In this research, pure water and recycled nanofluids (RNF) are utilized as heat transfer fluids in the thermoelectric cooling (TEC) system, and the effects of these fluids on the cooling performance are experimentally examined. In order to prevent nanofluid sedimentation and enhance stability, a surface modification process on Fe<sub>3</sub>O<sub>4</sub> particles is performed. With modified Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>-mix-(CH<sub>2</sub>)<sub>3</sub>Cl@Imidazol nanoparticles, water-based nanofluids are prepared at a constant volumetric concentration. This nanofluid is used in a TEC system and recycled. The sonication time is chosen as the experimental parameter in the preparation of RNF. The RNF are subjected to ultrasonication at different time periods, including 3.5, 7, and 14 hours. The temperature drops inside the cooling chamber, coefficient of performance (COP) value of the TEC system, and dimensionless numbers, including Reynolds and Nusselt of nanofluids, are evaluated and discussed in detail. It is determined that the performance of the TEC system can be increased significantly with the usage of nanofluids. Although some deterioration in heat transfer properties is observed for the RNF, these fluids provide a significant improvement in cooling performance compared to pure water. Increasing the nanofluid flow rate increases the cooling chamber performance up to a certain level. Moreover, a significant increase in TEC chamber performance is also achieved by decreasing the temperature of the water bath in the system.