All-around review on applying passive strategies to improve heat exchanger performance using inserts and turbulators applied in thermal storage

Improving the performance and efficiency of heat exchangers has led researchers to adopt various approaches related to heat transfer enhancement. Turbulators represent a widely used technique to create turbulent motion and enhance heat transfer. Utilizing nanofluids is another method which aims mainly at improving the conductivity of the working fluid. Recently, numerous studies have focused on improving heat exchanger performance combining the two methods, nanofluids and turbulators. The present paper aims to provide a comprehensive review on applying various passive strategies to improve heat exchanger performance using nanofluids. The objective is to critically evaluate and synthesize existing research on the use of nanofluids and turbulators as passive methods to enhance heat exchanger performance, identifying key trends, gaps, and opportunities for further research. The influence of different types of inserts in heat exchangers is reviewed. The advantages of nanofluids over conventional fluids are presented and discussed. The combined impacts of including both inserts and nanofluids on the improvement of heat exchanger performance is then addressed. The findings from the literature indicate that these passive methods significantly enhance heat exchanger performance through the combined effects of increased thermal conductivity from nanofluids and intensified mixing due to turbulence induced by inserts. Moreover, the review highlights that the optimal combination of nanofluids and turbulators can lead to substantial improvements in heat transfer efficiency, energy savings, and overall system performance. Major recommendations include further experimental studies to optimize the geometrical configurations of inserts and the concentration of nanofluids, as well as the development of predictive models to better understand and maximize these interactive effects. A comprehensive summary of these outcomes is presented and discussed throughout the present literature review and some directions for future research.