As the old saying goes, “Seeing is believing.” So goes proving to people how condensate behaves in a steam-heated rotating cylinder (e.g., a roll or a dryer). Trying to describe what is going on inside a rotating cylinder can be difficult. Add in trying to describe the heat transfer process that is being influenced by the condensate behavior and it is understandable how people get lost in the weeds.
People may be surprised to learn that when a pressurized roll is rotating, you can see what is going on inside the roll. All you need is a little light and a good camera with a cooling system and some cabling. What you also learn is that having the capability for both a rotating camera and a stationary camera brings unique perspectives. Each viewing method offers opportunities to learn different aspects of condensate behavior, which becomes crucial when you need to study both rotary and stationary syphon performance with and without dryer bars. Syphons get installed in the dryer to evacuate the condensate formed when the steam released its latent heat energy to the cylinder. Dryer bars get installed in the dryer to improve the cross-machine temperature profile and heat transfer.
One very visual event that also dramatically impacts heat transfer is when condensate transitions from cascading to a rimming condition. Cascading is when the condensate inside the cylinder is tumbling on itself and creating a lot of turbulence. This is good for heat transfer. As speed increases, the condensate will transition into what’s referred to as rimming condition. Rimming is when the condensate adheres to the inner circumference of the cylinder as a result of centrifugal force. The rimming layer of condensate insulates the dryer surface from the steam and lowers heat transfer relative to the cascading stage of condenate behavior. Determining the cascading to rimming transition speed for a given condensate depth is easy to do when you can watch the process live. This is critical information for selecting the proper syphon and steam system design.
Rotating cameras, those cameras that rotate with the cylinder, are great for capturing condensate resonance behavior when dryer bars are installed. Resonance sloshing is a description of what the condensate does between the dryer bars during rimming and explains how they create the conditions needed for good heat transfer. The video from the camera illustrates how speed effects the resonance frequency of the condensate.
Stationary cameras, those cameras that are fixed relative to the cylinder, are great for observing syphon vibration or motion. This is especially true for traditional “bent pipe” syphons used in smaller diameter rolls used in the corrugated packaging industry. Speeds in corrugated packaging production are increasing and traditional bent pipe syphons can exhibit some shocking behavior. Stationary cameras are also good for studying puddling condensate behavior. This behavior occurs when the speed is not fast enough for cascading and the condensate is beginning to climb up the side of the dryer. Knowledge of this process and the prediction of it are important when installing syphon equipment to ensure efficient and rapid condensate removal.
Optimizing drying and heat transfer performance from inside the cylinder is a key factor in getting the most production possible out your machine. Having a window into what is happening for your unique operating conditions makes this job a little easier.