In this study, numerical simulations were performed for laminar/turbulent flow and heat transfer of nano-fluids in wavy channels as a main part of the plate heat exchangers. The Reynolds numbers based on the inflow velocity and the height of channel were chosen in the range of 200-1600. The numerical results were compared with the reported numerical results and good agreement was obtained. A grid study was also performed with eight different mesh sizes to find the appropriate grid. In order to improve the performance of the plate heat exchangers, two passive heat transfer augmentation methods were employed including the corrugated (wavy) walls and addin g nanoparticles to the base fluid. In the first augmentation method, the walls of channel are corrugated and the effect of channel geometric parameters including wave amplitude, wave length, different phase between the upper and lower wavy walls, and wave shape on the characteristics of the flow field and heat transfer was investigated. The scaled wave amplitude and wave length considered for this parameter study are in the ranges of 0.1-0.5 and 1.1-4.4, respectively. The angles of 0°, 90° and 180° are considered for different phase between the upper and lower wavy walls and the Sine, Arc, Triangle and TetraPak wave shapes are employed to corrugate the walls of channel. To study the results obtained, Nusselt number, pressure drop, friction factor and also a thermal parameter (the relation between the key parameters of the velocity, friction factor f , and thermal boundary layers, Nusselt numbers) were provided to evaluate the optimized parameters of the wavy channel. The results show that suitable scaled wave amplitude, wave length and different phase between the upper and lower wavy walls of optimized wavy channel are 0.4, 2.2 and 0° respectively. Also results show that the wavy channel with TetraPak wave shape has the best performance in comparison with the other shapes considered. In the second augmentation method, the effect of adding the nanoparticles of Al 2 O 3 , CuO and TiO 2 to water, as the base fluid, with 1-5% volume fraction, on the heat transfer enhancement of the optimized wavy channel was studied to choose the most appropriate nanofluid. The results show that the heat transfer and pressure drop increase as the Reynolds number, the wave amplitude and the nanoparticle volume fraction increase. The heat transfer rate of base fluid flow in the optimized wavy channel is 2.49 times more than the flow in the simple channel (without wave). Also it was found that the water/CuO nanofluid has the best performance between the nanofluids considered in this study where the heat transfer rate of flow of water/CuO nanofluid with 5% volume fraction, in the optimized wavy channel increased 23% compared with the base fluid flow. Keywords Wavy channel, Nano-fluids, Heat transfer enhancement, Thermal performance parameter, Numerical simulation, plate heat exchangers