In this study, a wavy heat sink is roughened with rectangular ribs. It is expected that the proposed idea has a great impact on the hydrothermal performance of wavy heat sink. As the second heat transfer enhancement method, Al2O3/water nanofluids are used in the wavy heat sink. The tested parameters are waviness aspect ratio, rib arrangement, rib width, nanoparticles weight fraction, and Reynolds number. The numerical results are well validated with data obtained from the experimental part. The maximum deviation is not more than 10%. The results display higher values of heat transfer coefficient and pressure drop for the ribbed wavy heat sinks compared to the smooth ones. In the studied ranges, the heat transfer coefficient and pressure drop for the ribbed wavy heat sinks are 4–128% and 8–185% higher than those for the smooth wavy sinks, leading to a hydrothermal performance index between 0.93 and 1.75. The highest performance index is obtained for a ribbed wavy heat sink with corner arrangement, waviness aspect ratio of 0.1, rib width of 0.3 mm, and Reynolds number of 900. It is also found that the nanofluids propose higher heat transfer coefficient and pressure drop in comparison with water, and their values increase as the weight fraction goes up.

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