A CFD modeling of CPU cooling by eco-friendly nanofluid and fin heat sink passive cooling techniques

In this research, a three-dimensional (3D) Computational Fluid Dynamics (CFD) model-based Finite Volume Method (FVM) is performed to study the influence of single-phase green graphene/water nanofluid and two designs (snaky and sinusoidal spiral) of fin on the thermal management of a CPU in the electronic package. The thermophysical properties of eco-friendly nanofluid described by User Defined Function (UDF) code in ANSYS-Fluent 2021 R2 package. Besides the fin design, the impact of heat sink’s (fin and solid block) materials (silver, copper, and nickel), and the variations of nanoparticles volume fraction on the CPU cooling, pressure changes, pumping power, convective heat transfer coefficient, and thermal efficiency of fin heat sink have been investigated. Outcomes indicate that the sinusoidal spiral fin design is more efficient than the snaky-one. The number of sine arcs on the fins has a direct relationship with the heat transfer rate and an inverse relationship with the pressure changes. Because of the higher thermal conductivity of silver, the silver heat sink is more efficient than the copper and nickel heat sinks for CPU cooling. Increasing the wavelength of spiral and snaky fins led to a $7,11.5K$ temperature reduction in the center of the liquid block heat sink. Additionally, the best thermal performance of liquid block heat sink is about $6.82\%$ related to the nanofluid with a concentration of $\phi =0.100\%$, while it is about $6.83\%$ for the nanofluid with a concentration of $\phi =0.075\%$.     

Numerical investigation of natural convection of Al2O3-water nanofluid in a wavy cavity with conductive inner block using Buongiorno’s two-phase model

By employing the finite element method, thermophoresis and Brownian diffusion are studied numerically relating to the natural convection in a wavy cavity that is filled with an ${\text{Al}}_2{\text{O}}_3$-water nanofluid possessing a central heat-conducting solid block that is influenced by the local heater located on the bottom wall. An isothermal condition is established in the two wavy vertical walls, while adiabatic condition is for the top horizontal wall. Partial heating is applied to the bottom of the horizontal wall, while the remaining part remains in the adiabatic condition. Empirical correlations are employed for the thermal conductivity and dynamic viscosity of the nanofluid. The number of oscillations ($1?N\le 4$), Rayleigh number (${10}^3?\mathit{Ra}\le {10}^6$), nanoparticles volume fraction ($0??\le 0.04$) and dimensionless length of the bottom heater ($0.2?H?0.8$) govern the parameters in this study. The grid independency test, as well as experimental and numerical data from other published works, was employed to validate the developed computational code comprehensively. Based on the obtained results, it was found that the heat transfer inside the cavity is enhanced by introducing nanoparticles as well as a selection of optimal number of oscillations.     

Introducing C phase in additively manufactured Ti-6Al-4V: A new oxygen-stabilized face-centred cubic solid solution with improved mechanical properties

An oxygen-rich face-centred cubic (FCC) Ti phase was engineered in the microstructure of a Ti-6Al-4V alloy via additive manufacturing using laser powder bed fusion. Designated 'C', this oxygen-rich FCC phase has a lattice parameter of 0.406 nm and exhibits an orientation relationship with the parent α′ phase as follows: (0 0 0 1)_α′//{1 1 1}_C, and ${〈1\overline{2}10〉}_{\mathrm{\alpha }\prime }$ //${〈1\overline{1}0〉}_{\mathrm{C}}$. We propose that the formation of the C phase is facilitated by the combined effect of thermal gradients, deformation induced by the martensitic transformation, and local O enrichment. This enables an in-situ phase transformation from the hexagonal close-packed α′ phase to the C phase at elevated temperatures. Our density functional theory calculations indicate that oxygen occupancy in the octahedral interstices of the FCC structure is energetically preferred to corresponding sites in the α′ phase. The in-situ mechanical testing results indicate that the presence of the FCC phase significantly increases the local yield strength from 1.2 GPa for samples with only the α′ phase to 1.9 GPa for samples comprising approximately equal volume fractions of the α′ and FCC phases. No loss of ductility was reported, demonstrating great potential for strengthening and work hardening. We discuss the formation mechanism of the FCC phase and a pathway for future microstructural design of titanium alloys by additive manufacturing.     

Study on decolorization of Rhodamine B by raw coal fly ash catalyzed Fenton-like process under microwave irradiation

Coal fly ash (CFA) catalyzed Fenton-like process was studied under microwave (MW) irradiation for the decolorization of Rhodamine B (RhB) wastewater. The physical-chemical properties of CFA were characterized, including the specific surface area, micromorphology, chemical and crystal components, and the distribution and chemical valence of metallic elements. The metallic oxidants in the CFA indicate CFA can work as Fenton-like catalyst and MW-absorbent simultaneously. The results reveal OH is more significant in the decolorization of RhB than HO₂ and O₂^?. The generation of more OH in the MW-Fenton-like process (293–326 K) than that in the conventional heated Fenton-like process (326 K) reflects the function of hot spot effect and possible non-thermal effect of MW. Under the optimum condition ([H₂O₂] 2 mmol L^?1, [CFA] 15 g L^?1, pH 3, P_MW 0.1 kW), the decolorization rate reaches 91.6% after 20 min. The intrinsic kinetic model of RhB decolorization is $-\frac{\mathrm{d}{C}_{\mathrm{R}\mathrm{h}\mathrm{B}}}{\mathit{dt}}={1.76\times 10}^{-4}·C_{\mathrm{R}\mathrm{h}\mathrm{B}}·C_{{\mathrm{H}}_2{\mathrm{O}}_2}^{1.89}·C_{\mathrm{C}\mathrm{F}\mathrm{A}}^{1.97}-\mathrm{d}{\mathrm{C}}_{\mathrm{R}\mathrm{h}\mathrm{o}\mathrm{d}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{B}}/\mathrm{d}\mathrm{t}=1.76\times {10}^{-4}·{\mathrm{C}}_{\mathrm{R}\mathrm{h}\mathrm{o}\mathrm{d}\mathrm{a}\mathrm{m}\mathrm{i}\mathrm{n}\mathrm{e}\mathrm{B}}·{\mathrm{C}}_{{\mathrm{H}}_2{\mathrm{O}}_2}^{1.89}·{\mathrm{C}}_{\mathrm{c}\mathrm{o}\mathrm{a}\mathrm{l}\mathrm{f}\mathrm{l}\mathrm{y}\mathrm{a}\mathrm{s}\mathrm{h}}^{1.97}$. The loss of catalytic metallic elements causes the decline of catalytic capacity of CFA. The energy consumption (4313.3 kW·h kg^?1 RhB) is a limitation for the MW-Fenton-like process, which can be overcame by the safe application of nuclear energy. The intermediates and the path of RhB decolorization were detected and proposed, respectively.     

Distributional and inferential properties of some new multivariate process capability indices for symmetric specification region

Statistical quality control is used to improve performance of processes. Since most of the processes are multivariate in nature, multivariate process capability indices (MPCIs) have been developed by many researchers depending on the context. However, it is generally difficult to understand and calculate MPCIs, compared to their univariate counterparts like $C_p$, $C_{pk}$, and so on. This paper discusses a relatively new development in MPCIs, namely, $C_G(u,v)$, which is a multivariate analogue of $C_p(u,v)$—the celebrated superstructure of univariate process capability indices . Some statistical properties of $C_G(u,v)$ are studied, particularly of $C_G(0,0)$, a member MPCI of the superstructure, which measures potential capability of a multivariate process. A threshold value of $C_G(0,0)$ is computed, and this can be considered as a logical cut-off for other member indices of $C_G(u,v)$ as well. The expression for the upper limit of the proportion of nonconformance is derived as a function of $C_G(0,0)$. Density plots of asymptotic distributions of four major member indices of $C_G(u,v)$, namely, $C_G(0,0)$, $C_G(1,0)$, $C_G(0,1)$, and $C_G(1,1)$, are made. Finally, a numerical example is discussed to supplement the theory developed in this paper.     

Tensile strength of cohesive powders

Measurement and prediction of cohesive powder behaviour related to flowability, flooding or arching in silos is found to be very challenging. Previous round robin [52] attempts with ring shear testers did not furnish reliable data and have shown considerable degrees of scatter and uncertainty in key measurements. Thus studies to build a reliable experimental database using reference materials are needed in order to evaluate the repeatability and effectiveness of shear testers and the adopted procedures.In this paper, we study the effect of particle size on the yield locus for different grades of limestone (calcium carbonate). We use the nonlinear Warren Spring equation to obtain the values of cohesion C, tensile strength T, and the shear index n. We recover linear (n = 1) yield loci for $d_{50}>70$ μm with respectively small C and T, with consistent, finite macroscopic friction C/T = 0.7. With particle size decreasing below 70 μm the response becomes more and more cohesive and non-linear ($1<n<2$).Then we compare the values of the parameters $C,T$ and n obtained from two different shear testers (Schulze and Brookfield PFT). Both testers run at positive confining stresses (slightly different ranges) and give identical results for large fractions (weakly cohesive). For strongly cohesive samples, the PFT results are very similar to the ring shear tester, with slightly smaller values for T, C, and n. Further experiments with a variety of cohesive powders are needed to confirm or rebut this systematic difference the two testers display for cohesive powders.Finally, we compare the (extrapolated) values of T with a direct, transverse measurement running at negative stresses, using the Ajax tensile tester, and found a very good agreement, which validates the Warren Spring equation for negative stresses.