Wire and arc additive manufacturing (WAAM) has proven that it can produce medium to large components because of its high-rate deposition and potentially unlimited build size. Like all additive ...manufacturing (AM) technologies, however, an optimized process planning that provides uniform, defect-free deposition is key for the production of parts. Moreover, AM, particularly WAAM, is no longer just a prototyping technology, and most of today's attention is on its transformation to a viable and cost-effective production. With this transformation, a number of issues need to be addressed, including the accuracy and effectiveness of the manufactured components. Therefore, the emphasis should be on dimensional precision and surface finish in WAAM. This paper covers heat input and management concept, related to the resulting shrinkage, deformation, and residual stresses, which is particularly critical. In addition, we focus on process planning including build orientation, slicing, and path planning, as well as the definition of process parameter selection from a single track to multi-track and multilayer, and finally geometric features from a thin-wall to lattice structures with several case studies. Central to addressing component quality and accuracy, we summarize guiding designs and future needs through numerous WAAM-specific issues, which require for manufacturing of complex components.
Display omitted
•We review recent progress in wire and arc additive manufacturing with a focus on the part quality and accuracy.•We cover heat input and management concept, related to the resulting deformation and part quality.•We study process planning for different geometrical features, including several case studies.•We summarize guiding designs and future needs through the numerous WAAM geometrical issues.
Heat waves (HWs) and urban heat islands (UHIs) can potentially interact. The mechanisms behind their synergy are not fully disclosed. Starting from the localized UHI phenomenon, this study aims i) to ...reveal their associated impacts on human thermal comfort through three different definitions of HW events, based on air temperature (airT), wet-bulb globe temperature (WBGT) and human-perceived temperature (AppT) respectively, and ii) to understand the role of air moisture and wind. The analysis was conducted in four districts (NH, JD, MH and XJH) with different urban development patterns and geographic conditions, in the megacity of Shanghai with a subtropical humid climate.
Results evidenced the localized interplay between HWs and UHIs. The results indicate that less urbanized districts were generally more sensitive to the synergies. JD district recorded the highest urban heat island intensity (UHII) amplification, regardless of the specific HW definition. Notably, during AppT-HWs, the increment was observed in terms of maximum (1.3 °C), daily average (0.8 °C), diurnal (0.4 °C) and nocturnal UHII (1.0 °C). Nevertheless, localized synergies between HWs and UHIs at different stations also exhibited some commonalities. Under airT-HW, the UHII was amplified throughout the day at all stations. Under WBGT-HW, diurnal UHII (especially at 11:00–17:00 LST) was consistently amplified at all stations. Under AppT-HW conditions, the nocturnal UHII was slightly amplified at all stations. Air moisture and wind alleviated the synergistic heat exacerbation to the benefit of thermal comfort. The extent depended on geographic condition, diurnal and nocturnal scenarios, temperature type and HW/normal conditions. Stronger HW-UHI synergies indicate the necessity to develop specific urban heat emergency response plans, able to capture and intervene on the underlying mechanisms. This study paves to way to their identification.
•An adaptive thermoelectric cooling system is proposed.•Features combined functionalities of sensing and cooling local heat loads.•Removal of extra temperature sensors simplifies the system ...configuration.•Offers fast response desirable for addressing transient heat.•Consumes 47% less power than conventional thermoelectric cooling systems.
Current cooling systems such as convection-based heat sinks and vapor compression refrigeration systems are frequently inefficient in managing localized and transient heat sources due to their bulky design, large energy consumption, and slow response time. Here, we propose an adaptive thermoelectric cooling system that uses an array circuit of thermoelectric coolers to cool locally and eliminate transient heat efficiently. Compared to existing thermoelectric cooling systems, the proposed system provides a merit of combined functionalities of detecting and cooling localized and transient heat sources. As a proof of concept, six thermoelectric coolers are used for both tracking the temperature and cooling the hot spots without additional sensors. The temperature for each thermoelectric cooler is continuously monitored by scanning the Seebeck voltage of each cooler using a mechanical switching system. When localized heat is applied to specific locations and the temperatures of those locations exceed a designated limit, only particular thermoelectric coolers are activated to cool the over-heated spots selectively. The adaptive thermoelectric cooling system demonstrates fast cooling and effectively maintains the system temperature below the target temperature. Numerical analysis verifies that the adaptive thermoelectric cooling system offers exclusive cooling on hot spots preventing overcooling in other regimes, which makes it consume 47% less power than a conventional bulk thermoelectric cooling system. The proposed cooling system may provide an efficient heat management platform for numerous devices.
Photovoltaic (PV) technologies have achieved commercial acceptance, technological maturity and foresee a leading role in the current energy transition to combat the adverse environmental issues posed ...by fossil fuel-based power generation. The market of photovoltaic technology is rapidly evolving with a Compound Annual Growth Rate (CAGR) equal to 34% between 2010 and 2020. This review presents updated information on the solar PV development from the material, market, and engineering perspectives. Cell efficiencies, market trends, cost of PV systems, and global research efforts over the last years are provided. Real monitored performances reveal a decrease of up to 10% of PV power output due to soiling effects. This paper discusses soiling mitigation approaches, a critical technical pathway to improve the power output of solar PV systems. A particular emphasis was put into recent and novel experimental and numerical investigations pursued by the PV research community related to heat management in PV systems. Finally, critical challenges and prospects of the solar PV technology are highlighted and discussed.
•An updated literature review on PV energy system sis given.•Market trends, technology and efficiency progress are summarized.•Relevant techniques for mitigation soiling effects and heat management of PV cells are reported.•Critical challenges, prospects and research priority pathways are highlighted.
This critical review describes a framework that can help to guide catalyst design in fundamental or practical aspects, illustrate reaction mechanism, optimize reactor functions, and operate system ...integration in catalytic LMC with a new point of view.
Display omitted
As a primary type of clean energy, methane is also the second most important greenhouse gas after CO2 due to the high global warming potential. Large quantities of lean methane (0.1–1.0 vol%) are emitted into the atmosphere without any treatment during coal mine, oil, and natural gas production, thus leading to energy loss and greenhouse effect. In general, it is challenging to utilize lean methane due to its low concentration and flow instability, while catalytic combustion is a vital pathway to realize an efficient utilization of lean methane owing to the reduced emissions of polluting gases (e.g., NOx and CO) during the reaction. In particular, to efficiently convert lean methane, it necessitates both the designs of highly active and stable heterogeneous catalysts that accelerate lean methane combustion at low temperatures and smart reactors that enable autothermal operation by optimizing heat management. In this review, we discuss the in-depth development, challenges, and prospects of catalytic lean methane combustion technology in various configurations, with particular emphasis on heat management from the point of view of material design combined with reactor configuration. The target is to describe a framework that can correlate the guiding principles among catalyst design, device innovation and system optimization, inspiring the development of groundbreaking combustion technology for the efficient utilization of lean methane.
Direct carbon solid oxide fuel cells (DC-SOFCs) are promising energy-conversion devices that can directly convert the chemical energy of carbon into electricity with high efficiency and low ...pollution. The efficient and durable operation of DC-SOFCs is maintained by the effective coupling of electrochemical oxidation in the anode and the reverse Boudouard reaction in the carbon fuel. In this paper, we review recent advances in material design, fuel development, and heat management for improving the electrochemical output and conversion efficiency of DC-SOFCs. First, developments in state-of-the-art anode materials for the electrochemical oxidation of carbon are briefly reviewed. Second, various kinds of carbon fuels and catalysts for carbon gasification are outlined. Third, we introduce the present status of heat management in DC-SOFC systems. Finally, some conclusions involving challenges in DC-SOFCs and perspectives on them are systematically summarized.
•A comprehensive review of the advanced progress on DC-SOFCs is given.•State-of-the-art anode materials development for DC-SOFCs is reviewed.•The catalysts of carbon gasification and alternative carbon fuels are presented.•Current situations of the heat management for DC-SOFCs are introduced.•Critical challenges and perspectives of DC-SOFCs are proposed and summarized.
Display omitted
•Periodic open cellular structures (POCS) as novel catalyst support concept.•Comparison of POCS and randomly packed beds under reactive conditions.•POCS show superior performance in ...exothermic reactions.•Kinetic measurements and modeling for the oxidation of methanol to formaldehyde.•POCS enable process intensification by operation in new process window.
Heat transport in catalytic reactors is one of the most important factors in reactor design, especially for highly endo- or exothermic reactions. The limited thermal conductivity of randomly packed beds can be significantly improved when alternative catalyst supports are used. A new generation thereof are periodic open cellular structures (POCS), which are used in this study as catalyst support for the partial oxidation of methanol to formaldehyde, an exothermic gas phase reaction. A comparison to traditional packed bed reactors revealed that a POCS made of the highly conductive alloy AlSi10Mg can significantly reduce the hot-spot temperature, allowing almost isothermal operation at optimal reaction conditions. The improved temperature control allows for operation with higher methanol inlet concentrations and wall temperatures as compared to the commercial process. The beneficial heat transport properties of POCS were used to conduct isothermal kinetic measurements at elevated temperature. Based on these findings and the design freedom of additive manufacturing, an optimized cellular structure was designed and fabricated, which improved the heat transport especially in the critical inlet section of the reactor.
•A fabric roll based bionic evaporator (FRBE) with 3D spiral groove structure design was successfully prepared.•The prepared FRBE possessed superior heat management and salt pollution resistance ...performance.•Heat was transferred to each evaporation surface through regional water circulation to improve heat utilization.•This 3D evaporator realized efficient and low-cost purification of seawater.
Solar-driven evaporators offer a promising approach to obtaining fresh water due to their environmental protection and pollution-free operation, and because they require no other energy input. In this work, we prepared a low-cost fabric roll-based bionic evaporator (FRBE) with advanced heat management and salt pollution resistance based on a three-dimensional (3D) spiral groove structure design for the solar evaporation of seawater. The spiral groove structure, inspired by the vertical water supply of natural trees, had a super-strong regional water circulation ability between the yarns and fibers. The heat energy of the photothermal surface was quickly transmitted to the cold evaporation surface to realize rapid water evaporation, and the low evaporation surface temperature effectively reversed the usual heat loss phenomenon. Under 1.0 sun irradiation, the evaporation rate and evaporation efficiency of the prepared FRBE-4–2 reached 2.89 kg·m−2·h−1 and 130.04 %, respectively. In the evaporation tests with 10 wt% and 20 wt% NaCl solutions, the regional water circulation effectively promoted the dissolution and diffusion of salt on the evaporation surface, reflecting excellent salt pollution resistance performance. Therefore, the 3D spiral evaporation surface design developed in this study provided a new idea for efficient and sustainable steam generation.
Two series of smart yarns with programmed thermo-wetting behaviors have been produced in a scalable continuous routine. They can be processed solely or conjunctively into smart textiles with adaptive ...sweat wicking or intelligent moisture/heat regulation upon surrounding temperature change, which endows the design of moisture/heat conditioning textiles with extremely rich variety while balancing the wearing conventions and large-scale production.
Display omitted
Programmable smart textiles with adaptive moisture/heat conditioning (MHC) capabilities are globally being sought to meet the requirements of comfort, energy efficiency, and health protection. However, a universal strategy for fabricating truly scalable and customizable MHC textiles is lacking. In this study, we introduce a scalable in situ grafting approach for the continuous fabrication of two series of smart textile yarns with opposite thermoresponsive wetting behaviors. In particular, the wetting transition temperature can be precisely programmed by adjusting the grafting formula, making the yarns highly customizable. The smart yarns demonstrated excellent mechanical strength, whiteness, weavability, biocompatibility, and washability (with more than 60 home washes), comparable to those of regular textile yarns. They can serve as building blocks independently or in combination to create smart textiles with adaptive sweat wicking and intelligent moisture/heat regulation capabilities. A proposed hybrid textile integrating both the two series of smart yarns can offer dry-contact and cooling/keep-warming effects of approximately 1.6/2.8 °C, respectively, in response to changes in ambient temperature. Our method provides a rich array of design options for nonpowered MHC textiles while maintaining a balance between traditional wearing conventions and large-scale production.
PDF
