► Supercritical CO2 (scCO2) sprays evaluated against conventional metal working fluids (MWFs). ► Heat removal efficacy of scCO2 can be higher than aqueous MWFs. ► Lubrication efficacy of scCO2 can be ...higher than straight oils or minimum quantity lubrication. ► Increased penetration of MWF into cutting zone key to improved cooling and lubrication. ► scCO2 sprays give high cooling and high lubricity without a trade-off between the two.
This paper investigates the cooling and lubrication properties of supercritical carbon dioxide (scCO2) sprays as potential substitutes for aqueous emulsions and straight oils used in the metalworking industry today. Sprays of rapidly expanding scCO2 act to cool and lubricate machining and forming processes by delivering a mixture of dry ice and lubricant deep into the cutting/forming zone. In this work, experiments with turning, milling, drilling, thread cutting, and thread forming were performed with scCO2 and other metalworking fluids (MWFs) to evaluate their relative performance with respect to tool wear and machining torque. Observations reveal that scCO2–MWFs are more effective in removing heat from the tool-workpiece interface than conventionally delivered (flood) aqueous MWFs as well as other gas-based MWF sprays. In addition, scCO2–MWFs delivered in lubricant-expanded phase, where scCO2 is used to increase volume of lubricant in the spray field, are shown to provide better lubricity than straight oils and oil-in-air minimum quantity lubrication (MQL) sprays. As a result, scCO2–MWFs can reduce tool wear and improve machining productivity in a wide range of manufacturing operations leading to appreciable improvements in the economics of manufacturing. Also given that CO2 is a recovered waste gas that is non-toxic, scCO2–MWFs can improve the environmental and worker health performance of manufacturing operations.
The recently amended U.S. Corporate Average Fuel Economy (CAFE) standards determine fuel-economy targets based on the footprint (wheelbase by track width) of vehicles such that larger vehicles have ...lower fuel-economy targets. This paper considers whether these standards create an incentive for firms to increase vehicle size by presenting an oligopolistic-equilibrium model in which automotive firms can modify vehicle dimensions, implement fuel-saving technology features, and trade off acceleration performance and fuel economy. Wide ranges of scenarios for consumer preferences are considered. Results suggest that the footprint-based CAFE standards create an incentive to increase vehicle size except when consumer preference for vehicle size is near its lower bound and preference for acceleration is near its upper bound. In all other simulations, the sales-weighted average vehicle size increases by 2–32%, undermining gains in fuel economy by 1–4mpg (0.6–1.7km/L). Carbon-dioxide emissions from these vehicles are 5–15% higher as a result (4.69×1011–5.17×1011kg for one year of produced vehicles compared to 4.47×1011kg with no size changes), which is equivalent to adding 3–10 coal-fired power plants to the electricity grid each year. Furthermore, results suggest that the incentive is larger for light trucks than for passenger cars, which could increase traffic safety risks.
► New U.S. fuel-economy standards may create an incentive to increase vehicle size. ► We model firms as choosing vehicle designs and prices in oligopolistic equilibrium. ► Vehicle size increases 2–32% for 20 out of 21 scenarios of consumer preferences. ► Increases in size reduce fuel economy gains from 5–13%, resulting in 5–15% higher CO2 emissions. ► Incentive is larger for trucks than cars, which may increase traffic safety risks.
The US transportation sector is a major contributor to global greenhouse gas (GHG) emissions. As such, policymakers and stakeholder groups have proposed a number of policy instruments aimed at ...reducing these emissions. In order to fully evaluate the effectiveness of these policies, policymakers must consider both the direct responses associated with policy actions, and the indirect responses that occur through complex relationships within socioeconomic systems. In cases where multiple policy instruments are employed, these indirect effects create policy interactions that are either complementary or competing; policymakers need to understand these interactions in order to leverage policy synergies and manage policy conflicts. Analysis of these indirect effects is particularly difficult in the transportation sector, where system boundaries are uncertain and feedback among systems components can be complicated. This paper begins to address this problem by applying systems dynamics tools (in particular causal loop diagrams) to help identify and understand the role of feedback effects on transportation-related GHG reduction policies. Policymakers can use this framework to qualitatively explore the impacts of various policy instruments, as well as identify important relationships that can be later included in quantitative modeling approaches.
Solid Freeform Fabrication (SFF) technologies such as Direct Metal Deposition (DMD) have made it possible to eliminate environmentally polluting supply chain activities in the tooling industry and to ...repair and remanufacture valuable tools and dies. In this article, we investigate three case studies to reveal the extent to which DMD-based manufacturing of molds and dies can currently achieve reduced environmental emissions and energy consumption relative to conventional manufacturing pathways. It is shown that DMD's greatest opportunity to reduce the environmental impact of tool and die manufacturing will come from its ability to enable remanufacturing. Laser-based remanufacturing of tooling is shown to reduce cost and environmental impact simultaneously, especially as the scale of the tool increases.
With growing interest in recovering materials and subassemblies within consumer products at the end of their useful life, there has been an increasing interest in developing decision-making ...methodologies that determine how to maximize the environmental benefits of end-of-life (EOL) processing while minimizing costs under variable EOL situations. This paper describes a methodology to analyze how product designs and situational variables impact the Pareto set of optimal EOL strategies with the greatest environmental benefit for a given economic cost or profit. Since the determination of this Pareto set via enumeration of all disassembly sequences and EOL fates is prohibitively time-consuming even for relatively simple products, multi-objective genetic algorithms (GA) are utilized to rapidly approximate the Pareto set of optimal EOL trade-offs between cost and environmentally conscious actions. Such rapid calculations of the Pareto set are critical to better understand the influence of situational variables on how disassembly and recycling decisions change under different EOL scenarios (e.g., under variable regulatory, infrastructure, or market situations). To illustrate the methodology, a case study involving the EOL treatment of a coffee maker is described. Impacts of situational variables on trade-offs between recovered energy and cost in Aachen, Germany, and in Ann Arbor, MI, are elucidated, and a means of presenting the results in the form of a multi-situational EOL strategy graph is described. The impact of the European Union Directive regarding Waste Electric and Electronic Equipment (WEEE) on EOL trade-offs between energy recovery and cost was also considered for both locations.
•Supercritical CO2 MQL benchmarked against conventional aqueous flood coolants for tool wear.•ScCO2 MQL improves tool life under production level machining conditions.•ScCO2 MQL allows up to 40% ...increase in material removal rate (MRR) at comparable tool wear.•Roughly 70g/min of CO2 flow required for each kW of cutting power at the higher MRR.•Tools fail from crater wear and chip hammering in scCO2 MQL instead of notch formation.
This paper describes preliminary results of replacing water-based (aqueous) flood coolant with supercritical CO2-based minimum quantity lubrication (scCO2 MQL) in an external turning operation on an Inconel 750 combustor housing. Two series of tests were performed: the first series to compare tool wear performance observed with aqueous flood coolant and scCO2 MQL under identical machining conditions, and the second series to investigate tool wear performance with scCO2 MQL at higher metal removal rates (MRR) than the MRR used in production practice with aqueous flood coolant. All tests were performed using roughing cuts on unaged Inconel with coated carbide tooling, and vegetable oil lubricant. As a key enabler, special flank jet tool holders were used to eliminate chip blockage of the lubricant stream.
In the first series of tests, tool wear was observed to be consistently lower with scCO2 MQL than with the aqueous flood coolant. In the second series of tests, two process conditions were demonstrated for which MRR increased by 25% and 40%, respectively, with scCO2 MQL compared to aqueous flood coolant at equivalent tool life. Notch wear, the limiting factor for tool life under baseline conditions, was reduced for scCO2 MQL, but crater wear and chip hammering were more pronounced. Overall the results indicate that scCO2 MQL can provide increased tool life or material removal rate compared to aqueous flood coolants when machining Inconel 750 and similar nickel alloys by improving lubricity and changing the dominant wear mechanism from rapid notch wear to gradual crater wear and chip hammering. These tests, which involved extended cuts of over 10min under production conditions, represent an important extension of MQL machining to a hard metal alloy that cannot be machined by conventional MQL methods.
In order to pursue more sustainable alternatives in wastewater management, it is vital that we understand how a given infrastructure alternative will impact the various aspects of sustainability. A ...set of qualitative tools (force field diagrams and causal loop diagrams (CLDs)) for the assessment of wastewater management alternatives is proposed and demonstrated in the context of a decentralized wastewater infrastructure upgrade. The objective for the application of these tools is to improve decision makers' understanding of how a given alternative will impact the economic, environmental/ecological, social, and functional aspects of sustainability. In the proposed method, each aspect of sustainability is treated as a stock, and its movement (up or down) can be inferred using both qualitative and quantitative data. By incorporating these tools into a participatory planning process, project-specific CLDs can be developed and loops of interest can be identified to help elucidate stakeholder values. The ultimate goal of this methodology is to facilitate the pursuit of sustainability in wastewater management by allowing decision makers to address specific sustainability challenges without creating new ones.
► Anaerobic membrane bioreactors (AnMBRs) have been evaluated for domestic wastewater (DWW) treatment. ► Adequate DWW treatment in AnMBRs is achievable at low temperatures for long SRTs. ► Membrane ...fouling energy demands need to be reduced. ► Efficient permeate dissolved methane handling methods must be established. ► A quantitative environmental and economic evaluation framework is needed for AnMBRs.
Interest in increasing the sustainability of water management is leading to a reevaluation of domestic wastewater (DWW) treatment practices. A central goal is to reduce energy demands and environmental impacts while recovering resources. Anaerobic membrane bioreactors (AnMBRs) have the ability to produce a similar quality effluent to aerobic treatment, while generating useful energy and producing substantially less residuals. This review focuses on operational considerations that require further research to allow implementation of AnMBR DWW treatment. Specific topics include membrane fouling, the lower limits of hydraulic retention time and temperature allowing for adequate treatment, complications with methane recovery, and nutrient removal options. Based on the current literature, future research efforts should focus on increasing the likelihood of net energy recovery through advancements in fouling control and development of efficient methods for dissolved methane recovery. Furthermore, assessing the sustainability of AnMBR treatment requires establishment of a quantitative environmental and economic evaluation framework.
This paper describes a disposable flow cytometer that uses an air-liquid two-phase microfluidic system to produce a focused high-speed liquid sample stream of particles and cells. The susceptibility ...of thin liquid columns to instabilities may suggest that focusing of sample liquids with streams of air would be difficult. The design of channel geometry, control of flow rates, and use of appropriate surface chemistries on the channel walls, however, enabled the generation of thin (15-100 mum) and partially bounded sample streams that were stable and suitable for rapid cell analysis. Using an inverted epi-fluorescence microscope with a photo-multiplier tube, we demonstrated that the system is capable of counting the number of beads and C2C12 myoblast cells. The effects of different flow rates and surface chemistries of the channel walls on the air-liquid two-phase flows were characterized using optical and confocal microscopy. Use of air instead of liquids as a sheath fluid eliminates the need for large sheath liquid reservoirs, and reduces the volume and weight requirements. The low manufacturing cost and high volumetric efficiency make the air-sheath flow cytometer attractive for use as a stand-alone device or as an integrated component of bio-artificial hybrid microsystems.
A bench-scale anaerobic membrane bioreactor (AnMBR) equipped with submerged flat-sheet microfiltration membranes was operated at psychrophilic temperature (15 °C) treating simulated and actual ...domestic wastewater (DWW). Chemical oxygen demand (COD) removal during simulated DWW operation averaged 92 ± 5% corresponding to an average permeate COD of 36 ± 21 mg/L. Dissolved methane in the permeate stream represented a substantial fraction (40–50%) of the total methane generated by the system due to methane solubility at psychrophilic temperatures and oversaturation relative to Henry's law. During actual DWW operation, COD removal averaged 69 ± 10%. The permeate COD and 5-day biochemical oxygen demand (BOD5) averaged 76 ± 10 mg/L and 24 ± 3 mg/L, respectively, indicating compliance with the U.S. EPA's standard for secondary effluent (30 mg/L BOD5). Membrane fouling was managed using biogas sparging and permeate backflushing and a flux greater than 7 LMH was maintained for 30 days. Comparative fouling experiments suggested that the combination of the two fouling control measures was more effective than either fouling prevention method alone. A UniFrac based comparison of bacterial and archaeal microbial communities in the AnMBR and three different inocula using pyrosequencing targeting 16S rRNA genes suggested that mesophilic inocula are suitable for seeding psychrophilic AnMBRs treating low strength wastewater. Overall, the research described relatively stable COD removal, acceptable flux, and the ability to seed a psychrophilic AnMBR with mesophilic inocula, indicating future potential for the technology in practice, particularly in cold and temperate climates where DWW temperatures are low during part of the year.
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► Psychrophilic anaerobic membrane bioreactors (AnMBRs) can treat domestic wastewater. ► Permeate dissolved methane is a substantial portion of total methane production. ► Membrane fouling can be managed using biogas sparging and permeate backflushing. ► Combining biogas sparging and permeate backflushing is important for fouling control. ► Mesophilic inocula are suitable for psychrophilic AnMBR seeding.
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