Performance Enhancement of Heat Exchangers Using Nanofluids: A Review

In this review, the use of nanofluids as advanced working fluids is examined for improving the thermal-hydraulic performance of heat exchangers. Particular attention is given to compact, microchannel, plate, shell-and-tube, and coil-based configurations, where higher heat transfer rates must be obtained without excessive pressure drop. Experimental results, numerical simulations, and theoretical studies are examined to identify the main mechanisms responsible for heat transfer enhancement in nanofluid-based heat exchangers. The reported studies show that the improvement is not solely due to increased thermal conductivity. Changes in the thermal boundary layer, particle-fluid interaction, and microscale mixing also play important roles in the heat transfer process. The analysis indicates that nanoparticle material, particle size, particle shape, and concentration have a direct effect on convective heat transfer, pressure drop, and overall thermal-hydraulic performance. Hybrid nanofluids showed higher heat transfer performance than mono nanofluids due to particle interaction, although the increase in frictional loss, viscosity, and pumping power reduced their overall thermal-hydraulic benefit. The use of nanofluids in compact, microchannel, plate, and coil-based heat exchangers further improves thermal performance by promoting fluid mixing and disturbing the thermal boundary layer. The results also show that the practical application of nanofluids is strongly affected by suspension stability, fouling, erosion, corrosion, preparation cost, and the absence of uniform performance evaluation methods. Nanofluids can enhance the thermal performance of heat exchangers, but the benefits depend on balancing fluid composition, operational factors, design, hydraulic costs, and thermodynamic efficiency.