Improvement in Energy Performance of Tubular Heat Exchangers Using Nanofluids: A Review

Both mono and hybrid nanofluids, the engineered colloidal mixture made of the base fluid and nanoparticles, have shown many interesting properties and become a high potential nextgeneration heat transfer fluids in various heat exchangers for engineering applications. The present review focuses on improving the performance of tubular heat exchangers by using nanofluids. For this, the present review briefly summarizes the preparation, characterization and thermophysical properties (thermal conductivity, viscosity, specific heat capacity and density) of mono and hybrid nanofluids. Research works on heat transfer and pressure drop characteristics of nanofluids in the double tube and shell-tube heat exchangers with both straight and coiled tubes, and various engineering applications (power generation, refrigeration and air-conditioning, renewable energy, domestic cooling or heating, etc.) are well-grouped and thoroughly discussed. Physical mechanisms for the heat transfer enhancement using nanofluids are explored as well. Most of the studies reveal that there are significant enhancements in the heat transfer process and in the effectiveness of both straight and coiled tube heat exchangers with a slight increase in pressure drop using nanofluids. Hence, there is an excellent opportunity to use nanofluids in tubular heat exchangers; however, high cost (high payback period) and stability are the main challenges for practical implementation. Finally, some useful recommendations are also provided.