Hi.
By any chance are you guys talking about ATCS?
I remember one of my friend has a similar funny thing in his project.
I am attaching a reference which he forwarded to me.
Probably you will find this on internet also.
I don't believe we need a special time to clean our tubes. These systems are online, as you mentioned. And we may use them, either periodically or at the time when we realise that Heat Transfer Coefficient has gone down.
Now when to use them, how often to use them, for how long to use them becomes an operational issue.
In my friend's design, each ATCS runs for weeks together. They keep it online for about 300 hours, he says.
And the next cycle would be in the following month. Once we have this facility in place, manual cleaning is not required.
It would completely depend on the type of service you would using through your air coolers. If services like Oil with fouling factor around 0.001 m2.hr.0C/kcal, we will have to run it frequently and for longer duration.
Hope this helps.