Abstract

Liquid droplet radiator (LDR) is characterized by the compact arrangement and the low mass per unit power. It is a promising cooling system for the high-power spacecraft. The characteristics of the droplet layer in LDR determine the performance of the heat dissipation. Thus, the study of the droplet radiation heat transfer mechanism is vitally important for the optimal design of the whole LDR system. In the present paper, the radiation heat transfer characteristics of a sparse LDR system are studied from the aspects of the single droplet. The results reveal that the smaller the droplet radius is, the higher the droplet radiation energy per unit mass is. The slower the initial emission speed is, the higher the radiation energy per unit mass is. The higher the initial temperature of the droplet, the higher energy of radiation power per unit mass of the droplet is. Meanwhile, the radiation heat transfer characteristics of different working mediums are also given. These conclusions can provide basis for the optimal design of the sparse droplet radiators and provide guidance for the subsequent research on LDR.

Abstract

In order to reveal the supersonic condensation characteristics of carbon dioxide (CO2) in natural gas under low temperature condition, the mathematical models and numerical schemes for the CH4-CO2 mixture gas under supersonic flow condition were established, and the influence of inlet CO2 concentration on the CO2 removal efficiency of Laval nozzle was investigated. The results show that with the increase of CO2 concentration at nozzle inlet, the initial nucleation position is closer to nozzle throat, the maximum nucleation rate and the droplet number decrease but the droplet radius increases significantly, which eventually leads to an increase in liquefaction rate. When the inlet CO2 mole fraction is lower (less than 10%), the CO2 fraction in gas phase is almost 0, which indicates that low-temperature separation technology is practicable for the removal of CO2 from natural gas.

Abstract

Due to the environmental impacts brought by current energy schemes, the energy transition, a new paradigm-shift from fossil fuels to renewable energy, has been widely accepted and is being realized through collective international and local efforts. Electricity, as the most direct and effective use of renewable energy sources (RES), plays a key role in the energy transition. In this paper, we first discuss a viable pathway to energy transition through the electricity triangle, highlighting the role of RES in electricity generation. Further, we propose methodologies for the planning of wind and solar PV, as well as how to address their uncertainty in generation expansion problems. Finally, by using a web-based tool, “RES-PLAT” 1 , we demonstrate the scheme in a case study of the North Africa, which evaluates the impacts and benefits of a large-scale RES expansion.

Abstract

Growing interest in greenhouse gas mitigation strategies to address global climate change has resulted in the rapid expansion of renewable electricity sources. Increasing energy generation from variable renewable electricity sources, such as solar photovoltaics and wind turbines, has made balancing electricity supply and demand across the power grid more challenging. Some grid management challenges include sharp ramp up needs when the sun goes down, and the overgeneration of renewables when demand is low. In absence of cost-effective, utility-scale batteries, demand response strategies that leverage flexibility in electricity consumption have gained interest as readily available resources to address the temporal mismatch between renewable energy availability and high energy demand periods. The water industry (i.e., water supply and wastewater systems) includes industrial customers that are particularly attractive in terms of demand response potential as they can offer flexibility through large water storage capacities, large interruptible pumping loads, and energy generation opportunities. This study highlights an illustrative case in California to demonstrate the emissions benefits of load shifting in the water industry, followed by discussions regarding potential flexibility opportunities based on the recent literature and directions for future research opportunities to support the implementation of flexibility measures.

Abstract

Modern active distribution grids are characterized by the increasing penetration of distributed energy resources (DERs). The proper coordination and scheduling of a large numbers of these small-scale and spatially distributed DERs can only be achieved at the nexus of new technological approaches and policies. As such, this paper presents a distributed optimal power flow formulation for the distribution grid, applied to the problem of Volt-VAR optimization (VVO). First, we propose a convex model to describe the power physics of distribution grids of meshed topology and unbalanced structure, based on current injection and McCormick Envelopes. Second, we employ the distributed proximal atomic coordination (PAC) algorithm, which has several advantages over other distributed algorithms, including reduced local computational effort and improved privacy. We implement VVO by optimally coordinating DERs including PV smart inverters and demand response. Results from the IEEE-34 bus network are presented, under different DER penetration scenarios and using different VVO objective functions. Our results show the need for DER coordination to achieve desired grid performance. Finally, we discuss the extension of such an optimal power flow formulation to the development of market derivatives to provide financial compensation to DERs providing grid services such as reactive power support and voltage support, within a local retail market framework.

Abstract

This paper evaluates data from 10 centrifugal pumps in a large wastewater treatment facility to illustrate the impact of pump design, selection, maintenance, and operation on system efficiency. The paper explores the efficiency impact of several interventions and qualitatively presents trade-offs to implementation. Of the interventions explored, energy savings up to 3% were identified representing 239,000 kWh annually.

Abstract

Decentralized energy system offer fast and low-risk way to test energy transition pathways at local scale. The technology variety and increased role of user preferences call for a systematic design process in close collaboration with prosumers. We propose a novel methodology to design local energy systems that are technically robust and socially supported – the Participatory Approach to Community Energy Design. The methodology is applied to a neighborhood in the Netherlands. Among four alternative designs, a biogas-fueled and a smart grid systems consistently outperformed the alternatives, regardless of changing the user preferences.

Abstract

An H-channel microfluidic device system was built to simulate the dead-end structures in subsurface environments. The accessibility to these restriction regions where significant amount of oil and contaminants may be trapped is challenging. Hence, large amount of unnecessary chemicals might be required for remediation and enhanced oil recovery (EOR) applications, making the process expensive and environmentally unfavorable. In this work, we demonstrate the ability of salinity gradients that naturally exist in the subsurface environment to target-migrate nano-capsules in porous and fractured rock formations. Our results demonstrate the concept and provide evidence of the potential of utilizing existing chemical and thermal gradients to enable autonomous and sustainable migration of nano-capsules into constricted regions in the subsurface environment for more efficient and environmentally-friendly subsurface remediation and energy harvesting applications.

Abstract

Abstract

According to the Financial Times the steel industry emissions accounted for 7-9% of total GHG emissions worldwide in 2019. The main share is directly related to the use of fossil coke and coal as fuels and reducing agents. About four solutions can be adopted to address such issue: direct reduction with hydrogen or syngas, electric arc furnaces, carbon capture and storage and use of biofuels (so-called “biocarbon”). These solutions can also be integrated. We propose applying innovative methods to produce biocarbon by pelletizing biocarbon with pyrolysis oil and reheating it at high temperatures to obtain materials with sufficient hardness, reduced porosity and reduced reactivity. The upgrade takes biocarbon closer to the requirements usually applied to metallurgical coke. We present also the results of technical and economic analysis plus environmental analysis on the expected final use of biocarbon in steel industry.