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. © 2019, Zhejiang University Press. All right reserved.