Thermodynamic efficiency of expander-generator units at the plants for technological decompression of transported natural gas

The thermodynamic efficiencies of throttling devices and expander-generator units used for technological decompression of transported gas in gas distribution stations (GDS) and gas control points (GCP) of the gas supply system are compared. Various designs of the expander-generator units generating either electricity or electricity and cold are considered. The exergy efficiency is used as a criterion of the thermodynamic efficiency. It is shown that the replacement of the throttling device by the expander-generator unit under conditions taken for calculations leads to an increase in exergy efficiency of the station of technological decompression of the transported gas at all considered schemes of this unit inclusion: with no gas heating in the expander-generator unit, with gas heating after the expander, before the expander as well as before and after the expander.     

Influence of process parameters on thermodynamic efficiency of expander-generator units at the plants for technological decompression of transported natural gas

The article presents the research results of the influence of process parameters on the thermodynamic efficiency of expander-generator units, used as an alternative to throttling devices for technological reduction of pressure of transported natural gas at the plants of technological decompression of the gas supply system–gas distribution stations (GDS) and gas control points (GCP). The process parameters are the temperature of the outside air, the ratio between the pressures of the transported gas at the outlet and inlet of GDS and GCP, and the temperature of the gas heating before the expander. Various circuit designs of expander-generator units for generating either only electricity or electricity and cold are considered. Exergy efficiency is taken as a criterion for evaluating thermodynamic efficiency. The calculation results for the changes in flow exergy and exergy efficiency at changing process parameters are presented in graphical form. The thermodynamic efficiencies of throttling devices and expander-generator units are com-pared. It is shown that the replacement of the throttling device by the expander-generator unit for all the considered process parameters leads to an increase in the exergy efficiency of the stations for technological decompression of the transported gas in all the considered schemes of this unit inclusion: without heating the gas in the expander-generator unit, with heating the gas after the expander, as well as with heating before and after it.     

An engineering method for calculating the parameters and characteristics of pulse detonation engines

Theoretical fundamentals for calculating the thermodynamic cycle of engines with fuel detonation (FD cycle), which is realized in the thrust units of pulse detonation engines (PDE), are presented. A system of equations for calculating the parameters of the detonation waves under various conditions of their initiation is derived. These equations were used to examine how various factors influence the parameters of detonation waves and, consequently, the work of the cycle, thermal efficiency, and the specific parameters of the PDE. It was demonstrated that the maximum thermal efficiency of the FD cycle virtually coincides with the minimum losses caused by the irreversibility of heat input into the detonation wave. It was established that the losses are substantially dependent on the temperature of the working substance (compressed air or heated gas) supplied into the thrust units, more specifically, they decrease with increasing temperature.     

制冷剂饱和热力性质的隐式拟合方法

１前言准确、快速、稳定地计算制冷剂热力性质是计算机辅助设计和工程计算的要求。但目前流行的多项式类简化拟合函数在总体计算精度、外推以及求反计算等方面都有待改进［１－３］。本文从函数展开的角度剖析了现有多项式类拟合函数的不足,提出了一种低次的隐函数形式的...     

Physical model and demonstration of an aquifer thermal energy store

An experimental loop has been set up to demonstrate the technical feasibility of a hot water aquifer store and to validate an original physical model and code as well as the engineering based on it. The model applies to a “reference aquifer” and an appropriate exploitation system, as defined in the text. Experiments have been carried out for a period of 37 days, 15 days for injection of hot water at 40°C, 7 days of storage at rest, 15 days for pumping out stored hot water. The system has worked perfectly at the specified performance. Measured temperatures show a very good accordance with temperatures predicted by the numerical model. The rated 52% efficiency has been confirmed. Although more extended experiments shall be performed, one can conclude that the engineering of the system is appropriate and the physical model and numerical code developed by the authors are satisfactory.     

Critical evaluation and thermodynamic modeling of the Mn–Cr–O system for the oxidation of SOFC interconnect

A complete critical evaluation and thermodynamic modeling of the phase diagrams and thermodynamic properties of the Mn–Cr–O system at 1 bar total pressure are presented. Optimized equations for the thermodynamic properties of all phases are obtained, which reproduce all available and reliable thermodynamic and phase equilibrium data within experimental error limits from 25 °C to above the liquidus temperatures at all compositions and oxygen partial pressures. As results of optimization, the Gibbs energy function of MnCr₂O₄ is for the first time properly estimated and the discrepancies of the phase diagram experiments of the Mn–Cr–O system are resolved. In particular, unexplored phase diagrams and thermodynamic properties of the Mn–Cr–O system of importance for the oxidation of SOFC interconnect are predicted on the basis of the optimized model parameters. The database of the model parameters can be used along with software for Gibbs energy minimization in order to calculate any type of phase diagram sections and thermodynamic properties.     

捕获CO2的部分煤气化氢电联产系统

基于煤炭分级转化、成分对口应用、污染物控制一体化等系统集成思路,提出了一种捕获CO₂的部分煤气化氢电联产系统。该系统利用增压流化床完成煤炭部分气化,降低了气化难度与气化炉造价,具有较好经济性;全面揭示了系统的热力和环境特性规律,指出气化炉碳转化率是影响系统热力性能的主要因素;系统具有良好的热力特性与环境特性,当CO₂的分离率为59.7%时,系统（火用）效率为54.3%。本文的研究为煤炭的清洁高效利用提供了可选择的途径。     

Critical thermodynamic evaluation and optimization of the Fe-Mg-O system

A complete literature review, critical evaluation and thermodynamic modeling of the phase diagrams and thermodynamic properties at 1 bar total pressure of all oxide phases in the Fe-Mg-O system are presented. Optimized model equations for the thermodynamic properties of all phases are obtained which reproduce all available thermodynamic and phase equilibrium data within experimental error limits from 25 °C to above the liquidus temperatures at all compositions and oxygen partial pressures. The complex phase relationships in the system have been elucidated and discrepancies among the data have been resolved. The database of the model parameters can be used along with software for Gibbs energy minimization in order to calculate any type of phase diagram section. Sublattice models, based upon the compound energy formalism, were used for the spinel, pyroxene, olivine and monoxide phases. The use of physically reasonable models means that the models can be used to predict properties, phase equilibria, and cation site distributions in composition and temperature regions where data are not available.     

蒸汽喷射式制冷系统模型建立与仿真

对蒸汽喷射制冷工作过程中能量转化进行了深入分析,建立了制冷系统中的三个关键部件——喷射器、冷凝器及蒸发器的热力学模型.以此为基础,结合运行参数,采用Matlab软件,对喷射系数、蒸汽消耗量以及循环水耗量进行仿真计算.探讨了以喷射系数为评定标准时,工作蒸汽压力Pg、冷凝温度Tc、蒸发温度Te对系统性能的影响.分析结果表明...     

Thermal modelling and energy conservation studies on freon rankine cycle cooling system with regenerative heat exchanger

This communication presents a thermodynamic analysis and assessment of a Freon fluid Rankine cycle cooling system. The system consists of two subsystems—Rankine engine (RE) power cycle and a vapour compression (V-C) refrigeration cycle. The heat engine subsystem consists of a boiler, turbine, condenser and a feed pump while the cooling subsystem consists of a mechanical compressor, condenser, evaporator and an expansion valve. A number of working fluid combinations for the RE cycle and V-C cycle subsystems have been chosen on the basis of their thermodynamic properties and their suitability judged in terms of the performance parameters, namely, the thermal efficiency of the power cycle and the coefficient of performance (COP) of the refrigeration cycle. A regenerative heat exchanger (RHE) is incorporated in the RE cycle to improve the cycle efficiency and achieve energy conservation.The effects of various operation parameters, namely, component temperatures, adiabatic expansion/compression efficiencies and effectiveness of the RHE on the overall COP have been assessed. It is found that R114 + R22 give the best overall system performance and the presence of the RHE improves the system COP significantly. The effect of V-C cycle condenser temperature is more pronounced as compared to that of the RE cycle condenser and similarly the effect of evaporator temperature in the V-C cycle is more pronounced as compared to that of the boiler in the Rankine cycle subsystem.     

Second law of thermodynamics with discrete quantum feedback control

A new thermodynamic inequality is derived which leads to the maximum work that can be extracted from multi-heat-baths with the assistance of discrete quantum feedback control. The maximum work is determined by the free-energy difference and a generalized mutual information content between the thermodynamic system and the feedback controller. This maximum work can exceed that in conventional thermodynamics and, in the case of a heat cycle with two heat baths, the heat efficiency can be greater than that of the Carnot cycle. The consistency of our results with the second law of thermodynamics is ensured by the fact that work is needed for information processing of the feedback controller.     

吸收式制冷用氨-硝酸锂工质对及循环系统的研究

氨-硝酸锂作为新型吸收式制冷工质对有很多突出优点,但有关其热物理性质及循环系统的研究资料比较少。文中详细介绍了氨-硝酸锂吸收式制冷工质对的特点、热力学性质以及目前国内外对此工质对的研究进展,并提出利用此工质对的一种吸收压缩混合循环系统。利用此系统,可将总效率提高10%,具有较好的经济性。     

基于实际换热的ORC亚/跨临界综合评价

本文以有机朗肯循环(ORC)跨临界与亚临界工质换热特性最新研究成果为基础,采用热力学指标热源回收(火用)效率,以及经济学中的净现值(NPV)概念,结合换热面积分析,建立了考虑实际换热情况的热力学及经济性模型,更合理、更全面地对亚临界循环与跨临界循环的热力学性能和经济性进行了统一分析,为工程实际中亚临界和跨临界的选择提供...     

Critical temperature and thermodynamics of attractive fermions at unitarity

The unitarity regime of the BCS-BEC crossover can be realized by diluting a system of two-component lattice fermions with an on-site attractive interaction. We perform a systematic-error-free finite-temperature simulation of this system by diagrammatic determinant Monte Carlo method. The critical temperature in units of Fermi energy is found to be T(C)/epsilonF=0.152(7). We also report the behavior of the thermodynamic functions, and discuss the issues of thermometry of ultracold Fermi gases.     

Thermodynamic Efficiency of Interactions in Self-Organizing Systems

The emergence of global order in complex systems with locally interacting components is most striking at criticality, where small changes in control parameters result in a sudden global reorganization. We study the thermodynamic efficiency of interactions in self-organizing systems, which quantifies the change in the system’s order per unit of work carried out on (or extracted from) the system. We analytically derive the thermodynamic efficiency of interactions for the case of quasi-static variations of control parameters in the exactly solvable Curie–Weiss (fully connected) Ising model, and demonstrate that this quantity diverges at the critical point of a second-order phase transition. This divergence is shown for quasi-static perturbations in both control parameters—the external field and the coupling strength. Our analysis formalizes an intuitive understanding of thermodynamic efficiency across diverse self-organizing dynamics in physical, biological, and social domains.     

Thermodynamic functions of both simple (monomeric) and polymeric melts: MFA approach and Monte Carlo simulation

The influence of equilibrium polymerization on the thermodynamic properties of model systems consisting of building units with well-defined characteristics and interactions is investigated. The systems under study are thought to resemble more or less accurately undercooled melts, and the calculations performed give the configurational part of the thermodynamic functions of these melts. The whole investigation is performed by using two approaches. In the first one, the temperature courses of the entropies and the specific heat of the systems as well as the average flexibility and the mean chain length of the polymer molecules are obtained in the framework of a mean field approximation (MFA). In the second approach, the bulk characteristics and the configurational properties of the model systems are obtained by using Monte Carlo simulations (MCS). The correspondence and the differences between the thermodynamic properties for the same systems in the two approaches are analyzed and discussed. The model used in our MCS is a modified version of the so-called independent monomer state model proposed earliar by Jari? and Bennemann. The temperature course of the thermodynamic functions of the systems under investigation is analyzed and compared with existing experimental data. The existence of phase transition corresponding to melt-crystal or order-disorder transformation in the system is discussed based on the two approaches.     

基于分子动力学模拟的主链型液晶聚合物的新模型

在传统的Gay-Berne (GB)/Lennard-Jones (LJ)模型的基础上，发展了一种用于模拟半刚性主链型液晶聚合物(LCP)的分子级模型，命名为Solo-LJ-SP-GB 模型.单一的LJ联合体和非线性弹簧被用于描述LCP分子中的间隔体.用分子动力学模拟半刚性主链型LCP系统(该系统由169条分子链组成，每两个刚性体之间的间隔体个数为6)时，该模型所需的计算时间不到传统的GB/LJ 模型所需时间的十分之一，大大地提高了计算效率.通过采用该模型模拟半刚性主链型LCP的相变问题，观察到了与半刚性主链型LCP分子中间隔体个数相关的热力学的奇偶效应以及从等方相到向列相的相转变过程.这些模拟结果与当前的试验结果相当符合，从而表明了该模型可以较为准确地描述出半刚性主链型LCP的结构特性. 关键词： Solo-LJ-SP-GB模型 液晶聚合物 分子动力学模拟     

Thermodynamic modeling of oxide phases in the Fe–Mn–O system

A critical evaluation and thermodynamic modeling for thermodynamic properties of all oxide phases and phase diagrams in the Fe–Mn–O system are presented. Optimized Gibbs energy parameters for the thermodynamic models of the oxide phases were obtained which reproduce all available and reliable experimental data within error limits from 298 K to above the liquidus temperatures at all compositions covering from known oxide phases, and oxygen partial pressure from metal saturation to 0.21 bar. The optimized thermodynamic properties and phase diagrams are believed to be the best estimates presently available. Two spinel phases (cubic and tetragonal) were modeled using Compound Energy Formalism (CEF) with the use of physically meaningful parameters. The present Fe–Mn spinel solutions can be integrated into a larger spinel solution database, which has been already developed. The database of the model parameters can be used along with a software for Gibbs energy minimization in order to calculate any type of phase diagram section and thermodynamic properties.     

On the finite thermal conductivity of a one-dimensional rotator lattice

A heat transfer process is studied in a one-dimensional lattice of coupled rotators in which the orientation interaction between neighboring units is described by the periodic potential. Using this system as an example, it is demonstrated for the first time that one-dimensional lattices with a finite thermal conductivity in the thermodynamic limit can exist without substrate potential. As the temperature increases, the given system transforms from the state with an infinite thermal conductivity to the state with a finite thermal conductivity. The finiteness of the thermal conductivity stems from the existence of localized stationary excitations that interfere with heat transfer in the lattice. The lifetime and the concentration of these excitations increase with an increase in the temperature, which leads to a monotonic decrease in the thermal conductivity coefficient.