State-of-the-art review on water-based nanofluids for low temperature solar thermal collector application

In the last decade, nanofluids have set significant milestones as efficient working fluids in the field of solar energy conversion to meet rising energy demand. Research on thermophysical properties, long-term stability, and rheology is progressing to achieve effective practical deployment of nanofluids in renewable solar photo-thermal energy conversion sectors (i.e., solar collectors). Nonetheless, researchers and engineers are having a difficult time coping with nearly infinite culpable variables influencing the output of various types of nanofluids. This paper aims to provide an up-to-date analysis of the developments and challenges of widely used water-based nanofluids, with a focus on formulation methods, main properties (thermophysical, stability, and rheological), and effective implementation in low temperature solar collector systems. Previous experimental and numerical studies on the subject have been compiled and thoroughly scrutinized, providing crucial phenomena, mechanisms, flaws, and responsible parameters for achieving stable and optimized thermal properties that integrate with heat transfer performance. It has been discovered that optimizing the critical factors leads to superior behavior of the nanofluids, which results in improved thermal efficiency of the solar collectors. Finally, emerging concerns are identified, as are potential recommendations to resolve existing problems in the field for future advancement that would mobilize rapid progress and practical engineering use of water based nanofluids on solar collectors. •Water-based nanofluids are studied comprehensively.•Formulation methods and crucial thermo-physical properties are critically assessed.•Stability of the nanofluids is investigated in detail with associated factors.•Application of the nanofluids on low temperature solar collectors is scrutinized.•Existing challenges are disclosed, and future recommendations are made.