Preparation and Stability Study of Graphene/R141b Nanofluids for Heat Transfer Enhancement

The instability of nanofluids leads to particle agglomeration and sedimentation, which clog the heat transfer channels and deteriorate the overall performance of heat exchangers. Accordingly, preparing uniformly dispersed and structurally stable nanofluids serves as a fundamental prerequisite for their practical engineering applications. In this study, refrigerant R141b was selected as the base fluid, and graphene/R141b nanofluids were prepared via a two-step method assisted by ultrasonic oscillation. The effects of ultrasonic oscillation time, dosage of surfactant, and nanoparticle mass concentration on the stability of graphene/R141b were systematically investigated, and zeta potential, DLS particle size, Raman and XRD analysis were used to evaluate the stability of graphene/R141b. The experimental results demonstrate that ultrasonic oscillation time and nanoparticle mass concentration both exert significant influences on the stability of graphene/R141b nanofluid. The SDS surfactant can effectively improve the stability of the prepared graphene/R141b nanofluid. In conclusion, under the conditions of adding SDS surfactant and carrying out ultrasonic oscillation within 120–150 min, graphene/R141b with a mass concentration ranging from 0.05% to 0.4% exhibits satisfactory stability, while excessively prolonged sonication (180 min) reduces the stability of the nanofluid, which provides a promising candidate for future validation of heat-transfer-enhancement performance in heat-exchanger applications.