A chaotic convection effect mixing exchanger comprising a duct consisting of one or more members (1, 1?1, 12,..., 1n¿) arranged end to end and containing a flowing fluid to be mixed and/or subjected to a heat flow. A portion of said duct is made of a chaos-generating member including at least two curved portions defining two planes of curvature defined as the planes passing through the centre of the arc of the circle defining the curve and the tangent to said curved portion, said planes of curvature being orthogonal. Said exchanger may be used with viscous and fragile fluids.