Water-based Carbon Quantum Dot (CQD) suspension has great potential for different heat transfer applications as a novel coolant due to their unique colloidal stability, high thermal conductivity and low penalty for rheological properties once loading CQD. To this end, Fe₃O₄-CQD, and CuO-CQD nanocomposites were prepared by a simple hydrothermal procedure analyzed by TEM, XRD, FTIR and Zeta potential. Zeta potential revealed suitable stability of nanofluids. The results confirmed the successful fabrication of QDs with average particle size of 10–20 nm. The nanofluid samples were synthesized based on car radiator coolant and CQDs at the concentrations of 500, 1000, and 5000 ppm. Thermal conductivity (k) and convection heat transfer (h) coefficients were investigated as the main features of the fluid’s heat transfer characteristics. The presence of QDs enhance the viscosity and thermal conductivity of nanofluids considerably. The maximum thermal conductivity enhancement reaches up 25%, and 18% for the nanofluid containing 0.5% CuO -CQD, and Fe₃O₄-CQD at 45 °C in water as base fluids, respectively. In addition, the viscosity of each solution was measured, and the results show that it increases with increasing volume fractions of QDs nanoparticles and decreased with increasing of temperature. The results revealed that the the cooling tower effectiveness was found to be 25% higher for 0.5 wt% CuO-CQD nanofluid and water to air flow ration of 0.8556 than base fluid. On the other hand, with the use of Fe₃O₄-CQD nanofluid across all the concentrations, the effectiveness increased about 12%.The water consumption reduced about 7.5% and 16% for Fe₃O₄-CQD, and CuO-CQD under the same heat transfer capacity, respectively. These results can be used as a useful benchmark for finding and selecting appropriate combinations of cooling tower’s parameters and nanofluid types.

水基碳量子点 (CQD) 悬浮液由于其独特的胶体稳定性、高导热性和加载 CQD 后流变性能的低损失，作为一种新型冷却剂在不同的传热应用中具有巨大的潜力。为此，Fe ₃ O ₄-CQD 和 CuO-CQD 纳米复合材料是通过简单的水热程序制备的，通过 TEM、XRD、FTIR 和 Zeta 电位分析。Zeta 电位揭示了纳米流体的适当稳定性。结果证实了平均粒径为 10-20 nm 的量子点的成功制备。纳米流体样品是基于汽车散热器冷却剂和 CQD 合成的，浓度为 500、1000 和 5000 ppm。研究了热导率 (k) 和对流传热 (h) 系数作为流体传热特性的主要特征。量子点的存在显着提高了纳米流体的粘度和热导率。最大导热系数提高了25%，含有0.5% CuO-CQD和Fe ₃ O ₄的纳米流体提高了18%-CQD 在 45 °C 的水中分别作为基液。此外，测量了每种溶液的粘度，结果表明它随着 QDs 纳米颗粒体积分数的增加而增加，随着温度的升高而降低。结果表明，对于 0.5 wt% CuO-CQD 纳米流体和 0.8556 的水与空气流量比，冷却塔效率比基础流体高 25%。在另一方面，在使用的Fe ₃ ö ₄在所有浓度-CQD纳米流体，效力增加了约12％。该水的消耗减少有关的Fe为7.5％和16％的₃ ö ₄-CQD 和 CuO-CQD 分别在相同的传热能力下。这些结果可用作寻找和选择冷却塔参数和纳米流体类型的适当组合的有用基准。