检索结果-南通市图书馆

Entransy functions for steady heat transfer

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2019年第10期62卷 1726-1734页

作者： cheng xuetao LIANG XinGang Big Data Center of Maanshan City Maanshan243000China Bureau of Data Resource Management of Maanshan City Maanshan243000China Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of AerospaceTsinghua UniversityBeijing100084China

In this paper, the entransy functions for steady heat transfer are summarized and discussed based on the variational theory and the entransy theory. The entransy functions for steady convective heat transfer are derived for the first time. In steady heat transfer processes, it is shown that the steady distributions of heat flux and temperature(radiative thermal potential) should make the corresponding entransy functions reach their minimum values when the temperature(radiative thermal potential) or the heat flux of the boundary is given. The extremum entransy dissipation principles and the minimum entransy-dissipation-based thermal resistance principles are compared with the entransy functions. It is shown that the entransy functions can describe a steady state,but cannot directly give a way to optimize heat transfer processes, while the extremum entransy dissipation principles and the minimum entransy-dissipation-based thermal resistance principles act in an opposite way.

关键词： entransy entransy dissipation entransy function steady state heat transfer

Work entransy and its applications

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2015年第12期58卷 2097-2103页

作者： cheng xuetao LIANG XinGang Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of Aerospace Tsinghua University

The entransy theory has been applied to the analyses of heat-work conversion systems. The physical meaning and the applications of work entransy are analyzed and discussed in this paper. Work entransy, which is clarified to be a process dependent quantity, is not the entransy of work, but the system entransy change accompanying work transfer. The relationship between the work entransy and the output work is set up. When the application preconditions are satisfied, larger work entransy leads to larger output work. Entransy loss, which was proposed and applied to heat work conversion processes with irreversible heat transfer, is the net entransy flow into the system and the summation of work entransy and entransy dissipation. The application preconditions of entransy loss are also discussed.

关键词： work entransy entransy loss thermodynamic processes application limitation

Entransy analyses of the thermodynamic cycle in a turbojet engine

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2017年第8期60卷 1160-1167页

作者： cheng xuetao LIANG XinGang Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of Aerospace Tsinghua University Beijing 100084 China The Administrative Committee of the Modern Industrial Park New District of Zhengpu Port Maanshan 238261 China

The analysis and the design of turbojet engines are of great importance to the improvement of the system *** researchers focus on these topics,and many important and interesting results have been *** this paper,the thermodynamic cycle in a turbojet engine is analyzed with the entransy theory and the T-Q *** ideal thermodynamic cycle in which there is no inner irreversibility is analyzed,as well as the influences from some inner irreversible factors,such as the heat transfer process,the change of the component of the working fluid and the viscosity of the working *** the discussed cases,it is shown that larger entransy loss rate always results in larger output power,while smaller entropy generation rate does not *** corresponding T-Q diagrams are also presented,with which the change tendencies of the entransy loss rate and the output power can be shown very *** is shown that the entransy theory is applicable for analyzing the inner irreversible thermodynamic cycles discussed in this *** with the concept of entropy generation,the concept of entransy loss and the corresponding T-Q diagram are more suitable for describing the change of the output power of the analyzed turbojet engine no matter if the inner irreversible factors are considered.

关键词： turbojet engine entransy analyses T-Q diagram inner irreversible cycle

Theoretical analyses of the performance of a concentrating photovoltaic/thermal solar system with a mathematical and physical model, entropy generation minimization and entransy theory

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2018年第6期61卷 843-852页

作者： cheng xuetao XU XiangHua LIANG XinGang Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of Aerospace Tsinghua University Beijing 100084 China Yushan Administrative Center Yushan District Maanshan 243000 China

In this paper, the performance of a concentrating photovoltaic/thermal solar system is numerically analyzed with a mathematical and physical model. The variations of the electrical efficiency and the thermal efficiency with the operation parameters are calculated. It is found that the electrical efficiency increases at first and then decreases with increasing concentration ratio of the sunlight, while the thermal efficiency acts in an opposite manner. When the velocity of the cooling water increases, the electrical efficiency increases. Considering the solar system, the surface of the sun, the atmosphere and the environment, we can get a coupled energy system, which is analyzed with the entropy generation minimization and the entransy theory. This is the first time that the entransy theory is used to analyze photovoltaic/thermal solar system. When the concentration ratio is fixed, it is found that both the minimum entropy generation rate and the maximum entransy loss rate lead to the maximum electrical output power,while both the minimum entropy generation numbers and the maximum entransy loss coefficient lead to the maximum electrical efficiency. When the concentrated sunlight is not fixed, it is shown that neither smaller entropy generation rate nor larger entransy loss rate corresponds to larger electrical output power. Smaller entropy generation numbers do not result in larger electrical efficiency, either. However, larger entransy loss coefficient still corresponds to larger electrical efficiency.

关键词： solar energy photovoltaic/thermal system performance analyses entropy generation entransy

Role of viscous heating in entransy analyses of convective heat transfer

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2020年第10期63卷 2154-2162页

作者： cheng xuetao WANG XiangYu LIANG XinGang Department of Science and Technology of Anhui Province Hefei 230091China Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of AerospaceTsinghua UniversityBeijing 100084China

The entransy theory is widely used and found to be effective in thermal analyses and *** researchers considered the entransy variation due to viscous heating as part of entransy dissipation and analyzed convective heat transfer based on the differential relationship between entropy and ***,it has been pointed out that the derivation of the differential relationship between entropy and entransy is *** this paper,the convective heat transfer processes with viscous heating is reconsidered and analyzed from the viewpoint of the energy conservation and the entransy balance *** is shown that the influence of the viscous heating is equivalent to that of an inner heat ***,the contribution of viscous heating to system entransy should not be treated as part of entransy dissipation,but entransy flow into the ***-stream parallel and counter flow heat exchangers with viscous heating and a thermal insulation transportation problem of heavy oil are taken as examples to verify the theoretical analyses *** the examples,the numerical results show that the entransy dissipation rates could be negative when the influence of the viscous heating on the system entransy is treated as part of the entransy *** is obviously ***,when the entransy contribution from the viscous heating to the system entransy is treated as entransy flow into the system,it is shown that the entransy dissipation rate is always positive,and the heat transfer processes can be well explained with the entransy theory.

关键词： entransy dissipation viscous heating convective heat transfer thermal analyses

Discussion on the extensions of the entransy theory

在线全文

学校读者我要写书评

暂无评论

Science China(Technological Sciences) 2017年第3期60卷 363-373页

作者： cheng xuetao ZHAO JianMing LIANG XinGang Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of Aerospace Tsinghua University Beijing 100084 China The Administrative Committee of the Modern Industrial Park New District of Zhengpu Port Maanshan 238261 China PBC School of Finance Tsinghua University Beijing 100084 China

In this paper,the preconditions forthe extensions of the entransy theory are summarized and *** the physical meaning of

关键词： entransy potential energy similarity extension microeconomics

Entransy decrease principle of heat transfer in an isolated system

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2011年第9期56卷 847-854页

作者： cheng xuetao LIANG XinGang GUO ZengYuan Key Laboratory for Thermal Science and Power Engineering of Ministry of Education School of Aerospace Tsinghua University Beijing 100084China

The entropy increase principle for an isolated system and the criteria of thermal equilibrium for an isolated system and systems with prescribed temperature and volume can be derived on the basis of the concept of entropy and the first and second laws of thermodynamics. In this paper, the entransy decrease principle for an isolated system is introduced on the basis of the concept of entransy. It is found that the entransy of an isolated system always decreases during heat transfer. This principle can be taken as an expression of the second law of thermodynamics for heat transfer. The thermal equilibrium criteria for an isolated system and a closed system are also introduced. It is found that when an isolated system reaches thermal equilibrium, its entransy is a minimum value. This criterion is referred to as the minimum entransy principle. When a closed system reaches thermal equilibrium, its free entransy is also a minimum value. This criterion is referred to as the minimum free entransy principle. Therefore, like entropy, entransy can be considered an arrow of time in heat transfer and used to describe the thermal equilibrium state.

关键词：孤立系统传热原理热力学第二定律熵增加原理封闭系统平衡系统平衡条件时间箭头

Entransy analysis of open thermodynamic systems

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2012年第22期57卷 2934-2940页

作者： cheng xuetao WANG WenHua LIANG XinGang Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Engineering MechanicsTsinghuaUniversityBeijing 100084China

The concept of entransy developed in recent years can describe the heat transport *** paper extends this concept to the open thermodynamic system and defines the concept of enthalpy *** entransy balance equation of steady open thermodynamic systems,as well as the concept of entransy loss,is *** entransy balance equation is applied to analyzing and discussing the air standard *** is found that the entransy loss rate can describe the change in net power output from the cycle but the entropy generation rate cannot when the heat absorbed by the working medium is from the combustion reaction of the gas *** the working medium is heated by a high temperature stream,both the maximum entransy loss rate and the minimum entropy generation rate correspond to the maximum net power output from the ***,the concept of entransy loss is an appropriate figure of merit that describes the cycle performance.

关键词：热力学系统循环性能平衡方程功率输出工作介质生成速率损失率传输能力

Relationship between microstate number and available entransy

在线全文

学校读者我要写书评

暂无评论

Chinese Science Bulletin 2012年第14期57卷 3244-3250页

作者： cheng xuetao LIANG XinGang Key Laboratory for Thermal Science and Power Engineering of Ministy of Education Department of Engineering MechanicsTsinghuaUniversityBeijing 100084China

Based on the relationship between entransy and microstate number, we discuss the variations of the available transport entransy, the unavailable transport entransy, the available conversion entransy and the unavailable conversion entransy with the microstate number. We focus on physical processes in which heat is used for heating/cooling or doing work. When heat is transported for heating or cooling, the available transport entransy increases if the increase in microstate number is due to the increase in internal energy of the system, and decreases if the increase in microstate number is due to spontaneous heat transfer. When heat is used to do work, both the available conversion entransy and the unavailable conversion entransy increase if the increase in microstate number relates to the growth in internal energy of the system. The available conversion entransy decreases and the unavailable conversion entransy increases if the increase in microstate number results from spontaneous heat transfer.

关键词：微观状态数物理过程在系统热传导传输冷却加热热量

同方期刊数据库