Comparison of Conductivity of Al2O3 Nanofluids between Experiments and Maxwell Model

2013 ◽  
Vol 668 ◽  
pp. 571-574
Author(s):  
Jin Ze Yu ◽  
Bin Liu ◽  
Zhen Liang Li
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Mass Fraction ◽  
Base Fluid ◽  
Volume Fraction ◽  
Critical Role ◽  
Maxwell Model ◽  
Nano Particle ◽  
Coefficient Of Thermal Conductivity ◽  
Nano Fluids

The thermal properties of nano-fluids are affected by many factors. The effect of the diameter, mass fraction and volume fraction of Al2O3 in water on the thermal conductivity was measured by the method of hotwire. The diameter of nano-particle of Al2O3 was 10nm, 20nm, 50nm, 100nm and 500nm respectively. The mass fraction of Al2O3 in water was 10%, 12%, 15% and 20%. The results show that the diameter of the particle plays a critical role on thermal properties of the base fluid. And for the mass fraction, it will increase the thermal conductivity of the base fluid. When the size is more than 100nm, the coefficient of thermal conductivity is increased rapidly. Compared with the results calculated by the Maxwell model, the conductivity of the nanofulid with a diameter less than 10nm is consistent with the model’s result. And with the increasing of the diameter o f the nanoparticle, the deviation of the conductivity will also increase compared with the model’s results.

Prediction of effective thermal conductivity of nanofluids by modifying renovated Maxwell model

2016 ◽  
Vol 30 (3) ◽  
pp. 289-301 ◽  
Author(s):  
Deepti Chauhan ◽  
Nilima Singhvi
Keyword(s):  
Neural Network ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Base Fluid ◽  
Volume Fraction ◽  
Maxwell Model ◽  
Theoretical Models ◽  
Solid Particles ◽  
Nanoparticle Volume Fraction ◽  
Suspended Nanoparticles

Nanofluids, which are formed by suspending nanoparticles into conventional fluids, exhibit anomalously high thermal conductivity. Renovated Maxwell model was developed by Choi in which the presence of very thin nanolayer surrounding the solid particles was considered, which can measurably increase the effective thermal conductivity of nanofluids. A new model is proposed by introducing a fitting parameter χ in the renovated Maxwell model, which accounts for nanolayer, nonuniform sizes of filler nanoparticles together with aggregation. The model shows that the effective thermal conductivity of nanofluids is a function of the thickness of the nanolayer, the nanoparticle size, the nanoparticle volume fraction and the thermal conductivities of suspended nanoparticles, nanolayer and base fluid. The validation of the model is done by applying the results obtained by the experiments on nanofluids, other theoretical models, and artificial neural network technique. The uncertainty of the present measurements is estimated to be within 5% for the effective thermal conductivity.

scholarly journals Thermal Conductivity of Water Based Magnetite Ferrofluids at Different Temperature for Heat Transfer Applications

2018 ◽  
Vol 280 ◽  
pp. 36-42 ◽  
Author(s):  
H. Haiza ◽  
I.I. Yaacob ◽  
Ahmad Zahirani Ahmad Azhar
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Base Fluid ◽  
Volume Fraction ◽  
Heat Transfer Fluid ◽  
Water Based ◽  
Nanoparticles Concentration ◽  
C 30 ◽  
C 50

Magnetic magnetite, Fe3O4 nanoparticles produced by Massart’s procedure were used to prepare water based magnetite, Fe3O4 ferrofluids without addition of any stabilizing agent or surfactant. The thermal properties and suspension stabilization of the ferrofluids were investigated by varying the magnetite, Fe3O4 nanoparticles concentration in the ferrofluids prepared. The thermal conductivity of water based ferrofluids prepared using five different volume fraction of magnetite, Fe3O4 suspension (0.1, 0.05, 0.02, 0.01 and 0.005) were measured at five different temperature, 25°C, 30°C, 40°C, 50°C and 60°C in order to evaluate its potential application as heat transfer fluid. The results shows that the thermal conductivity of the ferrofluids are higher than the base fluid, and the thermal conductivity of the ferrofluids increased as the magnetite concentration in the ferrofluids decreased however reached its optimum for ferrofluids prepared using 0.01 volume fraction of magnetite suspension over 0.99 volume fraction of water. Accordingly, the thermal conductivity of the ferrofluids significantly increased as the temperature increased where 49.4% enhancement with respect to water were observed at temperature 60°C.

Thermal Characterization of Carbon-Carbon Composites

2011 ◽  
Author(s):  
Messiha Saad ◽  
Darryl Baker ◽  
Rhys Reaves
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Critical Role ◽  
Carbon Composite ◽  
Flash Method ◽  
Carbon Composites ◽  
Energy Storage Devices ◽  
Graphitized Carbon

Thermal properties of materials such as specific heat, thermal diffusivity, and thermal conductivity are very important in the engineering design process and analysis of aerospace vehicles as well as space systems. These properties are also important in power generation, transportation, and energy storage devices including fuel cells and solar cells. Thermal conductivity plays a critical role in the performance of materials in high temperature applications. Thermal conductivity is the property that determines the working temperature levels of the material, and it is an important parameter in problems involving heat transfer and thermal structures. The objective of this research is to develop thermal properties data base for carbon-carbon and graphitized carbon-carbon composite materials. The carbon-carbon composites tested were produced by the Resin Transfer Molding (RTM) process using T300 2-D carbon fabric and Primaset PT-30 cyanate ester. The graphitized carbon-carbon composite was heat treated to 2500°C. The flash method was used to measure the thermal diffusivity of the materials; this method is based on America Society for Testing and Materials, ASTM E1461 standard. In addition, the differential scanning calorimeter was used in accordance with the ASTM E1269 standard to determine the specific heat. The thermal conductivity was determined using the measured values of their thermal diffusivity, specific heat, and the density of the materials.

Study of the boundary layer heat transfer of nanofluids over a stretching sheet: Passive control of nanoparticles at the surface

2015 ◽  
Vol 93 (7) ◽  
pp. 725-733 ◽  
Author(s):  
M. Ghalambaz ◽  
E. Izadpanahi ◽  
A. Noghrehabadi ◽  
A. Chamkha
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Base Fluid ◽  
Stretching Sheet ◽  
Volume Fraction ◽  
Enhancement Ratio ◽  
Transfer Enhancement

The boundary layer heat and mass transfer of nanofluids over an isothermal stretching sheet is analyzed using a drift-flux model. The relative slip velocity between the nanoparticles and the base fluid is taken into account. The nanoparticles’ volume fractions at the surface of the sheet are considered to be adjusted passively. The thermal conductivity and the dynamic viscosity of the nanofluid are considered as functions of the local volume fraction of the nanoparticles. A non-dimensional parameter, heat transfer enhancement ratio, is introduced, which shows the alteration of the thermal convective coefficient of the nanofluid compared to the base fluid. The governing partial differential equations are reduced into a set of nonlinear ordinary differential equations using appropriate similarity transformations and then solved numerically using the fourth-order Runge–Kutta and Newton–Raphson methods along with the shooting technique. The effects of six non-dimensional parameters, namely, the Prandtl number of the base fluid Prbf, Lewis number Le, Brownian motion parameter Nb, thermophoresis parameter Nt, variable thermal conductivity parameter Nc and the variable viscosity parameter Nv, on the velocity, temperature, and concentration profiles as well as the reduced Nusselt number and the enhancement ratio are investigated. Finally, case studies for Al2O3 and Cu nanoparticles dispersed in water are performed. It is found that increases in the ambient values of the nanoparticles volume fraction cause decreases in both the dimensionless shear stress f″(0) and the reduced Nusselt number Nur. Furthermore, an augmentation of the ambient value of the volume fraction of nanoparticles results in an increase the heat transfer enhancement ratio hnf/hbf. Therefore, using nanoparticles produces heat transfer enhancement from the sheet.

Effect of Coating on the Thermal Conductivities of Diamond/Cu Composites Prepared by Spark Plasma Sintering (SPS)

2014 ◽  
Vol 722 ◽  
pp. 25-29 ◽  
Author(s):  
Q.L. Che ◽  
X.K. Chen ◽  
Y.Q. Ji ◽  
Y.W. Li ◽  
L.X. Wang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Theoretical Prediction ◽  
Volume Fraction ◽  
Interface Reaction ◽  
Copper Matrix ◽  
Bonding Force ◽  
Ti Alloys ◽  
Plasma Sintering ◽  
Spark Plasma

The carbide forming is proposed to improve interfacial bonding between diamond particles and copper-matrix for diamond/copper composites. The volume fraction of diamond and minor titanium are optimized. The microstructures, thermal properties, interface reaction production and its effect of minor titanium on the properties of the composites are investigated. The results show that the bonding force and thermal conductivity of the diamond/Cu-Ti alloys composites is much weaker and lower than that of the coated-diamond/Cu. the thermal conductivity of coated-60 vol. % diamond/Cu composites is 618 W/m K which is 80 % of the theoretical prediction value. The high thermal conductivity has been achieved by forming the titanium carbide at diamond/copper interface to gain a good interface.

Determination of the Thermal Properties of a PCB by Coupled Numerical and Experimental Approach

2020 ◽  
Author(s):  
Yener Usul ◽  
Mustafa Özçatalbaş
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Numerical Analysis ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Thermal Analyses ◽  
Analysis Model ◽  
Linear Temperature ◽  
Coefficient Of Thermal Conductivity

Abstract Increasing demand for usage of electronics intensely in narrow enclosures necessitates accurate thermal analyses to be performed. Conduction based FEM (Finite Element Method) is a common and practical way to examine the thermal behavior of an electronic system. First step to perform a numerical analysis for any system is to set up the correct analysis model. In this paper, a method for obtaining the coefficient of thermal conductivity and specific heat capacity of a PCB which has generally a complex composite layup structure composed of conductive layers, and dielectric layers. In the study, above mentioned properties are obtained performing a simple nondestructive experiment and a numerical analysis. In the method, a small portion of PCB is sandwiched from one side at certain pressure by jaws. A couple of linear temperature profiles are applied to the jaws successively. Unknown values are tuned in the analysis model until the results of FEM analysis and experiment match. The values for the coefficient of thermal conductivity and specific heat capacity which the experiment and numerical analysis results match can be said to be the actual values. From this point on, the PCB whose thermal properties are determined can be analyzed numerically for any desired geometry and boundary condition.

Influence of Mesocarp Fibre Inclusion on Thermal Properties of Foamed Concrete

2021 ◽  
Vol 87 (1) ◽  
pp. 1-11
Author(s):  
Siti Shahirah Suhaili ◽  
Md Azree Othuman Mydin ◽  
Hanizam Awang
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Volume Fraction ◽  
Thermal Constant ◽  
Volume Fractions ◽  
Foamed Concrete

The addition of mesocarp fibre as a bio-composite material in foamed concrete can be well used in building components to provide energy efficiency in the buildings if the fibre could also offer excellent thermal properties to the foamed concrete. It has practical significance as making it a suitable material for building that can reduce heat gain through the envelope into the building thus improved the internal thermal comfort. Hence, the aim of the present study is to investigate the influence of different volume fractions of mesocarp fibre on thermal properties of foamed concrete. The mesocarp fibre was prepared with 10, 20, 30, 40, 50 and 60% by volume fraction and then incorporated into the 600, 1200 and 1800 kg/m3 density of foamed concrete with constant cement-sand ratio of 1:1.5 and water-cement ratio of 0.45. Hot disk thermal constant analyser was used to attain the thermal conductivity, thermal diffusivity and specific heat capacity of foamed concrete of various volume fractions and densities. From the experimental results, it had shown that addition of mesocarp fibre of 10-40% by volume fraction resulting in low thermal conductivity and specific heat capacity and high the thermal diffusivity of foamed concrete with 600 and 1800 kg/m3 density compared to the control mix while the optimum amount of mesocarp fibre only limit up to 30% by volume fraction for 1200 kg/m3 density compared to control mix. The results demonstrated a very high correlation between thermal conductivity, thermal diffusivity and specific heat capacity which R2 value more than 90%.

Numerical Solution of Transient Heat Conduction Equation for Heat-Treatable Alloys Whose Thermal Properties Change With Time and Temperature

1977 ◽  
Vol 99 (3) ◽  
pp. 471-478 ◽  
Author(s):  
K. Farnia ◽  
J. V. Beck
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Differential Equations ◽  
Numerical Solution ◽  
Precipitation Hardening ◽  
Elevated Temperatures ◽  
Volume Fraction ◽  
Transient Heat Conduction ◽  
Computer Assisted ◽  
Al 2024

Changes in microstructure occur in as-received aluminum alloy (Al-2024-T351) when it is subjected to elevated temperatures (150–260°C). These changes, which are called precipitation hardening, in turn influence the thermal properties, making them time as well as temperature dependent. A computer-assisted transient experimental procedure has been developed to determine the values of thermal conductivity of as-received Al-2024-T351 under the influence of precipitation-hardening. Based on isothermal experimental data and related algebraic modeling of the thermal conductivity, a mathematical model in the form of two differential equations is proposed. Instantaneous values of volume fraction of precipitate and thermal conductivity can be predicted using this model. A method for the simultaneous numerical solution of the partial differential equation of conduction and the proposed differential equations of precipitation are also given. The influence of precipitation—hardening on temperature distribution and on values of thermal conductivity is shown graphically for several cases involving the Al-2024-T351 material.

Thermal properties of kinetic spray Al–SiC metal-matrix composite

2003 ◽  
Vol 18 (4) ◽  
pp. 855-860 ◽  
Author(s):  
Gary L. Eesley ◽  
Alaa Elmoursi ◽  
Nilesh Patel
Keyword(s):  
Thermal Conductivity ◽  
Thermal Expansion ◽  
Thermal Properties ◽  
Metal Matrix ◽  
Volume Fraction ◽  
Spray Deposition ◽  
Deposition Process ◽  
Matrix Composites ◽  
Kinetic Spray ◽  
Compositional Variations

Kinetic spray deposition provides a new means for producing composite materials with tailored physical properties. We report on measurements of the thermal conductivity and thermal-expansion coefficient for several compositional variations of kinetically sprayed Al–SiC metal-matrix composites. As a result of the deposition process, inclusion of SiC particles saturates in the 30–40% volume fraction range.

scholarly journals Synthesis of hybrid nanofluid with two-step method

2018 ◽  
Vol 67 ◽  
pp. 03057 ◽  
Author(s):  
Wayan Nata Septiadi ◽  
Ida Ayu Nyoman Titin Trisnadewi ◽  
Nandy Putra ◽  
Iwan Setyawan
Keyword(s):  
Thermal Conductivity ◽  
Base Fluid ◽  
Volume Fraction ◽  
Heat Transfer Fluid ◽  
Hybrid Nanofluid ◽  
Test Results ◽  
Step Method ◽  
Fluid Mixture ◽  
High Level ◽  
Better Than

Nanofluid is a liquid fluid mixture with a nanometer-sized solid particle potentially applied as a heat transfer fluid because it is capable of producing a thermal conductivity better than a base fluid. However, nanofluids have a weakness that is a high level of agglomeration as the resulting conductivity increases. Therefore, in this study, the synthesis of two nanoparticles into the base fluid called hybrid nanofluids. This study aims to determine the effect of nanoparticle composition on the highest thermal conductivity value with the lowest agglomeration value. This research was conducted by dispersing Al2O3-TiO2 nanoparticles in water with volume fraction of 0.1%, 0.3%, 0.5%, 0.7% in the composition of Al2O3-TiO2 ratio of 75%:25%, 50%:50%, 25%:75%. The synthesis was performed with a magnetic stirrer for 30 minutes. The tests were carried out in three types: thermal conductivity testing with KD2, visual agglomeration observation and absorbance measurements using UV-Vis, wettability testing with HSVC tools and Image applications. The test results showed that the ratio composition ratio of 75% Al2O3-25% TiO2 with a volume fraction of 0.7% resulted in an increase in optimum thermal conductivity with the best wettability and the longest agglomeration level.

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