Thermally driven refrigerators: Equivalent low-dissipation three-heat-source model and comparison with experimental and simulated results

[EN]In order to investigate the performance of a class of thermally driven refrigerators, usually driven by low-grade thermal energy, a generic thermodynamic model of three-heat-source refrigerator without involving any specific heat-transfer law is put forward by adopting low-dissipation assumptions. Based on the proposed model, the analytical expressions for the coefficient of performance (COP) and cooling power of the system are derived in terms of well-defined dissipation parameters and contact time durations between the system and heat reservoirs. One essential parameter accounting for the size ratio of the two coupled subsystems inside the overall system is introduced in light of the practical meaning of the reversible entropy change. With the help of the aforementioned parameter, the optimal relation between the COP and cooling power is obtained. The optimal operation region and optimal construction of the overall system are further determined for the first time. In addition, the influences of the dissipation and temporal symmetries are discussed in detail, according to which the upper and lower bounds of the COP at maximum cooling power are firstly obtained under two extreme situations. Experimental and simulated data from previous reported works are collected to illustrate the validity and practical significance of the proposed model and associated results. A limit case is presented to highlight the generality of the model.National Natural Science Foundation of China ; Junta de Castilla y León of Spain ; University of Salamanca contract 2017/X005/1

ECOS 2012

The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

A critical review on energy, exergy, exergoeconomic and economic (4-E) analysis of thermal power plants

AbstractThe growing energy supply, demand has created an interest towards the plant equipment efficiency and the optimization of existing thermal power plants. Also, a thermal power plant dependency on fossil fuel makes it a little bit difficult, because of environmental impacts has been always taken into consideration. At present, most of the power plants are going to be designed by the energetic performance criterion which is based on the first law of thermodynamics. Sometimes, the system energy balance is not sufficient for the possible finding of the system imperfections. Energy losses taking place in a system can be easily determined by using exergy analysis. Hence, it is a powerful tool for the measurement of energy quality, thereby helps to make complex thermodynamic systems more efficient. Nowadays, economic optimization of plant is also a big problem for researchers because of the complex nature. At a viewpoint of this, a comprehensive literature review over the years of energy, exergy, exergoeconomic and economic (4-E) analysis and their applications in thermal power plants stimulated by coal, gas, combined cycle and cogeneration system have been done thoroughly. This paper is addressed to those researchers who are doing their research work on 4-E analysis in various thermal power plants. If anyone extracts an idea for the development of the concept of 4-E analysis using this article, we will achieve our goal. This review also indicates the scope of future research in thermal power plants

Optimization of environmentally friendly solar assisted absorption cooling systems

La optimización de los sistemas de conversión de energía gana cada vez más importancia debido a su impacto ambiental y los limitados recursos de combustibles fósiles. Entre estos sistemas los de refrigeración tienen una contribución creciente en el consumo total de energía y en las emisiones de CO2. Los sistemas de absorción operados con energía solar son una de las alternativas más sostenibles frente a los sistemas de refrigeración convencionales. Por lo tanto, este trabajo se centra en su mejora siguiendo los métodos de optimización termo-económica y de programación matemática. El análisis exergético y la optimización termo-económica basada en el método estructural se han realizado para distintas configuraciones de ciclos de refrigeración por absorción con las mezclas de trabajo agua-LiBr y amoniaco-agua. En la sección de programación matemática se incluye la optimización multi-objetivo (frontera de Pareto), la optimización bajo incertidumbre de los precios de la energía, el uso de varios indicadores de impacto ambiental y el efecto del impuesto sobre las emisiones de CO2. Los resultados demuestran que se pueden obtener reducciones importantes del impacto ambiental frente a los sistemas convencionales. Los sistemas de refrigeración solar no sólo son atractivos para reducir el impacto ambiental, sino también pueden ser económicamente competitivos. Su implantación dependerá, en gran medida, del impuesto sobre las emisiones de CO2 y del coste de la energía.Optimizations of energy conversion systems become more important because of their environmental impact and the limitations of the fossil fuel resources. Among these systems cooling and refrigeration machines have an increasing share in the total energy consumption and contribution to CO2 emissions. Solar assisted absorption cooling systems are sustainable alternatives compared to the conventional cooling systems. Hence, this work is focused on improving the sustainability of cooling systems following the thermoeconomic optimization and mathematical programming approaches. In the first approach the energy, exergy and structural analysis are performed for different configurations of water/LiBr and ammonia/water absorption cooling cycles. In the second approach multi-objective optimization (Pareto frontier), optimization under uncertainty of energy prices, different environmental impact indicators, and the effect of CO2 emissions tax to reduce the global warming are discussed. The results of the multi-objective optimization show that a significant environmental impact reduction can be obtained. Results indicate that these systems are attractive not only to reduce the environmental impact but also in incurring the economic benefits. However, its practical impact largely depends on the CO2 emissions tax and the increase in the energy price

Study on the Performance Optimization and Parametric Design for a Class of Irreversible Solar-Driven Heat Engines

塔式、碟式太阳能热机系统由于聚光比较大，集热器工作于较高温区，这时辐射热漏不可忽略。因此研究集热器辐射对流热损对太阳能热机系统性能特性的影响有其重要意义。另一方面，和其它太阳能热设备一样，太阳能热机首期投资成本较高，为了使所得到的太阳能在热机系统中产生最大化的经济效益，有必要研究太阳能热机系统的热经济优化性能。本硕士学位论文围绕集热器工作于高温区的几种太阳能热机系统性能展开研究，探索多种不可逆因素对一类太阳能热机系统总效率或热经济函数的影响。主要内容包括以下两方面： 第二章，建立包括集热器存在辐射对流热损，工质与热源间有限速率热传导，循环回热损失及循环工质内不可逆性等的太阳能Stirling...For a solar-driven heat engine with tower or dish style collector, its collector’s temperature is generally in high temperature region because it has a large concentrating ratio. In this case, the collector’s radiation heat leak can not be ignored. So, investigating the influence of radiation-convection heat leak of the solar collector on the performance characteristic of solar-driven heat engine ...学位：理学硕士院系专业：物理与机电工程学院物理学系_理论物理学号：1982008115298

The equivalent low-dissipation combined cycle system and optimal analyses of a class of thermally driven heat pumps

[EN]The performance characteristics, operation, and design strategies of a class of thermally driven heat pumps are investigated due to their important roles in the efficient utilization of low-grade thermal energy. In order to establish a more generic thermodynamic model of thermally driven heat pumps mainly including absorption, adsorption, and ejector heat pumps, low-dissipation assumption is adopted. Accordingly, the associated dissipation parameters accounting for the specific information on the irreversibilities in each heat-transfer process are introduced rather than specifying heat-transfer law. Based on the proposed model, the theoretical results of the coefficient of performance and heat load are derived with regard to two key parameters denoting the size ratio of the two involved subsystems and the matching deviation from reversible limit. The performance characteristics and the optimally operating regions of the whole system are determined and the differences between thermally driven heat pump and refrigerator are highlighted. The proposed model and obtained results further develop the low-dissipation mode

THERMODYNAMICS OF DEVELOPMENT OF ENERGY SYSTEMS WITH APPLICATIONS TO THERMAL MACHINES AND LIVING ORGANISMS

We define and analyse thermodynamic limits for various traditional and work-assisted processes of sequential development with finite rates important in engineering and biology. The thermodynamic limits are expressed in terms of classical exergy change and a residual minimum of dissipated exergy, or some extension including time penalty. We consider processes with heat and mass transfer that occur in a finite time and with equipment of finite dimension. These processes include heat and separation operations and are found in heat and mass exchangers, thermal networks, energy converters, energy recovery units, storage systems, chemical reactors, and chemical plants. Our analysis is based on the condition that in order to make the results of thermodynamic analyses usable in engineering economics it is the thermodynamic limit, not the maximum of thermodynamic efficiency, which must be overcome for prescribed process requirements. A creative part of this paper outlines a general approach to the construction of `Carnot variables´ as suitable controls. Finite-rate, endoreversible models include minimal irreducible losses caused by thermal resistances to the classical exergy potential. Functions of extremum work, which incorporate residual minimum entropy production, are formulated in terms of initial and final states, total duration and (in discrete processes) number of stages

Comprehensive thermodynamic and operational optimization of a solar-assisted LiBr/water absorption refrigeration system

Absorption cooling systems have been investigated for many years due to their ability to use low-grade heat instead of electricity as the energy source. The aim of this work is to advance the performance of a single-effect Lithium bromide/water absorption cooling system. Taking the generator and evaporator temperatures as variables, the system is optimized to maximize exergetic and energetic efficiencies at different operational conditions using a multi-objective–multi-variable Genetic Algorithm. The Group Method of Data Handling neural network approach is adopted to derive correlations between the design variables and operational parameters. Finally, the system is coupled to evacuated tube solar collectors and compared to a similar system. The results reflect a maximum improvement in energetic and exergetic efficiencies of about 9.1% and 3.0%, respectively. This translates into savings of 187 dollars for every square meter of solar collector at present time. This improvement is achieved by decreasing the mean temperature of the generator by 6.2 °C and increasing the mean temperature of the evaporator by 1.6 °C. In the case of applying low-grade heat such as solar energy, it brings about both an improvement in the thermodynamic performances and a reduction in the generator temperature

Thermodynamic optimisation of the biofuel production based on mutualism

Recently, we have introduced a new bioeconomic indicator in order to avoid the difficulties in evaluating the process and technologies for sustainability. In this paper, we wish to improve this new indicator for the analysis of sustainability. Indeed, the indicator has been based on the exergy analysis of dissipation and irreversibility, and it was proven in some social and technical application. In this work, a more general definition has been introduced in order to use it in any evaluation of sustainability. In particular, it has been applied to improve the biofuel production obtained by microorganisms, starting from the biophysical behaviour of the microorganisms themselves. Indeed, in industrialised countries, the management of CO2emissions represents one of the present compelling issues. In this context, the improvement of the energy efficiency, and its rational use, can be considered a fundamental economic strategy for the sustainable development of the industrialised countries. Our indicator takes into account all these requests for the development and sustainability, resulting a very interesting thermoeconomic quantity to be used by decision makers. Moreover, it is used to prove that mutualism can represent a new approach for the optimisation of biofuels production