Numerical study of energy performance of nanofluids used in secondary loops of refrigeration systems

• Modelling of the energy performance of secondary loops of refrigeration system using nanofluids.
• Energy performance evaluated considering a ratio of heat transfer enhancement and pumping power losses.
• Simulations for various types of nanoparticles, volume fraction and fluid flow conditions.
• Very good energy performance according to the nanoparticles type and volume fraction.
• Model validated using classical existing correlations.

A mathematical model was developed in order to predict the energy performances of refrigerating systems using nanofluids for application in refrigeration plants of cold chain. The model was based on a combination of the Effectiveness-Number of Transfer Units method and classical heat transfer and fluid hydrodynamic correlations. The practical benefit of using nanofluids was evaluated through a global energy approach using the Performance Evaluation Criterion (PEC) which compared the heat flow rate transferred to the required pumping power in the refrigeration system. Simulations were done for a tubular heat exchanger in laminar and turbulent regimes, for various types of nanoparticles (Al2O3, Co, CuO, Fe, SiO2 and TiO2) and a wide range of volume fraction. It was shown that heat transfer coefficients significantly increased with the increase of nanoparticles concentration for laminar and turbulent flow regimes. However, the pressure drop which is directly related to the pumping power also increased with the increase of nanoparticles concentration whatever the flow regime. Calculation of PEC has shown that the energy performance is strongly dependent on the type of nanoparticles: some of the studied nanofluids (Al2O3, SiO2, TiO2) were clearly less efficient than the base fluid while the others (Co, CuO, Fe) had a favourable energy performance with PEC values reaching 80%. The model was validated using published data and it was shown that classical existing correlations success to represent heat transfer and pressure loss behaviours of nanofluids in heat exchangers, when the effective thermal and physical properties are taken into account. This study showed the great potential of nanofluids to improve cold chain efficiency by reducing energy consumption, emissions and global warming impact.