Nanofluids are engineered colloids made of a base fluid and nanoparticles (1-100 nm) Nanofluids have higher thermal conductivity' and single-phase heat transfer coefficients than their base fluids In particular the heat transfer coefficient increases appear to go beyond the mere thermal-conductivity effect, and cannot be predicted by traditional pure-fluid correlations such as Dittus-Boelter's In the nanofluid literature this behavior is generally attributed to thermal dispersion and intensified turbulence, brought about by nanoparticle motion To test the validity of this assumption, we have considered seven slip mechanisms that can produce a relative velocity between the nanoparticles and the base fluid These are inertia, Brownian diffusion, thermophoresis, diffusioplwresis, Magnus effect, fluid drainage, and gravity We concluded that, of these seven, only Brownian diffusion and thermophoresis are important slip mechanisms in nanofluids Based on this finding, we developed a two-component four-equation nonhomogeneous equilibrium model for mass, momentum, and heat transport in nanofluids A nondimensional analysis of the equations suggests that energy transfer by nanoparticle dispersion is negligible, and thus cannot explain the abnormal heat transfer coefficient increases Furthermore, a comparison of the nanoparticle and turbulent eddy time and length scales clearly indicates that the nanoparticles move homogeneously with the fluid in the presence of turbulent eddies so an effect on turbulence intensity is also doubtful Thus, we propose an alternative explanation for the abnormal heat transfer coefficient increases: the nanofluid properties may vary significantly within the boundary layer because of the effect of the temperature gradient and thermophoresis For a heated fluid, these effects can result in a significant decrease of viscosity within the boundary layer, thus leading to heat transfer enhancement A correlation structure that captures these effects is proposed

Convective Transport in Nanofluids

Buoyancy-driven heat transfer enhancement in a two-dimensional enclosure utilizing nanofluids

Heat transfer enhancement of nanofluids

Effective thermal conductivity of mixtures of e uids and nanometer-size particles is measured by a steady-state parallel-plate method. The tested e uids contain two types of nanoparticles, Al 2O3 and CuO, dispersed in water, vacuum pump e uid, engine oil, and ethylene glycol. Experimental results show that the thermal conductivities of nanoparticle ‐e uid mixtures are higher than those of the base e uids. Using theoretical models of effective thermal conductivity of a mixture, we have demonstrated that the predicted thermal conductivities of nanoparticle ‐e uid mixtures are much lower than our measured data, indicating the dee ciency in the existing models when used for nanoparticle ‐e uid mixtures. Possible mechanisms contributing to enhancement of the thermal conductivity of the mixtures are discussed. A more comprehensive theory is needed to fully explain the behavior of nanoparticle ‐e uid mixtures. Nomenclature cp = specie c heat k = thermal conductivity L = thickness Pe = Peclet number P q = input power to heater 1 r = radius of particle S = cross-sectional area T = temperature U = velocity of particles relative to that of base e uids ® = ratio of thermal conductivity of particle to that of base liquid ¯ = .® i 1/=.® i 2/ ° = shear rate of e ow Ω = density A = volume fraction of particles in e uids Subscripts

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Thermal Conductivity of Nanoparticle -Fluid Mixture

Mechanisms of heat flow in suspensions of nano-sized particles (nanofluids)

Bimetallic catalysts are ideal candidates for boosting electrochemical CO2 reduction reaction (CO2RR). However, these catalysts have largely relied on tedious synthesis technology and play electrolytic role with the help of a metal substrate or gas diffusion electrode. Herein, noble metal-free In–Sn nanoparticles (NPs) with a core–shell structure that contains a hybrid In–Sn core and native Sn-doped In2O3 shell have been successfully grown on the copper foam by the potential-driven volume diffusion strategy. These NPs which spontaneously result in the formation of the In–Sn bimetallic interface by adjusting the element composition significantly boost the yield of CO2 reduction into formate over a wide potential window (−0.77 to −1.17 V versus reversible hydrogen electrodes) compared with pure single-metal counterparts. The optimized In–Sn NPs deliver a great partial current density of 57.6 mA cm–2 and high faradaic efficiency of 97.0%, a remarkable performance in comparison to the state-of-the-art reported bimetallic catalyst. Such excellent performance is revealed via in situ Raman analyses and theoretical calculations, indicating that the unique structure of In–Sn NPs with the In–Sn bimetallic interface favorably regulates the reaction dynamics and facilitates the adsorption of the *OCHO intermediate. 

Bimetallic In–Sn Core–Shell Catalyst Enabling Highly Efficient Electrocatalytic CO2 Reduction to Formate

https://www.nature.com/articles/s41467-021-27755-x.pdf

Zinc ion thermal charging cell for low-grade heat conversion and energy storage

Design and application of a novel direct light-driven thermogravimetric analyzer

An integrated model for energy management of aero engines based on thermodynamic principle of variable mass systems

Ni-Phyllosilicate Nanotubes Coated by Ceria Nanolayer for Record-High Efficiency of 36.9% and Near-Limit Co2 Conversion in Solar-Driven Co2-to-Fuel Conversion

Yimin Xuan

Papers

Bimetallic In–Sn Core–Shell Catalyst Enabling Highly Efficient Electrocatalytic CO2 Reduction to Formate

Zinc ion thermal charging cell for low-grade heat conversion and energy storage

Design and application of a novel direct light-driven thermogravimetric analyzer

An integrated model for energy management of aero engines based on thermodynamic principle of variable mass systems

Ni-Phyllosilicate Nanotubes Coated by Ceria Nanolayer for Record-High Efficiency of 36.9% and Near-Limit Co2 Conversion in Solar-Driven Co2-to-Fuel Conversion