Renewable energy sources play a crucial role in securing sustainable energy with lower emissions. Among numerous sources of energy, ocean thermal energy conversion (OTEC) plays an integral role in the utilization of clean energy. It takes advantage of the temperature gradient between deep seawater and surface seawater. This makes it indispensable to improve and optimize the thermal efficiency of the heat exchangers employed in these systems. Numerous efforts have been made to explore the most favorable geometry for both channels and tubes in the thermo-plates and various techniques for the enhancement of heat transfer. Earlier investigations have shown that contracted-expanded type of channels has been broadly taken into consideration. Numerous investigations are using the concepts of the flow of fluids and heat transmission in parallel plate-type channels with periodical grooves. The numerical solver proposed in this work is validated using results from the previous literature and found to be similar. The grid independence study is also carried out to ensure a solution that is independent of mesh sizes. A finite volume-based computation was performed using the SIMPLE algorithm along with the flow assumption of two-dimensional, steady, laminar, and incompressible. The work aims to investigate heat and fluid flow parameters through periodically grooved channels due to geometric parameters like the concave–convex ratio. The Reynolds number is varied within a range of 50–250 in the study for different geometric attributes for analysis. The concave–convex ratio (R) is taken to be 0.5, 1, and 2. This parameter is indicative of the grooved region in every periodic length. This study shows how fluid flow phenomena and heat transmission characteristics are strongly influenced by the concave–convex ratio. A correlation among the Reynolds number, Nusselt number, and the concave–convex ratio is proposed which can be used instead of simulation.