To meet the increasing demand for efficient and durable catalysts for exhaust aftertreatment system, a mesoporous SiO2‐encapsulated nano‐Co3O4 catalyst was synthesized, which possesses a unique ...pitaya‐like structure with high CO oxidation activity and thermal stability. Though the silica matrix is inert, the encapsulated Co3O4 exhibits increased oxygen storage capacity, enhanced CO2 desorption behavior and high lattice oxygen reactivity. Additionally, the SiO2‐encapsulated Co3O4 catalyst can be effectively regenerated rather than the supported Co3O4/SiO2 and pure Co3O4. The kinetic results demonstrate that the L−H mechanism is followed over the pure Co3O4 nanoparticles catalyst, while the CO oxidation over the silica‐supported Co3O4 catalysts obey to both L−H and MVK mechanism. The encapsulation structure of the as‐prepared catalyst can effectively restrain the aggregation of Co3O4 during high temperature operations and improves the utilization efficiency of cobalt resources, as well, which would be suitable for practical applications.
Improved stability: Nano‐Co3O4 catalysts are incapsulated in mesoporous SiO2 matrix, which presents a unique pitaya‐like structure. Compared with the unsupported Co3O4 catalyst, the encapsulation structure can effectively restrain aggregation of Co3O4 nanoparticles under high temperature operating conditions and improves utilization efficiency of cobalt resources by exposing more active sites. The Co3O4@SiO2 catalyst exhibits high activity, and superior thermal stability and regeneration ability for CO oxidation, which could be potentially applied in practical catalytic systems.
The high penetration of renewable energy sources makes the two-by-one combined cycle gas-turbine (2 × 1 CCGT) with high operational flexibility (OPFL) become the mainstream of deep peak-load units. ...However, the thermos-exchanger water level (TEWL) often exceeds the limit and causes unit trip during flexible operations. For this reason, this paper proposes a flexible operational TEWL control strategy. First, by modeling and analyzing the thermodynamics of the thermal-supply system of 2 × 1 CCGT unit, the exhaust steam pressure of intermediate pressure cylinder (IPEP) is chosen as an upstream controlled variable with mathematical-model derived setpoint to stabilize the TEWL; Secondly, considering the heat storage utilization of heating network, the heating-network circulating water flow is selected as the manipulated variable of IPEP control, then forming a pilot IPEP control loop cooperating with the existing TEWL control loop to stabilize the TEWL. Several control algorithms are designed and compared to determine the most effective one for the IPEP pilot-TEWL control. The results show that the maximal deviation of TEWL can be reduced to 7 mm and the OPFL indexes can be significantly improved, i.e. the average power ramp rate is 6.74 MW/min, and the power capacity is 69.55 MW from 158 MW steam turbine.
•A control-oriented dynamic model of thermal-supply of 2 × 1 CCGT is presented.•A pilot control strategy is proposed to enhance the stability of the TEWL.•Several control algorithms are designed and compared on stabilizing TEWL.•The pilot control strategy can greatly improve the operational flexibility of CCGT.
In a virus pandemic context, buildings ventilation has been recognized as a solution for preventing transmission of the virus in aerosolized form. The impact of the widespread recommendation of ...window opening and sealing door on ventilation circuits needs to be considered with a multizone approach. We modeled the airflow distribution in a building where people are isolating in a pandemic context, including one infected person. We analyzed the impact of opening the window and sealing the door in the quarantine room on exposures and probability of infection for occupants of the flat and of adjacent flats. In order to study the sensitivity of the results, we tested three ventilation systems: balanced, exhaust‐only, and humidity‐based demand‐controlled, and several window‐ and door‐opening strategies. When the door of the quarantine room is sealed, we observe that opening the window in the quarantine room always results in increased exposure and probability of infection for at least one other occupant, including in neighbors' apartments. When all internal doors are opened, we observe moderate impacts, with rather an increase of exposure of the occupants of the same apartments and of their probability of infection, and a decrease for the occupants located in other apartments. Based on the analysis on the airflows distribution in this case study, we conclude that sealing the internal door has more influence than opening the window of the quarantine room, whatever the ventilation system. We observe that this widespread recommendation to open the window of a quarantine room and to seal the door is based on the consideration of a single zone model. We illustrate the importance of moving from such a single zone approach to a multizone approach for quantifying ventilation and airing impacts in multizone buildings as residences in order to prevent epidemics of viruses such as SARS‐CoV‐2. It highlights the need of air leakage databases.
Ventilation is an important means of reducing the concentration of volatile organic compounds (VOCs) in airplane painting hangars. Currently both an upside-supply and floor-exhaust (UF) system and an ...upside-supply and downside-exhaust (UD) system are used. However, these two conventional systems have low ventilation efficiency. To improve the VOCs exhaust efficiency, this study proposed a novel upside-supply and multiple air-exhaust (UM) system. The new system delivers conditioned air through ceiling inlets, as do the UF and UD systems, but it uses multiple portable exhaust hoods to extract VOCs. The VOC emission sources move with the painting locations; in response, the exhaust hoods should also be moved so that they are adjacent to the sources. The ventilation performance of the proposed UM system, and that of the UF and UD systems, was modelled with computational fluid dynamics (CFD). In addition, the UM system was measured on site after putting it into engineering application. The results revealed that the flow pattern of the UM system is similar to that of the push-pull ventilation, and the airborne pollutants are efficiently exhausted. Both the measured and simulated VOC concentrations in the occupied zone are significantly reduced as compared with the conventional UF and UD systems.
•Portable, multiple exhaust hood ventilation was proposed for hangars.•The new system was put into engineering application.•The proposed ventilation forms a push-pull flow pattern to exhaust pollutants.•The VOCs concentrations in the occupied zone are greatly reduced as compared with existing systems.
In industrial ventilation, Aaberg hood is an efficient device for the local capture of pollutants with larger capacity compared to the traditional exterior hood. This paper proposes a further ...optimization approach, using a swirling jet in place of the radial one in the basic Aaberg hood. Computational Fluid Dynamics simulation of the optimized device is presented. A comprehensive performance evaluation is realized by analyzing the airflow pattern, capture efficiency, and pollutant behavior. The principal direction of contaminant transport is specifically considered in the performance evaluation. Results show that as the momentum ratio changes, the optimized device has a transition between two working modes, one featuring a high momentum ratio with a jet detached from the suction flow, and the other a low momentum ratio with an attached jet to the suction flow, both having separate advantages in different installation settings. The detached jet can enhance the suction performance similar to an Aaberg hood while the swirling and returning of the attached jet can counteract the effect from the cross direction and confine the scope of pollutant dispersion. This work helps to find a more efficient device and the optimized working condition for the local capture of pollutants in different scenarios.
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•Structure optimization of the Aaberg hood using swirling jet.•Comprehensive performance evaluation of the optimized device.•Working parameter optimization based on work mode transition.•Comparison between the optimized hood and the basic Aaberg hood.
•Propose a silencing heat exchanger integrates a heat exchanger with a muffler.•Test thermal and acoustic performance of silencing heat exchanger.•The silencing heat exchanger achieves better thermal ...and acoustic performance.
The integrated design of gas heat exchanger and after-treatment unit can reduce the size and weight of the engine waste heat recovery system, releasing the back pressure of exhaust gas and enhancing net benefit of the waste heat recovery system. In this study, we propose a silencing heat exchanger that integrates an exhaust heat exchanger with an impedance composite muffler in the post-treatment system, using metal foam material instead of the sound absorbing material in the impedance composite muffler. By adapting ANSYS Fluent and LMS Virtual.Lab, thermal simulation and acoustic simulation of the silencing heat exchanger were realized, and comparative analysis of the modified structure and the basic structure was carried out. The modified silencing heat exchanger was then designed and fabricated, and the thermal and acoustic performance were tested. The results show that the modified silencing heat exchanger can achieve improved heat transfer and flow performance, and more uniform temperature distribution at the hot side, simultaneously resulting in an 8.4% reduction in exhaust pressure drop. Even more, the improvement of silence effect in the middle and high frequency band is fairly obvious, and the overall transmission loss is 44.4% higher than that of the basic structure.
To improve the understanding of catalysts, and ultimately the ability to design better materials, it is crucial to study them during their catalytic active states. Using in situ or operando ...conditions allows insights into structure–property relationships, which might not be observable by ex situ characterization. Spatially resolved X‐ray fluorescence, X‐ray diffraction and X‐ray absorption near‐edge spectroscopy are powerful tools to determine structural and electronic properties, and the spatial resolutions now achievable at hard X‐ray nanoprobe beamlines make them an ideal complement to high‐resolution transmission electron microscopy studies in a multi‐length‐scale analysis approach. The development of a system to enable the use of a commercially available gas‐cell chip assembly within an X‐ray nanoprobe beamline is reported here. The novel in situ capability is demonstrated by an investigation of the redox behaviour of supported Pt nanoparticles on ceria under typical lean and rich diesel‐exhaust conditions; however, the system has broader application to a wide range of solid–gas reactions. In addition the setup allows complimentary in situ transmission electron microscopy and X‐ray nanoprobe studies under identical conditions, with the major advantage compared with other systems that the exact same cell can be used and easily transferred between instruments. This offers the exciting possibility of studying the same particles under identical conditions (gas flow, pressure, temperature) using multiple techniques.
The development of an in situ gas/heating cell for X‐ray nanoprobe studies is presented. The capabilities are demonstrated by an investigation of the redox behaviour of supported Pt nanoparticles on ceria.
•Exergy efficiency of domestic heat pumps (HPs) varies with ambient conditions.•Cold heat source temperature as well as ambient air humidity have a large influence.•Coefficient of performance (COP) ...does not include water evaporation heat effects.•Ground source HPs are more efficient than air source HPs during cold months.•Integration with exit air heat recovery gives a significant further improvement.
Heat pump systems have been used for decades in refrigeration and the upgrading of heat to temperature levels demanded by consumers. Private housing in Northern Europe and other countries is moving away from direct electric heating, combustion-based heating and even district heating in favour of heat pumps that use a cheap renewable heat source and electricity. The system purchase is motivated by an attractive coefficient of performance (COP), the option to reverse the heat pump operation from heating during winter to cooling during summer, and the increasing availability of (cheap) zero-CO2 electricity. Assessment of the energy efficiency of heat pump systems using exergy analysis is complicated by features of the heat reservoirs, such as humidity of air in a building envelope, becoming important besides temperature levels. In modern buildings, exhaust air heat recovery (EAHR) systems replace the air inside a building every few hours, with a net in- or outflux of humidity as side-effect. In this paper, an exergy analysis is presented that quantifies energy efficiency of a heat pump system as partly determined by the humidity of a building envelope being heated using a ground source or air source heat pump. Humidity control introduces a significant energy penalty. As shown, an EAHR unit can result in a significant increased exergy efficiency, adding to the benefits offered by the heat pump, depending on indoor versus outdoor temperature and humidity, and whether a ground source or air source heat pump is used. Using weather data for 2018, during the coldest months a ground heat source heat pump is clearly more efficient than an air source heat pump for maintaining a modern housing space in Finland at 22 °C and 50% relative humidity year-round. Exergy (in practice electricity) consumption is 20% higher for an air source heat pump compared to a ground source heat pump, with maximum exergy efficiencies of 14% and 11.5%, respectively. Integration with an EAHR system can add up to 20%-points to the exergetic efficiency, irrespective of the type of heat pump making also that a powerful investment.
Featuring high levels of achievable oxygen non-stoichiometry
δ
, Ce
1−
x
Zr
x
O
2−
δ
solid solutions (CZO) are crucial for application as oxygen storage materials in, for example, automotive ...three-way catalytic converters (TWC). The use of CZO in form of films combined with simple manufacturing methods is beneficial in view of device miniaturization and reducing of TWC manufacturing costs. In this study, a comparative microstructural and electrochemical characterization of film and conventional bulk CZO is performed using X-ray diffractometry, scanning electron microscopy, and impedance spectroscopy. The films were composed of grains with dimensions of 100 nm or less, and the bulk samples had about 1 µm large grains. The electrical behavior of nanostructured films and coarse-grained bulk CZO (
x
> 0) was qualitatively similar at high temperatures and under reducing atmospheres. This is explained by dominating effect of Zr addition, which masks microstructural effects on electrical conductivity, enhances the reducibility, and favors strongly electronic conductivity of CZO at temperatures even 200 K lower than those for pure ceria. The nanostructured CeO
2
films had much higher electrical conductivity with different trends in dependence on temperature and reducing atmospheres than their bulk counterparts. For the latter, the conductivity was dominantly electronic, and microstructural effects were significant at
T
< 700 °C. Nanostructural peculiarities of CeO
2
films are assumed to induce their more pronounced ionic conduction at medium oxygen partial pressures and relatively low temperatures. The defect interactions in bulk and film CZO under reducing conditions are discussed in the framework of conventional defect models for ceria.
Various petroleum-based polymers are being widely used in the automobile and aviation industries. However, the scarcity of petroleum-based polymers, their lack of biodegradability, and stringent ...environmental regulations lead researchers to look for green biopolymers/biocomposites as an alternative to petroleum-based polymers. Biopolymers have potential applications in various exterior and interior parts of an automobile, including steering, doors, wheels, electrical components, engine parts, exhaust systems, and so on. Almost all automakers are currently focusing on developing novel biopolymers, and they have successfully used bio-based materials in their newer version of automobiles, eventually replacing petroleum-based polymers. However, biopolymer uses in the aviation industry are not yet widespread because of stricter property requirements. Some advanced biopolymers are applied in interior aircraft panels, waste and drainage systems, engine components, cockpits, portholes, windshields, aircraft tires and inner tubes, exterior lighting, and helicopter windscreens. These materials are expected to substitute traditional plastics with the help of modifying agents, cutting-edge manufacturing technology, and a reliable supply chain of biopolymers. This review discusses the current practices, recent advances, and prospects of biopolymers in automotive and aviation engineering applications.
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