scholarly journals Modelling Thermal Conduction in Polydispersed and Sintered Nanoparticle Aggregates

Nanomaterials ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 25
Author(s):  
Nikolaos P. Karagiannakis ◽  
Eugene D. Skouras ◽  
Vasilis N. Burganos
Keyword(s):  
Thermal Conductivity ◽  
Point Contact ◽  
Mass Conservation ◽  
Simulation Method ◽  
Morphological Properties ◽  
Sintering Process ◽  
Uniform Size ◽  
Particle Aggregates ◽  
Nanoparticle Aggregates ◽  
Size Uniformity

Nanoparticle aggregation has been found to be crucial for the thermal properties of nanofluids and their performance as heating or cooling agents. Most relevant studies in the literature consider particles of uniform size with point contact only. A number of forces and mechanisms are expected to lead to deviation from this ideal description. In fact, size uniformity is difficult to achieve in practice; also, overlapping of particles within aggregates may occur. In the present study, the effects of polydispersity and sintering on the effective thermal conductivity of particle aggregates are investigated. A simulation method has been developed that is capable of producing aggregates made up of polydispersed particles with tailored morphological properties. Modelling of the sintering process is implemented in a fashion that is dictated by mass conservation and the desired degree of overlapping. A noticeable decrease in the thermal conductivity is observed for elevated polydispersity levels compared to that of aggregates of monodisperse particles with the same morphological properties. Sintered nanoaggregates offer wider conduction paths through the coalescence of neighbouring particles. It was found that there exists a certain sintering degree of monomers that offers the largest improvement in heat performance.

scholarly journals Improvement of mechanical properties of HfB2-based composites by incorporating in situ SiC reinforcement through pressureless sintering

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
S. Ghadami ◽  
E. Taheri-Nassaj ◽  
H. R. Baharvandi ◽  
F. Ghadami
Keyword(s):  
Mechanical Properties ◽  
Thermal Conductivity ◽  
Relative Density ◽  
Pressureless Sintering ◽  
Sintering Process ◽  
Vacuum Atmosphere ◽  
Sic Reinforcement ◽  
Microstructural Studies ◽  
Composite Samples

AbstractHfB2, Si, and activated carbon powders were selected to fabricate 0–30 vol% SiC reinforced HfB2-based composite. Pressureless sintering process was performed at 2050 °C for 4 h under a vacuum atmosphere. Microstructural studies revealed that in situ SiC reinforcement was formed and distributed in the composite according to the following reaction: Si + C = SiC. A maximum relative density of 98% was measured for the 20 vol% SiC containing HfB2 composite. Mechanical investigations showed that the hardness and the fracture toughness of these composites were increased and reached up to 21.2 GPa for HfB2-30 vol% SiC and 4.9 MPa.m1/2 for HfB2-20 vol% SiC, respectively. Results showed that alpha-SiC reinforcements were created jagged, irregular, and elongated in shape which were in situ formed between HfB2 grains and filled the porosities. Formation of alpha-SiC contributed to improving the relative density and mechanical properties of the composite samples. By increasing SiC content, an enhanced trend of thermal conductivity was observed as well as a reduced trend for electrical conductivity.

Effect of Intermetallic Compounds Content on Laser Welding Performance of Al-Fe Alloy Sheets

2014 ◽  
Vol 794-796 ◽  
pp. 401-406 ◽  
Author(s):  
Pi Zhi Zhao ◽  
Yan Feng Pan ◽  
Jiang Tao ◽  
Xiang Jun Shi ◽  
Qi Zhang
Keyword(s):  
Thermal Conductivity ◽  
Laser Welding ◽  
Intermetallic Compounds ◽  
Nonuniform Distribution ◽  
Welding Parameters ◽  
Lower Content ◽  
Absorbed Energy ◽  
Size Uniformity ◽  
Distribution Uniformity ◽  
Weld Pools

The present study investigated the laser welding performance of Al-Fe aluminum alloy sheets with different contents of intermetallic compounds. Under the same welding parameters, the alloy of higher intermetallic compounds content has wide and deep weld pools with uniform sizes. The alloy of lower intermetallic compounds content has narrow and shallow weld pools with nonuniform sizes. The higher content of intermetallic compounds results in higher laser absorptivity and lower thermal conductivity, and then increases the effective absorbed energy during welding, which is beneficial to the formation of wide and deep weld pools. The distribution uniformity of intermetallic compounds influences the size uniformity of weld pools. In the alloy with lower content of intermetallic compounds, the nonuniform distribution of intermeallic compounds results in the formation of abnormal weld pool, leading to the nonuniform size of the weld pools. In the alloy with higher content of intermetallic compounds, uniform distribution of intermetallic compounds make the size of weld pools more uniform.

Electrical Simulation Experiment and the Analysis of Thermal Conductivity of Materials

2014 ◽  
Vol 989-994 ◽  
pp. 599-602
Author(s):  
Wen Bo Li ◽  
Yin Gai Jin ◽  
Shuang Yin ◽  
Pei Yan Chen
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Simulation Experiment ◽  
Simulation Method ◽  
Measuring Method ◽  
Electrical Simulation ◽  
Conductive Plate ◽  
Electric Simulation ◽  
Unsteady Heat Conduction ◽  
Different Shapes

s: Jilin university innovation experiment Electrical Simulation Experiment and the Analysis of Thermal Conductivity of Materials aims to solve the problem of thermocouple measuring tenderness in error. Thermocouple is used to measure temperature when measuring unsteady heat conduction in laboratory. The improved measuring method of unsteady heat conduction puts the breakthrough on the electric simulation method. The text bench is constructed by different shapes of conductive plate which is made of the graphite conductive paint, and voltmeter is refitted by diodes and controlled transformer. Through the test bench, we finished the simulation of unsteady heat conduction under the similar thermal conductive boundary conditions. Finally, the error analysis of experiment and the advantages of electric simulation method are given in this paper.

Synthesis of LiCoO2 particles with tunable sizes by a urea-based-homogeneous-precipitation method

2020 ◽  
Vol 111 (4) ◽  
pp. 347-355
Author(s):  
Munekazu Motoyama ◽  
Hiroki Iwasaki ◽  
Miyuki Sakakura ◽  
Takayuki Yamamoto ◽  
Yasutoshi Iriyama
Keyword(s):  
Size Distribution ◽  
Average Diameter ◽  
Precipitation Method ◽  
Homogeneous Precipitation ◽  
Uniform Size ◽  
Homogeneous Precipitation Method ◽  
Wide Range ◽  
Size Uniformity ◽  
Average Size ◽  
Uniform Size Distribution

Abstract This paper reports the synthesis of monodisperse spherical LiCoO2 particles in a wide range of average diameter using a urea-based-uniform-precipitation method. The average diameter of LiCoO2 particles can be varied from 2 to 14 lm with a uniform size distribution. The effective approach to maintain the size uniformity while changing the average size of LiCoO2 particles is to keep the ratio of [CO(NH2)2] to [CoSO4] at 8 even when the CoSO4 and urea concentrations are changed.

scholarly journals Influence of Structural, Thermoelectric Power and Catalytic Efficiency of Nd-Doped Mn3O4

2019 ◽  
Vol 32 (1) ◽  
pp. 147-152
Author(s):  
V.T. Geetha ◽  
G. Puthilibai ◽  
S. Induja
Keyword(s):  
Particle Size ◽  
Saturation Magnetization ◽  
Crystallite Size ◽  
Thermoelectric Power ◽  
Catalytic Efficiency ◽  
Reflectance Spectroscopy ◽  
Reducing Agent ◽  
Morphological Properties ◽  
Uniform Size ◽  
Hexagonal Shape

Hexagonal shape Nd doped Mn3O4 samples were prepared via microwave route using urea as reducing agent. Nd doped Mn3O4 magnetic, structural, optical and morphological properties of the synthesized hexagonal like particles were examined by diffused reflectance spectroscopy (DRS) and photoluminescence (PL), XRD, SEM, TEM and vibrating sample measurements (VSM) studies. Morphological results showed the hexagonal shape morphology and uniform size dispersal. The crystallite size and the particle size calculated and the TEM monographs designate the correlation of the data obtained from both measurements. It could be noted that saturation magnetization (Ms) and remanence (Mr) values reduce by maximizing neodymium replacement.

scholarly journals Microscopic and mechanical properties of undistributed and remoulded red clay from Guiyang, China

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yanzhao Zhang ◽  
Shaoyun Pu ◽  
Rita Yi Man Li ◽  
Jing Zhang
Keyword(s):  
Point Contact ◽  
Morphological Properties ◽  
Line Contact ◽  
Red Clay ◽  
Undisturbed Soil ◽  
Pore Area ◽  
Distribution Index ◽  
Curved Slice ◽  
Clay Aggregates ◽  
Scanning Electron

Abstract Unconsolidated-undrained (UU) tests were conducted to investigate the mechanical and morphological properties of undisturbed and remoulded red clay, with the microscopic characteristics determined by scanning electron microscopy (SEM). The microanalysis showed that the red clay aggregate was granular, curved-slice and thin layered and flower-shaped ellipsoid, with X and Y-type cracks and pores in the undisturbed red clay. Moreover, the contact modes of red clay aggregates were point contact, line contact, surface contact and mosaic contact. In addition, the main microstructure red clay was flocculation, honeycomb and pseudosphere structures. The pores in undisturbed soil were arranged in one direction, with no obvious directionality in remoulded red clay. The pore area, perimeter and maximum length of undisturbed red clay were smaller than those of remoulded red clay, with a larger probability entropy, probability distribution index and fractal dimension of pore distribution of undisturbed red clay than remoulded red clay. UU tests showed that the shear strength of undisturbed red clay was higher than that of remoulded red clay.

Bounds of the Thermal Conductivity in Discontinuously Reinforced Metal-Matrix Composites

2005 ◽  
Vol 475-479 ◽  
pp. 3335-3338
Author(s):  
F. Alhama ◽  
Diego Alcaraz ◽  
S. Gómez-Lopera
Keyword(s):  
Thermal Conductivity ◽  
Metal Matrix Composites ◽  
Metal Matrix ◽  
Computing Time ◽  
Simulation Method ◽  
Matrix Composites ◽  
Limit Values ◽  
Wide Range ◽  
Particulate Reinforced ◽  
Network Simulation Method

A simple model based on the network simulation method is proposed to estimate numerically the thermal conductivity of particulate reinforced metal-matrix composites. The estimation is carried out running the model in the standard Pspice code, the computing time being negligible. The 3-D solid is discretized in 1000 cubic volume elements which represent an acceptable approximation of the shape of the particles. For each reinforcement percentage and each combination of matrix and reinforcement more than 200 tests were carried out, so that the results may be considered close to the exact values. The limit values are scarcely influenced by the effect of the 3-D geometry and basically depend on the amount of the reinforcement. Applications to aluminum and titanium matrix composites reinforced with different types of particles are presented covering a wide range of reinforcement percentages.

The Behavior of Copper Nanoparticle Chain Aggregates Under Strain – A Molecular Dynamics Approach

2003 ◽  
Vol 778 ◽  
Author(s):  
Adamos S. Dalis ◽  
Sheldon K. Friedlander
Keyword(s):  
Molecular Dynamics ◽  
Plastic Deformation ◽  
Embedded Atom Method ◽  
Sintering Process ◽  
Nano Composite ◽  
Embedded Atom ◽  
Reinforcing Fillers ◽  
Nanoparticle Aggregates ◽  
Chain Aggregates ◽  
Interface Sliding

AbstractNanoparticle chain aggregates (NCA) serve as reinforcing fillers that are combined with molecular polymers to produce nano-composite materials, e.g. carbon black in rubber. The reinforcing mechanism due to the incorporation of nanoparticle aggregates is not well understood. Molecular dynamics (MD) computer simulations are employed to investigate the behavior of nanoparticle chain aggregates under strain. The interaction potential used is that of Cu obtained with the embedded atom method (EAM). Three single-crystal Cu nanoparticles are placed in contact in two different configurations (linear and kinked) and the structures are initially relaxed with MD steps for 300 ps. We observe plastic deformation during the sintering process for very small particles (∼2.5 nm in diameter) at temperatures as low as 300 K. The relaxed configurations are then strained to the breaking point at strain rates in the order of 1 m/s. We identify mechanisms of strain accommodation that lead to nanoparticle plastic deformation and eventually fracture. The linear and the kinked configurations break at strains of 0.263 and 0.344 respectively, while the maximum stress is close to 4 GPa (strain rate: 0.625 m/s). Both structures fail at the low-angle grain boundaries developed during the sintering process, while the higher strain for fracture for the kinked configuration is associated with interface sliding not observed in the linear case.

Mechanical Properties of Microscale Graphitic Carbon Foam Ligaments and Nodes

2009 ◽  
Author(s):  
S. Ganguli ◽  
A. K. Roy ◽  
R. Wheeler
Keyword(s):  
Thermal Conductivity ◽  
Thermal Management ◽  
Thermal Protection ◽  
Solid Phase ◽  
Coefficient Of Thermal Expansion ◽  
Carbon Foam ◽  
High Thermal Conductivity ◽  
Uniform Size ◽  
Open Cell ◽  
Carbon Foams

Carbon foam is recognized as having the greatest potential to replacement for metal fins in thermal management systems such as heat exchangers, space radiators, and thermal protection systems [1–5]. Carbon foam refers to a broad class of materials that include reticulated glassy, carbon and graphitic foams that are generally open-cell or mostly open-cell. They can be tailored to have low or high thermal conductivity with a low coefficient of thermal expansion and density. These foams have high modulus but low compression and tensile strength. Among the carbon foams, the graphitic foam offers superior thermal management properties such as high thermal conductivity. Graphitic foams are made of a network of spheroidal shell segments. Each cell has thin, stretched ligaments in the walls that are joined at the nodes or junctions. The parallel arrangement of graphene planes in the ligaments confers highly anisotropic properties to the walls of the graphitic foams. The graphene planes tend to be oriented with the plane of the ligaments but become disrupted at the junctions (nodes) of the walls. Since conduction is highest along parallel graphene planes, the thermal conductivity is highest in the plane of the ligaments or struts, and much lower in the direction transverse to the plane of these ligaments. In a previous study [6] extensive mechanical and thermal property characterization of carbon foams from Kopper Inc. (L1) and POCO Graphite, Inc. (P1) were reported. These foams were graphitic ones that are expected to have high thermal conductivity. Figure 1 shows sections of light microscopy images of the three foams of four foams. The most important thing to notice is that the images were not at the same magnification. The large cells in the GrafTech foam have an average diameter of only ∼100 μm but have a bimodal distribution cells with many small closed-cells few micrometers in diameter. Changes in density in the GrafTech foam was accompanied by a change in the large cells’ diameter — larger diameter giving greater porosity and lower density without changing the smaller cells’ sizes that filled the solid phase between the larger bubbles. The POCO foam has a fairly uniform size cell distribution of a few hundred micrometers. The Koppers’ foams show larger cells yet with the left (“L” precursor) having a uniform size while the right-hand (“D” precursor) is a less uniform and lower porosity.

Prediction of the Density & Thermal Conductivity of Light Bricks on the Effect of Aluminium Elements Using Artificial Neural Network (ANN)

2019 ◽  
Vol 964 ◽  
pp. 270-279
Author(s):  
Zulkifli ◽  
Gede Panji
Keyword(s):  
Neural Network ◽  
Thermal Conductivity ◽  
Artificial Neural Network ◽  
Raw Materials ◽  
Simulation Method ◽  
Acoustic Properties ◽  
Main Element ◽  
Artificial Neural ◽  
Artificial Neural Network Ann ◽  
Element Variation

Indonesia with abundant limestone raw materials, lightweight brick is the most important component in building construction, so it needs a light brick product that qualifies in thermal, mechanical and acoustic properties. In this paper raised the lightweight brick domains that qualify on the properties of thermal conductivity as building wall components.The advantage of low light density brick (500-650 kg/m3), more economical, suitable for high rise building can reduce the weight of 30-40% in compared to conventional brick (clay brick). To obtain AAC type lightweight brick product that qualifies for low thermal and density properties to the effect of Aluminum (Al) additive element variation using artificial neural network (ANN). The composition of the main elements of lightweight brick O (29-45 % wt), Si (25-35% wt) and Ca (20-40 % wt). Mixing ratio of the main element of light brick (Ca, O and Si) with Aluminum additive element (Al), is done by simulation method of artificial neural network (ANN), Al additive element as a porosity regulator is formed. The simulation of thermal conductivity to the influence of main element variation: Ca (22-32 % wt), Si (12-33 % wt). Simulation of thermal conductivity to effect of additive Al variation (1-7 % wt). Simulation of thermal conductivity to density variation (500-1200 kg/m3). The simulated results of four AAC brick samples showed the thermal conductivity (0.145-0.192 W/m.K) to the influence of qualified Aluminum additives (2.10-6.75 % wt). Additive Al the higher the lower density value (higher porosity) additive Al smaller than 2.10 % wt does not meet the requirements in the simulation.Thermal conductivity of AAC light brick sample (0.184 W/m.K) the influence of the main elements that qualify Ca (20.32-30.35 % wt) and Si (26.57 % wt). Simulation of artificial neural network (ANN) of light brick shows that maximum allowable Si content of 26.57 % wt, Ca content is in the range 20.32-30.35 % wt, and the minimum content of aluminum in brick is light at 2.10 % wt. ANN tests performed to predict the thermal conductivity of light brick samples obtained results of the average AAC light brick thermal conductivity of 0.151 W/m.K. The best performance with Artificial Neural Network (ANN) characteristics has a validation MSE of 0.002252.

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