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Wind turbine gearbox operates under a wide array of highly fluctuating and dynamic load conditions caused by the stochastic nature of wind and operational wind turbine controls. Micropitting damage is one of failure modes commonly observed in wind turbine gearboxes. This article investigates gear micropitting of high-speed stage gears of a wind turbine gearbox operating under nominal and varying load and speed conditions. Based on the ISO standard of gear micropitting (ISO/TR 15144-1:2010) and considering the operating load and speed conditions, a theoretical study is carried out to assess the risk of gear micropitting by determining the contact stress, sliding parameter, local contact temperature and lubricant film thickness along the line of action of gear tooth contact. The non-uniform distributions of temperature and lubricant film thickness over the tooth flank are observed due to the conditions of torque and rotational speed variations and sliding contact along the gear tooth flanks. The lubricant film thickness varies along the tooth flank and is at the lowest when the tip of the driving gear engages with the root of the driven gear. The lubricant film thickness increases with the increase of rotational speed and decreases as torque and sliding increase. It can be concluded that micropitting is most likely to initiate at the addendum of driving gear and the dedendum of driven gear. The lowest film thickness occurs when the torque is high and the rotational speed is at the lowest which may cause direct tooth surface contact. At the low-torque condition, the varying rotational speed condition may cause a considerable variation of lubricant film thickness thus interrupting the lubrication which may result in micropitting.

This paper proposes an optimization framework to deal with the uncertainty in a day-ahead scheduling of smart active distribution networks (ADNs). The optimal scheduling for a power grid is obtained such that the operation costs of distributed generations (DGs) and the main grid are minimized. Unpredictable demand and photovoltaics (PVs) impose some challenges such as uncertainty. So, the uncertainty of demand and PVs forecasting errors are modeled using a hybrid stochastic/robust (HSR) optimization method. The proposed model is used for the optimal day-ahead scheduling of ADNs in a way to benefit from the advantages of both methods. Also, in this paper, the ac load flow constraints are linearized to moderate the complexity of the formulation. Accordingly, a mixed-integer linear programming (MILP) formulation is presented to solve the proposed day-ahead scheduling problem of ADNs. To evaluate the performance of the proposed linearized HSR (LHSR) method, the IEEE 33-bus distribution test system is used as a case study.

Since 2015, the intended climate actions of the Paris Agreement signatories have been reported as nationally determined contributions (NDC). These climate actions are fully aligned with the 13th Sustainable Development Goal (SDG) which calls for urgent action to combat climate change. The same, however, cannot be said for their relation to the other 16 SDGs of the 2030 Agenda for Sustainable Development, since climate action can either enhance or compromise the prospects for SDG implementation. In light of this challenge, this paper proposes a simple method for quantifying the synergies and trade-offs between national climate actions and the SDGs. The method, referred to as Q-SCAN, makes use of a seven-step scale and the SDG Climate Action Nexus tool. The effectiveness of the method has been demonstrated on a case study of North Macedonia, a non-Annex I, Western Balkan country with a coal-intensive energy system. Based on the experience in the preparation of the country’s enhanced NDC, the paper elaborates how the method can be used to contribute to the alignment of the national climate actions with the SDGs and how it can be used to improve stakeholder engagement.

Vehicles with hybrid drive systems, are increasingly more often being equipped with solutions that increase the drive systems efficiency. One of such solutions is to use an increased supply voltage for electric motors of such vehicles. The battery voltage is increased several times in the inverter system in order to increase the electrical power supplied to the electric motor. This article presents possible uses of such voltage amplification (called boost) in urban traffic conditions. The tests used the latest models of vehicles with hybrid drive systems equipped with the same drive units: Lexus NX 300h and Toyota RAV4 Hybrid. The study analyses the conditions of starting such a system and the characteristics of its operation. It has been shown that the amplification of the voltage powering the electrical machinery in both vehicles occurs at high torque values. The maximum voltage amplification–almost threefold (up to 650 V) allows a two-fold increase in the torque of the drive system.

Abstract The paper presents a review of publications devoted to the use of thermal-electric analogy in the analyses of solar collectors’ performance, with special focus on the shortcomings of the proposed models of the equivalent thermal network (ETN). Additionally, the study describes the principles of construction of the ETN, especially for large-scale solar thermal circuits. The process of heating the working medium flowing through the collector battery was also shown. The ETN model was presented both analytically (nodal potential method) and with the use of the Simulink package (MATLAB), which made it possible to investigate the effect of operating conditions on the parameters of the solar collector.

This paper is focused on the energy performance of buildings containing massive exterior building envelope components. The effect of mass and insulation location on heating and cooling loads is analyzed for six characteristic wall configurations. Correlations between structural and dynamic thermal characteristics of walls are discussed. A simple one-room model of a building exposed to periodic temperature changes is analyzed to illustrate the effect of material configuration on the ability of a wall to dampen interior temperature swings. Whole-building dynamic modeling using DOE-2.1E is employed for the energy analysis of a one-story residential building with various exterior wall configurations for six different US climates. The best thermal performance is obtained when massive material layers are located at the inner side and directly exposed to the interior space.

Abstract The paper was aimed at evaluating the efficiency of impregnation of composite catalysts consisting of K, Na and/or Ca on a coal surface and the impact of composition of two-component catalysts and amount of three-component catalysts on the steam gasification reactions of coal. To this end, detailed analysis of the prepared samples was performed, and isothermal gasification measurements at various temperatures were carried out. The measurements enabled the examination of carbon conversion reaction and formation reactions of CO and H2 using reactivity indicators and kinetic parameters. The most efficient composites were 3 wt% of K/Na/Ca and 2 wt% of K/Na, although impregnation of Na was the least efficient, wherein the catalytic effect was observed only at low temperatures. In turn, higher amounts of three-component catalysts were catalytically inactive. Therefore, catalyst composition was more crucial than its amount or impregnation efficiency.

Abstract Currently, the first generation of silicon solar cells is dominating the photovoltaic market. Silicon cells are produced by various methods, which employ either crystalline or multi-crystalline substrates. However, both these manufacturing processes are expensive and potentially harmful to the environment and health. One example of this is that the surface is given its texture in a highly corrosive water solution of nitric and hydrofluoric acid. Additionally, both the diffusion and manufacturing of p-n junction and of metal contacts are associated with very high temperatures. This prompted us in our search for cheaper and more environmental friendly technologies. In this work, we discuss the possibility of producing components of photovoltaic cells by employing atomic layer deposition and hydrothermal technologies. This does not require the use of hazardous chemicals and high temperatures. The maximum efficiency of zinc oxide/silicon solar cells is 14% and 10% for textured and planar structures, respectively. A environmentally-friendly and simple procedure is thus being proposed, which, together with its relative efficiency, makes it an attractive alternative to the present procedure.

Pressure losses on the condensing-side of an air-cooled condenser (ACC) have the potential to inhibit condenser performance and, ultimately, curtail plant efficiency. However, little information is available on the magnitude and effect of these losses in an ACC under typical Rankine cycle operating conditions. This article seeks to improve current understanding on steam-side pressure losses in ACCs by presenting an experimental study on the losses in a full-scale ACC circular tube bundle. Saturated steam at low pressure was condensed by a cross flow of cooling air, provided by a bank of axial fans. Full condensation occurred in all measurements, which were carried-out over a steam pressure and temperature range of approximately 0.05e0.14 bar absolute and 33e55 � C, respectively. These test parameters ensured that measurement program test conditions were representative of those expected in an operational thermoelectric power plant. Experimental mass fluxes, per individual tube, varied from 0.7 to 2 kg/m 2 s during testing. The pressure drop characteristics were, therefore, analysed over a vapour Reynolds numbers range of 1890e5150 and liquid Reynolds number range of 25e95. Results indicate that the measured pressure drop through the tube bundle was relatively small, in the range of 130e250 Pa. As shown in this article, the reason for this was due to momentum recovery as the steam condenses to form liquid condensate. This phenomenon offsets the frictional losses, which are shown to be comparable in magnitude to momentum recovery in a condensing flow. However, this may not always be the case. Therefore, since the frictional component is traditionally the most problematic to predict, a range of liquidegas two-phase frictional pressure drop predictive models were reviewed, and are presented herein. Comparisons between these models and the experimental data show that the most applicable model was found to be that of Lockhart & Martinelli. This demonstrated reasonable accuracy of ±18%. © 2015 Elsevier Ltd. All rights reserved.