In the present study, experimental efforts have been performed to explore the forced convection heat transfer efficacy of using water-based suspensions of alumina nanoparticles (nanofluid) and microencapsulated phase change material (MEPCM) particles (PCM suspension) to replace the pure water as the working fluids in a minichannel heat sink (Mini-CHS). The heat sink fabricated from copper consists of 10 rectangular minichannels, each of which has a width of 1 mm, a depth of 1.5 mm, a length of 50 mm, having a hydraulic diameter of 1.2 mm. The minichannel heat sink was heated with a uniform base heat flux with the Reynolds numbers ranged from 133 to 1515. The mass fractions of the nanoparticles and MEPCM particles dispersed in the water-based suspensions were in the ranges of 2-10 wt%, respectively. Experimental results obtained reveal that the heat dissipation effectiveness of the nanofluid and PCM suspension depends significantly on their flow rates through the heat sink. For the nanofluid, the highest enhancement of 57% in the averaged heat transfer coefficient was detected under the highest flow rate; while for the PCM suspension, the highest enhancement of 51% under the lowest flow rate. For the hybrid water-based suspensions, the effect of simultaneous dispersion of the nanoparticles and MEPCM particles in water appears to be supplementary with added benefit of simultaneous increases in the effective thermal conductivity and specific heat such that the heat transfer effectiveness could be further increased up to 56% with little dependence on the flow rate. (C) 2013 Elsevier Ltd. All rights reserved.