The combustion characteristics of biomass in the packed bed is investigated based on the CFD-discrete element method (DEM). During the combustion process, the biomass particle experienced drying, pyrolysis, combustion and cooling. The mass loss leads to the change of particle density and diameter, as the remnant composition is mainly ash. In this work, the shrinkage of packed biomass volume is modelled as the particle diameter is decreased based on DEM. The different effects of compositions in the particle on particle diameter are considered. The simulation results show good agreement with the experimental measurement.
The long‐term production of U.S. tight oil is forecast by using a composite model combining the Generalized Weng and Gompertz models. We show that U.S. tight oil production is likely to reach a peak within ten years, between 2019 and 2028, at a production rate between 7 and 13 million barrels per day (Mb/d), depending on the size of the ultimately recoverable resource (URR) estimate. Our most‐likely ‘medium‐case’ URR scenario suggests the peak year is probably around 2025, at a production rate of about 10 Mb/d. Comparing our results with those of the U.S. Energy Information Administration (EIA) suggests that the EIA is over‐optimistic in its long‐term production forecast of U.S. tight oil.
Aiming at the demand of comprehensive vulnerability assessment in shipboard power system security defense, the paper proposed a vulnerability status description model of shipboard power system. The structure and physical properties of shipboard power network were fully analyzed. The product space which was called shipboard power network comprehensive vulnerability index set was established by degrees, betweenness, maximum connection sub-diagram scale, reliability indexes. Secondly, the normalized index sets were compactness and thepnormon the compactness sets were continuous were proved in this paper. The norm of vulnerability index was vulnerability output equation of shipboard power system. Using the norm on the product space, multi-scale integrated shipboard power network vulnerability norm was proposed, and the comprehensive structure performance evaluation of the shipboard power system network was formed. The index describes the change tendency of the shipboard power network comprehensive vulnerability. Finally, the test on a certain type of shipboard power network demonstrates the validity of the model.
Microthrusters are special category of propulsion device used to propel micro sized satellites. It is designed as per the mission requirements. There are various kinds of propulsion requirements such as continuous mode operation for orbit transfer (from one planet to another), orbit shift or adjustment for asteroid mining, pulsed mode operation for attitude control of satellites, and gravitation or solar drag compensation in orbit. Continuous mode operation is a high propellant consuming operation and designed cautiously to reach the destination with onboard available propellant. While pulsed mode operation is widely used for LEO (Low earth orbit) applications, where gravitation drag, atmospheric drag and solar drags are dominating. This paper focuses on the pulsed mode operation of vaporization liquid microthruster in vacuum operating condition. The pulsed mode operation involves timely thrust generation for the fine tuning of the positioning of the microsatellites. The operational timing in this mode of operation ranges from milliseconds to a few seconds at maximum. The operating time is decided based on the adjustment requirement for the positioning of the microsatellites. Vaporizing liquid microthrusters use green propellant to produce thrust. Tests are conducted under vacuum condition to simulate the actual space conditions and corresponding results are plotted. Results has shown a maximum thrust value of 290 μN at 1 sec of valve operating time, 335 μN at 2 seconds, 413 μN at 3 seconds, 524 μN at 4 seconds and 590 μN at 5 seconds of valve operating time for 200°C of a constant VLM temperature respectively. The effect of the dibble volume has also been discussed for the vaporization liquid microthruster using di-ionized water as liquid propellant.
In this paper, the performance of the moving average and moving median load estimation techniques is investigated using aggregated measurements of domestic smart meters. The load estimation techniques were tested using forward and backward walk approaches. Forward walk aims to estimate future load measurements using past measurements while backward walk estimates missing past measurements of the load using more recent measurements. Simulation results show that the moving average combined with forward walk produces load estimates with higher accuracies than the moving median and backward walk.
The rapid development of modern electronic devices urges an increasing need for better heat transfer techniques. Pool boiling heat transfer has great potential as it can provide high heat transfer capacity during the phase change of the working fluid. With the help of additive manufacturing technology, complex designs of pool boiling heat sinks can be achieved with selective laser melting (SLM) and they have shown great performances. In this study, heat sinks with one-layer and two-layer porous fin arrays are manufactured by SLM method using AlSi12 alloy powders and heat treated at 450℃ in nitrogen. Their pool boiling performances have shown great enhancement compared with plain copper heat sinks and the heat treated heat sinks have shown the best result both in heat transfer coefficient (HTC) and critical heat flux (CHF). The visualization data is collected during the experiments and used to analyze the heat transfer mechanism.
The growing global population and the resulting excess use of fossil fuels have brought the urgency for climate change mitigation leading to focus on renewable energy resources. Biomass is one of the earliest natural sources of energy, which has the potential to substitute for primary energy resource. However, commercial production of biofuel is still constrained by uncertainties such as biofuel demand. In this study, a two-stage stochastic mixed integer linear programing is formulated for biofuel supply chain based on macroalgae resource under uncertainties. The objective function in this formulation is total annual cost to be minimized. The approach is illustrated through a bioethanol supply chain case study in Korea, where macroalgae are among the dominant biomass resources.
In this paper, a data-driven approach is explored to evaluate the impact of weather conditions on the reliability of urban distribution system. The severity of power outages is divided into two levels according to the number of days with outages in one week. The actual outage records from the local utility are used for the analysis in this study. First, the difference of weather conditions under the two outage levels are intuitively described with the Kernel Density Estimation (KDE). Then, an extreme gradient boosting algorithm is applied to build a classification model for evaluating the outage levels of the local distribution system under given weather conditions. The importance of weather features on the outage level is discussed with the built model. Finally, the performance of the proposed data-driven model is assessed with the Receiver Operating Characteristic (ROC) curve.
Using conventional processes, biodiesel production is necessarily accompanied by the use of excess alcohol and production of a low value glycerol-rich co-product. There is currently a substantial worldwide surplus of this coproduct. While recovery of the alcohol is associated with high capital cost and energy requirement. This work tend to reduce the alcohol usage during biodiesel production and in situ convert the crude glycerol to an added valued product. The biodiesel was produced batch-wise at 130 – 160 oC with sulfuric acid as the catalyst. The effects of reaction temperature, catalyst concentration and molar ratio of triglyceride to methanol were studied. Approximately 100% conversion of the triglyceride was achieved. The glycerol conversion increased with increasing temperature and decreasing molar ratio. This represents proof-of-concept not only for reducing the excess methanol requirement, but also for combining production of fatty acid methyl esters with other added value products, whilst reducing glycerol production.
Polygeneration technology is an important way to realize clean and efficient coal utilization. Coal-steam gasification technology with thermochemical regenerative process is effective to enhance cold gas efficiency of coal gasification. In this paper, a novel methanol-electricity polygeneration system based on coal-steam gasification is proposed. In this novel polygeneration system, the component adjustment is cancelled and unreacted syngas partially recycled is adopted. The Aspen Plus software is selected to simulate the polygeneration systems. As a result, the energy efficiency of the novel polygeneration system based on coal-steam gasification is 53.5% when chemical to power output ratio is 1.1, while energy efficiency of polygeneration system based on traditional gasification is 47.3%. Furthermore, the energy saving effects of system integration method and gasification process improvement are distinguished.