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Abstract Flow in manifold systems is encountered in designs of various industrial processes, such as fuel cells, microreactors, microchannels, plate heat exchanger, and radial flow reactors. The uniformity of flow distribution in manifold is a key indicator for performance of the process equipment. In this paper, a discrete method for a U-type arrangement was developed to evaluate the uniformity of the flow distribution and the pressure drop and then was used for direct comparisons between the U-type and the Z-type. The uniformity of the U-type is generally better than that of the Z-type in most of cases for small ζ and large M . The U-type and the Z-type approach each other as ζ increases or M decreases. However, the Z-type is more sensitive to structures than the U-type and approaches uniform flow distribution faster than the U-type as M decreases or ζ increases. This provides a simple yet powerful tool for the designers to evaluate and select a flow arrangement and offers practical measures for industrial applications.

The technical challenges and obstacles to scaling-up of fuel cells are diverse, including such issues as water, heat, materials, catalyst, and flow fields because of multiple chemical and physical interactions at the atomic level and stack system level. The current results and data, even assumptions and guidelines are separated, inconsistent or unconnected. The unconnected data is partly the result of different disciplines. This paper is a first attempt toward understanding and analyzing the massive but spread-out work, which has been done and reported in the literature on fuel cell performance, reliability and durability. In this, we analyze the procedure of fuel cell research and development, and break down the barriers of scaling-up into four different stages: component, individual cell, stack and system control. We find that there are three different operating windows at each stage of the components, individual cells, and stack. While the operating window of components (e.g., membrane) are defined as ranges of temperature and relative humidity (RH), the operating window of a cell must include channel velocity and pressure drop within the cell. The operating window of a stack becomes narrower than that of its individual cells due to uneven flow distribution and load change. We have also found that there are knowledge gaps in the different stages of development. A solution for fuel cell scaling-up and a connection can be built among the components, cells, stack, process and system control through the operating windows and flow fields. The concepts of the three operating windows and flow field designs can build a connection among properties of the material and structures of components (e.g., wettability, porosity, and hydrophobicity), flow field, cells and performance of a stack and macro operation conditions (e.g., pressure, humidity and flow rates). This clarifies key ambiguities and converges our future directions on how to bridge different stages or disciplines of research and development. These can provide a new insight for future research to address the key issues of durability and reliability that remain unsolved.

An ecosystem in a cold climate river basin is vulnerable to the effects of climate change affecting permafrost thaw and glacier retreat. We currently lack sufficient data and information if and how hydrological processes such as glacier retreat, snowmelt and freezing-thawing affect sediment and nutrient runoff and transport, as well as N2O emissions in cold climate river basins. As such, we have implemented well-established, semi-empirical equations of nitrification and denitrification within the Soil and Water Assessment Tool (SWAT), which correlate the emissions with water, sediment and nutrients. We have tested this implementation to simulate emission dynamics at three sites on the Canadian prairies. We then regionalized the optimized parameters to a SWAT model of the Athabasca River Basin (ARB), Canada, calibrated and validated for streamflow, sediment and water quality. In the base period (1990-2005), agricultural areas (2662 gN/ha/yr) constituted emission hot-spots. The spring season in agricultural areas and summer season in forest areas, constituted emission hot-moments. We found that warmer conditions (+13% to +106%) would have a greater influence on emissions than wetter conditions (-19% to +13%), and that the combined effect of wetter and warmer conditions would be more offsetting than synergetic. Our results imply that the spatiotemporal variability of N2O emissions will depend strongly on soil water changes caused by permafrost thaw. Early snow freshet leads to spatial variability of soil erosion and nutrient runoff, as well as increases of emissions in winter and decreases in spring. Our simulations suggest crop residue management may reduce emissions by 34%, but with the mixed results reported in the literature and the soil and hydrology problems associated with stover removal more research is necessary. This modelling tool can be used to refine bottom-up emission estimations at river basin scale, test plausible management scenarios, and assess climate change impacts including climate feedback.

Abstract It is a major challenge to transform a laboratory scale production of fuel cells to an industrial scale in terms of throughput, operating lifetime, cost, reliability and efficiency. In spite of a number of efforts, the durability, reliability and cost of fuel cells still remain major barriers to scaling-up and commercialization. Unless these challenges are fully understood there is little chance of overcoming them. In fact, though much fundamental research has been performed, there is still no clear understanding of both the theoretical solution and technical measures needed to solve the durability and performance degradation of fuel cells in the scaling-up process. In this critical review, we will revisit advances in theory of flow field designs. Then, we will analyze main issues and challenges in concepts and criteria of flow field designs and development of theoretical models. We will focus on uneven flow distribution as a root cause of low durability and reliability and performance degradation and why flow field designs are a strategic solution to integrated performance, flow conditions, structure and electrochemical processes. Finally, we will discuss criteria and measures to tackle uneven flow distribution as well as critical durability and performance degradation in the scaling-up of fuel cells.

Abstract The laser technique was developed for measurement of transient burning rates of solid propellant during oscillatory combustion. the design and operation of the system are discussed. A high pressure window bomb was used for the combustion chamber. A modulating disk was used to induce the pressure oscillation above the combustion bomb. The oscillatory frequency was controlled easily with selecting the rotating velocity of the disk. Test results with AP/PS propellants, were in agreement with the results of previous techniques.

Agricultural soils are a leading source of atmospheric greenhouse gas (GHG) emissions and are major contributors to global climate change. Carbon dioxide (CO2) makes up 20% of the total GHG emitted from agricultural soil. Therefore, an evaluation of CO2 emissions from agricultural soil is necessary in order to make mitigation strategies for environmental efficiency and economic planning possible. However, quantification of CO2 emissions through experimental methods is constrained due to the large time and labour requirements for analysis. Therefore, a modelling approach is needed to achieve this objective. In this paper, the DeNitrification-DeComposition (DNDC), a process-based model, was modified to predict CO2 emissions for Canada from regional conditions. The modified DNDC model was applied at three experimental sites in the province of Saskatchewan. The results indicate that the simulations of the modified DNDC model are in good agreement with observations. The agricultural management of fertilization and irrigation were evaluated using scenario analysis. The simulated total annual CO2 flux changed on average by ±13% and ±1% following a ±50% variance of the total amount of N applied by fertilising and the total amount of water through irrigation applications, respectively. Therefore, careful management of irrigation and applications of fertiliser can help to reduce CO2 emissions from the agricultural sector.

Abstract A laser technique of transient burning rate measurement of solid propellant has been investigated. A photocell detects a laser beam passing through the propellant strand, and the cross-section of the laser beam is regulated so that the laser energy varies linearly along the height of the strand. Using a photo-controlled depressurization system, it is desirable to set up the starting time of depressurization in advance, and the initial rate of depressurization can be easily reproduced. Experimental results show that: (1) for a short time after depressurization begins, the burning rate remains unchanged; (2) during the depressurization process, the burning rate, while continuously decreasing in magnitude, exhibits low frequency oscillations; (3) the amplitude and the frequency of the burning rate oscillations, referenced to a smooth rate–time curve, increases as the depressurization rate increases; (4) for a short time after depressurization, the transient burning rates is higher than the steady state burning rate at the corresponding pressure, and then the transient burning rates oscillate around the quasi-steady rate. The experimental dynamic burning rates are compared with those available by microwave and capacitance methods. The discrepancies in the three experimental results have been discussed.

Stream temperatures, which influence dynamics and distributions of the aquatic species and kinetics of biochemical reactions, are expected to be altered by the climate change. Therefore, predicting the impacts of climate change on stream temperature is helpful for integrated water resources management. In this study, our previously developed Soil and Water Assessment Tool (SWAT) equilibrium temperature model, which considers both the impacts of meteorological condition and hydrological processes, was used to assess the climate change impact on the stream temperature regimes in the Athabasca River Basin (ARB), a cold climate region watershed of western Canada. The streamflow and stream temperatures were calibrated and validated first in the baseline period, using multi-site observed data in the ARB. Then, climate change impact assessments were conducted based on three climate models under the Representative Concentration Pathways 4.6 and 8.5 scenarios. Results showed that warmer and wetter future condition would prevail in the ARB. As a result, streamflow in the basin would increase despite the projected increases in evapotranspiration due to warmer condition. On the basin scale, annual stream temperatures are expected to increase by 0.8 to 1.1 °C in mid-century and by 1.6 to 3.1 °C in late century. Moreover, the stream temperature changes showed a marked temporal pattern with the highest increases (2.0 to 7.4 °C) in summer. The increasing stream temperatures would affect water quality dynamics in the ARB by decreasing dissolved oxygen concentrations and increasing biochemical reaction rates in the streams. Such spatial-temporal changes in stream temperature regimes in future period would also affect aquatic species, thus require appropriate management measures to attenuate the impacts.

Abstract In this study, a hybrid system of solar-microturbine with and without a combustion chamber, was investigated in a cold climate region (Edmonton, Canada). We developed a thermodynamic model to analyse the effects of environmental conditions on the system performance and power output during the year considering monthly changes in temperature, daylength and solar radiation using real climate and geographical data. The results showed that for a 30 m2 dish collector aperture area, the cycle outlet power was estimated from 3.70 kW in winter to 9.87 kW in summer, while the lowest and the highest cycle efficiencies were 19.44% and 35.07%, respectively for sunny days. The performance of the cycle was also compared with different climates and latitudes in Toronto and Phoenix. The total efficiencies in Edmonton were similar as that in Phoenix in summer but much lower in winter. However, the total electricity output in summer was higher in Edmonton than other two cities. It is found that the highest electricity output in winter is only a half of that in summer day in Edmonton. Furthermore, the cycle could achieve the highest total daily electricity output and fuel consumption in Edmonton in summer due to longer daylength, and higher latitude despite a colder climate if including a combustion chamber. Particularly, more than a half day has no electricity output in Edmonton in winter day if without combustion chamber. Therefore, it demonstrates that this state-of-the-art hybrid system can produce electricity and recover heat in a cold climate region but the climate effects should be considered.