In this study, the effect of three methods of heat transfer enchancment, including using wavy wall, hydrophobic surface, and nano-fluid on macro/micro channel have been investigated. The fluid flow and the convectional heat transfer were assessed assuming a 2D steady flow of nano-fluid with constant and single phase (homogenous) properties. All numerical simulations were conducted using FLUENT software. In the results section, fluid flow and heat transfer of a macro-channel have initially been simulated and the average Nusselt number, pressure loss, and performance coefficient have been calculated for two working fluids, namely water and Alumina nano-fluid. Slip and no slip boundary conditions were also considered for the problem.Simulations were conducted for volume fractions of 1, 3, and 5 and in the Reynolds number range of 100-5000 with slip lengths equal to 25, 50, and 100 microns. In the subsequent investigation of fluid flow and heat transfer, pressure loss and heat performance coefficient were simulated in a microchannel containing water and Alumina nanofluid with volume fractions of 1, 3, and 5. To this aim, four microchannels with heights of 60, 100, 150, and 200 microns were selected and the assessments were all carried out in the Reynolds number range of 20-150 and slip lengths equal to 2.5, 5, and 10 percent channel height. Finally, the impact of the wavy wall parameters (namely the amplitude, phase shift, and the wavelength of the wavy wall) on heat transfer, pressure loss, and micro-channel performance coefficient was investigated and the channel with best performance was introduced. My results for macro-channels show that imposing slip and temperature jump boundary conditions increase both Nusselt number and heat transfer while it tends to decrease pressure loss. Moreover, using a nano-fluid increases heat transfer and pressure loss. In the micro-channel results section, it is observed that reducing the channel size brings about an increase in both heat transfer and pressure loss. Also, the maximum Nusselt number was obtained in a microchannel with a phase shift of 180 degrees, a non-dimensional wavelength of 4.4, and a non-dimensional amplitude equal to 0.5. Keywords: Numerical simulation, micro-channel, wall curvature, hydrophobic surfaces, nano-fluid, heat transfer enhancement, performance coefficient