A method and a reactor made by a method for increasing heat transfer from a heat source outside a vessel to the fluid inside the vessel are characterized by expanding a structure within the vessel toward the inner vessel surface so as to decrease the spacing between the structure and the vessel wall. The structure may be any of the various so-called structured packings, for example, ceramic honeycombs, metal honeycombs, plate stacks, and the like. The structure may comprise catalyst. The reactor provides high activity, low pressure drop, and high heat transfer. The reactor may be especially suitable for steam hydrocarbon reforming.