水平板上固着碳纳米管燃油液滴的蒸发特性
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摘要
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、50nm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.
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 nanofuel 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 (gasliquid-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.
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 nanofuel 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 (gasliquid-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.
引文
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[2]KUMAR S,DINESHA P,BRAN I.Influence of nanoparticles on the performance and emission characteristics of a biodiesel fuelled engine:an experimental analysis[J].Energy,2017,140:98-105.
[3]王亮,张新塘,朱新绪,等.纳米CeO2、Fe燃油添加剂对柴油机性能影响的研究[J].柴油机,2017,39(5):17-22.WANG Liang,ZHANG Xin-tang,ZHU Xin-xu,et al.Study on the effect of nanoscale CeO2 and Fe fuel additives on diesel engine performance[J].Diesel Engine,2017,39(5):17-22.
[4]GUMUS S,OZCAN H,OZBEY M,et al.Aluminum oxide and copper oxide nanodiesel fuel properties and usage in a compression ignition engine[J].Fuel,2016,163:80-87.
[5]BASHA J S,ANAND R B.Performance,emission and combustion characteristics of a diesel engine using carbon nanotubes blended jatropha methyl ester emulsions[J].Alexandria Engineering Journal,2014,53(2):259-273.
[6]王琪,朱宝忠,孙运兰,等.乙醇基纳米流体燃料液滴着火燃烧研究[J].燃烧科学与技术,2017,23(5):465-470.WANG Qi,ZHU Bao-zhong,SUN Yun-lan,et al.Ignition and combustion characteristics of ethonal based nanofluid droplets[J].Journal of Combustion Science and Technology,2017,23(5):465-470.
[7]KIM Y C.Evaporation of nanofluid droplet on heated surface[J].Advances in Mechanical Engineering,2015,7(4):1-8.
[8]郭亚丽.纳米流体固着液滴蒸发等流动与传热问题的LBM分析[D].大连:大连理工大学,2009.GU Ya-li.Study of flow and heat transfer in the proeess such as evaporation of nanofluid sessile droplet with LBM[D].Dalian:Dalian University of Technology,2009.
[9]刘剑洪,吴双泉,何传新,等.碳纳米管和碳微米管的结构、性质及其应用[J].深圳大学学报理工版,2013,30(1):1-11.LIU Jian-hong,WU Shuang-quan,HE Chuan-xin,et al.Structure,property and application of carbon nanotubes and carbon microtubes[J].Journal of Shenzhen University Science and Engineering,2013,30(1):1-11.
[10]陈强,黄永华,翁捷敏,等.碳纳米管本征热导率的研究进展[J].化工新型材料,2013,41(11):1-4.CHEN Qiang,HUANG Yong-hua,WENG Jie-min,et al.Advance on the intrinsic conductivity of carbon nanotubes[J].New Chemical Materials,2013,41(11):1-4.
[11]李晓东,杨荣杰.碳纳米管催化二硝酰胺铵燃烧和热分解[J].新型炭材料,2010,25(6):444-448.LI Xiao-dong,YANG Rong-jie.Combustion and thermal decomposition of ammonium dinitramide catalyzed by carbon nanotubes[J].New Carbon Materials,2010,25(6):444-448.
[12]JADAV M,NAIR N,PATEL R,et al.Investigation of drying mechanism in evaporating micellar nanofluid drops[J].Journal of Nanofluids,2016,5(2):216-219.
[13]BHUIYAN M H U,SAIDUR R,AMALINA M A,et al.Effect of nanoparticles concentration and their sizes on surface tension of nanofluids[C].Bsme International Conference on Thermal Engineering,2015,105:431-437.
[14]ALAWI O A,SIDIK N A C,HONG W X,et al.Thermal conductivity and viscosity models of metallic oxides nanofluids[J].International Journal of Heat and Mass Transfer,2017,116: 1314-1325.
[15]ERBIL H Y.Evaporation of pure liquid sessile and spherical suspended drops:a review[J].Advances in Colloid and Interface Science,2012,170(1/2):67-86.
[16]MOGHIMAN M,ASLANI B.Influence of nanoparticles on reducing and enhancing evaporation mass transfer and its efficiency[J].International Journal of Heat and Mass Transfer,2013,61(1):114-118.
[17]BERBER S,KWON Y K,TOMANEK D.Unusually high thermal conductivity of carbon nanotubes[J].Physical Review Letters,2000,84(20):4613.
[18]王宝和,李群.单液滴蒸发研究的现状与展望[J].干燥技术与设备,2014(4):25-31.WANG Bao-he,LI Qun.Present status and prospect of studies on single droplet evaporation[J].Drying Technology and Equipment,2014(4):25-31.
[19]SEMENOV S,TRYBALA A,AGOGO H,et al.Evaporation of droplets of surfactant solutions[J].Langmuir the Acs Journal of Surfaces and Colloids,2013,29(32):10028.
[20]SEFIANE K,SKILLING J,MACGILLIVRAY J.Contact line motion and dynamic wetting of nanofluid solutions[J].Advances in Colloid and Interface Science,2008,138(2):101-120.
[21]CONWAY J,KORNS H,FISCH M R.Evaporation kinematics of polystyrene bead suspensions[J].Langmuir,1997,13(3):426-431.
[22]DASH S,GARIMELLA S V.Droplet evaporation on heated hydrophobic and superhydrophobic surfaces[J].Physical Review E Statistical Nonlinear and Soft Matter Physics,2014,89(4):1-8.
[23]DUNN G J,WILSON S K,DUFFY B R,et al.The strong influence of substrate conductivity on droplet evaporation[J].Journal of Fluid Mechanics,2009,623(23):329-351.
[24]CHEN X,ZHU Z Q,LIU Q S,et al.Thermodynamic behaviors of macroscopic liquid droplets evaporation from heated substrates[J].Microgravity Science and Technology,2015,27(5):1-8.