Packaging

Maximized flexibility in terms of viscosity and output

Monday 22. November 2010 - At the Pack Expo Krones AG, Neutraubling, Germany, is showcasing a demonstration unit of new tube modules for shell-and-tube heat exchanger systems. To assure optimally gentle product heat-up and cool-down respectively, the flow dynamics inside the heat-exchanger tube are of crucial importance. With a low-viscosity product in a smooth pipe, the laminar boundary layer will be thin and heat transfer very good, whereas a highly viscous product in a smooth pipe results in a very thick boundary layer, with concomitantly poorer heat transfer.

The reasons for this are different flow velocities and different temperature layers. The weak heat transfer function means the product is not adequately treated. One option here would be to pass the highly viscous product through a singly corrugated tube, which causes the laminar layer to break up, thus producing a medium, moderate heat transfer function, but the turbulences are still not strong enough. A cross-corrugated tube, of the kind used by Krones, by contrast, is considerably more effective. Here, the high-viscosity product’s laminar layer is at the tube’s edge broken up very effectively indeed. Despite the low-turbulence flow pattern, very good heat transfer is obtained here.

These cross-corrugated tubes are usually used in the pre-warming and cool-down zones. In the heater area, by contrast, where viscosity frequently decreases due to higher temperatures, i.e. approaches that of water, smooth tubes are installed. As of now, Krones is making use of this combination: both for the new shell-and-tube heat exchanger in the low-output category from 3,000 to 10,000 litres an hour, and for medium and high outputs ranging from 15 and 30 through to 60 cubic metres an hour.
It is thanks not least to this combination of smooth and cross-corrugated tubes that maximised flexibility is assured in terms of viscosity. This is essential for handling a wide range of viscosity variants – from water-viscous to highly viscous products. The combination of smooth and cross-corrugated tubes, moreover, provides a high degree of flexibility in terms of output adjustment: the system’s volume flow can be regulated from 100 to 30 per cent to suit the product involved, enabling large and small containers to be handled at the filler without any intermediate discharges.