Abstract: A tubular reactor passes a flowing stream of reactants through a plurality of mixing devices that simultaneously provide indirect heat exchange of the reactants to improve the uniformity of reactant temperatures and concentrations. The mixing devices provide intimate mixing by passing the reactants through a plurality of narrow channels defined by parallel plate elements that channel a heat exchange fluid on their opposite side to provide the simultaneous indirect heat exchange. The heat exchange channels can have any desired degree of mixing intensity by providing irregularities in the channel walls or flow path that supply the desired degree of fluid shear. Preferably the mixing reactor provides a series of mixing devices with heat exchange along the length of the conduit flow path with space between the devices for remixing of the fluid reactants.