Microchannel heat exchangers and chemical reactors have extensive applications in process industries, especially in electronics cooling, air conditioning, and chemical industries. Microchannel devices provide enhanced heat and mass transfer characteristics by controlled flow conditions and high surface-to-volume ratios. The different designs of microchannels are based on planar structures from various fabrication technologies. In the present study a novel three-dimensional micro-structured device, the micro coiled flow inverter (MCFI) with 0.38-0.8 mm internal diameter, has been numerically investigated as a micro heat exchanger. In comparison micro helical coil (MHC) and straight tube of same heat transfer area (d(t) = 0.5 mm, A = 3.9 x 10(-4) m(2)) has been studied, too. The Reynolds and Prandtl numbers are varied from 25 to 1200 and 0.74 to 150, respectively. The MCFI offers a four-fold heat transfer enhancement as compared to straight tube of same heat transfer area at N-Re = 1200 and N-Pr = 7. Furthermore, the heat transfer coefficient in MCFI augments by 38.5% as compared to MHC, with slight increase (5-16%) in friction factor. New design correlations are developed for Nusselt number and friction factor in MCFI. The MCFI device offers 1.15-1.7-folds higher thermal merit as compared to micro straight tube. (C) 2014 Elsevier B.V. All rights reserved.