A hydrodynamic separator configured to separate a liquid having dispersed particles having a diameter (a), comprising: a substrate (110; 210; 310); a liquid channel (120; 220; 320) defined by the substrate (110; 210; 310), the liquid channel (120; 220; 320) being configured to receive a liquid having a Reynolds number (Re) within the channel, the liquid channel (120; 220; 320) having an inlet (122; 222; 322) and an outlet (124; 224; 324), wherein: the liquid channel (120; 220; 320) is generally curved, has a curved inner wall defining an inner radius (R C ) and a curved outer wall defining an outer radius, wherein the inner radius (R C ) is constant from the inlet (122; 222; 322) to the outlet (124; 224; 324), the liquid channel (120; 220; 320) has a liquid channel length (L D ) along the curved inner wall , the liquid channel (120; 220; 320) has a rectangular cross-section along the liquid channel length, and the rectangular cross-section has a channel width (w) between the inner wall and the outer wall , where the channel (120; 220; 320) has a tapered region where the channel width (w) tapers between the inlet (122; 222; 322) and the outlet (124; 224; 324), further wherein the channel width (w) increases towards the outlet (124; 224; 324). a substrate (110; 210; 310); a liquid channel (120; 220; 320) defined by the substrate (110; 210; 310), the liquid channel (120; 220; 320) being configured to receive a liquid having a Reynolds number (Re) within the channel, the liquid channel (120; 220; 320) having an inlet (122; 222; 322) and an outlet (124; 224; 324), wherein: the liquid channel (120; 220; 320) is generally curved, has a curved inner wall defining an inner radius (R C ) and a curved outer wall defining an outer radius, wherein the inner radius (R C ) is constant from the inlet (122; 222; 322) to the outlet (124; 224; 324), the liquid channel (120; 220; 320) has a liquid channel length (L D ) along the curved inner wall , the liquid channel (120; 220; 320) has a rectangular cross-section along the liquid channel length, and the rectangular cross-section has a channel width (w) between the inner wall and the outer wall , where the channel (120; 220; 320) has a tapered region where the channel width (w) tapers between the inlet (122; 222; 322) and the outlet (124; 224; 324), further wherein the channel width (w) increases towards the outlet (124; 224; 324). the liquid channel (120; 220; 320) is generally curved, has a curved inner wall defining an inner radius (R C ) and a curved outer wall defining an outer radius, wherein the inner radius (R C ) is constant from the inlet (122; 222; 322) to the outlet (124; 224; 324), the liquid channel (120; 220; 320) has a liquid channel length (L D ) along the curved inner wall , the liquid channel (120; 220; 320) has a rectangular cross-section along the liquid channel length, and the rectangular cross-section has a channel width (w) between the inner wall and the outer wall , where the channel (120; 220; 320) has a tapered region where the channel width (w) tapers between the inlet (122; 222; 322) and the outlet (124; 224; 324), further wherein the channel width (w) increases towards the outlet (124; 224; 324). <EOS>