This work investigates the design of large scale oxy-fuel circulating fluidized bed (CFB) boilers in two industrial pathways of constant thermal power scenario and constant furnace size scenario ...using a new version of a model validated with 100 kWth and 4 MWth oxy-fuel CFB boilers. This work suggests that the major approach for elevating the circulating solids flux is to utilize more efficient cyclones with better efficiency which leads to higher share of fines and nanoparticles in the CFB loop while the amount of aerosols is reduced. Maximum heat flux from furnace walls is 2.4 times and CO peak is 2.2 times in constant furnace size scenario compared to constant thermal power scenario respectively, showing more intense combustion in the prior scenario. Based on the results found in this work, if the industry is to aim to operate the large-scale oxy-fuel CFB boilers at high O2 concentrations, the utilization of the constant thermal power scenario is much safer for the industry compared to constant furnace size scenario. This work shows that the aspect ratio of future large-scale oxy-fuel CFB furnaces are larger than the current air-fired ones leading the oxy-CFB furnace geometry to approach the fluid catalytic cracking fluidized beds.
•Design scenarios for large-scale oxy-fuel CFB boilers are investigated.•Circulating solids flux, temperatures, heat flux and heat extraction duties are studied.•The safest pathway for oxy-fuel CFB scale-up is constant thermal power scenario.
It is well established that when a turbulent flow is subjected to a non-uniform body force, the turbulence may be significantly suppressed in comparison with that of the flow of the same flow rate ...and hence the flow is said to be laminarised. This is the situation in buoyancy-aided mixed convection when severe heat transfer deterioration may occur. Here we report results of direct numerical simulations of flow with a linear or a step-change profile of body force. In contrast to the conventional view, we show that applying a body force to a turbulent flow while keeping the pressure force unchanged causes little changes to the key characteristics of the turbulence. In particular, the mixing characteristics of the turbulence represented by the turbulent viscosity remain largely unaffected. The so-called flow laminarisation due to a body force is in effect a reduction in the apparent Reynolds number of the flow, based on an apparent friction velocity associated with only the pressure force of the flow (i.e. excluding the contribution of the body force). The new understanding allows the level of the flow ‘laminarisation’ and when the full laminarisation occurs to be readily predicted. In terms of the near-wall turbulence structure, the numbers of ejections and sweeps are little influenced by the imposition of the body force, whereas the strength of each event may be enhanced if the coverage of the body force extends significantly away from the wall. The streamwise turbulent stress is usually increased in accordance with the observation of more and stronger elongated streaks, but the wall-normal and the circumferential turbulent stresses are largely unchanged.
This paper examines the nature of linkages between core competence of a firm and key characteristics of its product/output and thus presents an alternative theoretical framework for innovation and ...regional development. Within this framework, it is the externally observable characteristics of what a firm produces, rather than its internal functions, that establishes whether a distinct core competence potentially exists, in order to operationalize it for R&D and innovation activities. To demonstrate potential applications of this framework, a literature-based- questionnaire was designed to collect primary data from 330 firms located in North East England, a peripheral region of the UK. Collected data were subjected to a detailed statistical analysis to estimate the conditional probability that a firm has a core competence, given the presence of one or more of its key output/product characteristics. Based on this approach, the paper presents a theoretical/empirical framework for the promotion of innovation via enhancement of a firm's core competence, and improvement in its output/product characteristics. This framework might be employed as a strategic management tool (1) by a firm to help in allocation of scarce resources for innovation and innovation management and (2) by regional policymakers for targeting and assisting firms in peripheral regions to enhance regional development via firms' innovation and exporting activities.
The triboelectric nanogenerator (TENG) is a promising technology for mechanical energy harvesting. TENG has proven to be an excellent option for power generation but typically TENGs output power ...drops significantly in humid environments. In this work, the effect of electrode's material on power output, considering smooth and nanostructured porous structures with various surface hydrophobicity, is investigated under various humidity conditions. A vertical contact-separation mode TENG is experimentally and numerically studied for four surface morphologies of Ti foil, TiO
thin film, TiO
nanoparticulated film, and TiO
nanotubular electrodes. The results show that the TENG electrical output in the flat structures such as Ti foil and TiO
thin film at 50% RH is reduced to 50% of its initial state, while in the nanoporous structures such as nanoparticle and nanotube arrays, this is observed at RH above 95%. The results show that the use of porous nanostructures in TENG due to their high surface-to-volume, and that the process of water adsorption on the pore leads to better performance than the flat surface in humid environments. Based on our study, employing nanoporous layers is vital for nanogenerators either for power generation or active sensor applications at high humidity conditions.
This work presents first-of-a-kind results on the enhanced oil recovery (EOR) by CO2 stream of oxy-fuel-fired circulating fluidized bed (CFB) boilers for Constant Furnace Size Scenario and Constant ...Thermal Power Scenario. The CO2 flow rate, the associated impurities and the furnace thermal properties are investigated. The total mass flow rate of the EOR gas in Constant Furnace Size Scenario for the oxy-fuel case of 70% O2 concentration becomes more than 2.6 times of the one with 29% O2 concentration. The oxy-fuel CFB usage for EOR offers the opportunity of reconfigurable manufacturing system (RMS) where the CO2 production capacity is flexible to market demand. While the increased CO2 mass flow rates at elevated O2 concentrations is in favor of Constant Furnace Size Scenario, the mass flow rates of the impurities of O2, CO and H2O also increase leading to higher costs for gas cleaning before sending the CO2 stream for EOR injection. The relatively low outgoing CO level in addition to considerably lower furnace CO maxima compared to the other scenario are merits of Constant Thermal Power Scenario.
•EOR using CO2 from oxy-fuel boilers is investigated.•The oxy-fuel technology for EOR offers a reconfigurable manufacturing system (RMS).•The properties of EOR gases and thermal properties of the oxy-furnaces are studied.
In 2019, a new infectious disease called pandemic COVID-19 began to spread from Wuhan, China. In spite of the efforts to stop the disease, being out of the control of the governments it spread ...rapidly all over the world. From then on, much research has been done in the world with the aim of controlling this contagious disease. A mathematical model for modeling the spread of COVID-19 and also controlling the spread of the disease has been presented in this paper. We find the disease-free equilibrium points as trivial equilibrium (TE), virus absenteeism equilibrium (VAE) and virus incidence equilibrium (VIE) for the proposed model; and at the trivial equilibrium point for the presented dynamic system we obtain the Jacobian matrix so as to be used in finding the largest eigenvalue. Radius spectral method has been used for finding the reproductive number. In the following, by adding a controller to the model and also using the theory of optimal control, we can improve the performance of the model. We must have a correct understanding of the system i.e. how it works, the various variables affecting the system, and the interaction of the variables on each other. To search for the optimal values, we need to use an appropriate optimization method. Given the limitations and needs of the problem, the aim of the optimization is to find the best solutions, to find conditions that result in the maximum of susceptiblity, the minimum of infection, and optimal quarantination.
As the inclusion of youths in decision-making around their media use is increasingly normalized in the family context in the Global North, one could ask how media literacy support can be adjusted for ...youths in vulnerable situations, situations where their family cannot be involved in regulating their media use, such as gaming. Drawing on interviews conducted in 2021 with 13 unaccompanied refugee youths (16–25 years old) and 10 social actors working in eight organizations, this study investigates the gaming habits of such youths in Norway and the ways in which relevant social actors are involved in guiding their gaming practices. This study shows that social actors’ views on gaming vary according to their level of involvement in the youths’ housing arrangements. Whilst those working directly with such arrangements are involved in direct or indirect rule-setting for gaming practices, others struggle to find their role within this context. The youths, however, emphasize the importance of gaming in building relationships with other unaccompanied refugees, learning about the culture of socialization, and mitigating trauma. Moreover, there is a lack of a dialogical approach to welfare services’ regulation of these youths’ gaming practices. Employing such an approach could not only give these youths a voice but also expand gaming’s democratization ability beyond the family context.
This paper investigates the heterogeneous and homogeneous reactions involved in the formation and reduction of carbon monoxide (CO) in a 100 kW oxy-fuel-fired circulating fluidized-bed furnace, using ...CO as an indicator of the progress of combustion. A mathematical combustion model, which takes into account both the mixing and kinetics, is developed for simulating char and gas combustion under air- and oxy-fuel-fired conditions. The experimental results demonstrate that, for similar fluid dynamic and thermal conditions, oxy-fuel conditions typically yield a vertical CO profile with higher peak concentrations than are obtained with air-firing, mainly because of the higher inlet concentrations of O2, whereby CO released from the increased fuel feeding is diluted in the same total volumetric flow of gas. On the basis of a comparison of the modeling results and the experimental results, it is proposed that the effects of CO2 should be considered in determining the rate of CO oxidation that is valid for both air- and oxy-fuel-fired conditions. The vertical in-furnace profiles of CO from the combustion model were compared to the corresponding experimental results from five test runs under air- and oxy-fuel-fired conditions. The results show good agreement, with the agreement for oxy-fuel-fired conditions made possible by adding a CO2-dependent term to the expression for the CO oxidation rate.
The coronavirus disease (COVID-19) screening project has been conducted by the Red Crescent Society for 17 days with the aim of identifying and treating people with COVID-19, reducing road trips, and ...sensitizing people to the problem. Due to the shortage of testing devices, passengers were screened by measuring skin temperature. In 851 screening posts, 95 371 volunteers of Red Crescent monitored 21 640 866 people. Besides screening people, the stations have had other functions, including urging people to stay at home, restricting road trips, especially during the Iranian New Year holidays, reassuring the people that all relevant organizations are doing their best to respond to COVID-19, and the like. However, future research is still needed to analyze the cost-benefit of this plan and other possible options.
Poly（4-vinylpyridinium） perchlorate has been used as an efficient solid acid catalyst for the synthesis of 3,3＇-（arylmethylene）bis（4-hydroxycoumarins） and bis（indolyl）methanes, with the products ...being formed in excellent yields over very short reaction times under mild and environmentally friendly conditions. This catalyst can be reused several times without any appreciable loss in its activity.
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