Manimaran Mageswari, Norizan Mohd Nurazzi, Kassim Mohamad Haafiz Mohamad, Adam Mohd Ridhwan, Abdullah Norli, Norrrahim Mohd Nor Faiz
Bioresource Technology Division, School of Industrial Technology, Universiti Sains Malaysia Penang 11800 Malaysia
Green Biopolymer, Coatings & Packaging Cluster, School of Industrial Technology, Universiti Sains Malaysia Penang 11800 Malaysia.
RSC Adv. 2025 May 1;15(18):14088-14125. doi: 10.1039/d5ra00844a. eCollection 2025 Apr 28.
Thermal conductivity is undoubtedly the most significant physicochemical property for evaluating the thermal efficiency of nanofluids. In addition to thermal conductivity, stability is another crucial factor that must be assessed, as maintaining long-term stability in closed-circuit and continuous-cycle applications remains a major challenge. Notably, stability is closely linked to thermal conductivity in nanofluid applications. Recent studies on nanofluids have explored the incorporation of multiple types of nanoparticles known as hybrid nanofluids into heat transfer fluids such as water, ethylene glycol (EG), oil, and refrigerants. These hybrid nanofluids aim to enhance the thermal properties of conventional base fluids. However, nanoparticles at the nanoscale exhibit a strong tendency to aggregate owing to substantial van der Waals interactions, resulting in sedimentation and clogging, which compromise stability. This aggregation negatively impacts both stability and thermal conductivity. This review provides an in-depth analysis of the latest advancements in water-based hybrid nanofluids, incorporating various nanoparticle hybridizations, including metals, metal oxides, carbon-based materials, and plant-based nanomaterials such as nanocellulose in combination with synthetic nanoparticles, an area that remains relatively unexplored. Furthermore, this review discusses characterization techniques and strategies for improving the stability and thermal conductivity of hybrid nanofluids, including chemical modifications such as the addition of surfactants or surface functionalization as well as physical modifications such as optimizing the volume fraction of hybrid nanocomposites, selecting appropriate nanoparticle types and sizes, adjusting ultrasonication time, and modifying pH levels. This review is based on recent studies published between 2019 and 2024.
热导率无疑是评估纳米流体热效率最重要的物理化学性质。除了热导率外，稳定性是另一个必须评估的关键因素，因为在闭路和连续循环应用中保持长期稳定性仍然是一个重大挑战。值得注意的是，在纳米流体应用中，稳定性与热导率密切相关。最近关于纳米流体的研究探索了将多种类型的纳米颗粒（即混合纳米流体）掺入水、乙二醇（EG）、油和制冷剂等传热流体中。这些混合纳米流体旨在增强传统基础流体的热性能。然而，纳米级的纳米颗粒由于大量的范德华相互作用而表现出强烈的聚集倾向，导致沉降和堵塞，从而损害稳定性。这种聚集对稳定性和热导率都有负面影响。本综述深入分析了水基混合纳米流体的最新进展，包括各种纳米颗粒的杂化，如金属、金属氧化物、碳基材料以及植物基纳米材料（如纳米纤维素）与合成纳米颗粒的组合，这一领域仍相对未被探索。此外，本综述讨论了提高混合纳米流体稳定性和热导率的表征技术和策略，包括化学改性（如添加表面活性剂或进行表面功能化）以及物理改性（如优化混合纳米复合材料的体积分数、选择合适的纳米颗粒类型和尺寸、调整超声处理时间以及改变pH值）。本综述基于2019年至2024年发表的近期研究。
