In this study, thermo-hydraulic characteristics of arrays of circular and diamond shaped cross-sections in periodic flow are investigated numerically. The main purpose of this study is to configure diamond shaped cross-sections in order to obtain better thermal performance compared to circular shaped cross-section. The optimization frameworks are constructed by using multi-objective genetic algorithm (MOGA) for both circular and diamond shaped cross-sections to obtain maximum heat transfer and minimum pressure drop while keeping the mass flow rate constant. The study can be divided into two parts: Firstly, an optimization study is carried out to achieve an optimum design for the circular type. Later, a new optimization scheme is constructed where the optimum design of circular type's heat transfer and pressure drop values are given as constraints. Thus, the optimization algorithm seeks better thermal performances with respect to the circular one. Moreover, optimum designs are illustrated graphically and given in the tabular form. Compared to circular geometries, it is found that the average Nusselt number of diamond shaped geometry can be increased by 10.11%, while pressure drop and volume of diamond shaped geometries are reduced by 11.90% and 52.76%, respectively.