When viscous fluids are involved, laminar hydraulic conditions and heat and mass transfer intensification are conflicting phenomena. A channel geometry based on Split-And-Recombine (SAR) patterns is experimentally investigated. The principle implements the Baker's transformation and 'chaotic' structures are generated to promote heat and mass transfer. This work assesses the energy efficiency of different heat exchanger/reactors integrating these SAR patterns. The heat transfer capacity is assessed and compared with the energy consumption of each mock-up. It is sensitive to the cooling mode and to the number of SAR patterns per length unit as well. The continuous oxidation of sodium thiosulfate with hydrogen peroxide has been implemented. Conversions up to 99% are reached according to the utility fluid temperature and the residence time. Finally, the whole performances of the SAR geometries are compared to a plate-type heat exchanger/reactor with a corrugated pattern. The more viscous the fluid, the more the energy efficiency of the SAR design increases compared to the corrugated design because of the balance between advection and diffusion mechanisms. The interest in terms of energy efficiency in working with SAR heat exchanger/reactor appears from Reynolds numbers below 50. (C) 2016 Elsevier B.V. All rights reserved.