Welding Metallurgy of

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

A Benchmark Study on the Thermal Conductivity of Nanofluids

Thermal conductivity of hybrid nanofluids: A critical review

This paper presents a state-of-the-art review on various techniques of heat transfer enhancement in latent heat thermal energy storage (LHTES) systems. Heat transfer enhancement in LHTES systems can be achieved through either geometric configuration and/or thermal conductivity enhancement. The use of extended surfaces such as fins or heat pipes is a common technique for heat transfer enhancement in LHTES systems and therefore, reviewed in details in this paper. Next, we studied the thermal conductivity enhancement techniques, which include the use of porous materials, nanoparticles with high thermal conductivity, and low-density materials. Finally, studies involving combined techniques for heat transfer enhancement are reviewed in the paper. The paper discusses research gaps in the methods of heat transfer enhancement for LHTES systems and proposed some recommendations.

Heat transfer enhancement of phase change materials for thermal energy storage applications: A critical review

Effects of various carbon nanofillers on the thermal conductivity and energy storage properties of paraffin-based nanocomposite phase change materials

Performance assessment of heat storage by phase change materials containing MWCNTs and graphite

Heat dissipation from electrical appliances is a significant issue with contemporary electrical devices. One factor in the improvement of heat dissipation is the heat transfer performance of the working fluid. In this study, we used plasma arc technology to produce a nanofluid of carbon nanoparticles dispersed in distilled water. In a one-step synthesis, carbon was simultaneously heated and vaporized in the chamber, the carbon vapor and particles were then carried to a collector, where cooling furnished the desired carbon/water nanofluid. The particle size and shape were determined using the light-scattering size analyzer, SEM, and TEM. Crystal morphology was examined by XRD. Finally, the characterization include thermal conductivity, viscosity, density and electric conductivity were evaluated by suitable instruments under different temperatures. The thermal conductivity of carbon/water nanofluid increased by about 25% at 50°C compared to distilled water. The experimental results demonstrated excellent thermal conductivity and feasibility for manufacturing of carbon/water nanofluids.

/pdf/preparation-and-characterization-of-carbon-nanofluid-by-a-20izbgyiyf.pdf

Preparation and characterization of carbon nanofluid by a plasma arc nanoparticles synthesis system

The Spot Varestraint test was used to evaluate the hot cracking susceptibility of several aluminium alloys namely 6061-T6, 6061-T6 (H), 7075-T6, 7075-T6 (H). The effects of augment strain, the number of thermal cycles and cold working (rolling) on the cracking susceptibility were investigated, and the total crack length was used to evaluate the hot cracking susceptibility. The results indicate that the number of thermal cycles is irrelevant to the hot cracking susceptibility in the weld fusion zone, but does affect this susceptibility in the heat affected zone (HAZ). More thermal cycles correspond to larger hot cracks in the HAZ, especially in the weld metal HAZ. The hot cracking susceptibility of materials increased with augment strain in both the fusion zone and the HAZ. Cold working of the materials can reduce their hot cracking susceptibility. The hot cracking susceptibility of 7075-T6 aluminium alloys is higher than that of 6061-T6. There was significant Cu segregation in the HAZ of 7075-T6 a...

Hot cracking of welds on heat treatable aluminium alloys

The purpose of this study is to investigate the effect of activating flux on the depth-to-width ratio (DWR) and hot cracking susceptibility of Inconel 718 alloy tungsten inert gas (TIG) welds. The Taguchi method is employed to investigate the welding parameters that affect the DWR of weld bead and to achieve optimal conditions in the TIG welds that are coated with activating flux in TIG (A-TIG) process. There are eight single-component fluxes used in the initial experiment to evaluate the penetration capability of A-TIG welds. The experimental results show that the Inconel 718 alloy welds precoated with 50% SiO2 and 50% MoO3 flux were provided with better welding performance such as DWR and hot cracking susceptibility. The experimental procedure of TIG welding process using mixed-component flux and optimal conditions not only produces a significant increase in DWR of weld bead, but also decreases the hot cracking susceptibility of Inconel 718 alloy welds.

https://ir.nctu.edu.tw:443/bitstream/11536/23615/1/000330209800014.pdf

Ching-min Cheng

Papers

Performance assessment of heat storage by phase change materials containing MWCNTs and graphite

Preparation and characterization of carbon nanofluid by a plasma arc nanoparticles synthesis system

Hot cracking of welds on heat treatable aluminium alloys

Effects of Flux Precoating and Process Parameter on Welding Performance of Inconel 718 Alloy TIG Welds

Hot Cracking in AZ31 and AZ61 Magnesium Alloy