A Review on the Discrete Boltzmann Model for Nanofluid Heat Transfer in Enclosures and Channels

Utilizing nanofluids to enhance heat transfer is shown to be a promising option with many practical applications. As the dimensions of the enclosures and channels for fluid flows steadily decrease, the energy carrying particle behavior for thermal transport becomes more significant. Therefore, the thermal analysis requires a mesoscale approach to describe the enhanced mechanism of heat transfer at the micro-scale level, and the interactions between the multicomponent fluid and its boundary conditions. For this purpose, the spatial and temporal discretization of the Boltzmann model leading to a thermal lattice Boltzmann method (LBM) recovers the macroscopic conservations of momentum and energy through particle collisions and streaming at mesoscale discrete nodes. In this article, the LBM studies for convective heat transfer, including the external forces, is reviewed in order to allow us to identify the research gaps and to reveal the promising future possibilities of its use for nanofluids.     

Controlling fibroblast adhesion and proliferation by 1D Al2 O3 nanostructures

The fibrotic encapsulation, which is mainly accompanied by an excessive proliferation of fibroblasts, is an undesired phenomenon after the implantation of various medical devices. Beside the surface chemistry, the topography plays also a major role in the fibroblast–surface interaction. In the present study, one‐dimensional aluminium oxide (1D Al₂ O₃) nanostructures with different distribution densities were prepared to reveal the response of human fibroblasts to the surface topography. The cell size, the cell number and the ability to form well‐defined actin fibres and focal adhesions were significantly impaired with increasing distribution density of the 1D Al₂ O₃ nanostructures on the substratum.Inspec keywords: biomechanics, adhesion, surface chemistry, biomedical materials, cellular biophysics, surface topography, nanostructured materials, alumina, nanomedicineOther keywords: fibrotic encapsulation, medical devices, surface chemistry, human fibroblasts, surface topography, cell size, cell number, well‐defined actin fibres, focal adhesions, distribution density, fibroblast adhesion, 1D nanostructures, distribution densities, fibroblast proliferation, fibroblast‐surface interaction, one‐dimensional aluminium oxide nanostructures, Al₂ O₃      

Response to thermal exposure of the mechanically alloyed Al–Ti/C powders

Al–TiC_p composites have been extensively studied in recent years not only because of their attributes as wear-resistant structural materials but also on account of their potential as very efficient grain refiners. Al–Ti–C alloys of various compositions have already been commercialized as grain refining master alloys and have long been in use in aluminium foundries world wide. The present work was undertaken to investigate the possibility of manufacturing Al–TiC_p grain refiner master alloy tablets by the mechanical alloying route. Carbon was mechanically alloyed into Al–Ti alloy powder grains via high energy ball milling. The Al–Ti/C powder blend thus obtained was heat treated to promote the precipitation of TiC. Al₄C₃ was the first phase to form inside the powder grains upon thermal exposure. The Al₄C₃ particles which were too small to be identified with the optical microscope until 750 °C, have grown until 850 °C where they have started to react with Al₃Ti to produce TiC. A very fine dispersion of TiC particles was thus generated inside the powder particles while the Al₃Ti phase has almost vanished.     

Thixoforming of EN AW-2014 alloy at high solid fraction

EN AW-2014 extruded alloy slugs were thixoformed at 615 °C where the solid fraction is estimated to be 80%. The recrystallization process occurred during heating to the thixoforming temperature, between 550 °C and 600 °C, well above the solidus temperature owing to the pinning of grain boundaries by Al₂Cu precipitates. The equiaxed polygonal grains thus obtained have become increasingly globular upon soaking. Si was enriched in the grain boundaries during soaking while the solid solution matrix was gradually depleted off Cu. The grain boundary composition has moved closer to that of the Al-Cu-Si ternary eutectic with a lower melting point than the binary Al-Cu eutectic, facilitating grain boundary melting. The liquid phase has then penetrated between the grains, forming a more or less continous intergranular network. Microstructural features essential for forming in the semi-solid state were obtained after about 10 min at 615 °C. The subsequent forming process has occurred in the semi-solid state with no evidence of grain deformation. The thixoformed EN AW-2014 part was solutionized at 500 °C for 2 h and was subsequently quenched in water. Artificial ageing at 160 °C has produced hardness values as high as 160 HV after only 8 h. It is concluded that the high strength wrought EN AW-2014 alloy feedstock processed by the RAP route respond to a thixoforming operation in a very favorable fashion.     

Age hardening of EN AW 2014 alloy extruded in the semi-solid state

Response to T6 heat treatment of thixoextruded EN AW 2014 aluminium alloy was investigated in the present work. Extrusion of a 2014 slug heated to a liquid fraction of 15%, takes place in the semi-solid state until the liquid fraction in the final part of the slug is reduced via segregation to a level where semi-solid forming is no longer possible. Hence, the final part of the slug is extruded in the solid-state with a concurrent recrystallization process. This process has produced two distinctly different structures at the front and rear ends and an unexpected hardness profile in T6 temper along the length of the thixoextruded rod. The response to T6 heat treatment of the globular front has been age hardening as usual. The inferior age hardening potential with respect to the hot extruded counterpart is attributed to the grain boundary Al₂Cu phase which has grown too coarse via liquid segregation to be readily solutionized at typical solutionizing temperatures. The rear end of the extrudate on the other hand, has softened upon T6 heat treatment owing to Cu depletion and a fully recrystallized structure.     

Precipitation during homogenization cooling in AlMgSi alloys

Precipitation during the industrial cool down takes place predominantly above 300 °C in the EN AW-6082 and 6005 alloys. The phase precipitation throughout cooling is equilibrium β phase. A considerable capacity is retained after the cool down for further precipitation during a subsequent heating cycle. The β-Mg₂Si is once again the predominant phase that forms during a scan heating cycle employed in exactly the same manner with the industrial billet preheating operation. The precipitation in the 6060 alloy, on the other hand, occurs predominantly below 300 °C with additionally β′-Mg₂Si particles formed below 200 °C.     

Physical and mechanical properties of materials prepared using Class C fly ash and soybean oil

In present work; epoxidized soybean oil (ESO), fly ash (FA) and natural clay (C) are used to produce 45 kinds of biocomposite materials and by analyzing the physical–mechanical properties of these novel materials, their use as an insulation material is investigated. The compressive strength, tensile strength, abrasion loss, thermal conductivity and oven-dry mass of each sample are measured. The minimum thermal conductivity of 0.273 W/mK is observed with the samples containing ESO–FA–C. It is increased with the decrease of ESO and FA. The compressive and tensile strengths are varied from 13.53 to 6.31 MPa and 1.287 to 0.879 MPa, respectively.