Abstract

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 subdiagram scale, reliability indexes. Secondly, the normalized index sets were compactness and the p norm on 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, multiscale 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.

Abstract

Reasonable mechanical ventilation strategy and system design can effectively save building energy usage for space cooling in summer. In this paper, the climatic cooling potential of major cities in China is evaluated based on the CCP index values, and a guide map for accessing night cooling potential is provided. Furthermore, for ventilation strategy optimization in city buildings, the ideal air change rate (ACH) is obtained by using inverse problem approach. The preliminary results indicate that the ideal ventilation strategy is favorable for free cooling energy exploitation in the night, to save cooling energy consumption in summer. It also shows that both CCP value and energy saving ratio of ventilation optimization decreases from north to south in China. This study is significant in guiding and optimizing building ventilation systems in engineering applications.

Abstract

This paper presents a three-dimensional numerical investigation on the effect of thermoelectric geometry on hybrid photovoltaic-thermoelectric (PVTE) performance under varying weather conditions. Four thermoelectric (TE) geometries corresponding to four different cases are considered under transient conditions and different thermoelectric leg height are investigated. The effect of the thermoelectric geometry and leg height on the efficiency and power output of the PV-TE is studied for a duration of 24 hours under actual weather conditions (solar radiation, ambient temperature and wind speed). Results show that the symmetrical thermoelectric legs (case 1) are beneficial for hybrid PV-TE under transient conditions. Although asymmetrical thermoelectric legs (case 4) provide higher thermoelectric generator (TEG) power output compared to other TE geometries, it also increases the PV temperature the most, therefore the overall PV-TE performance using such geometry is reduced. Consequently, asymmetrical TEG (case 4) is recommended for TEG only system while symmetrical TEG (case 1) is recommended for hybrid PV-TE under transient conditions. In addition, shorter thermoelectric legs provide enhanced performance.

Abstract

Aiming at the defects of low-efficiency power generation of medium-low temperature geothermal power plants, a medium-low temperature hybrid solargeothermal power generation system was proposed. Through MATLAB simulation calculation, the performance analysis of the stand-alone geothermal plant and the hybrid solar- geothermal plant (HSGP) was carried out. According to ambient temperature, solar radiation intensity and geothermal resources, this paper selected areas with typical meteorological conditions for time-by-time simulation. The results show that the HSGP has better performance than the stand-alone geothermal power plant. When the power-increasing operation scheme is adopted, the HSGP in the Lhasa area has the largest increase in power generation compared to the stand-alone geothermal power plant, and the annual average monthly increase percentage is 3.0%. When the geothermal water-saving operation scheme is adopted, the HSGP in Xi’an area has the largest amount of geothermal water saving compared to the stand-alone geothermal power plant, and the annual average monthly savings is 4.0%. The simulation results provide a theoretical basis for the location and performance evaluation of the HSGPs.

Abstract

The effects of temperature and organic load rate (OLR) stress on dark fermentative hydrogen production from food wastes (FW) were investigated through analysis of shaping metabolic pathways, microbial communities and energy balance in the long-term hydrogen production systems. The gas production rate (GPR) of 9.32 mL/g VS·h and hydrogen proportion of 58.19% were reached with 6 g VS/L·d under thermophilic condition. In depth analysis of metabolite profiles and microbial communities showed that thermophilic fermentation favored a stable community dominated by Thermoanaerobacterium, which was in the ascendant with increasing of OLR. In contrast, mesophilic fermentation led to ever changing microbial community comprised Lactobacillus, Olsenella, Caproiciproducens, Roseburia, Streptococcus, performed low hydrogen production, high butyric and acetic acids concentrations in long-term system. The energy assessment showed the higher energy recovery rate was obtained in thermophilic fermentation than that of the mesophilic system. Results suggested that stability and shock resistance capability of microbial community are crucial elements related hydrogen production and metabolic pathways.

Abstract

In the conventional downhole heat transfer mode, using the two-phase closed thermosyphon (TPCT) can greatly improve the heat extraction capability from geothermal reservoirs. In this paper, a set of laboratory-scale performance testing device is built for TPCTs with internal tubes and charged with CO2-nanofluids mixed working fluid. Based on the conditions of geothermal reservoir and heating season, experimental investigations are carried out by various heating temperature (50~70 ℃), heating water flow rate (1.0~3.0m3 /h), cooling temperature (5~15 ℃) and cooling water flow rate (1.0~3.0m3 /h). The results show that the increase of heating temperature plays a dominant part in heat transfer performance, but not always be positively correlated due to the increase in temperature difference between the evaporator section and the condenser section. From the perspective of their own structure, outer fins have the most obvious improvement on their performance and another method of reducing the aspect ratio takes second place.

Abstract

Thermal properties of geopolymer concrete (GPC) are enhanced by adding phase change material (PCM) capsules. The capsules were developed and tested in our previous research. In total, five compositions of GPC cubes were developed for testing, one pure geopolymer as a reference, two compositions by 50% volume substitution of pure geopolymer with the two different PCM capsules and two compositions by 50% substitution of each porous material for comparison. Thermal and structural tests were conducted to investigate the effects of capsules on the properties of produced GPC. The produced thermally enhanced GPC can reduce heat transmission to indoors in the hot climates like the United Arab Emirates and its compressive strength is acceptable for non-loadbearing wall components.

Abstract

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.

Abstract

Industrial and chemical plants, especially oil refineries, are highly energy-consuming plants. Several energy efficiency interventions are being currently performed: besides gas recovery solutions, also energy recovery in liquid flows can be applied. In this paper, a case study of an Italian oil refinery regarding the use of a Hydraulic Power Recovery Turbine (HPRT), which is installed in a Hydrogen Sulphide (H2S) removal process from the Syngas produced by an Integrated Gasification Combined Cycle (IGCC), is analysed and presented. The real performance data of the process are discussed: on average, 353.4 t/h of liquid SELEXOL can be elaborated by the HPRT with 445.4 m of head. Finally, the recovered electrical energy on a yearly basis is equal to 2966 MWh, or 531 tons of carbon dioxide equivalent. The pay-back period of the intervention ranges indicatively between 6 and 9 years, depending on the discount rate.

Abstract

This paper addresses the issue of social inequality by comparing German household data (gross income, Food‐Energy‐(Watervirtual)‐Nexus expenditures) from 2008 and 2013. The distribution of gross income and of the FE(Wvirtual)‐Nexus related consumption expenditures based on this income is analysed using a three step approach: First, the real distribution is determined, secondly, the dispersion (based on Rawls’ philosophical concept) is analysed, and finally, the normative distribution according to the Atkinson index is calculated to reveal a view on social inequality. The six main household groups were selected for the cross section analysis comparing the social conditions of 2008 and 2013: self‐employed households, public servant households, white‐collar and blue‐collar worker households, unemployed households and retiree households. The three‐dimensional model delivers data about the real and normative distribution of the households’ gross income and consumption expenditures for the time period from 2008 to 2013 considering the inequality perception of society.