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Seashells and mussels reducing heattransfer


  When sea water is used to produce drinking water or as cooling media in heat exchangers or machines, there are always along with the well known problems of corrosion and scaling, the problem of marine growth. Technically speaking marine growth is the general term for all kind of mussels, sea shells, barnacles. All these marine growth have the common characteristic, they settle on all surface, stick to them and grow bigger and bigger. This is a very common problem for instance on ship hulls, but as well inside systems. About ship hulls we will not talk at this place, but we will concentrate on piping system and heat exchangers. When water is taken from the sea into a ship or a cooling unit, it is not to avoid that together with the water also sea life or marine growth is taken in.
In order to avoid major problems the common countermeasure is to install filter systems, in order to keep the sea life out. As a filter is reducing the flow as well, there have to be found a balance in between what is hold back, and that there still is sufficient flow of water.
Normally this is managed quiet well, so there are next to no seashells or mussels entering a water system. But the problem are the larvae of these. This larvae are so small, they can easy pass the filter, once inside the water system they might start to grow, mainly at places with less flow or other favorable conditions to grow. As the flow rates in such pipes are rather high, the mussels once they reach a certain size are taken by the water down stream and are very often accumulated at the inlet of a plate heat exchanger.

See as well the two pictures. In the picture above it could be seen a lot of mussels have settled at the inlet of the heat exchanger plates and are blocking the flow of water significant, and reducing the heat capacity of the heat exchanger. The picture to the right shows a dismantled heat exchanger plate, and where water is supposed to flow it is full of mussels or seashells.
Pursanova TM has proven in several cases on ships and onshore, where seawater is used for cooling, such as internal Heat exchangers or so called box coolers installed in the seawater itself, that Pursanova Disk TM are able to lessen significant or even stop entirely this kind of marine growth. Pursanova DiskTM is installed as close as possible to the filtering unit, in order to solve the problem from the beginning. On a ship this is typically direct behind the sea chest. Onshore Pursanova TM will be installed when the pipe reaches the land, as it is not possible to install Pursanova TM sub sea. Depending how much consumers are connected it might be necessary to install more Pursanova TM direct ahead of the machine where the problem occurs. In the case shown at the pictures this would be direct at the inlet to the plate heat exchanger.
 
Two effects of the Pursanova TM are taken place. The effect against scaling or fouling helps to establish clean surface inside the pipe. A clean surface gives less spots for the larvae where they might settle, and the larvae are just taken downstream and are passing the heat exchanger, and wnat cause a problem. The second effect, Pursanova TM is establishing a film of water at the inside of the pipe wall. So the larvae will have less spots where they can settle, because the film of water prevent a hold for the larvae.
  For barnacles the same effect as described above is happening. See also the related case study Barnacles on the MV"Waterway". There will be less barnacles in the entire system Pursanova TM is also constant in search for application to proof the same effect happening not only inside a piping system but outside as well, where surfaces like a ship hull is in direct contact with sea water. Several technical problems, especially how to apply the oscillations of the Pursanova TM outside a pipe has to be solved. There are ideas and soon we hope we will come up with a solution.
For an overview for our marine applications we are doing please have look at Pursanova TM in the marine.