We describe an optical beam deflection technique for measurements of the thermal diffusivity of fluid mixtures and suspensions of nanoparticles with a precision of better than 1%. Our approach is tested using the thermal conductivity of ethanol-water mixtures; in nearly pure ethanol, the increase in thermal conductivity with water concentration is a factor of 2 larger than predicted by effective medium theory. Solutions of C60–C70 fullerenes in toluene and suspensions of alkanethiolate-protected Au nanoparticles were measured to maximum volume fractions of 0.6% and 0.35vol%, respectively. We do not observe anomalous enhancements of the thermal conductivity that have been reported in previous studies of nanofluids; the largest increase in thermal conductivity we have observed is 1.3%±0.8% for 4nm diam Au particles suspended in ethanol.

http://absimage.aps.org/image/MAR06/MWS_MAR06-2005-001994.pdf

Thermal conductivity of nanoparticle suspensions

Lightweight materials are of paramount importance to reduce energy consumption and emissions in today's society. For materials to qualify for widespread use in lightweight structural assembly, they must be weldable or joinable, which has been a long-standing issue for high strength aluminum alloys, such as 7075 (AA7075) due to their hot crack susceptibility during fusion welding. Here, we show that AA7075 can be safely arc welded without hot cracks by introducing nanoparticle-enabled phase control during welding. Joints welded with an AA7075 filler rod containing TiC nanoparticles not only exhibit fine globular grains and a modified secondary phase, both which intrinsically eliminate the materials hot crack susceptibility, but moreover show exceptional tensile strength in both as-welded and post-weld heat-treated conditions. This rather simple twist to the filler material of a fusion weld could be generally applied to a wide range of hot crack susceptible materials.

/pdf/nanoparticle-enabled-phase-control-for-arc-welding-of-4fgm69e8sr.pdf

Nanoparticle-enabled phase control for arc welding of unweldable aluminum alloy 7075.

Application of nanofluids in thermosyphons: A review

Influence of filler metals and welding techniques on the structure–property relationships of Inconel 718 and AISI 316L dissimilar weldments

Investigations on the microstructure, tensile strength and high temperature corrosion behaviour of Inconel 625 and Inconel 718 dissimilar joints

http://www.ysxbcn.com/down/paperDown.aspx?id=30932

Effect of pulsed current on temperature distribution, weld bead profiles and characteristics of gas tungsten arc welded aluminum alloy joints

Friction stir welding (FSW) is an important welding technique where in, and optimizing the process parameters will improve the joint strength of the welds. The FSW process and tool parameters play a major role in determining the joint strength. In this paper, an attempt has been made to establish an empirical relationship between the FSW process parameters (rotational speed, welding speed, and axial force) and predicting the maximum tensile strength of the joint. Statistical tools such as design of experiments, analysis of variance, and regression analysis are used to develop the relationships. A non-heat treatable aluminum alloy Aluminium Association 5059 of 4 mm thickness was used as the base material. Response surface methodology is employed to develop the mathematical model. Analysis of variance technique is used to check the adequacy of the developed mathematical model. The developed mathematical model can be used effectively at 95 % confidence level. The effect of FSW process parameter on mechanical property of Aluminium Association 5059 aluminum alloy has also been analyzed in detail.

A study to estimate the tensile strength of friction stir welded AA 5059 aluminium alloy joints

AA 5059 aluminium alloy is a material well suited for military applications because of its high strength to weight ratio and high toughness. Due to the high magnesium content, this material is frequently used in ship hull structure building because of its good corrosion resistance and good strength characteristics. Friction stir welding is a solid state welding process and it is a suitable method for joining non-ferrous materials such as aluminium alloys. The objective of this work is to predict the temperature distribution in butt welding of AA 5059 aluminium alloy of 4 mm thick plates during friction stir welding. Numerical simulations were developed as a three dimensional, non-linear finite element model using COMSOL multi-physics to predict the complete thermal history of the welded specimens. Experimental work has also been carried out to explore the thermal history of a workpiece. The temperatures predicted numerically are compared to the experimental values in order to evaluate the joint p...

Numerical predictions and experimental investigation of the temperature distribution of friction stir welded AA 5059 aluminium alloy joints

This paper compares temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded AZ31B magnesium alloy joints. The effect of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution are reported. The use of pulsed current technique has been found to improve the tensile properties of the welds compared to those of continuous current welds due to grain refinement occurring in the fusion zone.

/pdf/effect-of-pulsed-current-on-temperature-distribution-and-f2k8ib5vu7.pdf

Effect of Pulsed Current on Temperature Distribution and Characteristics of GTA Welded Magnesium Alloy

A thermosyphon is an efficient heat transfer device, which transports heat using gravity for the evaporation and condensation of the working fluid. In the present study the Box-Benhnken (BBD) design approach was chosen for the Two-Phase Closed Thermosyphon (TPCT) with CeO2 nanofluid using 0.1% volume of Nanofluid with surfactant of ethylene glycol. The experiment resulted in identifying the optimised set of parameters for 405SS TPCT, to achieve lower thermal resistance and better heat transfer. This work gains significance in the sense that with the number of experiments, reliable model has been generated validated and further, the process has been optimised with one objective which is thermal resistance. To obtain the optimum condition, the response surface methodology (RSM) through Box – Behnken (BBD) was applied.

https://www.ije.ir/article_72922_e8341562ca5247f7abd56c4a203751fd.pdf

N. Karunakaran

Papers

Effect of pulsed current on temperature distribution, weld bead profiles and characteristics of gas tungsten arc welded aluminum alloy joints

A study to estimate the tensile strength of friction stir welded AA 5059 aluminium alloy joints

Numerical predictions and experimental investigation of the temperature distribution of friction stir welded AA 5059 aluminium alloy joints

Effect of Pulsed Current on Temperature Distribution and Characteristics of GTA Welded Magnesium Alloy

Performance Investigation of 405 Stainless Steel Thermosyphon using Cerium (IV) Oxide Nano Fluid