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Nanoparticles have the capability to effectively improve the thermal conductivity of base fluids, thus improving the heat transfer coefficient of heat transfer systems. In this study, a non-equilibrium molecular dynamics method based on the Fourier law is employed to study the thermal conductivity of TiO2 (r-TiO2)-water nanofluids with temperatures ranging between 303 K and 333 K and volume fractions in the range of 1%-2%. The ordered layer structure as a shell is analyzed and its influence is surveyed by calculating the number density and radial distribution function. The results revealed that a clear, solid-like nanolayer of about 0.5 nm can be observed around the nanoparticle. In this regard, the thickness of the nanolayer is less affected by variations in volume fraction and temperature. The g(r) values and the number density decreased with the increase in temperature. Additionally, the g(r) values and the number density at the level of the nanolayer were much higher compared to those at other parts. This indicates the existence of more water molecules in the nanolayer, thereby reducing contact thermal resistance and improving thermal conductivity. Macroscopically, the thermal conductivity increases with the increase in volume fraction. It was found that the increase in the volume fraction from 1%-2% at 303 K resulted in an increase in the effective thermal conductivity from 1.027 and 1.042, respectively. In other words, the thermal conductivity of the nanofluid was 2.7% and 4.2% higher than that of the base liquid under the same conditions. [ABSTRACT FROM AUTHOR]

The lance is a critical component of the bottom-blowing pool melting process, and its placement has an important impact on the pool's gas-liquid two-phase flow. In this study, a mathematical model of the bottom-blowing process is established, and the flow pattern, trajectory, wake vortex, and velocity of bubbles under four lance spacings are simulated. Results show that there are three basic bubble flow patterns appear in the flow field: bubbles coalesce before leaving the nozzle (Pattern II), bubbles coalesce after leaving the nozzle (Pattern I), and no coalescence during the rise of bubbles (Pattern III). The bubble pattern varies from Pattern I to Pattern III with the increase in lance spacing. The intensity of the influence of the wake vortex on the bubbles decreases. The Q (the Q is the second Galilean invariant of the velocity gradient tensor ∇v) value of the wake vortex is small, but the vortex structural distribution is complex. Moreover, there is a large velocity difference between gas and liquid at the beginning of gas injection, but the velocity difference between them decreases after gas injection, so the average turbulent kinetic energy in the pool initially increases sharply, and then approaches dynamic equilibrium. The top and bottom velocities of the bubbles are consistent, and the velocity fluctuation is orderly. Moreover, the greater the lance spacing is, the greater the disturbance in the pool is. The mixing effect of D = 0.2 m is the best among the four spacings. [ABSTRACT FROM AUTHOR]

Nanofluids due to their good thermal conductivity and stability, have been proposed as a way to surpass the performance of currently available heat transfer fluids in the near future. In this work, we focuses on the preparation of nanofluids with excellent stability and thermal conductivity, which a new type of stable bismuth iodate oxide (BiOIO3) (one type of infrared non-linear optical crystal) nanofluids is successfully prepared by using the two-step method. After the initial physical characterization of BiOIO3 particles, five different dispersants are used to disperse the BiOIO3 nanoparticles, and the best performing nanofluids with a zeta potential value of 144.45 and an average particle size of 22.90 nm could be prepared with PVP dispersant. Furthermore, the addition of PVP dispersant in UV-visible experiments smooth the light absorption curve of the nanofluids, reach a peak of 1.1 at around 350 nm. In the most important thermal conductivity test, the value of thermal conductivity of BiOIO3 nanofluid becomes larger with increasing concentration at 50 °C, reaching a maximum value of 1.52 at 0.134 vol.%, which increases by 0.72 over the same volume concentration of TiO2, indicating the importance of the laminar structure. In view of the excellent properties, new laminar structured nanofluids with light-absorbing properties are expected to receive more attention and exploration in the future. [ABSTRACT FROM AUTHOR]

In the movement process of continuous bubbles, different liquid-flow state and initial temperature of bubbles have important influence on bubble movement and heat transfer. In this study, the flow and heat transfer characteristics of high temperature bubbles in normal temperature liquid are investigated. The rising process of and temperature of bubbles are studied by numerical simulation and compared with experimental results for verification. The results show that the shape, velocity and temperature of the bubble are affected by the initial position of the bubble. Because the closer the initial position of the bubble is to the bottom of the cylinder, the greater decrease of the bubble aspect ratio, w*, the faster decrease of bubble temperature, and the larger bubble velocity would be. The increase of the bubble diameter would mitigate the influence of liquid jet on the bubble motion. Finally, as the bubble surface tension increases, the liquid jet would have less influence on the bubble movement. [ABSTRACT FROM AUTHOR]

This paper focuses on the convective heat transfer characteristics of Fe3O4-water magnetic nanofluids under laminar and turbulent conditions. After verifying the accuracy of the experimental apparatus, the effects of magnetic field strength, concentration, Reynolds number and temperature on the convective heat transfer coefficient have been studied. The convective heat transfer characteristics of nanofluids under laminar and turbulent flow conditions were studied in depth, and the influence of each factor on the heat transfer coefficient was analyzed by orthogonal experimental design method. Under the laminar flow conditions, the convective heat transfer of magnetic nanofluids performed best when the Reynolds number was 2000, the magnetic field strength was 600, the temperature was 30 °C, and the concentration was 2%. The convective heat transfer coefficient, h, increased by 3.96% than the distilled water in the same conditions. In turbulent state, the convective heat transfer of magnetic nanofluids performed the best when the Reynolds number was 6000, the magnetic field strength was 600, the temperature was 40 °C, and the concentration was 2%. The h increased by 11.31% than the distilled water in the same Reynolds number and the magnetic field strength conditions. [ABSTRACT FROM AUTHOR]