• Energy Research
• 7. Clean energy close
• 11. Sustainability close
• Polytechnique Montréal close

In this paper, we present the conjugate heat transfer analysis in a 167-kVA dry-type transformer using the parallel version of the computational fluid dynamics code Fluent 6.0. The renormalization group kappa-epsiv model is proposed to compute the turbulent aspect of the convective airflow inside the transformer metal tank for Air Natural/Air Natural cooling conditions. An experimental approach was used to assess Joule losses in the low-/high-voltage windings and eddy-current losses in the magnetic core. The resulting mathematical model was solved using 14 compute nodes on a distributed machine.

Abstract The importance of integrating resources criticality assessment into Life Cycle Assessment (LCA) under the Life Cycle Sustainability Assessment (LCSA) framework has been discussed for some time. However, the question how to proceed towards integration remain unclear. Only very few work is published on this issue and to our knowledge only Schneider et al. (2014) have developed one operational model. In this paper we review existing literature critically and explain why integration is important and how it could be done, using knowledge from outside the LCA field. The criticality assessment method proposed by Graedel et al. (2012) is identified as the best starting point. This paper shows based on a critical review why bridging towards such a method could help addressing criticality in LCSA, what are possible options and which research needs exists. It reveals that currently LCA does not adequately cover resource criticality and that methods like Graedel et al. (2012) are inspiring further development of LCA; both approaches have a complementary nature and hence could be developed towards integration within the LCSA framework. Currently resource indicators are not meaningful in LCA, wherefore there is no consensus in LCA community on what to recommend; hence the Area of Protection Natural Resources needs to be rethought. Broadening the scope of LCA towards LCSA provides a conceptual framework to keep LCA relevant for assessing sustainability challenges like access to resources.

Abstract The choice of the calculation pathways used to estimate the environmental impact of human activities is of importance since it could modify the results of such studies. This is the case for the Life Cycle Analysis (LCA) which is now commonly used to perform environmental assessments: the allocation methods used have an important impact on calculations and can potentially affect the final results. This could have a very negative impact on the LCA in terms of adoption and trust in the results. In the current study, the Canadian swine sector has been used as a case study and the carbon footprint of pork production has been estimated regionally for the year 2006. In this study, these calculations were performed using different allocation approaches to study the impact and usefulness of each method. No-allocation, economic-allocation, and mass-allocation approaches were used. Owing to climate and production-type specificities, calculations were done for eastern and western Canada in addition to the national estimates. Total greenhouse gas emissions were higher in the east (3.5 Mt CO2e) than in the west (3.1 Mt CO2e). However, the carbon footprint followed an opposite trend. Considering the primal cut products and, in turn, the mass allocation, the economic allocation and no allocations, the CFs were 2.6 kgCO2e, 3.8 kgCO2e and 4.0 kgCO2e per kg of product for the east and 3.2 kgCO2e, 4.7 kgCO2e and 5.0 kgCO2e per kg of product for the west. The current study shows that, in fact, allocation methods are not interchangeable and should be selected based on the specificity of each study: the no-allocation approach can be used to analyze on-farm production, economic allocation is oriented to market studies, and mass allocation is well suited to environmental sustainability assessments.

This work aimed to investigate the effects of biomass species on fermentable sugar production, with respect to both energy consumption and sugar yield, using the modified traditional mechanical system from Pulp & Paper Mills as a potential biorefinery step. The study explored four lignocellulosic biomass species including corn stover, alfalfa, white birch and black spruce during the pretreatment process with and without the addition of NaOH. This was followed by a disk refining pretreatment under various operating conditions of gap size and consistency through a pilot scaled disk refining system. The study characterized and analyzed the chemical components and sugar streams obtained from the biomasses using the thermochemical and refining pretreatment and also analyzed the energy consumption of the disk refining system. The results show that for all the biomasses, the thermochemical process mainly removed lignin and hemicelluloses through a steaming pretreatment. From low to high, the lignin contents of the four biomasses are shown as follows: corn stover, alfalfa, white birch and black spruce. With respect to the refining pretreatment, when the gap size remains constant, black spruce has the longest fibers while corn stover has the shortest. Moreover, using enzymatic hydrolysis to evaluate the sugar yield revealed that the thermochemical pretreatment increased the sugar yield in accordance with how much lignin was removed from each biomass as well as their final lignin content. However, the additional refining treatment had a greater effect on corn stover and alfalfa than on white birch and black spruce due to the reduction in fiber length. Therefore, with respect to existing mechanical refining equipment, the modified thermochemical disk refining pretreatment (TCDRP) has a greater effect on agricultural biomass and hardwood (white birch). Specifically, the sugar yield of the TCDRP corn stover was the highest (97.3%) when compared to the other biomasses, while its energy consumption was 196 kWh/ton.

AbstractThe aim of this paper is to present a low‐cost solution for low‐power applications. A high‐frequency AC to DC converter respecting the EN 61000‐3‐2 standard and suitable for application in the power range of 300 W is presented. Its topology is based on a full‐bridge series‐resonant converter that operates below half the resonant frequency. The converter features zero‐current for both turn‐on and turn‐off and reduces the switching current for the output rectifier. These advantages make the series‐resonant topology suitable for operation at high frequency. A method for the design of an integrated LCT structure (Inductor–Capacitor–Transformer) is presented. Also, results of the application of a newly developed FEA (Finite Elements Analysis) formulation for the constructed LCT prototype are presented. It is shown that the necessary capacitance can be achieved by using a bifilar primary and the leakage inductance of the transformer replaces the physical inductor. Finally, two PFC (Power Factor Correction) series‐resonant converters, using integrated and discrete LCT, were built, tested and compared. Copyright © 2004 John Wiley & Sons, Ltd.

The draft tube design of a hydraulic turbine, particularly in low to medium head applications, plays an important role in determining the efficiency and power characteristics of the overall machine, since an important proportion of the available energy, being in kinetic form leaving the runner, needs to be recovered by the draft tube into static head. For large units, these efficiency and power characteristics can equate to large sums of money when considering the anticipated selling price of the energy produced over the machine's life-cycle. This same draft tube design is also a key factor in determining the overall civil costs of the powerhouse, primarily in excavation and concreting, which can amount to similar orders of magnitude as the price of the energy produced. Therefore, there is a need to find the optimum compromise between these two conflicting requirements. In this paper, an elaborate approach is described for dealing with this optimization problem. First, the draft tube's detailed geometry is defined as a function of a comprehensive set of design parameters (about 20 of which a subset is allowed to vary during the optimization process) and are then used in a non-uniform rational B-spline based geometric modeller to fully define the wetted surfaces geometry. Since the performance of the draft tube is largely governed by 3D viscous effects, such as boundary layer separation from the walls and swirling flow characteristics, which in turn governs the portion of the available kinetic energy which will be converted into pressure, a full 3D meshing and Navier-Stokes analysis is performed for each design. What makes this even more challenging is the fact that the inlet velocity distribution to the draft tube is governed by the runner at each of the various operating conditions that are of interest for the exploitation of the powerhouse. In order to determine these inlet conditions, a combined steady-state runner and an initial draft tube analysis, using a stage interface between them, must first be performed for each operating condition. Due to the computationally intensive nature of the evaluation process, the efficiency of the optimization algorithm becomes important. Therefore, a state-of-the-art hierarchical-metamodel-assisted evolutionary algorithm is used.

Abstract Liquid-to-liquid thermoelectric generators are now being considered for the purpose of converting low cost heat to electricity for local energy uses. The importance in investigating their system efficiency lies in the fact that the generator's purpose is to maintain a heat source and a heat sink for its embedded thermoelectric modules. Of particular importance is the generator's ability to maintain an asymmetric thermal field across its embedded modules since this mechanism partially dictates the devices' thermal to electric conversion efficiency. Indeed, since the modules' semiconductor materials' ability to generate an electromotive force is dependent on the quality of the thermal dipole across the material, gains in thermoelectric generator energy conversion efficiency are made possible with thermal system management. In an effort to improve the system conversion efficiency of a liquid-to-liquid thermoelectric generator (TEG), the present work builds upon recent advancements in TEG inner pipe flow optimisation by investigating the thermoelectric power enhancement brought upon by flow impeding panel inserts in a thermoelectric generator's flow channels for fixed thermal input conditions and with respect to varying insert panel densities. The pumping penalty associated with the flow impedance is measured in order to present and to discuss the net thermoelectric power enhancement.

Abstract An exergy-electrical analogy, similar to the heat transfer electrical one, is developed and applied to the case of integrated energy systems operating in buildings. Its construction is presented for the case of space heating with electric heaters, heat pumps and solar collectors. The proposed analogy has been applied to a set of system arrangement options proposed for satisfying the building heating demand (space heating, domestic hot water); different alternatives to connect the units have been presented with switches in a visualization scheme. The analogy for such situation has been performed and the study of a solar assisted heat pump using ice storage has been investigated. This diagram directly permits energy paths and their associated exergy destruction to be visualized; hence, sources of irreversibility are identifiable. It can be helpful for the comprehension of the global process and its operation as well as for identifying exergy losses. The method used to construct the diagram makes it easily adaptable to others units or structures or to others models depending on the complexity of the process. The use of switches could be very useful for optimization purposes.