László Kiss

Assessment of the Current Intensity for Preventing Ice Accretion on Overhead Conductors

This paper concerns the determination of the electric current requirements for an anti-icing technique based on the Joule effect. The minimum current intensity needed for preventing ice accretion depends on several conductor parameters, including external diameter, electrical resistance, as well as surface geometry (number and diameter of external strands). It depends also on meteorological conditions, such as air temperature, wind velocity, and liquid water content. The study comprises the elaboration of a mathematical model and the laboratory experiments for validation. This research work is mainly concerned with power-line conductor and atmospheric parameters. Therefore, four different types of single A1/S1 power-line conductors are investigated. The analytical model was validated with the experiments performed in the wind tunnel of CIGELE Icing Research Pavilion at the University of Quebec, Chicoutimi. In order to complete the mathematical model, it is necessary to assess the overall heat transfer coefficient (HTC) for stranded conductors. The HTC measurements are presented for conductors with different surface geometries

Transport Properties of Bulk Thermoelectrics: An International Round-Robin Study, Part II: Thermal Diffusivity, Specific Heat, and Thermal Conductivity

For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, partxa0II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.

Transport Properties of Bulk Thermoelectrics—An International Round-Robin Study, Part I: Seebeck Coefficient and Electrical Resistivity

Recent research and development of high-temperature thermoelectric materials has demonstrated great potential for converting automobile exhaust heat directly into electricity. Thermoelectrics based on classic bismuth telluride have also started to impact the automotive industry by enhancing air-conditioning efficiency and integrated cabin climate control. In addition to engineering challenges of making reliable and efficient devices to withstand thermal and mechanical cycling, the remaining issues in thermoelectric power generation and refrigeration are mostly materials related. The dimensionless figure of merit, ZT, still needs to be improved from the current value of 1.0 to 1.5 to above 2.0 to be competitive with other alternative technologies. In the meantime, the thermoelectric community could greatly benefit from the development of international test standards, improved test methods, and better characterization tools. Internationally, thermoelectrics have been recognized by many countries as a key component for improving energy efficiency. The International Energy Agency (IEA) group under the Implementing Agreement for Advanced Materials for Transportation (AMT) identified thermoelectric materials as an important area in 2009. This paper is partxa0I of the international round-robin testing of transport properties of bulk thermoelectrics. The main foci in partxa0I are the measurement of two electronic transport properties: Seebeck coefficient and electrical resistivity.

A Mesh-Free Solid-Mechanics Approach for Simulating the Friction Stir-Welding Process

In this chapter, we describe the development of a new approach to simulate the friction stir-welding (FSW) process using a solid-mechanics formulation of a mesh-free Lagrangian method called smoothed particle hydrodynamics (SPH). Although this type of a numerical model typically requires long calculation times, we have developed a very efficient parallelization strategy on the graphics processing unit (GPU). This simulation approach allows the determination of temperature evolution, elastic and plastic deformation, defect formation, residual stresses, and material flow all within the same model. More importantly, the large plastic deformation and material mixing common to FSW are well captured by the mesh-free method. The parallel strategy on the GPU provides a means to obtain meaningful simulation results within hours as opposed to many days or even weeks with conventional FSW simulation codes.

On‐line Monitoring of Individual Anode Currents to Understand and Improve the Process Control at Alouette

In 2014, Alouette acquired a system to monitor the on-line anode current on two pots. This system, developed and supplied by WIT, reports all anodes current and the pot voltage for every second of operation. The following paper describes some of the resulting improvements that apply to the process control of the aluminum electrolysis cell.

Comparative Analysis of the Environmental Impacts of Aluminum Smelting Technologies

This paper focuses on the global warming potential (GWP) of primary aluminum production analyzing the hotspots of greenhouse gas (GHG) emission. The major GHG emission of primary aluminum production is caused by aluminum smelting. Inert anodes or non-consumable anodes are considered as a solution to mitigate GHG emission of the Hall-Heroult process.

Behavior of Powders on the Surface of a Liquid

Agglomerates in the Hall-Heroult cell reduce the alumina dissolution rate and affect the stability of the process. Alumina agglomerates have been thoroughly studied, however their formation is not completely understood yet. This study focuses on the behavior of powders on the surface of a liquid, in an attempt to shed light on how alumina powder enters the electrolytic bath, as it could influence the formation of agglomerates. The ability of an object to float on the surface of a liquid could be determined by analyzing the force balance. Besides liquid properties, the shape of the object, bulk density and contact angle were analyzed. Beyond the analysis of single particles, the condition of floating of particle agglomerates was also examined, which could lead to the deeper understanding of the behavior of powders on a liquid surface and to a more accurate modeling of alumina feeding into the bath.

International Round-Robin Testing of Bulk Thermoelectrics

Two international round-robin studies were conducted on transport properties measurements of bulk thermoelectric materials. The study discovered current measurement problems. In order to get ZT of a material four separate transport measurements must be taken. The round-robin study showed that among the four properties Seebeck coefficient is the one can be measured consistently. Electrical resistivity has +4-9% scatter. Thermal diffusivity has similar +5-10% scatter. The reliability of the above three properties can be improved by standardizing test procedures and enforcing system calibrations. The worst problem was found in specific heat measurements using DSC. The probability of making measurement error is great due to the fact three separate runs must be taken to determine Cp and the baseline shift is always an issue for commercial DSC. It is suggest the Dulong Petit limit be always used as a guide line for Cp. Procedures have been developed to eliminate operator and system errors. The IEA-AMT annex is developing standard procedures for transport properties testing.

Conceptual Design of an Aluminium Bridge in Alma, QC

The City Council of Alma, Quebec, Canada intends to erect a new footbridge celebrating the 150-year anniversary of the city. Functioning as communal and cultural ground, an island will be built on the 100 m wide River Petite Décharge hosting a pedestrian area with pathways plants and artistic installations, being a symbolic landmark. The bridge has to provide connection between both the river sides and the island. Original and aesthetic design ideas for the bridge structure are searched. In the first phase of our work, preliminary study proposing 10 alternatives for the bridge was completed. The city has been selected three alternatives for further studies: double-arch classic bridge, classic cable stayed bridge with single pylon, artistic/industrial truss bridge with three lane decks. In the second phase of the work, we prepared the general preliminary design calculations, technical drawings, perspective drawings for the three selected versions. Common factor in all variants is the need and intent to apply advanced, state-of-the-art aluminium technology. The paper describes the evolution of the conceptual design of the bridge.

Development of a Mechanized Bath Sampling Method

The injection and the dissolution of alumina in the molten cryolite are crucial steps of the Hall-Heroult process because of their impact on the cell efficiency and stability. A better understanding of the dissolution can support the scientists to optimize the energy consumption of the electrolysis process. This requires the study of the dissolution kinetics of alumina experimentally. In order to follow the evolution of the alumina concentration with good precision after its injection, a semi-automatic mechanical sampling system has been developed. The computer controlled system is able to take molten bath samples at around 1000°C for later chemical and microstructural analysis. The appropriate operation of the sampling system required the resolution of several problems, like the choice of appropriate dimensions and material suitable for a very destructive environment. In the present paper, the design process, including problems and solutions, of a semi-automatic molten cryolite sampling system is presented.