Surface imperfections such as pin fins and surface roughness in minichannels have proven to increase thermal performance. The use of nanofluid as the working medium in minichannels has also shown significant increase in thermal performance. To determine the heat removal ability of both multi-walled carbon nanotubes (MWNTs) grown in a silicon minichannel and the use of Al2O3/H2O nanofluid at a volume concentration of 0.01% as the working medium, an experimental investigation was conducted. Minichannel devices containing two different MWNT structures - one fully coated surface of MWNTs and the other with a 6 x 12 (rows, columns) circular staggered fin array of MWNTs - were tested and compared to a minichannel device with no MWNTs. The performance is evaluated based on a constant heat flux applied to the silicon base versus the corresponding silicon base temperature. The experiment was performed at a volumetric flow rate of 80 mL/min for a range of power inputs and was conducted multiple times to understand the extended performance after nanoparticles sediment on the channel surface. It was observed that the sedimentation of Al2O3 nanoparticles on a channel surface with no MWNTs increases the surface roughness and the thermal performance. When using both nanofluid and the MWNTs structured surface, the thermal performance had little to no increase for all experimental runs compared to the experiment with using deionized water. With the nanoparticle residue on the initial bare channel surface, the experiment was then run using deionized water and improved thermal performance was achieved. (C) 2013 Elsevier Ltd. All rights reserved.