This review article explores the preparation, properties, stability, and thermal performance enhancement of nanofluids in heat transfer applications. Nanofluids, composed of nanoparticles dispersed in a base fluid, exhibit enhanced thermal and rheological properties, making them valuable for improving heat exchanger efficiency. The concentration, size, and shape of nanoparticles significantly impact the thermophysical properties and flow characteristics of nanofluids, which in turn affect heat transfer efficiency and pressure loss. High thermal conductivity nanoparticles, such as MgO, TiO₂, and ZnO, can increase heat transfer efficiency by up to 30% compared to base fluids. Stability is crucial for the usability of nanofluids, and methods like adding surfactants, ultrasonic mixing, and pH control are employed to enhance stability. The review discusses equations for determining heat transfer rate and pressure drop in double-pipe heat exchangers, emphasizing the influence of nanofluid thermal conductivity on heat transfer efficiency and viscosity on pressure loss. Increasing nanoparticle volume concentration can enhance heat transfer efficiency up to a certain point, after which it may reduce due to increased viscosity and density. The review offers insights into enhancing the thermal performance of heat transfer equipment and serves as a fundamental resource for applying nanofluids in heat transfer applications.This review article explores the preparation, properties, stability, and thermal performance enhancement of nanofluids in heat transfer applications. Nanofluids, composed of nanoparticles dispersed in a base fluid, exhibit enhanced thermal and rheological properties, making them valuable for improving heat exchanger efficiency. The concentration, size, and shape of nanoparticles significantly impact the thermophysical properties and flow characteristics of nanofluids, which in turn affect heat transfer efficiency and pressure loss. High thermal conductivity nanoparticles, such as MgO, TiO₂, and ZnO, can increase heat transfer efficiency by up to 30% compared to base fluids. Stability is crucial for the usability of nanofluids, and methods like adding surfactants, ultrasonic mixing, and pH control are employed to enhance stability. The review discusses equations for determining heat transfer rate and pressure drop in double-pipe heat exchangers, emphasizing the influence of nanofluid thermal conductivity on heat transfer efficiency and viscosity on pressure loss. Increasing nanoparticle volume concentration can enhance heat transfer efficiency up to a certain point, after which it may reduce due to increased viscosity and density. The review offers insights into enhancing the thermal performance of heat transfer equipment and serves as a fundamental resource for applying nanofluids in heat transfer applications.