A heat exchanger including a passageway having an internal passage adapted to form a first flow path, and an array of conduits having internal passages that collectively form a second flow path. The conduits extend through the internal passage of the passageway, and a first conduit of the array is provided with a lower total heat exchange surface area per unit volume therein than a second conduit of the array. A method of performing chemical processes is provided that includes providing a catalyst bed within the second flow path, and minimizing a temperature differential between a maximum temperature of a fluid in the second flow path and a minimum temperature of the fluid in the second flow path.