A duct for separating particles suspended in a fluid, the duct comprising duct portions differing in their shape in a cross-section of the duct, each portion extending along a part of the duct's length; the duct portions comprising: at least one basic channel portion configured to allow the fluid to flow therein along a flow direction; and at least one trapping-bay portion (10, 20) disposed downstream of the basic channel portion, said trapping-bay portion having a main channel constituting a continuation of the basic channel portion and extending along a curved central line and one or more trapping bays (12, 21, 22) coextensive with the main channel along the central line; said basic channel portion being free of trapping bays and being configured to provide a pre-determined particles distribution in the fluid flow upstream of the trapping-bay portion and the trapping-bay portion being configured to maintain said particles distribution while trapping at least a part of said particles in its one or more trapping bays; the main channel and at least one of the bays are as follows in a cross-section of the trapping-bay portion taken perpendicularly to said central line: - the main channel has a basic polygonal shape defined by at least four channel walls including an outer channel wall, an inner channel wall, an upper channel wall and a lower channel wall; and - the trapping bay protrudes from at least one of the inner and outer channel walls away from the central line and has bay walls (2, 6, 7) generally parallel to the corresponding walls of the main channel oriented in the same way, the area of said bay being smaller than that of the main channel; characterized in that said duct further comprises at least one partitioned portion (30, 40) which has a main channel and a trapping bay similar to those of the trapping-bay portion and which further comprises at least one partition wall (31, 32, 46, 47, 48, 49) extending along a length of the partitioned portion and disposed between the outer or inner wall of the main channel and the central line, and configured to enable continuation of fluid flow along the main channel while preventing movement of trapped particles back to the main channel. at least one basic channel portion configured to allow the fluid to flow therein along a flow direction; and at least one trapping-bay portion (10, 20) disposed downstream of the basic channel portion, said trapping-bay portion having a main channel constituting a continuation of the basic channel portion and extending along a curved central line and one or more trapping bays (12, 21, 22) coextensive with the main channel along the central line; said basic channel portion being free of trapping bays and being configured to provide a pre-determined particles distribution in the fluid flow upstream of the trapping-bay portion and the trapping-bay portion being configured to maintain said particles distribution while trapping at least a part of said particles in its one or more trapping bays; the main channel and at least one of the bays are as follows in a cross-section of the trapping-bay portion taken perpendicularly to said central line: - the main channel has a basic polygonal shape defined by at least four channel walls including an outer channel wall, an inner channel wall, an upper channel wall and a lower channel wall; and - the trapping bay protrudes from at least one of the inner and outer channel walls away from the central line and has bay walls (2, 6, 7) generally parallel to the corresponding walls of the main channel oriented in the same way, the area of said bay being smaller than that of the main channel; - the main channel has a basic polygonal shape defined by at least four channel walls including an outer channel wall, an inner channel wall, an upper channel wall and a lower channel wall; and - the trapping bay protrudes from at least one of the inner and outer channel walls away from the central line and has bay walls (2, 6, 7) generally parallel to the corresponding walls of the main channel oriented in the same way, the area of said bay being smaller than that of the main channel;