Abstract

Multi-stream heat exchanger is one of the most important components in CO2 purification process, which is characterized as high efficiency, low consumption and high energy density. This work aims to develop a CFD model for a multi-stream heat exchanger, based on which the impact of the impurities on heat transfer characteristics is studied. Three streams are considered, including two streams flowing in two concentric pipes and one stream flowing perpendicularly to the pipes. Based on the model, this work calculates the pressure drop and the average heat transfer coefficient which is calculated from the average heat transfer coefficient of two interfaces formed from these three fluids. It is found that the average heat transfer coefficient and friction pressure drop have an obvious downward trend with the increase of the volume fraction of impurity gas; under the same volume fraction of impurity gas, both of them increase with the increase of refrigerant velocity.

Abstract

In order to limit the negative effects of large circumferential thermal gradient in parabolic trough collectors (PTCs), enhancing the flow and heat exchange of the working fluid by embedding spiral slices in the absorber tube is a promising method. The absorber tube with the secondary reflector (SRAT) was proposed which solar flux is significantly uniformly distributed. The thermodynamic performance of the embed spiral slices absorber tube (ESAT) is analyzed and compared with that of the SRAT by building a thermal-structure coupled model. It can be found that compared to traditional absorber tubes, the circumferential temperature difference of ESAT with different pitches is reduced by 13%-53%, and the maximum thermal stress displacement is reduced by 32%-50%, which is much less than that of SRAT. However, under the simulated conditions, ESAT eliminates the high-temperature boundary zone of the working fluid and the useful energy of the working fluid increases by about 7% compared to SRAT, but the outlet pressure loss increases. This research can improve the energy efficiency, economy, and reliability of parabolic trough collectors.

Abstract

In the context of climate change and the increasing demand for sustainable solutions in the energy sector, it is of particular interest to consider environmental impacts of alternative energy systems or transformation pathways. In this study, this is achieved by combining an energy system model with a life cycle assessment, enabling the consideration and optimization of factors such as global warming potential, metal depletion potential and land occupation potential in addition to system costs. The individual optimization of these four objectives is extended by a multi-objective optimization using the augmented ε-constraint method. This is applied to the Rhenish Mining Area, a lignite region in Germany that currently undergoes significant structural change, with an electricity system expansion planning for 2040. Depending on the objective, gas-fired power plants or onshore wind energy are strongly preferred. For every objective, the electricity generation in the considered region decreases, especially when environ-mental impacts are minimized, which transforms the Rhenish Mining Area from a current electricity export region to an import region.

Abstract

The effects of anaerobic co-digestion at household level with waste activated sludge and food waste as co-substrates were studied in a GD-BMP test with mix ratio volatile solids basis of 20:80, 30:70, 50:50, 70:30 and 80:20 (WAS/OW) respectively. The results obtained were used to assess the feasibility of energy generation and the volume of each waste that can be treated. The highest specific methane yield calculated was of 431.31mLCH4/gVSadded from the 30:70 mix ratio sample with an RSD of 4.68%. It was hypothesized that the benefits of adding food waste will shift the C/N ratio leading to a potential coverage to reduce the energy demand from households by 50%. In addition, the benefits from a house scale SBR with microbubble aeration followed by SCSTR anaerobic co-digestor. Using the 30:70 mix ratio analyzed, a calculation to obtain the electrical energy that can be recovered from a single household resulted in a 30% reduction of energy coming from the grid. This paper reflects that biogas can be used as a replacement of fossil fuels, reducing the carbon dioxide footprint and the strong link to the WEF Nexus cycle, and discusses the implications.

Abstract

An optical-thermal coupled model was developed to study the performance of a typical molten-salt solar power tower, which was proven to be reliable by comparing with testing data. It is found that the mean absolute deviations between simulation and testing data are about 0.8% for the receiver efficiency under full-power condition. The model reveals that the detailed distributions of the solar flux and temperature in the receiver are extremely non-uniform, which resulted in high thermal stress at the tube crown. Moreover, failure analysis of the receiver indicates that the high strain introduced by high flux can result in fatigue failure, but it can be avoided by reasonable aiming strategy. The validated model and results from this work can offer helps for appropriate performance predictions in solar power tower.

Abstract

This paper provides a performance assessment of different fractions of crude plant digestive juices produced by Nepenthes mirabilis (N. mirabilis) which were used to pretreat mixed agro-waste to determine which fraction produces more holocelluloses while reducing phenolic compounds in the hydrolysate. Fractionation (<3kDa, ˃ 3kDa and <10kDa, ˃ 10kDa) was done with the different fractions being used to pretreat the mixed agro-waste (1:1 ratio, i.e., 25% (w/w) for each; 1 g orange peels, 1 g apples peels, 1 g maize cobs, 1 g grape pomace and 1 g oak plant yard litter) of various particle sizes, i.e., >106µm, >75µm <106µm. The highest results obtained indicated 46,63 (min) to 115,19 (max) g/L for total reducing sugars (TRS) production with a maximum of 6,61 g/L for total residual phenolic compounds (TRPCs) being observed using the <10 kDa/>106µm fraction/particle size of N. mirabilis/agrowaste after 72 hrs, revealing the efficacy of different juice fractions to pretreat the agro-waste. Overall, the digestive enzymes in N. mirabilis pods must be fractionated for agro-waste pretreatment, i.e., using a green chemistry approach for the development of biorefineries, for sustainable renewable energy generation and security.

Abstract

The pitch system plays a key role in the large offshore wind turbine for regulating pitch angle to the desired one and hence to stabilize the power out. However, due to the uncertainty of time-varying parameters and various unknown disturbances acting on the turbine blades, accurate and rapid regulation of pitch angle can hardly be achieved using the existing available pitch control strategy. Moreover, the actuator faults of the pitch system may occur in the long-term operation of the wind turbine, which greatly reduces the reliability and power generation efficiency. Aiming at the above problems, a nonlinear model of the pitch system considering time-varying parameter uncertainties and unknown disturbances is established, based on which a neural adaptive fault-tolerant control strategy with a rate function is proposed. A co-simulation is developed, and the merits of the proposed method are verified.

Abstract

Wearable electronics are demonstrating great potential in many areas, but finite capacity of chemical batteries become a bottleneck of their applications. We develop three kinds of wrist-worn energy harvesters that have different power enhancement mechanisms to address this issue. A compact energy harvester with magnetic frequency-up converter is developed to increase energy conversion capacity while a tiny repulsive magnetic spring is introduced to enhance response motion. Besides, a proof-massless energy harvester is investigated to improve motion capture capacity of wrist-worn energy harvester. A general model is constructed to predict the performances of these energy harvesters. The experimental results show that these energy harvesters achieve significant power improvement and their power output and power density can reach ten times that of the counterparts.

Abstract

The United Nations Industrial Development Organization (UNIDO) implemented the Mediterranean Transfer of Environmentally Sound Technology (MED/TEST) Phase II in the Southern Mediterranean Region between 2016 and 2018. This paper reports the findings of resource efficiency demonstrations with 58 companies in three North African countries (Algeria, Morocco, and Tunisia). The paper draws on the findings of Material Flow Cost Accounting that estimates the full costs of energy, water and rawmaterials used in production processes, and of Resource Efficiency and Cleaner Production Assessments that identify feasible and cost-effective interventions. The combination of these two tools allows for a comparison of the payback periods of a full range of potential resource efficiencymeasures.Not surprisingly, there are severalwater and raw materials measuresthat havereturns on investment similar to those for energymeasures.

Abstract

Recent years have witnessed a transition in energy structure, where large number of electronic devices and systems are introduced in multiple fields including industry, academia, commerce, and so forth. Safe and efficient operations of these systems are critical to ensure productivity as well as to avoid hazard, which poses strict demands on fault diagnosis. Most of traditional methods tend to focus on algorithm design or certain types of hardware or software flaws under given operational conditions, thus not suitable for modern electronic systems that may suffer from a variety of different faults. In this paper, on top of our previous work on big data, a systematic way of fault diagnosis in electric vehicles is put forward, which covers data processing, feature extraction, model-based diagnosis, and model fusion. The proposed method is trained and validated using data from real-world electric vehicles, which are representative examples of modern complex systems. Results show a diagnosis accuracy over 95% can be achieved with a comprehensive consideration of fault modes under a variety of operational scenarios. The proposed algorithm can also be used to indicate key features leading to faults so that system level upgrade can be performed accordingly. The design criteria and idea of the algorithm is also adaptable to other systems or applications with minor changes.