纳米TiO2流体表面改性及对真空闪蒸制冰的影响

利用电镜扫描法、紫外分光光度法及烘干称重法对纳米TiO₂流体的分散稳定性进行了综合评价，研究了表面活性剂种类及浓度对其分散稳定性的影响。将纳米TiO₂流体引入真空闪蒸制取冰浆系统，研究了纳米TiO₂浓度、表面活性剂浓度及对吸附作用下纳米TiO₂流体真空闪蒸制冰的影响。结果表明，表面活性剂类型对纳米TiO₂流体分散稳定性的影响很大，复合型的分散稳定性最佳，其次是阴离子型；纳米粒子及表面活性剂可以增强真空下纳米TiO₂流体的成核效果，增大含冰率，降低过冷度；表面活性剂浓度是影响真空闪蒸制冰系统压力及闪蒸率的重要因素，系统压力及闪蒸率均随着表面活性剂浓度的增大而增大；另外，确定了在吸附作用下真空闪蒸制冰系统中使用纳米TiO₂流体的最佳条件。在最佳条件下，含冰率为18.35%，过冷度为0.51℃，热导率为0.920W/(m·K)，对比蒸馏水有较大改善。吸附作用下真空闪蒸制冰可行性较高，制取冰浆效果优良。

TiO2 nanofluids surface modification and the influence on the vacuum flash ice-making

Electron microscopy, UV spectrophotometry and drying weighing were adopted in the experiment to make a comprehensive assessment of the dispersion stability. The effects of surfactant type surfactant and concentration on the dispersion stability of TiO₂ nanofluids were analyzed. In addition, the TiO₂ nanofluids was used for producing ice slurry in the vacuum flash system. The effects of nano-TiO₂ concentration and surfactant concentration on vacuum flash ice-making of TiO₂ nanofluids under the adsorption condition were analyzed. According to the experimental results, four conclusions were gained. ① The type of surfactant has great impact on the dispersion stability of TiO₂ nanofluids. The flash performance of nanofluids with composite surfactant is the best, followed by the anions. ② Both nano-particles and surfactants can enhance the nucleating effect of TiO₂ nanofluids under vacuum, increase the ice packing factor and reduce the supercooling degree. ③ Surfactant concentration has great effects on system pressure and flash rate in vacuum flash system. With the increase of surfactant concentration, both system pressure and flash rate increase. ④ The best experimental condition of the vacuum flash system by using TiO₂ nanofluids are determined. Under the best condition, the ice packing factor is 18.35%, the supercooling degree is 0.51℃, and the thermal conductivity is 0.920W/(m·K). Compared with the parameters of distilled water, it is improved greatly.