An aftertreatment system may include an exhaust gas passageway and a mixer assembly. The exhaust gas passageway may receive exhaust gas from an engine. The mixer assembly is disposed within the exhaust gas passageway and may include an upstream baffle, a downstream baffle, and a tube extending between and connected to the upstream and downstream baffles. The tube may include an inner surface defining a first flow path through the mixer assembly. The upstream and downstream baffles may be attached to each other, the tube and the exhaust gas passageway. The upstream and downstream baffles may cooperate to define a second flow path through the mixer assembly. The second flow path may extend in a rotational direction around an outer surface of the tube.