Advances and Challenges in Hybrid Nanofluid Applications for Compact Heat Exchangers: A Critical Review

Abstract: Hybrid nanofluids—suspensions containing two or more types of nanoparticles—have emerged as powerful alternatives to conventional coolants in compact and micro heat exchanger applications. By combining the advantages of different nanoparticles within a base fluid, hybrid nanofluids significantly enhance thermal conductivity, convective heat transfer, and overall heat exchanger efficiency. This review critically analyzes recent advances, mechanisms, and challenges associated with their application in thermal systems. It explores key performance factors such as nanoparticle type, concentration, fluid viscosity, and operating temperature, highlighting how each influences thermal performance. Design considerations for integrating hybrid nanofluids into compact heat exchangers are also addressed, including flow behavior under laminar and turbulent regimes, stability issues, and nanoparticle sedimentation. Despite demonstrated performance gains, major obstacles persist—most notably cost-effectiveness, dispersion stability, and large-scale manufacturing feasibility. Emerging solutions, including AI-based thermal optimization, one-pot synthesis techniques, and integration with smart sensors, are discussed as pathways to industrial scalability. Furthermore, regulatory, environmental, and sustainability considerations are evaluated, emphasizing the need for eco-friendly materials and lifecycle analysis. Overall, hybrid nanofluids present a promising frontier in thermal management, but realizing their full industrial potential will require multidisciplinary collaboration and innovative design strategies.