Suchergebnisse

Abstract: Energy flow and transformation, being a fundamental driving force behind organization, should be subject to long term government policy. A pre‐requisite for formulating energy policy is detailed knowledge of the dynamics and thermodynamics of energy supply and utilization. The lack of coherent policy in the past has led to the development of a society which is physically, institutionally and psychologically locked into an unsustainable liquid fuel consumption pattern requiring not only high but also growing consumption. An expression of this situation is the widespread assumption that coal and nuclear energy are the only significant realistic longer term options for the future, even though these would involve unproven technology and considerable environmental and social risks. The other long term option—the diffuse energy option based on widely distributed, renewable energy sources such as wind and the sun—is generally regarded as unrealistic. This is a social judgement determined more by the inertia of existing institutions and perceptions of our needs than by technical reality. It is possible however, that the measures which might be taken to deal with the crisis of oil depletion in the next couple of decades may swing community structure and attitude and bureaucratic organization into a conservation‐minded pattern in which the long term option based on low, stable consumption, diffuse energy sources and decentralized conversion systems seems as realistic to policy makers as the other extreme—the centralized, nuclear‐electric, growth society. This flexibility could only emerge, however, if energy research expenditure is diversified very soon.

On behalf of a committee of the German parliament, a study of the mass, energy and monetary flows of the German building stock has been initated. The approach was macro-economic (top-down) for the calculation of the overall flows and process oriented (bottom-up)for the detailed flows created by new construction, refurbishment, demolition and utilisation of buildings. The building stock has been modelled with a stochastic replacement model for a reference population of 160 building materials. Specific data sets were used for the upstream and downstream parts. A scenario for the development of the building stock and the induced mass, energy and monetary flows was ...

The massecuite circulates in a loop within the evaporating crystallizing vessel. The massecuite flows upwards through the heating tubes. In the room above the calandria the massecuite flow changes its direction to radial inwards and then to vertical downwards. An impeller in the central tube forces the circulation. Below the calandria the main direction of flow is radially outwards until threads of the massecuite stream enter the heating tubes in upwards direction. Within the tubes heat is transferred to the massecuite. At low temperature differences between heating steam and massecuite and higher levels of the massecuite in the crystallizer vapor bubbles are not found in the tubes. Vapor bubbles can be formed at a massecuite level in the crystallizer where the temperature of the massecuite is higher than the local boiling temperature of water, which depends on the local pressure (including the static pressure of the massecuite at this point) and the boiling point elevation of the mother liquor. The surface tension of the liquid is a resistance against the bubble formation, which has to be overcome by the local superheating i.e. the part of the enthalpy of the massecuite exceeding the local boiling temperature. The formation and the flow of the bubbles change the density of the massecuite/bubbles mixture and has an influence on the massecuite flow. The formation of a vapour bubble is connected with a local drop of the massecuite temperature which changes the local supersaturation.

Today the heat transfer into the magma is quite well known but the process of bubble formation is quite unknown. Some basic considerations about the formation of bubbles and its influence on local supersaturation based on calculation of heat and mass balances and models of bubble formation are be given and discussed. Experiments for basic investigations are proposed.

Methods are described for studying the metabolic cost of increased and diminished gravitational work done by the human subject during normal locomotion at various speeds and slopes on the treadmill. It is shown that the energy expenditure is a linear function of the gravitational work and, as long as the gait is of a smooth and natural character, appears to be dependent upon the true vertical lift per step multiplied by the number of steps per minute. The true vertical lift is defined as the lift resulting from muscle action, as contrasted with components due to treadmill motion. Methods are also described for recording the vertical and translational motions of the torso during a single step, and for analyzing the flow of mechanical energy into and out of the torso during each phase of the walking cycle. Implications for calculation of efficiency are briefly discussed.

Globalisation and the outsourcing of industrial manufacturing from developed to less developed countries has an increasing effect on the national energy balances of most developed economies. The current standard metric Total Primary Energy Supply of a country does not take into account the energy embodied in goods and services imported from other countries, leading to the perverse outcome of a country appearing to be more sustainable the more it outsources its energy-intensive industries. Academia has addressed this problem by suggesting the use of the Total Primary Energy Footprint as an additional metric, but there has not been a clear proposal put forward by academia to governments or international institutions about how to officially adopt Consumption-Based Accounting in the field of energy. This article states that acknowledging the existence of embodied energy flows is indispensable when formulating new national and international energy policies for the transition towards energy systems that are socially and environmentally more sustainable. In this study, the Hidden Energy Flow indicator of 44 countries has been quantified using, for the first time, five different Global Multi-Regional Input-Output databases for the latest available year, 2011. The proposed indicator provides a percentage to be added to or subtracted from the Total Primary Energy Used value of a country, provided by the International Energy Agency, to get its real consumption-based energy requirement. This study demonstrates that, from 44 countries analysed, the ten most developed countries demand on average 18.5% more energy than measured by the International Energy Agency; the medium developed 24 countries demand 12.4% more, and the ten least developed countries demand 1.6% less. This means that most developed and medium developed countries displace their indirect energy consumption towards less developed countries in a hidden way. Furthermore, this research supports evidence that direct energy consumption in households is less relevant than the energy embodied in goods and services purchased by households, reaching 59.1% in the case of Switzerland, used as a reference among developed countries. The proposed Hidden Energy Flow indicator supports scientists, policymakers and citizens in the effort to focus the energy transition actions towards conducting the necessary energy consumption and production changes in the most effective way, improving energy justice and energy democracy.

In this paper, a comparison of two different methods for a steam turbine energy analysis is presented. A high-pressure steam turbine from a supercritical thermal power plant (HPT) was analysed at three different turbine loads using the energy flow stream (EFS) method and isentropic (IS) method. The EFS method is based on steam turbine input and output energy flow streams and on the real steam turbine produced power. The method is highly dependable on the steam mass flow rate lost through the turbine gland seals. The IS method is based on a comparison of turbine steam expansion processes. Observed energy analysis methods cannot be directly compared because they are based on different sources of steam turbine energy losses, so, an overall steam turbine energy analysis is presented. Unlike most steam turbines from the literature, the analysed HPT did not have the highest overall energy efficiency at a full load due to exceeding the water/steam critical pressure at the turbine inlet during such operation.

The paper presents an approach to the assessment of technical and economic efficiency for an electric energy (EE) transport in a distribution grid. It is focused on the extent of renewable energy sources (RES) integration efficiency according to energy prices in a grid. A two-step procedure for calculation is used in terms of the approach. The first one includes the obtaining of energy flows distribution in a grid. The next step provides the calculation of costs flows and nodal prices for electric energy. Both stages are performed using a developed branch flow model. Unlike power flow distribution describing the instant point of time, energy flow distribution developed for any operation duration deals with the integral values of the flows. This is of great importance for the deeply varying output profiles of the intermittent renewables. The model provides the direct utilization of electric energy meters data available in a grid. The approach presented is essential for locating the particular consumers of the renewable energy in terms of a grid's deep state and circuit diversity as well as for analyzing the influence of a renewable energy for electricity prices, and estimating the necessary renewables' levelised cost of energy (LCOE). © 2020, European Association for the Development of Renewable Energy, Environment and Power Quality (EA4EPQ). All rights reserved. ; The work was supported by Act 211 Government of the Russian Federation, contract № 02.A03.21.0006.

Abstract
Grass carp (Ctenopharyngodon idellus) is the most productive freshwater fish in China, but its traditional aquaculture model still has problems, such as poor water quality and frequent diseases. We have taken monoculture and 80:20 polyculture grass carp ponds as the research object and used EwE software to build the Ecopath model of two ponds. We analyzed and compared the characteristics of ecological structure and energy flow in two ponds. The result showed the highest effective trophic level in the polyculture pond that was higher than that in the monoculture pond, and fish in polyculture had higher EE values which showed the production of fish in polyculture contributed more to the energy conversion efficiency of the ecosystem. Flows into detritus were the largest component of TST both in the two ponds, which accounted for 49.34% and 50.37%. And the average transfer efficiency in monoculture was 13.07%, while that in polyculture was 15.6%. The ascendency/total development capacity (A/TDC) and overhead/total development capacity (O/TDC) were 0.35 and 0.65 both in the two ponds, respectively, which indicated that both systems had a strong anti-perturbation ability, but the stability could be improved. Finn's cycling index (FCI) in polyculture was higher and showed that the polyculture pond was more mature and stable. Unused energy of functional groups will flow to detritus, and that in the monoculture pond was higher, the energy of C. idellus that flowed to detritus in monoculture was 48.17% higher than that in polyculture; unused energy of bacteria and phytoplankton were also high. The result showed that polyculture could improve energy utilization, increase transfer efficiency, and raise the stability of the ecosystem. Grass carp ponds still need to be improved in the aspects of mixed species and energy consumption. It is necessary to improve the ecological and economic benefits of grass carp ponds by optimizing the aquaculture structure and adjusting the aquaculture proportion.