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Adding to other comments, some installations where a fan blae has broken did not trip the motor equipped with only mechanical vibration switch especially when operating below 2 Hz. This should be checked with OEM of the switch. If you do not have a good fan guard screen attached to your inlet bell, a broken blade can damage equipment below the ACC as well as being a safety hazard. Most A-framed ACC do have the fan guard but some do not.
Hello Marcel,
One of the more common issues on ACCs are cracks in fan blades, failures of fan blade hardware, and fan blade failure. These have been issues primarily on the windward sides of ACC. High wind and wind gusts can be the root cause. I have photos of broken fan blades and cracked fan blades. As stated by the prior respondent, a minor crack can be cosmetic and can occur in the resin rich portion of the blade. However most larger cracks can be significant and you should consider blade replacement. Some fan suppliers have blades that are matched pairs so that replacement should be done as pairs. Galebreaker has provided perimeter mounted wind screens that reduce the stress on fan blades and provides trouble free operation. Our first install was in 1998 in Belgium. Since then we have installed our screens on 50 + ACCs and they can be cofigured to reduce performance deficiencies. You can contact me at gmirsky@galebreaker.comHello Joshua,
Cracks in fan blades has historically been an issue on A framed ACCs through many years. It is a forced draft arrangement and on the windward side of the ACC the air flowing into the fans is turbulent creating almost a cavitation effect. At high ambient wind speeds there can be a downdraft on the windward side and a updraft on the leeward side. So as the fan blades rotate inside of the fan bell the blades are being stressed which over time can fatigue the fiberglass laminate and result in blade cracking. Galebreaker offers perimeter mounted wind screens which causes the airflow on the wind ward side to be more uniform , thus resulting in less stress on the fan blades. We are installing this concept on 4 ACCs starting this week which had blade stress issues. Sorry to hear about your problem and you can discuss further with me at gmirsky@galebreaker.comSounds like you are describing either a support at the partition wall or a vibration stiffener that might run from the motor bridge to the inside top of the A Frame. Hamon staff can be found at RC Cooling or you might contact EVAPCO-BLCT who would have staff that might have
knowledge of these details.Please excuse the fact that I am a vendor not an owner/operator. But as such have heard many examples of wind induced back pressure issues that might trip the turbine. Properly designed wind screens are intended to reduce the areas of fan back flow or stall to help reduce back pressure increases
One point that may be missed here is that on windy days, lets say > 5 mph, the wind and wind direction will reduce fan airflow into the ACC especially on the windward fans. If you are operating on a hot day, the loss of airflow will certainly increase your back pressure and even possibly trip the turbine. The windscreens described in the referenced report were installed only for protection of the fan blades. There have been wind screen configurations optimized using CFD Analysis, that have been proven to reduce wind related deficiencies. If you would like to discuss this further you can contact me at gmirsky@galebreaker.com
I have a few years in the cooling equipment industry,45, cooling towers and ACC. I have thought about this change in concept. In a way, it seems similar to the difference of a counterflow tower vs. a crossflow tower. My feeling is that specifiers must be more aware of the difference in recirculation. CFD analysis would be a good way to compare if there is an appreciable difference.
The next concern might be concerns for wind ward freezing in the winter in the fin tubes.
The last concern is the gear reducer and motor are sitting in the hot air stream as opposed to sitting in the cold air stream. Cooling gear reducer oil needs to be addressed. Most motor insulation is rated at 40 degree C ambient. So, a higher level of insulation for the motors needs to be addressed. Removing the mechanical equipment also seems to be more of a challenge.
Dear Maikol,
I represent a HP spray cooling system company and Galebreaker wind screens. We have a test facility to prove the benefits of spray cooling for an ACC. We combine wind screens with the spray cooling to best assure the spray goes into the fans it is intended for. I would be pleased to discuss with you further. You may contact me at gmirsky@galebreaker.com
You might consider wind screens placed around the perimeter to reduce the uneven loading on the fan blades as they rotate.
Hi pressure misting systems has been used especially on some horizontal units with very good success. Demin water is a good idea and wind screens to assure the mist stays in the cells it is intended for are normally incorporated. These systems can be readily retrofitted.
The designer of the ACC should assure that fan pass frequency or fan blade natural frequency does not come within 10 to 20% of the motor bridge natural frequency. I believe the API suggests 20%.
There are two excellent presentations that discuss this topic on the ACCUG website.
The first is by N. Romano which was presented in 2015 no. 3 paper, Wind Loads on Fan Blades and Blade Dynamics. He discusses how not only do you think about the motor bridge but actually the prevailing wind side has downward flow and on the leeward side there is upwards flow. So as blades pass through this region there is a vibration inducement. For this reason, I favor off numbers.
The second presentation by Mr. Scottt Basham presented in 2014 as paper no. 10 named Maintenance and Vibration Issues and Solutions. They also experienced many vibration related trips an discuss how they solved this problem.
Just a thought that some of the wear can be due to the uneven loading on the fan blades due to wind caused stress. Saw photos of similar, actually worse at a larger facility .
Gary
