
Safely Stopping, Holding and Locking Out Cooling Tower Mechanical Sets Duane Byerly, Rexnord Industries 2009
Abstract: Safety is becoming an ever increasing factor while working around and inside of cooling towers. When a fan motor is not energized, fans free-wheel from wind and updraft in cooling towers. Entering a fan cell or removing a stack section with the fan rotating is an OSHA violation. Stopping and holding a fan to conduct maintenance operations can be dangerous to personnel. This paper presents methods for stopping and holding fans for maintenance operations and high wind conditions. It will also present various material and mounting options.
Investigation on Fan Noise Generation and Its Reduction Carlo Gallina, Cofimco Srl 2008
Abstract: Nowaday the concept of pollution is involving new aspects of our life and the target given to the industry are getting more and more stringent: noise is one of the most important aspects of the modern pollution.
Fan Stall Problems; Cause or Effect Charles Foster, Diagnostic Cooling Solutions, Inc. 2008
Abstract: The occurance of fan stall appears to be a common factor in an increasing number of cooling tower thermal performance problems. Frequently such problems arise following well intentioned but ill-advised retrofits. Because fan stall is not readily detected, it is often overlooked as a possible sole cause or contributor to performance problems, or as a symptom of other physical or mechanical problems. The mechanism and characteristics of fan stall and discussed in some detail together with detection methods enabling defective cells to be identified and targeted for prioritized repair.
The Cost of Noise Robert Giammaruti, Hudson Products/Cofimco USA
Jess Seawell, Composite Cooling Solutions, L.P.
Abstract: Today, owner/operators, OEM's and suppliers are facing lower and lower near and far field noise limits with respect to their equipment. However, lost in this race to see who can out quiet who is the impact of cost. Specifically, the cost of noise with respect to not only fans, but the fan mechanical and structure parts as well.
Fan Air Flow Testing on Cooling Towers and ACHEs Robert Giammaruti, Hudson Production Corporation 2005
Abstract: Over the past several years, the frequency of fan air flow testing to verify new or existing fan performances in cooling towers and air-cooled heat exchangers has increased. Whether for new or replacement fans, customers want to verify that they are getting all the performances they were promised by the fan manufacturer - (i.e. does the fan air flow test meet or exceed what the fan manufacturer predicted). Proper fan air flow testing, while not an exact science, can usually spell the difference between a satisfied or unsatisfied customer. Two fan testing methods - one for wet cooling towers and one for air cooled heat exchangers - will be discussed in detail as well as examples given of actual performance versus predicted performance.
Verification of the Benefits of a New Fan Blade Tip Design in a Practical Application Sander Venema, Howden Cooling Fans 2004
Abstract: This paper is a continuation of the paper presented last year, entitled "Vibration Control: New Fan Blade Tip Reduces Pulsation: (TP03-05). That paper discusses the various vibration modes that can be generated by the interaction of a fan with the air-cooled installation. It focuses in particular on the vibration of the fan stack at blade passing frequency.
Motor Efficiency - A Guide for Reduced Consumption John Malinowski Baldor Electric Company 2003
Abstract: This paper will compare motor efficiency levels based on a Department of Energy survey, EPAct and NEMA Premium™ efficiency levels. It will focus on how a user can reduce the operating cost of cooling towers by use of premium efficient motors and adjustable speed drives. Motor purchase price is only 2-4% of the life operating cost of that motor; operating cost should be considered on any new project. A software tool for energy surveys and calculations will be introduced.
A Flexible Blade-to-Hub Connecting System Opposed to a Rigid Element in an Axial Fan. Riccardo Provasi, Cofimco S.p.A. 2002
Abstract: Axial fans are subjected to significant loads and vibrations generated in the blade sections and transmitted to the power transmission equipment through the hub-to-blade connecting elements. In the standard configurations fan blades are rigidly clamped to the hub; in this solution high stress levels occur in the connecting elements and, generally, in all fan components. In this paper the influence of the flexibility degree of the connecting element on the reduction of loads and vibrations is discussed. Two different solutions are proposed and compared with standard solution and the results of comprehensive tests on a large fan are reported.
Cooling Tower #4, Fan Failure Dennis P. Shea, Shelby Sustala, Solutia, Inc. 2001
Abstract: The Chocolate Bayou Plant is a world class chemical plant located in Alvin, Texas about 40 miles south of Houston. The plant chemical processes are cooled by 3 mechanical draft-cooling towers with a combined recirculation rate of 267,000 gpm. In March, Cooling Tower 4 experienced a catastrophic failure of the #8 fan. The root caused investigation indicated serious corrosion problems with fan equipment, reliability problems with vibration detection system and ineffective routine inspection on both fan and vibration detection equipment. The root cause analysis recommended immediate investigation into the mechanical integrity of all plant cooling tower fans and vibration detection equipment. The results of the system wide investigation resulted in extensive repairs to existing mechanical fan equipment, repairs to vibration detection systems and significant changes in preventative maintenance routines.
Evaluation of the Unsteady Loads on a Fan Blade Giorgio Cipelletti, Cofimco S.P.A. 2000
Abstract: The knowledge of the unsteady loads is fundamental for the fan blade fatigue design and for the evaluation of the cooling tower vibration level. The most significant unsteady loads are generated by the effect of the aerodynamic interference between the fan-gearbox supporting beams and the fan blades. This paper discusses the origin and the effect of the aerodynamic interference, presents a methodology for calculating the unsteady loads and the relevant stress on the fan blade, and shows the experimental results and their correlation with the theory. A simple method for reducing the unsteady loads is also discussed.
Structural Design Evolution of a Large Fiberglass Fan Blade Larry Burdick, The Marley Cooling Tower Company 1999
Abstract: Structural design considerations for large diameter fiberglass fan blades are an important factor in determining the strength capability and reliability life of the product. This paper discusses structural design issues including applied loads, cross section properties, and stress calculation and strength verification-methods.
Advanced Airfoils for Cooling Tower Fan Blades James Tangler & Cris Bosetti, National Renewable Energy Lab; Dan Somers, Airfoils Inc. 1999
Abstract: The objective of this study was to explore the benefits of advanced airfoil technology for industrial cooling tower fan blades. An existing fan performance prediction code was used to identify desirable airfoil characteristics for large tapered/twisted blades. The Eppler Airfoil design and analysis Code was then used to design advanced airfoils for the bade root and tip region. Results show and new airfoils allow a 20% reduction in blade chord relative to current blades. The predicted power reduction using the new airfoils was 1% to 2%. Further power reductions may be realized as a result of lower cascade flow losses and improved airfoil insensitivity to roughness effects.
Noise Testing of Cooling Tower Fan Drives Craig Burriss, Amarillo Gear Co. 1998
Abstract: More stringent noise emission requirements and advances in noise reduction of other cooling tower components are focusing more attention on the noise emitted by the cooling tower gear drive. This paper discusses a state-of-the-art test system for determining noise and vibration characteristics of right angle cooling tower gear drives. The test system applies torque and axial thrust loads to simulate actual fan loading conditions. System capabilities, data collection techniques, and results of sound power and vibration analysis are presented. The uses of accurate sound and vibration data to improve gear drive design and manufacturing methods are discussed. The paper concludes with a discussion of the expected benefits of this testing to the cooling tower industry.
The Influence of Materials of Construction on Leading Edge Erosion of Fiberglass Fan Blades Used on Cooling Towers Larry F. Burdick, Marley Cooling Tower Company 1997
Abstract: Leading edge erosion is a maintenance concern for fiberglass fan blades on wet cooling towers. An experiment has been developed and executed to demonstrate the differences in leading edge erosion depending on the type of material used in fan blade construction. The differences in erosion are shown for three types of fan blades, namely an epoxy resin matrix with and without an erosion barrier strip and blades molded with vinyl ester resin having a barrier strip. Both pictorial and weight loss results are provided for the reader.
Maximizing Fan Performance Robert C. Monroe, Hudson Products Corporation 1997
Abstract: Maximum fan performance usually means maximum airflow for minimum horsepower, but it also means maximum service life and sometimes-minimum noise. This paper describes the many points to consider beginning with selection of an optimum operating point and many factors concerning the fans operating environment. This includes tip clearance, obstruction to airflow, vibration, blade loading, resonant frequency concerns and other important parameters.
Auto Pitched Fans in Cooling Towers (TP-88-13) Charles Chittom, Chittom Int'l 1988
Abstract: This paper is the history of four fan installations, the problems encountered, if any, and the user satisfaction level. Different control methods will be shown as well as their services.
Hydraulic Cooling Tower Driver the Innovation (TP-88-14) John A. Dickerson, Hem, Inc. 1988
Abstract: Expensive fan wrecks and down time occur when motor shaft couplings break or gearboxes self-destruct. A viable alternative eliminates shafts, couplings, and gearboxes. The first step is to move the motors to ground level, which are then close coupled to a hydraulic pump, which transmits fluid under pressure to a hydraulic motor at the top of the tower, which directly drives the fan. Microprocessor controllers can provide inexpensive energy conservation control at a fraction of the cost of conventional AC-DC innoverters. The entery aspect alone pays for the retrofit with the lower maintenance cost an extra bonus.
Anomalies in Fan Efficiency Calculations (TP-87-12) Weyert E. De Boer, Ventilatoren Stork Hengelo 1987
Abstract: Fan total efficiencies as calculated by the CTI Field Test Handbook (Chapter 5.5) can, in certain situations, exceed 100%. This has caused confusion among specifiers and users. Therefore, efficiencies calculated from experimental data are sometimes adjusted downward to maintain credibility. The net result is that fan motor horsepower, as specified, are sometimes higher than actually needed. The reason for this anomaly is the incorrect assumption that the static pressure at the fan outlet is zero. In actuality, it is a negative number due to rotational flow and turbulence effects. This paper will discuss the problem and propose corrective action. In addition, the influence of inlet shape and obstacles will be discussed. Supporting data will be presented.
Single-Cell Cooling Tower Performance Studies (TP-202A) W.R. Brock & J.S. Woodard, Union Carbide, Oak Ridge Gaseous Diffusion Plant 1979
The Effect of Fan Tip Clearance on Cooling Towers Performance (TP-212A) Joe M. Schwinn, Ecodyne Cooling Products Division 1979
Abstract: One of the parameters that affect the performance of axial flow fans of induced draft cooling towers is the clearance between the tip of the fan blade and the fan stack. Fan performance in turn influences the behavior of the cooling tower as a whole. Very little full-scale information is available to indicate the magnitude of the effect of tip clearance on cooling tower performance. This paper presents test data taken on actual cooling tower installations showing the impact of fan tip clearance on overall tower performance. Such data are helpful in evaluating the economic trade-off between improved tower performance and increased costs of a more efficient air movement system.
Fan Performance Consideration in Cooling Towers (TP-158A) David Stackhouse & Kenton Whitehead, Ecodyne Cooling Products Division 1977
Cooling Tower Fans - Today and Tomorrow (TP-120A) Robert C. Monroe, Hudson Products Corporation 1974
Fan Noise Levels in Cooling Towers (TP-62A) W.E. Robb, Chittom Equipment Company 1969
Axial Flow Fans and Their Application to Cooling Towers (TP-36A) E.M. Davidson, Hudson Products Corporation 1968
Field Tests of Fan Performance on Induced Draft Cooling Towers (TPR-122) D.D. Herrman 1962

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