An exhaust treatment device comprising: an outer housing including opposite first and second end walls (64, 66) and a length that extends between the first and second end walls (64, 66), the outer housing also including a side wall that extends along the length from the first end wall to the second end wall, the outer housing defining an interior space; a divider wall within the interior space of the outer housing, the divider wall being positioned at an intermediate location along the length of the outer housing, the divider wall separating the interior space of the outer housing into a first region and a second region, the first region being defined between the divider wall and the first end wall and the second region being defined between the divider wall and the second end wall; a device inlet that is in fluid communication with the first region of the interior space; a device outlet that is in fluid communication with the second region of the interior space; an exhaust treatment substrate mounted in the second region of the interior space; an exhaust treatment and mixing assembly including: a swirl chamber positioned adjacent to the first end wall of the outer housing; a mixing passage defined by an inner conduit that extends along the length of the outer housing, the mixing passage providing fluid communication between the swirl chamber and the second region of the interior space; an exhaust passage that surrounds the inner conduit, the exhaust passage being configured to direct exhaust flow into the swirl chamber; a swirl structure for swirling the exhaust flow directed from the exhaust passage into the swirl chamber; and a dispenser mounting location provided at the first end wall of the outer housing for mounting a dispenser used for dispensing a reactant into the swirl chamber. an outer housing including opposite first and second end walls (64, 66) and a length that extends between the first and second end walls (64, 66), the outer housing also including a side wall that extends along the length from the first end wall to the second end wall, the outer housing defining an interior space; a divider wall within the interior space of the outer housing, the divider wall being positioned at an intermediate location along the length of the outer housing, the divider wall separating the interior space of the outer housing into a first region and a second region, the first region being defined between the divider wall and the first end wall and the second region being defined between the divider wall and the second end wall; a device inlet that is in fluid communication with the first region of the interior space; a device outlet that is in fluid communication with the second region of the interior space; an exhaust treatment substrate mounted in the second region of the interior space; an exhaust treatment and mixing assembly including: a swirl chamber positioned adjacent to the first end wall of the outer housing; a mixing passage defined by an inner conduit that extends along the length of the outer housing, the mixing passage providing fluid communication between the swirl chamber and the second region of the interior space; an exhaust passage that surrounds the inner conduit, the exhaust passage being configured to direct exhaust flow into the swirl chamber; a swirl structure for swirling the exhaust flow directed from the exhaust passage into the swirl chamber; and a swirl chamber positioned adjacent to the first end wall of the outer housing; a mixing passage defined by an inner conduit that extends along the length of the outer housing, the mixing passage providing fluid communication between the swirl chamber and the second region of the interior space; an exhaust passage that surrounds the inner conduit, the exhaust passage being configured to direct exhaust flow into the swirl chamber; a swirl structure for swirling the exhaust flow directed from the exhaust passage into the swirl chamber; and a dispenser mounting location provided at the first end wall of the outer housing for mounting a dispenser used for dispensing a reactant into the swirl chamber.