Heat transfer with the internal flow of the pipes and channels has vast industrial applications, among which heat exchangers are highly important. Heat exchangers are generally a type of equipment that exchange the heat between two fluids without their physical contact. Increasing heat transfer in the heat exchangers can effectively save energy and material. This can be only achieved by designing lighter and more efficient heat exchangers. So far, plenty of methods have been proposed to improve the heat transfer in the heat exchangers. Most of these methods are based on disordering and exchanging the boundary layer, which is close to the heat transfer surface, with the central stream to generate new boundary layer. Using wavy pipes is one of the pathways employed to increase the heat transfer in the heat exchangers. Sinusoidal tubes were found to be considerably efficient for transferring heat in heat exchangers, condensers, and evaporators. In this study, heat transfer and pressure drop in the sinusoidal tubes with different profiles were investigated. Also, the most effective profile, which could provide the maximum heat transfer and the minimum pressure drop, was finally determined. In the first section, two types of double-pipe heat exchangers were simulated. The first one had a simple internal tube while the second one possessed a wavy symmetric axial one. Based on the simulations, a lower total heat transfer coefficient and a higher pressure drop were observed in wavy double-pipe heat exchangers compared to simple ones. It can be therefore concluded that wavy exchangers do not necessarily have better heat transfer features than simple ones. The effect of slope and frequency of the internal tube on the heat transfer and pressure drop was consequently explored in wavy double-pipe exchangers. In order to achieve that the candidate profile was investigated at a constant total heat transfer area and the Reynolds number was changed with two methods. The optimum geometry from heat transfer perspective was then determined by investigating the trend of total heat transfer coefficient and pressure drop. In the first method, a couple of geometry with similar heat transfer area was selected for the internal tube. The analysis and comparison of these geometries exhibit that the pressure drop decreases with decreasing the slope of the wavy tube. Trend of the total heat transfer is inconsistent with the slope changes though. It primarily decreases with enhancing the slope and then at a certain point it starts to increase. In the second method, optimization was performed using software called “Design Exploration”. Optimization results indicate that the slope of the optimum geometry increases with enhancing the Reynolds number. Consequently, wavy tubes with increasing Reynolds number seem to be highly applicable. Keywords : Heat exchangers, wavy pipe, straight pipe, heat transfer coefficient, pressure drop, optimization