Review on nanofluid preparation, stability analysis, and heat enhancement by nanofluids in pipe with passive elements

Heat enhancement applications such as heat exchangers, heating, ventilation, and air-conditioning systems, nuclear and chemical plants, etc., help to increase the thermal rating and performance of the system in addition to decreasing the cost, and size of the system. The heat exchanger design is very complex compared to other designing procedures, which requires proper heat transfer value and consideration of pressure drop, performance of the system, reliability, and durability of the system. The major drawback of the conventional fluid is its low thermal conductivity, which creates a negative impact on heat transfer, the nanofluids need to overcome this limitation. This paper reviews the preparation of nanofluid, stability analysis of nanoparticles, typical nanoparticles, and base fluids in heat transfer augmentation. Passive element heat enhancement techniques like twisted tapes showed positive results in laminar flow compared to turbulent flow, and ribs on the geometry, conical nozzles, and rings are better for turbulent flows than laminar flows. This article highlighted the main gaps and challenges for future research.