Abstract

The study of flow pattern in the flow boiling process holds great significance for the safety and automation production in nuclear, aerospace and other industries. A numerical simulation study on flow patterns for water boiling in horizontal heated tubes was conducted by volume of fluid (VOF) multiphase flow model and LEE evaporation-condensation model. And the effect of heat flux on the flow pattern evolution was analyzed. Four boiling flow patterns was obtained in the tubes, namely bubble, slug, annular, and stratified flows. The increment of heat flux pushes the starting point of each flow pattern toward the inlet of the tube, which gradually compresses the range of bubble and slug flow and expands the region of stratified flow. Due to the formation of stratified flow, the tube metal in the upper part is at high temperature, resulting in tube failure.

Abstract

Large amount of water and energy are consumed in the food production process, including food production, trade and consumption. This study employs Linear Interactive and General Optimizer (Lingo) to simulate the inter-provincial food trade pattern in China. Using ecological footprint, we evaluate the efficiency and resource benefits of water and energy footprint in food trade. Our research shows that provinces with food surpluses are primarily distributed in the north and provinces with food deficit are mainly in the south, resulting in national food trade amount of 304.23 million tons. The spatial distribution of the total water footprint and energy footprint of food production is the same, with eastern > central > western region. In 2020, nationwide food trade has saved 57.2 billion m³ of water resources and result in 3.13 million tce waste of energy.

Abstract

The transient response of proton exchange membrane fuel cell (PEMFC) during start-up is an important issue for a system. In this paper, the start-up process of the 6-cell stack with the dead-end anode and recirculation cathode is studied. The effects of starting load, step size on voltage variation are studied via the measurement of time evolution of the stack voltage. In addition, the different start-up responses of the single-cell under the flow-through and recirculation are compared. It is found that increasing the start-up current density and reducing the step load change can shorten the start-up time. However, the shorter start-up time will result in the lower critical membrane dehydration temperature. Compared with the gas-through mode, when the stack with dead-end anode and cathode recirculation is started, the single cell near the outlet is more likely to be flooded at the moment of high current density start-up due to the closing of anode outlet.

Abstract

The various power market challenges of the conventional power system are projected to be addressed by a smart grid. It entails a synergy between the three pillars of electricity trading, 1) energy market economics, 2) power network balancing, and 3). market policies and regulations. This paper explores an overview of peer-to-peer (P2P) trading under a smart grid milieu from these three pillars’ perspectives. The first pillar delineates the energy user’s role flipping between the consumer and prosumer due to behind-the-meter distributed energy resources integration to maximize their payoffs. At the power network, P2P trading necessitates a). robust and sophisticated network infrastructure, and b). bi-directional Internet and communication technologies for successful electricity trading in the distributed electricity market. This is defined as physical and virtual levels of P2P architecture under the second pillar of P2P. Lastly, the third pillar is essential for adequately constructing an optimal business strategy to maximize the player’s profit function.

Abstract

CO2 huff and puff is an important means to achieve efficient development of tight reservoirs. The authors carried out CO2 huff and puff simulation experiments by using one-dimensional long core to simulate the whole process of CO2 huff and puff development in tight reservoirs. The main mechanism and the effect of well stuffing time and production pressure difference on the development effect of CO2 huff and puff in tight reservoir are expounded.The simulation results show that compared with the flow sweep caused by pressure difference, the contribution of molecular diffusion sweep to CO2huff and puff recovery is higher.

Abstract

Intermittent electricity generation from variable renewable energies will lead to an increased demand for flexibility options in the future. Power-to-heat-to-power storage technologies present high potentials for large-scale application. However, investments in such technologies are still hampered by technical and economic challenges. To address the latter the possible revenues in electricity markets need to be analyzed. For this, we simulate the German electricity market in ambitious defossilization scenarios. We use different operational strategies for the storage (minimizing system costs versus maximizing storage profits) that show a wide range of storage profitability. The operator benefits from its attributed market power (i.e. assuming perfect foresight in a rolling horizon window) to generate positive net profits. Further research may focus on market situations with increased market competition.

Abstract

This study proposed a new thin cambered bent biomimetic wind turbine design that adopted the 3D geometry of the wing of a Borneo camphor seed sample. The wings of the Borneo camphor seed are thin, cambered, and bent. The unique geometry and orientation of the wings cause the seed to autorotate during propagation, subsequently slowing down its falling speed. It was presumed that by mimicking the wings of a Borneo camphor seed, a high-performance biomimetic wind turbine design could be proposed since the wind turbine, and Borneo camphor seed shares a similar rotating mechanism. Computational fluid dynamics was adopted to predict the power coefficient, thrust coefficient, and torque of the proposed biomimetic wind turbine models. The results show that the highest power coefficient was 0.3861 for the biomimetic wind turbine model, which is 20.14% higher than that of a benchmark case when the fold axis and fold angles are equal to 30° and 30°, respectively. The findings of this study concluded that the proposed biomimetic wind turbine design is cost-effective and worthy of further investigation.

Abstract

Detailed energy consumption data is key to data-driven urban energy modeling efforts. However, privacy considerations often prevent such data to be shared directly with researchers. Here, we present an approach based on the “15/15 rule,” used in several states in the United States, to enable energy data to be shared while protecting the information of individual customers. We do so based on a case study typical for urban energy data, where public information is combined with privacy-sensitive data. We compare two implementations, showing that our custom algorithm achieves a 1,000 times higher computational speed at only a 10% increase in information loss compared to a previously published clustering method. Our work aims to provide a mechanism to accelerate broader energy data sharing and serve as a baseline for similar efforts in different regulatory contexts, including potential future policy frameworks based on differential privacy.

Abstract

This work presents a two-stage stochastic Mixed Integer Linear Programming model for the optimization of the design of an aggregated energy system (AES) (i.e., multi-energy systems, microgrids, energy districts, etc.) serving a university campus featuring electricity and heating demands. The off-grid system design is obtained by considering a set of representative periods for both demands by means of a carefully modified k-medoids algorithm. N-1 reliability is also considered in the model, by introducing the concept of “break-down scenarios” that allows the solution of the problem to be able to meet the user demands for every possible contingency in which one of the AES’s units fails. The effect of including N-1 reliability in the model is then showed by comparing the optimal design obtained by considering such approach against one with no break-down scenarios.

Abstract

Decarbonizing the electricity sector is not an easy task. To reach the decarbonization of the electricity sector in Latvia by 2050, there are a lot of barriers that need to be addressed. To reduce or completely remove different social, technical, economic, administrative, and other barriers, a set of policies needs to be defined. Research results show that there is a combination of policy instruments that would allow for complete decarbonization of the electricity sector, however, it is crucial to implement the whole set of policies, not just one or two of them, and implement them as soon as possible to gain the maximum effect.