A Comprehensive Review on Performance Enhancement of Vapor Compression Refrigeration Systems Using Nanoparticle-Enhanced Refrigerants and Capillary Tube Optimization

Vapor Compression Refrigeration Systems (VCRS) are widely used in domestic, commercial, and industrial applications due to their reliability and compact design. However, increasing energy demand and environmental concerns associated with conventional refrigerants have driven researchers to explore advanced techniques for improving system efficiency. One promising approach involves the use of nanoparticle-enhanced refrigerants (nano-refrigerants) and optimization of expansion devices such as capillary tubes. This review paper presents a comprehensive analysis of recent research on the application of metal and metal-oxide nanoparticles, including CuO, SiO₂, Al₂O₃, ZnO, and MnO₂, dispersed in conventional refrigerants such as R134a. The influence of nanoparticle type, concentration, stability, and capillary tube diameter on system performance parameters—such as coefficient of performance (COP), heat transfer rate, compressor power consumption, and pressure characteristics—is critically reviewed. The study highlights performance improvements reported in experimental and numerical investigations and discusses the challenges related to nanoparticle dispersion, system compatibility, and long-term reliability. Future research directions for achieving sustainable and high-efficiency refrigeration systems are also outlined.