Double wall exchangers and oil hydraulics

Double wall heat exchangers are a particular kind of exchangers that is also employed in oil hydraulics applications. The main characteristic of these exchangers is to have a double plate, or double wall, to avoid the possibility of mixing between primary and secondary fluid in case of breaking, corrosion or perforation of the plates.

This kind of exchangers is employed in hydraulics plants especially in case of extremely sensitive applications. An example is the cooling of the hydraulic oil of a gearbox in a turbine for power generation, where the mechanical component is a core part of the application. In this case, having the presence of water within the oil leads to irreparable damages.

The most common solution employs tube-in-tube shell and plate exchangers, double tube then, or double wall. These exchangers have special heads that, in case of leakage of fluids, allow the leakage to flow within a special chamber between the two heads. Allowing the detection of the leakage and a prompt repair intervention.

In case of double wall plate heat exchangers, the presence of a double gasket in the nozzle area avoid the possibility of fluid’s mixing. In case of breaking of a gasket, indeed, along the external perimeter of the exchanger or in the nozzle section, the leakage flows towards the outside of the exchanger. In case of cracking of a plate, there is an air chamber passing between the two plates, with therefore a visible leakage of fluids toward the outside, making it easy to repair it.

Advantages and disadvantages of the double wall solution. The advantages are all related to the security, making double wall exchangers a mandatory choice when is strictly necessary to avoid any possible mixing between the primary and secondary fluid, in this case hydraulic oil and water. The disadvantages are many, on the other side, first of all the higher costs due to the fact that the number of plates gets duplicated. Thus increasing the amount and costs of construction materials. In addition, having a higher thickness and an internal chamber air between the two plates, the thermal transfer coefficient rates are lowered. And so, not only a higher amount of construction materials is needed, but also the thermal transfer surface must be increased, in order to achieve the same thermal duty. Anyway, it remains a necessary solution to prevent any possible problem of fluid’s mixing, protecting the oil hydraulic plant from serious issues.

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Posted in Cooling, Corrosione, Heat exchangers, Scambiatori a piastre

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