周期性双势垒锯齿势中温差驱动的布朗热机

研究了周期性双势垒锯齿势中, 布朗粒子在外力作用下沿空间坐标方向交替地和高、低温热库接触构成的布朗热机的热力学性能. 考虑布朗粒子动能的变化以及高、 低温库之间热漏的存在, 通过数值计算分析势垒高度、势比、外力等参数对布朗热机效率的影响. 研究表明：当考虑热漏时, 布朗热机始终是不可逆的, 效率小于卡诺效率; 并且当热漏很小时, 势比的增大在一定程度上可提高布朗热机的效率; 其功率与效率之间的关系曲线为闭合线. 当不考虑热漏时, 其功率与效率之间的关系曲线为开型线, 但由于布朗粒子动能的变化引起的不可逆热流, 热机的效率依然小于卡诺效率. 关键词： 布朗热机 双势垒锯齿势 热漏 热力学性能     

一维晶格中费曼棘齿-棘爪热机

研究了一维晶格中费曼棘齿-棘爪热机模型. 用粒子的概率主方程来描述粒子在晶格中的动力学特性, 推导出热流、 功率和效率的表达式. 通过数值计算分析势垒高度、 外力和温比对热流以及热机功率和效率的影响. 研究表明: 在粒子稳态概率流为零时, 存在非零的热流从高温库流入低温库, 类似于经典不可逆卡诺模型中的热漏; 热漏的存在使得热机的效率远远小于卡诺效率, 功率与效率之间为闭合的关系曲线, 热机为不可逆热机; 对热机性能参数进行优化, 可以使热机工作在最优性能状态下.     

非线性二极管系统构成的不可逆热机性能特征分析

研究了一个非线性二极管系统构成的不可逆热机的性能,它是由分别处于两个温度不同的热库中,完全相同的两个非线性二极管反向连接后并联上一个电容器组成的.运用非线性系统涨落理论计算出从两个热库中吸收的热流,考虑热漏损失后得出热机的功率和效率.通过数值模拟可以绘出热机的性能特征曲线以及优化性能参数随两热库温度比等主要参量的特征曲线.分析了二极管的非线性强度、热漏损失和温度比对热机性能特性的影响.最后,讨论了理想二极管热机的性能特征.     

以广义Redlich-Kwong气体为工质的不可逆回热式斯特林热机循环输出功率和效率

研究了热阻、回热损失和热漏等多种不可逆因素对以广义Redlich-Kwong气体为工质的斯特林热机性能的影响,给出了斯特林热机输出功率和效率的具体表达式并分析非理想回热特性及循环主要性能参数(如循环体积比及工质高低温比等)对循环输出功率和效率的影响.同时指出,只有在理想回热及无热漏的情况下,气体斯特林热机的效率才能达到卡诺效率.     

辐射对流传热对不可逆太阳能Braysson热机性能的影响

建立高温端同时辐射对流传热、低温端对流传热的不可逆太阳能Braysson热机循环新模型,探索有限速率热传导和绝热过程不可逆性等对热机循环性能的影响,基于热力学分析方法,导出热机输出功率和效率的解析表达式,数值计算结果揭示了等压温比、内不可逆参量及与热传导系数和面积有关的匹配参量等对热机性能特性的影响,所得结论不仅能导出其它不可逆太阳能热机的优化性能.且可为太阳能热机的参数设计和性能评价提供新理论参考.     

热质的运动与传递-微尺度导热中的热质动能效应

基于热质(热量的当量动质量)的概念,通过建立和分析热质的运动方程得到了反映热质动能变化的稳态导热微分方程,表明Fourier导热定律只有在热质的动能变化相对热质势能变化很小而可以忽略时才成立;在高热流密度和低温的情况下热质的动能变化不可忽略,这种动能效应表现为热流密度和温度梯度不再成线性关系.动能效应也导致Fourier导热定律不能通过热流和温度梯度准确地获得物体的导热系数,本文基于热质运动方程给出了导热系数动能效应的修正式.最后针对高热流密度和低温一维稳态导热进行了分子动力学模拟验证.     

不可逆回热式循环热机的功率与效率关系

给出了不可逆回热式热机循环模型 ,得到了与实际观测的热机特性相一致的p - η关系 ,讨论了热阻、热漏等不可逆困素对热机特性的影响 ,并与不可逆卡诺热机循环模型作了比较     

以一维谐振子势阱中的单粒子为工质的量子热机性能分析

建立了以一维谐振子势阱中的单粒子为工质的量子热机模型.当势阱壁宽度和粒子的量子态缓慢改变时, 该热机类似于经典卡诺热机对外做功.假设势阱壁移动速度非常缓慢并且考虑热漏, 推导出量子热机循环的输出功率和效率等重要性能参数的一般表达式.通过优化分析, 获得了热机循环中各主要性能参数的最佳优化值和优化区间.     

有热漏时定常态不可逆卡诺热机功率效率特性

对变热漏情况下定常态不可逆卡诺热机进行了有限时间热力学分析。导出最佳效率时的功率与等熵温比指数、效率与等熵温比指数的关系式,以及最佳面积比,进而得到最佳效率与功率关系。对最佳功率与最佳效率时的热机性能进行分析和讨论,给出一些有益的结论。     

不可逆双谐振通道电子热机生态学性能优化

建立了考虑电子源间热漏的不可逆双谐振通道能量选择性电子热机模型,联合统计力学和有限时间热力学理论,导出了系统的功率、效率、熵产率、生态学函数等主要性能参数的表达式。由数值计算对系统的生态学性能进行了分析和优化,得到了功率、效率、生态学函数等特性参数的最优区间和相互关系;获得了热漏、中心能量位置等设计参数对系统最优性能的影响特点。所得结果对多层固态热离子装置等实际电子机系统的设计和运行具有理论指导意义。     

Performance characteristics of an irreversible thermally driven Brownian microscopic heat engine

Brownian particles moving in a spatially asymmetric but periodic potential (ratchet), with an external load force and connected to an alternating hot and cold reservoir, are modeled as a microscopic heat engine, referred to as the Brownian heat engine. The heat flow via both the potential energy and the kinetic energy of the particles are considered simultaneously. The forward and backward particle currents are determined using an Arrhenius' factor. Expressions for the power output and efficiency are derived analytically. The maximum power output and efficiency are calculated. It is expounded that the Brownian heat engine is always irreversible and its efficiency cannot approach the efficiency η_C of the Carnot heat engine even in quasistatic limit. The influence of the main parameters such as the load, the barrier height of the potential, the asymmetry of the potential and the temperature ratio of the heat reservoirs on the performance of the Brownian heat engine is discussed in detail. It is found that the Brownian heat engines may be controlled to operate in different regions through variation of some parameters.     

Modeling and Performance Optimization of an Irreversible Two-Stage Combined Thermal Brownian Heat Engine

Based on finite time thermodynamics, an irreversible combined thermal Brownian heat engine model is established in this paper. The model consists of two thermal Brownian heat engines which are operating in tandem with thermal contact with three heat reservoirs. The rates of heat transfer are finite between the heat engine and the reservoir. Considering the heat leakage and the losses caused by kinetic energy change of particles, the formulas of steady current, power output and efficiency are derived. The power output and efficiency of combined heat engine are smaller than that of single heat engine operating between reservoirs with same temperatures. When the potential filed is free from external load, the effects of asymmetry of the potential, barrier height and heat leakage on the performance of the combined heat engine are analyzed. When the potential field is free from external load, the effects of basic design parameters on the performance of the combined heat engine are analyzed. The optimal power and efficiency are obtained by optimizing the barrier heights of two heat engines. The optimal working regions are obtained. There is optimal temperature ratio which maximize the overall power output or efficiency. When the potential filed is subjected to external load, effect of external load is analyzed. The steady current decreases versus external load; the power output and efficiency are monotonically increasing versus external load.     

Thermodynamic characteristics of a Brownian heat pump in a spatially periodic temperature field

This paper has studied the thermodynamic performance of a thermal Brownian heat pump,which consists of Brownian particles moving at a periodic sawtooth potential with external forces and contacting with the alternating hot and cold reservoirs along the space coordinate.The heat flows driven by both potential and kinetic energies are taken into account.The analytical expressions for the heating load,coefficient of performance(COP) and power input of the Brownian heat pump are derived and the performance char...     

Heat flow and efficiency in a microscopic engine

We study the energetics of a thermal motor driven by temperature differences, which consists of a Brownian particle moving in a sawtooth potential with an external load where the viscous medium is periodically in contact with hot and cold heat reservoir along space coordinate. The motor can work as a heat engine or a refrigerator under different conditions. The heat flow via both potential and kinetic energy is considered. The former is reversible when the engine works quasistatically and the latter is always irreversible. The efficiency of the heat engine can never approach Carnot efficiency.     

Thermodynamic Performance Characteristics of a Brownian MicroscopicHeat Engine Driven by Discrete and Periodic Temperature Field

A Brownian microscopic heat engine with a particle hopping on a one-dimensional lattice driven by a discrete and periodic temperature field in a periodic sawtooth potential is investigated. In order to clarify the underlying physical pictures of the heat engine, the heat flow via the potential energy and the kinetic energy of the particles are considered simultaneously. Based on describing the jumps among the three states, the expressions of theefficiency and power output of the heat engine are derived analytically. The general performance characteristic curves are plotted by numerical calculation. It is found that the power output-efficiency curve is a loop-shaped one, which is similar to one for a real irreversible heat engine. The influence of the ratioof the temperature of the hot and cold reservoirs and the sawtooth potential on the maximum efficiency and power output is analyzed forsome given parameters. When the heat flows via the kinetic energy isneglected, the power output-efficiency curve is an open-shaped one,which is similar to one for an endroeversible heat engine.     

Recent advance on the efficiency at maximum power of heat engines

This review reports several key advances on the theoretical investigations of efficiency at maximum power of heat engines in the past five years. The analytical results of efficiency at maximum power for the Curzon-Ahlborn heat engine, the stochastic heat engine constructed from a Brownian particle, and Feynman's ratchet as a heat engine are presented. It is found that: the efficiency at maximum power exhibits universal behavior at small relative temperature differences; the lower and the upper bounds might exist under quite general conditions; and the problem of efficiency at maximum power comes down to seeking for the minimum irreversible entropy production in each finite-time isothermal process for a given time.