An overview on the thermal performance of dual-tube heat exchangers in the presence of nanofluids

In this review article, the thermal performance of dual-tube heat exchangers with smooth walls is investigated in the presence of nanofluids. Important challenges in industrial and engineering processes, such as the failure of thermal devices to respond to higher capacities, conservation, saving, and optimization of energy, have been discussed in recent years. Heat exchangers are one of the types of thermal devices that are used in a wide range of engineering and industrial applications. The use of nanofluids is one of the most effective ways to enhance the thermal conductivity of heat exchangers in the industry. In this research, the types of heat exchangers are first introduced. Then, the methods of heat transfer enhancement (active, passive, and combined) are discussed. The introduction and method of preparing nanofluids are discussed, and finally, the studies on dual-tube heat exchangers in the presence of nanofluids are described. This review article examines previous studies on dual-tube heat exchangers and the use of nanofluids in them (216 references and 73 journals). The purpose of this article is to familiarize the readers with the types of heat exchangers and to understand the mechanisms of heat transfer in the context of using nanofluids in smooth dual-tube heat exchangers. It can be concluded that nanofluids are a very good substitute for other fluids because the use of nanofluids in heat exchangers leads to an improvement in their performance, a reduction in their energy consumption and costs, a decrease in their volume, a reduction in environmental effects, etc. Eventually, the challenges in the use of nanofluids in flat dual-tube heat exchangers are discussed. The most important ones include the economic costs of using nanofluids, deposition and accumulation of nanoparticles over time, stability of nanofluids, and lack of standardization among various researches and evaluations.