水平板上固着碳纳米管燃油液滴的蒸发特性

以正十四烷（C14）为基液，表面活性剂溴化十六烷三甲基铵（CTAB）为助溶剂，采用两步法配制分别含有20、50 nm碳纳米管（CNT）的纳米燃油. 分析比较基液燃油与纳米燃油的黏度特性，采用接触角测量仪记录燃油液滴在加热平板上的蒸发变形，探究不同粒径及质量浓度的CNT对正十四烷燃油液滴蒸发特性的影响. 研究表明，纳米粒子的加入增加了基液的黏度，并且黏度随着纳米粒子质量浓度增大或粒径减小而增加. CNT纳米燃油液滴蒸发过程符合部分润湿状态下单组分液滴蒸发的一般规律. 在液滴蒸发定接触线阶段，纳米燃油导热系数增强，液滴从外界吸收的热量加快向液体内部传递，延滞了液滴边缘处（三相线处）液体分子的挥发. 纳米粒子在液滴边缘处沉积，阻滞了接触线向内收缩，增加了液滴在定接触线阶段蒸发的持续时间，纳米燃油在此阶段的蒸发速率比基液燃油低，且蒸发速率的差异随燃油中纳米粒子数量的增多而加大. 在定接触角与混合蒸发阶段，“自销钉”效应阻滞接触线收缩，液滴与底板的接触面积较大，液滴中纳米粒子质量浓度的增加使液滴吸收更多的热量，在后2个蒸发阶段，纳米燃油的蒸发速率明显加快，大于基液燃油的蒸发速率. 在整个蒸发过程中，纳米燃油的平均蒸发速率高于基液燃油.

Evaporation characteristics of sessile droplet for fuel with CNT on a heated substrate

Nano-fuel with 20 nm and 50 nm carbon nanotubes (CNTs) was prepared by two step method using C14 as base fuel and cetyltrimethyl ammonium bromide (CTAB) as cosolvent. The viscosity characteristics of CNT nano-fuel with various mass fractions were evaluated. The influence of particle size and mass concentration of CNT on the evaporation characteristics of C14 fuel sessile droplets on a heated substrate was investigated experimentally, using contact angle goniometer for shape analysis of fuel droplets. Results showed that the viscosity increased with the increase of mass fraction and the decrease of particle size. The evaporation process of CNT nano-fuel droplets accorded with the general evaporation law of single-component droplet under partial wetting condition. In the constant contact line phase, the heat transfer coefficient of nano-fuel increased, the heat transfer from the outside to the inside was accelerated, which delayed the volatilization of fuel molecules located in the triple contact line (gas-liquid-solid). The sedimentation of nanoparticles in the edge of droplet blocked the contraction of the contact line and increased the duration time of the evaporation at the constant contact line phase. As a result, the evaporation rate of nano-fuel droplet was lower than that of base fuel, and the difference in evaporation rate was larger with the increasing number of nanoparticles in fuel. At the phases of constant contact angle and hybrid evaporation, the " pinned effect” of nanoparticle blocked the contraction of the contact line, the contact area of nano-fuel was larger than that of base fuel, and the increase in the mass fraction of nanoparticles caused the droplet to absorb more heat, therefore, the droplet evaporation rate of nano-fuel droplet was obviously larger than that of base fuel in the last two phases. In summary, the average evaporation rate of nano-fuel is higher than that of base fuel for the whole evaporation.