Field of invention

The present invention relates to a fluid separation unit comprising a magnetic filtering unit that is capable of removing ferromagnetic particles from a fluid. The present invention also relates to a fluid filtration method for removing ferromagnetic particles from a fluid.

Prior art

Humans are exposed to ferromagnetic particles in many places where they work and commute [Wang, J., Li, S., Li, H., Qian, X., Li, X., Liu, X., Lu, H., Wang, C. and Sun, Y., 2017. Trace metals and magnetic particles in PM2. 5: Magnetic identification and its implications. Scientific reports, 7(1), pp.1-11.]. At high concentrations, ferromagnetic particles are found in metro and train stations [N. Kappelt, H. S. Russell, D. Fessa, 0. Hertel and M. S. Johnson, Particulate Air Pollution in the Copenhagen Metro Part 1 : Mass Concentrations and Ventilation, Environment International, 2022 and Smith, J.D., Barratt, B.M., Fuller, G.W., Kelly, F.J., Loxham, M., Nicolosi, E., Priestman, M., Tremper, A.H. and Green, D.C., 2020. PM2. 5 on the London Underground. Environment international, 134, p.105188]. These particles are found in high concentrations in steel workshops and foundries as well.

Mechanical fibrous filters can remove particles, but the energy usage is high due to the high-pressure drop over the filter [S. Kwiatkowski, M. Polat, W. Yu and M. S. Johnson, Industrial Emissions Control Technologies: Introduction, In: Meyers R. (eds) Encyclopedia of Sustainability Science and Technology, Springer, New York, NY, 2019, https://doi.org/10.1007/978-l-4939-2493-6 1083-1.1. Mechanical filters remove particles by blocking the passing particles. Therefore the fiber structure should be very tight to capture the particles following the airflow. There have been some attempts to use magnetic fields to remove ferromagnetic particles. For example, environmental researchers sometimes quantify the fraction of airborne particulate matter that is attracted by magnetic fields [Castaneda-Miranda, A.G., Bohnel, H.N., Molina- Garza, R.S. and Chaparro, M.A., 2014. Magnetic evaluation of TSP- filters for air quality monitoring. Atmospheric environment, 96, pp.163- 174.]. While electrostatic precipitators based on static electrical charges and electrophoresis are known [S. Kwiatkowski, M. Polat, W. Yu and M. S. Johnson, Industrial Emissions Control Technologies: Introduction, In: Meyers R. (eds) Encyclopedia of Sustainability Science and Technology, Springer, New York, NY, 2019, https://doi.org/10.1007/978-l-4939- 2493-6_1083-l], relatively little is known about using magnetophoresis as the basis of filtration. One of the problems of the existing solutions is that the magnetic fields do not effectively trap particles due to high- velocity particles, and the Clean Air Delivery Rate (CADR) of such systems is low considering the energy input.

JP 2019209298 A discloses an air filter configured to adsorb and remove magnetic dust such as iron powder. The air filter is arranged in an air intake port of electric equipment. The air filter comprises permanent magnets arranged oppositely to sandwich air flow passing through the air intake port, and a magnetic filter arranged between the permanent magnets. The magnetic filter is made of thin wires made of magnetic materials. This filter tends to clog as magnetic or magnetisable particles are caught by the magnetic filter. Hereby, an increased pressure difference is required to force air through the magnetic filter and thus the efficiency of the filter is significantly reduced.

US20140367340A1 discloses a magnetic particle separator suitable for separating magnetic and non-magnetic particles from a thermal fluid flowing in a heating system. The magnetic particle separator comprises a hollow body configured with an upper particle separation chamber and for circulation of the thermal fluid between an inlet and an outlet port, and a quieting chamber beneath the particle separation chamber for accumulation of the particles separated from the fluid: an annular support element for permanent magnets being removably fastened outside the quieting chamber of the separator. The energy efficiency of this filter, however, is poor. Accordingly, it would be desirable to have an alternative to this solution.

Accordingly, there is a need for a method and an apparatus which reduces or even eliminates the above-mentioned disadvantages of the prior art.

Summary of the invention

The object of the present invention can be achieved by a fluid separation unit as defined in claim 1 and by a method as defined in claim 13. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings.

The fluid separation unit according to the invention is a fluid separation unit comprising a:

- housing having an inlet port for receiving a fluid, an outlet port for discharging fluid and a conduit extending between the inlet port and the outlet port;

- at least one permanent magnet arranged to attract magnetic or magnetisable particles in the fluid, wherein the at least one permanent magnet is at least partly covered by a magnetisable covering structure, wherein a flow entrainment section is arranged inside the housing, wherein the flow entrainment section is arranged and configured to reduce the velocity of a portion the fluid and recirculate a portion of the fluid inside the conduit.

Hereby, it is possible to provide a fluid separation unit that does not clog as easy as the prior art fluid separation units. Moreover, it is possible to provide a fluid separation unit having an improved efficiency.

The fluid separation unit is configured to filter a fluid being a liquid or a gas or a combination thereof.

The housing may be made in various materials including plastic, wood, metal and ceramic materials. The housing comprises an inlet port for receiving a fluid, an outlet port for discharging fluid and a conduit extending between the inlet port and the outlet port.

The fluid separation unit comprises at least one permanent magnet arranged to attract magnetic or magnetisable particles in the fluid.

The at least one permanent magnet is at least partly covered by a magnetisable covering structure. In an embodiment, the magnetisable covering structure is made of steel. In an embodiment, the magnetisable covering structure is made of stainless steel.

The flow entrainment section is arranged inside the housing.

In an embodiment the flow entrainment section is arranged and configured to reduce the velocity of a portion the fluid with at least 50 % and recirculate that portion of the fluid inside the conduit.

In an embodiment, the flow entrainment section is arranged and configured to reduce the velocity of a portion the fluid with at least 60 %.

In an embodiment, the flow entrainment section is arranged and configured to reduce the velocity of a portion the fluid with at least 70 %.

In an embodiment, the flow entrainment section is arranged and configured to reduce the velocity of a portion the fluid with at least 80 %. In an embodiment, the flow entrainment section is arranged and configured to reduce the velocity of a portion the fluid with at least 85 %.

In an embodiment, the flow entrainment section is arranged and configured to reduce the velocity of a portion the fluid with at least 90 %.

The magnetic or magnetisable particles may include ferromagnetic particles.

The current invention uses the least amount of energy to remove ferromagnetic particles compared to the existing technologies and, therefore, can be applied in spaces such as train/metro stations and steel workshops as an energy-efficient solution.

In an embodiment, the at least one permanent magnet extends (basically) along the direction of the flow of the inside the flow entrainment section. Hereby, the time for attracting and catching the magnetic or magnetisable particles can be maximized.

In an embodiment, the length of the at least one permanent magnet is at least 2 cm.

In an embodiment, the length of the at least one permanent magnet is at least 2 cm.

In an embodiment, the length of the at least one permanent magnet is at least 2.5 cm.

In an embodiment, the length of the at least one permanent magnet is at least 3 cm.

In an embodiment, the length of the at least one permanent magnet is at least 3.5 cm. In an embodiment, the length of the at least one permanent magnet is at least 4 cm.

In an embodiment, the length of the at least one permanent magnet is at least 5 cm.

In an embodiment, in the flow entrainment section a magnetic assembly is provided, wherein the magnetic assembly comprises a plurality of parallel rod-shaped permanent magnets that are covered by a magnetisable metal section.

In an embodiment, the housing comprises:

- a first part constituting a portion of a spherical structure;

- a second part constituting a portion of a spherical structure;

- a straight or conical front portion comprising the inlet port and

- a straight or conical outlet portion comprising the out port, wherein the first part is sandwiched between the front portion and the second part and the second part is sandwiched between the first part and the outlet portion, wherein the width of the first part is larger than the width of the second part.

In an embodiment, the at least one permanent magnet is arranged in the second part.

In an embodiment, the width of the front portion is smaller than the width of the outlet portion.

In an embodiment, the flow entrainment section is designed as a ring extending in the conduit along the inner wall of at portion of the first part and the second part.

In an embodiment, the distal portion of the low velocity reducing section comprises a conical inner wall. In an embodiment, the volume of the flow entrainment section is less than 1000 ml.

In an embodiment, the volume of the flow entrainment section is less than 900 ml.

In an embodiment, the volume of the flow entrainment section is less than 800 ml.

In an embodiment, the volume of the flow entrainment section is less than 700 ml.

In an embodiment, the volume of the flow entrainment section is less than 600 ml.

In an embodiment, the volume of the flow entrainment section is less than 500 ml.

Since the magnetic force decreases by the cube of the distance, it may be an advantage to keep the ducts through which fluid passes the magnetisable structure and/or magnetisable portion small. Accordingly, it may be an advantage to keep the volume of the flow entrainment section below a predefined level e.g. 1000 ml.

In an embodiment, the proximal portion of the low velocity reducing section comprises an inwardly arced inner wall.

In an embodiment, the proximal portion of the low velocity reducing section comprises an inwardly arced and concave inner wall.

In an embodiment, the magnetic assembly comprises a plurality of ducts arranged along the periphery of a portion of the housing, wherein each duct comprises one or more rod-shaped permanent magnets ex- tend along the longitudinal axis of the duct, wherein each permanent magnet is covered by a magnetisable covering structure.

In an embodiment, a plurality of parallel rod-shaped permanent magnets that at covered by a magnetisable metal section.

The method according to the invention is a method for removing magnetic or magnetisable particles by means of a fluid separation unit comprising a:

- housing having an inlet port for receiving a fluid, an outlet port for discharging fluid and a conduit extending between the inlet port and the outlet port;

- at least one permanent magnet arranged to attract magnetic or magnetisable particles in the fluid, wherein the at least one permanent magnet is at least partly covered by a magnetisable covering structure, wherein the method comprises the step of reducing the velocity of a portion the fluid and recirculate that portion of the fluid inside the conduit.

Hereby, it is possible to provide a method for removing magnetic or magnetisable particles in an improved manner. The methods can significantly increase the time before the fluid separation unit clogs. Moreover, the method has an improved performance (a lower pressure difference is required to force a fluid through the fluid separation unit).

In an embodiment, the at least one permanent magnet extends basically along the direction of the flow of the inside the flow entrainment section.

In an embodiment, the at least one permanent magnet extends along the direction of the flow of the inside the flow entrainment section. In an embodiment, the length of the at least one permanent magnet is at least 2 cm.

In an embodiment, the fluid separation unit comprises a flow entrainment section comprising a magnetic assembly that comprises a plurality of parallel rod-shaped permanent magnets that are covered by a magnetisable metal section.

In an embodiment, the method comprises the step of reducing the velocity of a portion the fluid with at least 50 % and recirculate that portion of the fluid inside the conduit.

In an embodiment, the distal portion of the low velocity reducing section comprises a conical inner wall.

In an embodiment, the volume of the flow entrainment section is less than 1000 ml.

In an embodiment, the proximal portion of the low velocity reducing section comprises an inwardly arced (concave) inner wall.

In an embodiment, the magnetic assembly comprises a plurality of ducts arranged along the periphery of a portion of the housing, wherein ion each duct comprises one or more rod-shaped permanent magnets extend along the longitudinal axis of the duct, wherein each permanent magnet is covered by a magnetisable covering structure.

In an embodiment, a plurality of parallel rod-shaped permanent magnets that are covered by a magnetisable metal section.

Description of the Drawings

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1A shows a cross-sectional side view of a fluid separation unit according to the invention;

Fig. IB shows a side view of the fluid separation unit shown in Fig 1A;

Fig. 2 shows a prior art air filter device for removing ferromagnetic particles from air;

Fig. 3 shows a magnetic assembly of a fluid separation unit according to the invention;

Fig. 4 shows a cross-sectional side view of a magnetic assembly of a fluid separation unit according to the invention;

Fig. 5A shows a front view of a magnetic assembly of a fluid separation unit according to the invention;

Fig. 5B shows a permanent magnet and the surrounding magnetisable structure of the magnetic assembly shown in Fig. 5 A;

Fig. 6A shows a front view of a magnetic assembly of a fluid separation unit according to the invention;

Fig. 6B shows a permanent magnet and the surrounding magnetisable structure of the magnetic assembly shown in Fig. 6A;

Fig. 7A shows a front view of a magnetic assembly of a fluid separation unit according to the invention;

Fig. 7B shows a plurality of permanent magnets and the surrounding magnetisable structures of the magnetic assembly shown in Fig. 7A;

Fig. 8A shows a perspective side view of a fluid separation unit according to the invention and

Fig. 8B shows a perspective side view of a fluid separation unit corresponding to the one shown in Fig. 1A and in Fig. IB. Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a fluid separation unit 2 of the present invention is illustrated in Fig. 1.

Fig. 1 illustrates a cross-sectional side view of a fluid separation unit 2 according to the invention. The fluid separation unit 2 comprises a housing 4 having an inlet port 6 for receiving a fluid 8, an outlet 30 comprising an outlet port 12 for discharging fluid 8 and a conduit 10 extending between the inlet port 6 and the outlet port 12.

In an embodiment, the fluid separation unit 2 is configured to filter air. In an embodiment, the fluid separation unit 2 is configured to filter a liquid (e.g. water).

The fluid separation unit 2 comprises at plurality of permanent magnets (not shown) arranged to attract magnetic or magnetisable particles 16 in the fluid 8. The permanent magnets are at least partly covered by a magnetisable covering structure 18.

The fluid separation unit 2 comprises a flow entrainment section 20 arranged inside the housing 4. The flow entrainment section 20 is arranged and configured to reduce the velocity of a portion the fluid 8 and recirculate fluid inside the conduit 10. In an embodiment, the flow entrainment section 20 is arranged and configured to reduce the velocity of a portion the fluid 8 with at least 50 %.

The inside the central portion of the housing 4 a main channel of the conduit 10 extends along the longitudinal axis of the housing 4. A fluid 8 (e.g. air) enters the housing 4 via the inlet port 6. The inlet port has a width D2 large enough to receive a predefined desired flow (e.g. 1-10 L/min) of the fluid 8. When the fluid 8 has entered the main channel, the majority of the fluid continues along a straight path, through which the fluid 8 leaves the housing 4 through an outlet port 12 having a larger width D3 that the width D2 of the inlet port 6. Hereby, the velocity of the fluid 8 is continuously reduced from the inlet port 6 to the outlet port 12. Section 20 acts as entraining flow section.

A minor percentage of the fluid (e.g. 10 %) 8 will, however be sucked into a flow entrainment section 20. The flow entrainment section 20 comprises a first portion 24 and a second portion 26. The second portion comprises an arched part arranged next to a straight part. A magnetic assembly 32 comprising a plurality of permanent magnets (not shown) being at least partly covered by a magnetisable covering material 18, is arranged in the straight part of the second portion.

The first portion 24 comprises a straight part and an arched portion 22. The straight part of the first portion 24 is arranged next to the straight part of the second portion 26. The arched portion 22 of the first portion is configured to guide the fluid 8 that has passed through the magnetic assembly 32 to be recirculated into the main channel of the conduct 10.

The magnetic field generated by the magnetic assembly 32 will attract metal particles from the flow passing from the conduit 10. Hereby, the efficiency of the fluid separation unit 2 can be increased.

The flow entrainment section 20 comprises an inner wall 34 and an outer wall. The inner wall 34 is a converging-diverging nozzle configured to allow the fluid 8 pass through and, together with the outer wall, creates the bypass channel. The main flow enters the nozzle from the inlet port 6 and entrains the fluid molecules from the bypass fluid flow.

The nozzle outlet area A _nO zzie outlet is given by width D ₅ of the nozzle outlet:

( 1 ) Anozzle outlet ^— 71 (^Ds)^ Anozzie outlet will typically be between 0.8 to 1.2 times the area Aoutiet port of the outlet port 12.

(2) Aoutiet port ^— 71 (J^D. ) ²

The narrow area of the nozzle has an area A _na rrow nozzle that is larger than the area Ainiet port of the inlet port 6 but smaller than the area Anozzie outlet of the outlet port.

(3) Anarrow nozzle ⁼ 71 (J^Ds)^

(4) Ainiet port ⁼ 71 (J D2) ²

The distance L between the inlet region of the conduct 10 and the inlet of the nozzle is between 40% to 60% of the inlet's effective width. The effective width is the area Ainiet port of the inlet port 6 squared.

Therefore, the fluid pressure gradually increases along the center channel of the conduct 10 due to the increase in the cross-section area. The lowest pressure value can be found at the end of the nozzle (in which the width is Ds) due to the flow, which induces a wake at this point.

Th width Di of the magnetic assembly 32 is indicated. It can be seen that the width Di of the magnetic assembly 32 is smaller than half the width D2 of the inlet port 6. Typically, the width Di of the magnetic assembly 32 corresponds to 25-40% of the width D2 of the inlet port 6. In an embodiment, the width Di of the magnetic assembly 32 corresponds to 30-35% of the width D ₂ of the inlet port 6.

The inlet port 6 is designed as a cylindrical portion. The outlet port 12, however, is conical. It can be seen that the distal end of the outlet port 12 is larger than the proximal end of the outlet port 12. Accordingly, the velocity of the fluid 8 will gradually be reduced as indicated by the arrows indicating the velocity of the fluid 8. The cross-sectional area of the outlet port 12 will typically be 2 to 7 times the cross-sectional are of the inlet port 6.

In an embodiment, the width D3 of the outlet port 12 is more than 50 % larger than the width D2 of the inlet port 6.

In an embodiment, the magnetic assembly 32 consists of a multichannel duct, wherein one or more permanent magnets are arranged in each duct.

In an embodiment, the fluid separation unit 2 may comprise a ventilator arranged to provide a pressure different that can suck fluid 8 into the inlet port 6 of the fluid separation unit 2 and/or outlet cleaned fluid 8 out through the outlet port 12.

The fluid separation unit 2 comprises a front portion 28 comprising the inlet port 6. The front portion 28 may be straight or conical. By having a front portion 28, it is possible to achieve a fully developed velocity profile (a homogeneous flow along the cross section of the end portion of the front portion 28). If front portion 28 is removed, the velocity profile would not be homogeneous as the central portion having largest distance to the wall would have significantly higher velocity than the regions near the wall.

Fig. IB illustrates a side view of the fluid separation unit 2 shown in Fig 1A. The fluid separation unit 2 comprises a housing 4 having an inlet port 6 and an outlet port 12. The inlet port 6 has a width D ₂ and the outlet port 12 has a larger width D4. A fluid 8 enters the inlet port and exits the fluid separation unit 2 via the outlet port 12.

Fig. 2 illustrates a prior art air filter device for removing ferromagnetic particles 48 from air. The art air filter device comprises several perma- nent magnets 46, 46' and a magnetisable material 44. The magnetisable material 44, which is typically steel wool is arranged between adjacent magnets 46, 46'. Accordingly, the magnetisable material 44 is magnetised and capable of attracting ferromagnetic particles 48 from air. It, however, important to both have a low flow velocity and a high density of the magnetisable material 44 in order to be able to catch the ferromagnetic particles 48 from air because the extension of the magnetisable material 44 along the flow path is quite small. Accordingly, the prior art air filter device will get clogged quite easily. Moreover, a large pressure is required to pass the magnetisable material 44. Therefore, it is desirable to have a filter device that is more efficient (requires less pressure) and does not get clogged quite easy.

Fig. 3 illustrates a magnetic assembly 32 of a fluid separation unit according to the invention. The magnetic assembly 32 comprises a cylindrical duct 40 having a longitudinal axis X. A plurality of rod-shaped permanent magnets 14, 14' extending along the longitudinal axis X. Since the flow directions extends along the longitudinal axis X, the magnetic assembly 32 is designed to provide the longest possible time to catch magnetic or magnetisable particles in the fluid to be filtered by using the magnetic assembly 32.

Each of the permanent magnets 14, 14' are cylindrical. A magnetisable structure 36 surrounds the axial periphery of each of the permanent magnets 14, 14'. The magnetisable structure 36 may be made of steel. In an embodiment, the magnetisable structure 36 is shaped as steel brushes protruding radially from the periphery of the magnet 14, 14' that it surrounds.

The magnets 14, 14' are attached to a magnetisable portion 38 arranged inside the provided in the duct 40. In an embodiment, the magnetisable portion 38 is made of steel. In an embodiment, the magnetisable portion 38 is shaped as a grate. It can be seen that a free space 42 is provided between the inner wall of the duct 40 and the magnetisable portion 38. Fluid passing through the magnetic assembly 32 may travel via the space 42. The magnetic or magnetisable particles in the fluid will, however, be attracted to the magnetisable structure 36 surrounds the axial periphery of each of the permanent magnets 14, 14'. Accordingly, the magnetic or magnetisable particles will in most cases get caught (due to the magnetic attraction) and thus removed from the fluid.

Since there is a large space between adjacent magnetisable structures 36. The magnetic assembly 32 has a very large capacity for collecting magnetic or magnetisable particles without getting clogged.

Fig. 4 illustrates a cross-sectional side view of a magnetic assembly 32 of a fluid separation unit according to the invention. The magnetic assembly 32 comprises a plurality of parallel cylindrical permanent magnets 14, 14', 14". The permanent magnets 14, 14', 14" extend along the longitudinal axis X of the magnetic assembly 32.

Each of the permanent magnets 14, 14', 14" are surrounded by a magnetisable structure 36. The magnetisable structures 36 are shaped as brushes comprising a plurality of brush members extending radially. The magnetisable structures 36 extends radially from a structure that is in contact with or connected to a structure that is in contact with a magnet 14, 14'. Accordingly, the magnetisable structures 36 are magnetised by the magnets 14, 14'. Therefore, the magnetisable structures 36 will attract and catch magnetic or magnetisable particles in the fluid being filtered.

The magnetisable portion 38 illustrated may optionally be arranged between the brush structures of the magnetisable structures 36 and optionally in at least some of the other spaces of the magnetic assembly 32. Fig. 5A illustrates a front view of a magnetic assembly 32 of a fluid separation unit according to the invention. Fig. 5B illustrates a permanent magnet 14 and the surrounding magnetisable structure 36 of the magnetic assembly 32 shown in Fig. 5A.

The magnetic assembly 32 comprises an inner wall 34 and an outer wall 35. The magnetic assembly 32 comprises a plurality of parallel cylindrical permanent magnets 14. Each of the permanent magnets 14 are surrounded by a magnetisable structure 36 shaped as brushes comprising a plurality of brush members extending radially.

It can be seen that space a 42 is provided between the magnetisable structures 36 and the wall 34, 35 of the magnetic assembly 32.

In Fig. 5B one can see that the magnetisable structures 36 extend radially from a surrounding portion 50 (surrounding the magnet 14) that is in contact with the magnet 14 via attachment structures 52 extending between the inside of the surrounding portion 50 and the magnet 14. Accordingly, the magnetisable structures 36 are magnetised by the magnet 14. Thus, the magnetisable structures 36 will attract and catch magnetic or magnetisable particles in the fluid being filtered.

It is possible to arrange a magnetisable portion 38 between the structures arranged between the inner wall 34 and the outer wall 35.

Fig. 6A illustrates a front view of a magnetic assembly 32 of a fluid separation unit according to the invention. Fig. 6B illustrates a permanent magnet 14 and the surrounding magnetisable structure 36 of the magnetic assembly 32 shown in Fig. 6A. It is important to underline, the permanent magnet 14 may be replaced with an electromagnet. Accordingly, in an embodiment, the magnetic assembly 32 of the fluid separation unit comprises an electromagnet (not shown) surrounded by a magnetisable structure 36 of the magnetic assembly 32. By having an electromagnet it is possible to shut off the power and hereby turn off the magnetic field generated by the electromagnet. This may be an advantage when cleaning the filter (removing the collected particles).

The magnetic assembly 32 comprises an inner wall 34 and an outer wall 35. The magnetic assembly 32 comprises a plurality of parallel cylindrical permanent magnets 14. The permanent magnets 14 are surrounded by a magnetisable structure 36 shaped as brushes comprising a plurality of brush members extending radially.

A space 42 is provided between the magnetisable structures 36 and the wall 34, 35 of the magnetic assembly 32. Even though it is not shown, it is possible to arrange a magnetisable portion 38 between the structures arranged between the inner wall 34 and the outer wall 35.

Fig. 6B illustrates that the magnetisable structures 36 extend radially from a surrounding portion 50 (surrounding the magnet 14) that is in contact with the magnet 14 via attachment structures 52 extending between the inside of the surrounding portion 50 and the magnet 14 so that the magnetisable structures 36 are magnetised by the magnet 14. Thus, the magnetisable structures 36 will attract and catch magnetic or magnetisable particles in the fluid being filtered. The magnetisable structure 36 is arranged inside a duct 40.

Fig. 7A illustrates a front view of a magnetic assembly 32 of a fluid separation unit according to the invention. Fig. 7B illustrates a plurality of permanent magnets 14 and the surrounding magnetisable structures 36 of the magnetic assembly 32 shown in Fig. 7A.

The magnetic assembly 32 comprises an inner wall 34 and an outer wall 35. The magnetic assembly 32 comprises a plurality of ducts 40 corre- sponding to the one shown in Fig. 7B.

Each duct 40 comprises a plurality of permanent magnets 14 are surrounded by a magnetisable structure 36 shaped as brushes comprising a plurality of brush members extending radially. The magnets 14 are attached to a magnetisable portion 38. A space 42' is provided between the magnetisable portion 38 and the inner wall of the duct 40.

A space 42 is provided between the ducts 40 and the wall 34, 35 of the magnetic assembly 32. Even though it is not shown, it is possible to arrange a magnetisable portion between the ducts 40, the inner wall 34 and the outer wall 35.

The brushes shown in and explained with reference to Fig. 5A, Fig. 5B, Fig. 6A, Fig. 6B, Fig. 7A and Fig. 7B are designed to facilitate the capture and removal of ferromagnetic particles from the fluid flow. In this way, the magnetic assembly 32 removes ferromagnetic particles from the flow. The arrows shown in Fig. 1A illustrate the fluid flow directions.

A steel brush provided with cylindrical permanent magnet 14 extending along the central line of the brush, generates a uniform magnetic field. This magnetic field is capable of capturing particles while the fluid 8 can pass the brush hairs with the smallest possible pressure drop. In an embodiment, a magnetisable portion of steel wool is placed between the brushes and around them. Since the magnetic assembly 32 is placed at the diverging part of the nozzle, it can attract the ferromagnetic particles 16 passing through the nozzle and increase the probability of directing them to the bypass channel.

In an embodiment, the fluid separation unit 2 is configured to be installed and applied in train and metro stations to remove ferromagnetic particles from the air.

In an embodiment, the fluid separation unit 2 is configured to be in- stalled in series on the walls or the ceilings of spaces with high ferromagnetic particle concentrations.

In an embodiment, the fluid separation unit 2 is configured to be installed on the body of the trains to remove the ferromagnetic particles from the tunnels' air. Tunnels are full of ferromagnetic particles, and their air enters stations due to the piston effect. Cleaning the air in tunnels by trains can be very effective as the cleaning is close to the pollution source.

In an embodiment, the fluid separation unit 2 is configured to be installed outside of the trains. The fluid separation unit 2 will start removing ferromagnetic particles when trains start braking. The air will pass through the system due to the movement of the train, and therefore, it does not need to have any fan to move air.

In an embodiment, the fluid separation unit 2 is configured to be installed on the walls of train/metro tunnels to remove ferromagnetic particles. The air can move through the fluid separation unit 2 due to the movement of trains, a fan, or any other type of air-moving mechanism.

A fan will typically be used if the device is used as a standalone device. Such standalone device may be installed at a train station or at a wall by way of example.

In an embodiment, the fluid separation unit 2 is configured to be used in combination with mechanical filters, such as fibrous filters, to remove all types of particles from the air of tunnels, stations, steel workshops, or foundries.

In an embodiment, the fluid separation unit 2 is configured to be used with gas removal technologies to remove gas pollutants and particulate matter. Fig. 8A illustrates a perspective side view of a fluid separation unit 2 according to the invention. The fluid separation unit 2 comprises similar features as the fluid separation unit shown in and explained with reference to Fig. 1A. The geometry of the structures is, however, different. The fluid separation unit 2 comprises a housing having a planar bottom surface.

The fluid separation unit 2 comprises a box-shaped front portion 28 shaped as a tubular structure designed to receive the fluid and provide a fully developed velocity profile (a homogeneous flow along the cross section of the end portion of the front portion 28).

The fluid separation unit 2 comprises a flow entrainment section comprising a first portion 24 and a second portion 26. The fluid separation unit 2 comprises an outlet portion 30 designed to discharge fluid.

Fig. 8B illustrates a perspective side view of a fluid separation unit corresponding to the one shown in Fig. 1A and in Fig. IB. The fluid separation unit 2 comprises a housing 4 having an inlet port 6 for receiving a fluid 8, an outlet 30 comprising an outlet port 12 for discharging fluid 8. The fluid separation unit 2 comprises a conduit extending between the inlet port 6 and the outlet port 12.

The fluid separation unit 2 comprises a flow entrainment section comprising a first portion 24 and a second portion 26. The second portion comprises an arched part arranged next to a straight part (see Fig. 1A).

The first portion 24 comprises a straight part and an arched portion (see Fig. 1A). The straight part of the first portion 24 is arranged next to the straight part of the second portion 26. List of reference numerals

2 Fluid separation unit

4 Housing

6 Inlet port

8 Fluid

10 Conduit

12 Outlet port

14, 14', 14", 14"' Permanent magnet

16 Particle

18 Covering structure

20 Flow entrainment section

22 Arched portion

24 First portion

26 Second portion

28 Front portion (tubular structure)

30 Conical portion

32 Magnetic assembly

34 Inner wall

35 Outer wall

36 Magnetisable structure

38 Magnetisable portion

40 Duct

42, 42' Space

44 Magnetisable material

46, 46' Permanent magnet

48 Particle

50 Surrounding portion

52 Attachment structure

Di, D2, D3, D4, D5 Width ance