黏弹性流体基纳米流体(viscoelastic fluid based nanofluid,VFBN)是一种具有湍流减阻和对流换热相对强化特性的新型换热工质,其湍流减阻机理与流变学特性关系密切。通过对以2.5×10-3、5×10-3、1×10-2三种质量分数的十...黏弹性流体基纳米流体(viscoelastic fluid based nanofluid,VFBN)是一种具有湍流减阻和对流换热相对强化特性的新型换热工质,其湍流减阻机理与流变学特性关系密切。通过对以2.5×10-3、5×10-3、1×10-2三种质量分数的十六烷基三甲基氯化铵/水杨酸钠水溶液为基液,粒子体积分数为0.1%、0.25%、0.5%、1.0%的铜纳米流体的剪切黏度、零剪切黏度以及松弛时间的测量,实验结果表明VFBN有明显的剪切稀变特性,同时纳米粒子的添加增大了基液的零剪切黏度,并导致基液黏弹性增强。以Giesekus本构模型为理论基础,利用实验参数得到了描述VFBN剪切黏度的实验关联式。展开更多
Our previous experimental studies have confirmed that viscoelastic-fluid-based nanofluid(VFBN) prepared by suspending nanoparticles in a viscoelastic base fluid(VBF, behaves drag reduction at turbulent flow state) can...Our previous experimental studies have confirmed that viscoelastic-fluid-based nanofluid(VFBN) prepared by suspending nanoparticles in a viscoelastic base fluid(VBF, behaves drag reduction at turbulent flow state) can reduce turbulent flow resistance as compared with water and enhance heat transfer as compared with VBF. Direct numerical simulation(DNS) is performed in this study to explore the mechanisms of heat transfer enhancement(HTE) and flow drag reduction(DR) for the VFBN turbulent flow. The Giesekus model is used as the constitutive equation for VFBN. Our previously proposed thermal dispersion model is adopted to take into account the thermal dispersion effects of nanoparticles in the VFBN turbulent flow. The DNS results show similar behaviors for flow resistance and heat transfer to those obtained in our previous experiments. Detailed analyses are conducted for the turbulent velocity, temperature, and conformation fields obtained by DNSs for different fluid cases, and for the friction factor with viscous, turbulent, and elastic contributions and heat transfer rate with conductive, turbulent and thermal dispersion contributions of nanoparticles, respectively. The mechanisms of HTE and DR of VFBN turbulent flows are then discussed. Based on analogy theory, the ratios of Chilton–Colburn factor to friction factor for different fluid flow cases are investigated, which from another aspect show the significant enhancement in heat transfer performance for some cases of water-based nanofluid and VFBN turbulent flows.展开更多
文摘黏弹性流体基纳米流体(viscoelastic fluid based nanofluid,VFBN)是一种具有湍流减阻和对流换热相对强化特性的新型换热工质,其湍流减阻机理与流变学特性关系密切。通过对以2.5×10-3、5×10-3、1×10-2三种质量分数的十六烷基三甲基氯化铵/水杨酸钠水溶液为基液,粒子体积分数为0.1%、0.25%、0.5%、1.0%的铜纳米流体的剪切黏度、零剪切黏度以及松弛时间的测量,实验结果表明VFBN有明显的剪切稀变特性,同时纳米粒子的添加增大了基液的零剪切黏度,并导致基液黏弹性增强。以Giesekus本构模型为理论基础,利用实验参数得到了描述VFBN剪切黏度的实验关联式。
基金supported by the National Natural Science Foundation of China(Grant No.51276046)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20112302110020)+1 种基金the China Postdoctoral Science Foundation(Grant No.2014M561037)the President Fund of University of Chinese Academy of Sciences,China(Grant No.Y3510213N00)
文摘Our previous experimental studies have confirmed that viscoelastic-fluid-based nanofluid(VFBN) prepared by suspending nanoparticles in a viscoelastic base fluid(VBF, behaves drag reduction at turbulent flow state) can reduce turbulent flow resistance as compared with water and enhance heat transfer as compared with VBF. Direct numerical simulation(DNS) is performed in this study to explore the mechanisms of heat transfer enhancement(HTE) and flow drag reduction(DR) for the VFBN turbulent flow. The Giesekus model is used as the constitutive equation for VFBN. Our previously proposed thermal dispersion model is adopted to take into account the thermal dispersion effects of nanoparticles in the VFBN turbulent flow. The DNS results show similar behaviors for flow resistance and heat transfer to those obtained in our previous experiments. Detailed analyses are conducted for the turbulent velocity, temperature, and conformation fields obtained by DNSs for different fluid cases, and for the friction factor with viscous, turbulent, and elastic contributions and heat transfer rate with conductive, turbulent and thermal dispersion contributions of nanoparticles, respectively. The mechanisms of HTE and DR of VFBN turbulent flows are then discussed. Based on analogy theory, the ratios of Chilton–Colburn factor to friction factor for different fluid flow cases are investigated, which from another aspect show the significant enhancement in heat transfer performance for some cases of water-based nanofluid and VFBN turbulent flows.
