A duct for directing a flow of exhaust gases, the duct comprising: - a flow mixer having an inlet portion adapted to receive the flow of exhaust gases and an outlet portion adapted to discharge the flow of exhaust gases; - a plurality of flutes, defined at the outlet portion, the plurality of flutes including a first flute (206, 221) and a second flute (208, 223), spaced from the first flute, the first flute having a first peak, a first trough, a first height dimension, and a first width dimension, generally perpendicular to the first height dimension, the second flute having a second peak, a second trough, a second height dimension, and a second width dimension generally perpendicular to the second height dimension; and - at least two flute ties, wherein a first flute tie is coupled to the first trough and wherein a second flute tie is coupled to the second trough; and - at least one retainer, directly attached to the first trough and the second trough of the flutes in addition to or instead of the at least two flute ties and extending generally parallel to at least one of the first width dimension and the second width dimension; - wherein: - the at least one retainer is coupled to the flute tie; and - the at least one retainer is configured to restrain relative movement between the first flute and the second flute and relative movement among the first flute, the second flute, and at least one of the inlet portion and the outlet portion during the flow of exhaust gases through the duct. - a flow mixer having an inlet portion adapted to receive the flow of exhaust gases and an outlet portion adapted to discharge the flow of exhaust gases; - a plurality of flutes, defined at the outlet portion, the plurality of flutes including a first flute (206, 221) and a second flute (208, 223), spaced from the first flute, the first flute having a first peak, a first trough, a first height dimension, and a first width dimension, generally perpendicular to the first height dimension, the second flute having a second peak, a second trough, a second height dimension, and a second width dimension generally perpendicular to the second height dimension; and - at least two flute ties, wherein a first flute tie is coupled to the first trough and wherein a second flute tie is coupled to the second trough; and - at least one retainer, directly attached to the first trough and the second trough of the flutes in addition to or instead of the at least two flute ties and extending generally parallel to at least one of the first width dimension and the second width dimension; - wherein: - the at least one retainer is coupled to the flute tie; and - the at least one retainer is configured to restrain relative movement between the first flute and the second flute and relative movement among the first flute, the second flute, and at least one of the inlet portion and the outlet portion during the flow of exhaust gases through the duct. - the at least one retainer is coupled to the flute tie; and - the at least one retainer is configured to restrain relative movement between the first flute and the second flute and relative movement among the first flute, the second flute, and at least one of the inlet portion and the outlet portion during the flow of exhaust gases through the duct.