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ABSTRACT
Nanoparticle suspensions, known as nanofluids, exhibit many potential applications in thermal and chemical engineering, of which the thermal transport characteristics have a great dependence with the corresponding flow process and heat transfer process. Recently, a shear flow-induced enhancement of the thermal transport in the nanoparticle suspensions was previously reported. Here, the effective thermal conductivity (ETC) of deionized water based silicon oxide nanoparticle suspensions in the shear flows at different temperatures were experimentally measured to elucidate the effect of temperature on the thermal transport in sheared nanoparticle suspensions. The results show that the ETC enhancement induced by shear flows is more obvious at lower temperatures, which can be attributed to the easily formed nanoparticle agglomerates for the lower mobilities of nanoparticles. Meanwhile, a correlation for quantitatively predicting the ETC enhancements, i.e., the ratios of infinite-shear thermal conductivity to zero-shear thermal conductivity, is proposed with considering the effect of temperature. In summary, the thermal transport in sheared nanoparticle suspensions demonstrates distinctive characteristics at different temperatures for the distinguishing nanoparticle structures.
Nomenclature
| Br | = | Brinkman number |
| C1, C2, C3, C4 | = | Constant |
| CTWB | = | Constant-temperature water bath |
| D | = | Annular gap width (m) |
| d | = | Diameter (m) |
| DW | = | Deionized water |
| ETC | = | Effective thermal conductivity |
| g | = | Gravitational acceleration (m s−2) |
| i.c. | = | Inner cylinder |
| k | = | Thermal conductivity (W m−2 K−1) |
| l | = | Heating length (m) |
| n | = | Rotation speed (min−1) |
| o.c. | = | Outer cylinder |
| Qac | = | Actual heating power (W) |
| R | = | Radius (m) |
| r | = | Distance in r-direction (m) |
| Ra | = | Rayleigh number |
| RSC | = | Rotation speed controller |
| T | = | Fluid temperature (K) |
| Ta | = | Taylor number |
| u | = | Velocity (m s−1) |
Greek symbols
| α | = | Thermal diffusivity (m2 s−1) |
| αv | = | Volume expansion coefficient (K−1) |
| γ | = | Shear rate (s−1) |
| φ | = | Volume fraction |
| μ | = | Dynamic viscosity (Pas) |
| ρ | = | fluid density (kg m−3) |
| υ | = | Kinematic viscosity (m2 s−1) |
| ω | = | angular velocity (rads−1) |
Subscripts
| ave | = | Average |
| b | = | Constant-temperature water bath |
| e | = | Effective |
| i | = | Inner |
| l | = | Base fluid |
| o | = | Outer |
| w | = | Wall |
| θ | = | Circumference |
| ∞ | = | Infinite |
| 0 | = | Static fluid |
Additional information
Funding
Notes on contributors
Chengzhen Sun
Chengzhen Sun is an associate professor at the State Key Laboratory of Multiphase flow in Power Engineering in Xi'an Jiaotong University. He obtained his Ph.D. degree in 2014 at Power Engineering and Engineering Thermophysics. Currently, his research focuses on mass and energy transport in nanoscale spaces, including mass transport in two-dimensional nanopores, and gas/oil/water multiphase flow in nanoslits.
Bofeng Bai
Bofeng Bai is a distinguished professor at the State Key Laboratory of Multiphase Flow in Power Engineering in Xi'an Jiaotong University. He received his Ph.D. degree in Power Engineering and Engineering Thermophysics from Xi'an Jiaotong University in 1999. He is the winner of the Distinguished Young Scientists of National Natural Science Foundation of China. His main research interests include the fundamentals of multiphase flow and heat transfer and their applications in petroleum engineering and power engineering, such as oil & gas recovery, phase-change heat exchangers, propulsion, and power systems.
Wen-Qiang Lu
Wen-qiang Lu is an honor professor at the University of Chinese Academy of Science. He was a member of multiphase flow in engineering thermophysics in China and a review expert for key projects in National Natural Science Foundation of China. His research interests include multiphase flow and heat transfer, microscale and nanoscale heat and mass transfer, and multiscale simulation methods.