THIS INVENTION relates to gas filters. More particularly, the invention relates to a filter for removing droplets or particulate matter from a gas steam.

According to one aspect of the invention there is provided a gas filter which includes: a frame; and a plurality of overlapping elongated baffles arranged side-by-side in series and mounted in the frame to prevent straight-line flow of a gas stream through the frame from one side of the frame to the other, each baffle comprising a spine in the form of an elongated strip having parallel side edges, and a pair of elongated deflector panels extending along the length of each side edge of the elongated strip, the deflector panels of each pair projecting from the associated edge of the spine at an angle to each other, and the deflector panels of adjacent baffles overlapping one another.

The free edge of one deflector panel of each pair of the deflector panels may be provided with a flange extending along its length, the flange projecting from the associated free edge at an angle to the one deflector panel; and the free

edge of each flange may in turn be provided with a lip extending along its length and projecting from said flange free edge at an angle to the flange.

The deflector panels of each baffle may overlap the deflector panels of at least one adjacent baffle to cause at least four changes in direction of flow of any gas stream passing through the frame from one side of the frame to the other; and the overlapping deflector panels may be arranged to cause changes in direction of flow in one direction which alternate with changes in direction of flow in the opposite direction, so that any gas stream passing through the frame from one side of the frame to the other follows a zig-zag path.

The overlapping deflector panels may be arranged so that the sum of the angular changes in direction of the flow of the gas stream is in total between 500° and 540°, i. e. between 250° and 270° in total in one direction and between 250° and 270° in total in the opposite direction. The overlapping deflector panels may be arranged so that the changes in direction of the flow of the gas stream include, in series, two approximately 180° direction changes, which 180° direction changes are alongside each other.

The spine of each baffle may comprise a pair of registering elongated sheet metal plates joined face-to-face with each other; and the registering elongated sheet metal plates may be flat and rectangular, each plate having two of the deflector panels forming extensions of opposite side edges thereof.

The plates, including their extensions, may be identical to each other, each plate being generally c-shaped in cross-section. It will be appreciated that each identical plate can be manufactured by the same tooling and, further, that generally c-shaped plates require bending the metal in one direction only, thereby simplifying and economising the manufacturing of the baffle.

According to a further aspect of the invention there is provided a baffle for a filter, the baffle comprising a spine in the form of an elongated strip having parallel side edges, and a pair of elongated deflector panels extending along the length of each side edge of the elongated strip, the deflector panels of each pair projecting from the associated edge of the spine at an angle to each other.

The invention is now described, by way of example, with reference to the accompanying drawings.

In the drawings, Figure 1 shows schematically a cross-section of some of the baffles and part of the frame of a portion of a first embodiment of a gas filter in accordance with the invention; Figure 2 shows schematically a similar view of a second embodiment of a gas filter in accordance with the invention; Figure 3 shows schematically a similar view of a third embodiment of a gas filter in accordance with the invention; Figure 4 shows schematically a similar view of a fourth embodiment of a gas filter in accordance with the invention; and

Figure 5 shows schematically a three dimensional view of some of the baffles and part of the frame of a portion of a third embodiment of the gas filter.

In the drawings, reference numeral 10 generally refers to a gas filter in accordance with the invention.

The gas filter 10 includes a frame 12 and a plurality of overlapping elongated baffles 14 which are arranged side-by-side and mounted in the frame 12.

The overlapping of the elongated baffles 14 prevents straight-line flow of the gas stream indicated by the arrow 16 through the frame 12 from one side 18 of the frame 12 to the other side 20 of the frame 12. Each baffle 14 comprises a spine 22 in the form of an elongated strip having parallel side edges 24.1 and 24.2 along the length of each of which a pair of elongated deflector panels 26 1 and 26.2 extends, the deflector panels 26.1 and 26.2 of each pair projecting from their associated edge 24.1 or 24.2 of the spine 22 at an angle to each other. The deflector panels 26.1 and 26.2 of adjacent baffles 14 overlap one another.

The free edge 28, i. e. the edge remote from the spine 22, of one deflector panel 26.2 of each pair is provided with a flange 30 extending along its length.

Each flange 30 projects from the free edge 28 of the associated deflector panel 26.2 at an obtuse angle to the deflector panel 26.2. The free edge 32 of the flange 30 is in turn provided with a lip 34 extending along its length and projecting from said free edge 32 at an angle to the flange 30. In the first and third embodiments of the invention as shown in Figures 1 and 3, the lip 34 projects from the free edge 32 of the flange 30 at a right angle to the flange 30. In the

second embodiment of the invention as shown in Figures 2 and 4, the lip 34 projects from the free edge 32 of the flange 30 at an acute angle to the flange 30.

The overlapping deflector panels 26.1, 26.2 of each adjacent pair of baffles 14 are arranged to cause at least four zig-zag changes in direction of flow of the gas stream 16 passing through the frame 12. The changes in direction of flow in one direction alternate with changes in direction of flow in the opposite direction. The sum of the angular changes in direction of the flow of the gas stream 16 is in total approximately 540°, i. e. approximately 270° (180° +90°) in total in one direction and approximately 270° (180°+90°) in total in the opposite direction. There are four direction changes of the flow of the gas stream 16 including two 180° direction changes in series in opposite directions, which 180° direction changes are alongside each other, there being first and last direction changes of 90° in opposite directions. Each baffle 14 comprises an adjoining pair of elongated sheet metal plates 14.1 and 14.2 joined to each other. Each elongated plate 14.1 and 14.2 is divided by a plurality of longitudinal bends into the panels 26.1, 26.2, a said flange 30, a said lip 34, and a spine portion at 22, where the plates 14.1 and 14.2 are joined to each other. Each elongated plate 14.1 and 14.2 thus has two of the deflector panels 26.1 and 26.2 respectively forming transverse extensions of its spine portion, at opposite edges 24.1 and 24.2 thereof. The elongated plates 14.1 and 14.2, including the extensions 26.1 and 26.2 (including flanges 30 and lips 34) are identical to each other and each plate 14.1 and 14.2 is broadly c-shaped in cross-section.

The frame 12 has opposed channel-shaped end members 35, into which the ends of the baffles 14 are affixed, and opposed similarly channel-shaped side members 36 each provided on its inside with a special end plate 38 from which substitute flanges 40.1 and 40.2, being substitutes for a flange 30 (with its lip 34) and for a deflector panel 26.1 respectively, project. In the fourth embodiment of the invention as shown in Figure 4, the special end plate 38 of Figure 3 is omitted and the opposed side members 36 of the frame 12 are provided instead with a special end plate 42 providing a platform 44 connected face to face with the spine portion of an elongated plate 14.1.

In use, the filter 10 can for example be removably mounted above an oven or grill of a restaurant, in an air extraction duct, usually with its end members 35 horizontal and its side members 36 and baffles 14 vertical. The air above the oven or grill is typically mixed with droplets and/or particulate matter such as soot originating from the heated, fried or grilled foodstuffs. The droplets and/or particulate matter become entrained in the air stream extracted through the extraction duct from one side of the gas filter to its other side. During the flow of the air stream through the tortuous passageways of the filter 10 the droplets and/ or particulate matter are filtered from the air stream. Typically, the baffle will be removed to be cleaned or replaced from time to time. As illustrated in figures 1 to 3 of the drawings, air entering the frame makes a 90° left-hand turn, followed successively by a 180° right-hand turn, a 180° left-hand turn and a 90° right- hand turn, i. e. a total of 540°. These turns are expected to subject droplets and/or particles to substantial centrifugal forces, so that their inertia causes them to strike the passage walls (spines 22, deflector plates 26.1 and 26.2 of the

baffles 14, and its associated flanges 30 and lips 34), and to enter dead zones, e. g. in corners defined thereby. This causes the droplets and/or particles to adhere to the passageway walls, and or to precipitate from the air stream.

It is known to the Applicant that droplets or particulate matter entrained in a gas or air stream can be removed by causing changes in the direction of flow of the stream along tortuous passageways, the inertia of the droplets or particulate matter and centrifugal forces arising from the changes in the flow direction causing droplets or particulate matter to strike the walls of the passageways and/or to enter dead zones in the passageways, thereby to end the entrainment thereof by causing precipitation thereof or adherence thereof to the passage walls. The bigger and sharper the change in the direction of the stream, the more effective the removal of the droplets or particulate material from the stream. Filters using the above principles are known as inertial filters and usually comprise a series of baffle plates having overlapping fluid flow deflectors defining the tortuous passageways.

The tortuous passageways provide a large surface area on which droplets, condensate, and/or particles can impinge, adhere, and/or condense. The construction shown in the drawings permits good airflow and ease of cleaning of the filter. Liquid condensate on the baffles can drain down the baffles and out of weep holes (not shown) provided for drainage purposes at the bottom of the frame, thereby resisting any reduction of air flow through the filter arising from build-up of droplets, condensate, and/or particles.

The gas filters of the invention will typically be of a stainless steel or aluminium construction. Thus the baffles 14 and end plates 38,42 can be stainless steel strips or extruded aluminium profiles, as can the members 35,36 of the frame 12. The various parts of the gas filter can be connected together by welding, adhesively, or in any other suitable fashion.

The applicant believes that the invention, particularly as shown in the drawings provides an effective air filter for filtering droplets or particulate matter from a stream of air, by virtue of the radical changes in the flow direction of the stream. The applicant further believes that the invention provides a filter which is economical and practical to manufacture.