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  • Other low-carbon energy technologies  (13)
  • Oxford University Press  (13)
  • Public Library of Science
  • 2015-2019  (13)
  • 1965-1969
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  • 2016  (13)
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  • 1
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    Review of heat pipe heat exchangers for enhanced dehumidification and cooling in air conditioning systems (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-08-26
    Beschreibung: Heat pipe heat exchangers could be employed as run-around coils in air conditioning systems for enhanced dehumidification and cooling. This article reviews some of the works conducted on the cooling and dehumidification aspects in various air conditioning systems. They have been proved to be effective in enhancing dehumidification and reducing air conditioning costs especially in hot and humid tropical countries.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 2
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    Towards clean and sustainable distributed energy system: the potential of integrated PEMFC-CHP (2016)
    Oxford University Press
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    Publikationsdatum: 2016-08-26
    Beschreibung: The mitigation options to meet the ambitious carbon reduction targets set by the UK government are discussed in this paper, including the use of carbon capture and storage (CCS) technology, clean renewable energy integration and a proposed system of integrated fuel cell combined heat and power (FC-CHP) technology. Analysis shows that the use of CCS technology within the current infrastructure can abate half the electricity-associated CO 2 emissions; however, this comes at a high cost penalty. The emissions associated with domestic heat cannot be prevented without changes in the energy infrastructure. Hydrogen-powered fuel cells can provide clean energy at a range of scales and high efficiencies, especially when employed with a CHP system. However, production of CO 2 -free hydrogen is essential for fuel cell technology to contribute substantially to a low carbon economy globally. In this work, three methods were investigated for small-scale distributed hydrogen production, namely steam methane reforming, water electrolysis (WE) and cold plasma jet (CPJ). The criteria used for comparisons include the associated CO 2 emissions and the cost of energy production. CPJ decomposition of methane shows a high potential when combined with integrated FC-CHP technology for economically viable and CO 2 -free generation of energy, especially in comparison to WE. Including the value of the solid carbon product makes the plasma system most attractive economically.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 3
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    Endoreversible modeling and optimization of multistage isothermal chemical engines under linear mass transfer law via Hamilton-Jacobi-Bellman theory (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-08-26
    Beschreibung: A multistage continuous isothermal endoreversible chemical engine system with a finite driving fluid is investigated in this paper, and the mass transfer law obeys the linear mass transfer law [ $$g\propto \mathrm{\Delta }\mu $$ ]. Under the condition that both the initial time and the initial key component concentration in the driving fluid are fixed, the maximum power output of the multistage chemical engine system and the corresponding optimal concentration configuration of the key component in the driving fluid are derived by applying Hamilton–Jacobi–Bellman (HJB) theory, and numerical examples for three different boundary conditions are given. The results show that the difference between the chemical potential of the key component and the Carnot chemical potential for the maximum power output is a constant, and the key component concentration in the driving fluid decreases with the increase of time nonlinearly; when both the process period and the final concentration of the key component are fixed, there is an optimal control strategy for the maximum power output of the multistage chemical engine system, and the maximum power outputs of the system and the corresponding optimal control strategies are different for different final concentrations. The obtained results can provide some theoretical guidelines for the optimal designs and operations of practical energy conversion systems.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 4
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    Thermodynamic analysis and optimization of the Atkinson engine by using NSGA-II (2016)
    Oxford University Press
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    Publikationsdatum: 2016-08-26
    Beschreibung: Recently, several studies have been conducted regarding the Atkinson cycle and Atkinson engine which have resulted in various thermal efficiency and output power analysis. In the present study, output power and engine thermal efficiency are maximized via employing the NSGA-II approach and thermodynamic analysis. The multi-objective evolutionary approach on the basis of the NSGA-II method is implemented throughout this work for optimizing the above-mentioned variables. To evaluate the aforementioned goal, two objective functions which comprises the power output ( W ) and cycle efficiency ( ) have been included in the optimization process simultaneously.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 5
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    Control of micro-CHP and thermal energy storage for minimising electrical grid utilisation (2016)
    Oxford University Press
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    Publikationsdatum: 2016-02-05
    Beschreibung: The efficient use of combined heat and power (CHP) systems in buildings presents a control challenge due to their simultaneous production of thermal and electrical energy. The use of thermal energy storage coupled with a CHP engine provides an interesting solution to the problem—the electrical demands of the building can be matched by the CHP engine, while the resulting thermal energy can be regulated by the thermal energy store. Based on the thermal energy demands of the building the thermal store can provide extra thermal energy or absorb surplus thermal energy production. This paper presents a multi-input multi-output inverse-dynamics-based control strategy that will minimise the electrical grid utilisation of a building, while simultaneously maintaining a defined operative temperature. Electrical demands from lighting and appliances within the building are considered. In order to assess the performance of the control strategy, a European Standard validated simplified dynamic building physics model is presented that provides verified heating demands. Internal heat gains from solar radiation and internal loads are included within the model. Results indicate the control strategy is effective in minimising the electrical grid use and maximising the utilisation of the available energy when compared with conventional heating systems.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 6
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    Thermodynamic optimization of a triple-shaft open intercooled, recuperated gas turbine cycle. Part 2: power and efficiency optimization (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-02-05
    Beschreibung: The power and the efficiency of a triple-shaft open intercooled, recuperated gas turbine cycle are analyzed and optimized based on the model established using thermodynamic optimization theory in Part 1 of this paper by adjusting the low-pressure compressor inlet relative pressure drop, the mass flow rate and the distribution of pressure losses along the flow path. First, the power output is optimized by adjusting the intercooling pressure ratio, the air mass flow rate or the distribution of pressure losses along the flow path. Second, the thermodynamic first-law efficiency is optimized subject to a fixed fuel flow rate and a fixed overall size by seeking the optimal intercooling pressure ratio, the compressor inlet pressure drop and optimal flow area allocation ratio between the low-pressure compressor inlet and the power turbine outlet. The numerical examples show that increase in effectiveness of intercooler increases power output and its corresponding efficiency and increase in effectiveness of recuperator decreases power output appreciably but increases its corresponding efficiency; there exist an optimal low-pressure compressor inlet relative pressure drop and an optimal intercooling pressure ratio, which lead to a maximum power. For a fixed fuel mass rate and a fixed overall area of low-pressure compressor inlet and power turbine outlet, maximum thermodynamic first-law efficiency is obtained by optimizing low-pressure compressor inlet relative pressure drop and intercooling pressure ratio. The double-maximum thermodynamic first-law efficiency is obtained by searching optimal flow area allocation between low-pressure compressor inlet and power turbine outlet.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 7
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    Transient simulation of a solar absorption cooling system (2016)
    Oxford University Press
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    Publikationsdatum: 2016-02-05
    Beschreibung: With non-renewable energy sources depleting quickly, solar energy could prove a viable option owing to its abundance and eco-friendliness. Modeling and simulation of a solar energy-driven single-stage absorption chiller was carried out using the transient simulation software ‘TRNSYS’. An evacuated tube collector coupled with an insulated tank served as heat source for the absorption chiller. Experiments were conducted to evaluate the efficiency parameters of the collector as well as the loss coefficient for the storage tank. These parameters along with standard chiller performance data were used to model the system. The influence of climatic conditions, storage capacity and various control schemes with and without auxiliary heating on the output of the system is analyzed and presented in the paper.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 8
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    Thermochemical cooling system based on adsorption pumping pipe (2016)
    Oxford University Press
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    Publikationsdatum: 2016-02-05
    Beschreibung: Based upon the theoretical principle of the thermochemical energy storage pumping pipe system, a new cooling system has been presented. In order to analyse the performance and design of the system based on adsorption pumping pipe process, a simplified mathematical model is developed. Both simulation and experimental results are given and discussed. The comparison of various methods (ammonium dissolves, evaporation of CO 2 , etc.) showed that it is the simplest and most reliable to use adsorbents such as zeolite in this cooling system. A total of 250 g zeolite 13X could reduce the temperature of 330 ml by 15°C in 2–3 min (for beverage self-cooling applications). For future work, a large scale demonstration system is required to prove the viability and long term performance of thermochemical cooling/energy storage system.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 9
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    Thermodynamic optimization of a triple-shaft open intercooled-recuperated gas turbine cycle. Part 1: description and modeling (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-02-05
    Beschreibung: Considering the flow processes of the working fluid with the pressure drops, a thermodynamic model for a triple-shaft open intercooled-recuperated gas turbine cycle is established using thermodynamic optimization theory in Part 1 of this paper. The relative pressure drops associated with the flow through various cross-sectional areas are derived as functions of the low-pressure compressor inlet relative pressure drop. The analytical formulae of the cycle's power and efficiency are derived. The performance of the model cycle is optimized by adjusting the compressor inlet pressure, the mass flow rate and the distribution of pressure losses along the flow path in Part 2 of this paper.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 10
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    Power and power density analyzes of an endoreversible modified variable-temperature reservoir Brayton cycle with isothermal heat addition (2016)
    Oxford University Press
    Details
    Publikationsdatum: 2016-02-05
    Beschreibung: The mistakes in recent literatures are analyzed, and a new model for an endoreversible closed modified Brayton cycle with isothermal heat addition coupled to variable-temperature reservoirs is established using finite-time thermodynamics in this paper. The range of isothermal heat addition modification is determined, and the analytical formulae of the dimensionless power output, thermal efficiency and dimensionless power density of the cycle are derived. The effects of the cycle parameters on the global performances of power output and power density and the performances at maximum power design and maximum power density are analyzed by numerical calculations. The results show that there exist optimal compressor pressure ratios, respectively, which lead to maximum dimensionless power output and maximum dimensionless power density, that the optimal compressor pressure ratio and the thermal efficiency at maximum power design are always smaller than the corresponding ones at maximum power density design, and that dimensionless power output and maximum specific volume at maximum power design are always bigger than the corresponding ones at maximum power density design. The results imply that the power density design possesses the advantages such as smaller equipment volume and higher thermal efficiency at the cost of disadvantages such as bigger compressor pressure ratio and power output loss. Maximizing the power density gives a compromise between power and the size of the engine. The calculations also show that an endoreversible closed modified Brayton cycle with isothermal heat addition cannot work at the maximum thermal efficiency design point.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 11
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    Effects of thermocouples physical size on the performance of the TEG-TEH system (2016)
    Oxford University Press
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    Publikationsdatum: 2016-08-26
    Beschreibung: The effects of thermocouples physical size on the performance of a thermoelectric heat pump (TEH) driven by a thermoelectric generator (TEG) device are investigated in this article. The physical size refers to the length and the cross-sectional area of the thermocouples. The performance analysis is multiobjective, including stable electrical current, heating load, coefficient of performance, maximum heating load and maximum heating temperature difference. A characteristic parameter, i.e. area–length ratio, is defined to describe the thermocouples physical size. The influences of the parameter are analyzed by detailed numerical examples. A practical example is proposed to show how to select appropriate thermoelectric modules (TEMs) to construct a high-performance TEG–TEH system satisfying different requirements. The results show that an improvement in its performance is possible by optimizing internal physical size of thermocouples. The conclusion obtained could be used for the selection of TEMs and the design of the TEG–TEH system.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 12
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    Effect of the working liquid to the capillary pumped loop performance (2016)
    Oxford University Press
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    Publikationsdatum: 2016-08-26
    Beschreibung: The purpose of this paper is to present a theoretical analysis of the capillary pumped loop (CPL) performance using different working liquids. CPL is a passive heat transfer device, using no mechanical pump to circulate the working liquid, usually composed of a liquid tank, an evaporator, a condenser, a liquid and a vapor line. Heat load is applied on the external surface of the evaporator, partially transferred to the wick inside. Because of this heat load capillary forces are developed inside the porous structure, due to meniscus formation between liquid and vapor surface of the liquid, causing a pressure oscillation capable to pump the flow out of the evaporator. In this paper CPL performance is evaluated using different working liquids, such as water, ammonia, acetone and freon-134. These have different thermophysical properties such as latent heat, viscosity and density, causing different behavior when used as working liquid. Water was found more stable for higher temperature differences, due to higher latent heat of vaporization, while ammonia could take advantage of its viscosity for small temperature differences.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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  • 13
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    Design and optimization of a thermoacoustic heat engine using reinforcement learning (2016)
    Oxford University Press
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    Publikationsdatum: 2016-08-26
    Beschreibung: The thermoacoustic heat engine (TAHE) is a type of prime mover that converts thermal power to acoustic power. It is composed of two heat exchangers (the devices heat source and sink), some kind of porous medium where the conversion of power takes place and a tube that houses the acoustic wave produced. Its simple design and the fact that it is one of a few prime movers that do not require moving parts make such a device an attractive alternative for many practical applications. The acoustic power produced by the TAHE can be used to generate electricity, drive a heat pump or a refrigeration system. Although the geometry of the TAHE is simple, the behavior of the engine is complex with 30+ design parameters that affect the performance of the device; therefore, designing such a device remains a significant challenge. In this work, a radical design methodology using reinforcement learning (RL) is employed for the design and optimization of a TAHE for the first time. Reinforcement learning is a machine learning technique that allows optimization by specifying ‘good’ and ‘bad’ behavior using a simple reward scheme r . Although its framework is simple, it has proved to be a very powerful tool in solving a wide range of complex decision-making/optimization problems. The RL technique employed by the agent in this work is known as Q-learning. Preliminary results have shown the potential of the RL technique to solve this type of complex design problem, as the RL agent was able to figure out the correct configuration of components that would create positive acoustic power output. The learning agent was able to create a design that yielded an acoustic power output of 643.31 W with a thermal efficiency of 3.29%. It is eventually hoped that with increased understanding of the design problem, in terms of the RL framework, it will be possible to ultimately create an autonomous RL agent for the design and optimization of complex TAHEs with minimal predefined conditions/restrictions.
    Schlagwort(e): Other low-carbon energy technologies
    Print ISSN: 1748-1317
    Digitale ISSN: 1748-1325
    Thema: Energietechnik , Maschinenbau
    Publiziert von Oxford University Press
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