The dynamic responses of Solid oxide fuel cell (SOFC) power system across multiple time scales from micro seconds to minutes due to the phenomena of different nature that governing. Mismatching the time scale differences may lead to fuel starving and thermal shock during the fast load following. In this paper, the singular perturbation (SP) theory was introduced for modeling the mutli-time scale system dynamics. The dynamic model of SOFC power system in the coordinates in which slow and fast variables were explicitly defined and exactly separated. The resulting multi-single time scale models facilitate a better understanding of system dynamics, key parameters and their interactions, such as temperature, mass flow rate, current and voltage. Effective SOFC power system controllers can be designed based on these results.
Hydro power production strictly depends on the geography and weather peculiarity of locations where power plants are settled. In this paper, we produce long term estimates of hydro power capacity factors for all European countries based on future climate scenarios. We use machine learning techniques for formalizing models able to capture the complex relation between climate variables and energy production on a European scale and use the results of regional and global climate models for future projections.
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.
The hybrid wind-based pumped hydro storage system that absorbs the wind curtailment due to grid limitations is considered to be a solution to improve wind energy penetration and the cost-effectiveness of wind farms. An offshore wind-pumped hydro storage hybrid power system connected to thermal supplied main grid is proposed in this paper. The contribution of this paper can be summarized as follows: (1) a multi-objective dynamic economic optimization model for the proposed system based on evolutionary algorithms is established to optimize size for offshore wind-based pumped hydro storage system; (2) design parameters include the capacity of pump, turbine and reservoirs, and the key financial parameters such as wind power feed-in tariff and capacitor price of pumped hydro storage power station are also taken into account; and (3) examine the attainability of various objectives to analyze the influence on the operation and economic effectiveness. The results show that the optimizing size study is importance to test the economic feasibility of the system. The case study presented in this paper provides decision makers with the flexibility to choose the appropriate capacity installation under different expectations.
Liquid air energy storage system using Kapitza cycle is thermodynamically optimized with selected critical process variables by partial enumeration. With this method, the contour maps for the independent variables are illustrated, that give intuition to the behavior of the LAES systems. The Interaction between the variables can be found and thermodynamically analyzed. The optimized thermodynamic efficiency 40.0%, 48.8%, and 51.2% when compression pressure is set at 40 bar, 80 bar, and 120 bar, respectively.
In this paper, an AC/DC hybrid microgrid with PET is firstly modeled, and then a two-layer optimization model is established with the objective of minimizing the operating cost of AC/DC hybrid microgrid. Finally, the above two-layer optimization model is converted to a single-layer optimization model through KKT method for solving. According to the analysis of the case, the scheduling method based on two-layer optimization considers the cost of purchasing the PET in the upper layer and the operating cost of the different microgrids in the lower layer, and realizes the flexible scheduling between the main grid and microgrids through PET. Compared with the AC/DC hybrid microgrid with AC/DC converter, the hybrid microgrid with PET has flexible power regulation characteristics, and has advantages in reducing operating costs, fully absorbing and efficiently utilizing the renewable energy.
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.