热-功转换过程热力学第一定律通用方程式

提出了过程可逆性这一概念。依据过程是否具有可逆性,过程被分为两类:具有可逆性的过程和没有可逆性的过程。没有可逆性的过程为本质不可逆过程。状态函数的变化与过程是否有关取决于过程的类型。按照可逆性的物理意义,热-焓转换是本质不可逆过程。本质不可逆过程的状态函数变化与过程无关。这样,对于传热过程是否可逆,热力学和传热学有了一致的观点。热-功转换是具有可逆性的过程,分为可逆过程,不可逆过程和完全不可逆过程。所以热-功转换过程的状态函数变化与过程的可逆程度有关。基于对不可逆过程功耗散的分析,提出了热产这一概念。给出了热产与损失功之间的关系以及热产对过程的影响。阐述了“可逆”的本质是热-功转换效率。定义了可逆系数用于定量描述过程的可逆程度。提出了两个热力学第一定律通用方程式,分别适用于活塞型热机和涡轮型热机的热-功转换过程。“通用”是指方程式既适用于可逆过程也适用于不可逆过程,既适用于产功过程也适用于压缩过程。在两个通用方程式中,使用可逆系数和理想功代替实际功。因为理想功是始态和终态的状态量,可逆系数是热机的性能参数,所以通用方程式能够定量表述可逆程度对过程的影响。当表征始态、终态和多变指数的5个变量中的4个变量已知时,通用方程式能够用于计算在不同可逆程度的条件下过程的热量、热产、实际功、终态和状态函数变化。讨论了热-功转换过程中焓变、热量和机械功三者之间的制约关系,给出了表述热和功之间关系的公式。

Novel Optimization Approach to Mixing Process Intensification

An approach was presented to intensify the mixing process. Firstly, a novel concept, the dissipation of mass transfer ability(DMA) associated with convective mass transfer, was defined via an analogy to the heat-work conversion. Accordingly, the focus on mass transfer enhancement can be shifted to seek the extremum of the DMA of the system. To this end, an optimization principle was proposed. A mathematical model was then developed to formulate the optimization into a variational problem. Subsequently, the intensification of the mixing process for a gas mixture in a micro-tube was provided to demonstrate the proposed principle. In the demonstration example, an optimized velocity field was obtained in which the mixing ability was improved, i.e., the mixing process should be intensified by adjusting the velocity field in related equipment. Therefore, a specific procedure was provided to produce a mixer with geometric irregularities associated with an ideal velocity.

Optimization of heat transfer and heat-work conversion based on generalized heat transfer law

Examples of heat transfer and heat-work conversion are optimized with entropy generation and entransy loss,respectively based on the generalized heat transfer law in this paper.The applicability of entropy generation and entransy loss evaluation in these optimization problems is analyzed and discussed.The results show that the entransy loss rate reduces to the entransy dissipation rate in heat transfer processes,and that the entransy loss evaluation is effective for heat transfer optimization.However,the maximum heat transfer rate does not correspond to the minimum entropy generation rate with prescribed heat transfer temperature difference,which indicates that the entropy generation minimization is not always appropriate to heat transfer optimization.For heat-work conversion processes,the maximum entransy loss rate and the minimum entropy generation rate both correspond to the maximum output power,and they are both appropriate to the optimization of the heat-work conversion processes discussed in this paper.

Entransy and Exergy Analyses for Optimizations of Heat-Work Conversion with Carnot Cycle

The concept of entransy has been newly proposed in terms of the analogy between heat and electrical conduction and could bc useful in analyzing and optimizing the heat-work conversion systems. This work presents comparative analyses of entransy and exergy for optimizations of heat-work conversion. The work production and heat transfer processes in Carnot cycle system are investigated with the formulations of exergy destruction, entransy loss, work entransy, entransy dissipation, and cfficiencics for both cases of dumping and non-dumping of used source fluid. The effects of source and condensation temperatures on the system performance arc systematically investigated for optimal condition of producing maximum work or work cntransy.

Quantum dot-sensitized solar cells employing Pt/C_(60) counter electrode provide an efficiency exceeding 2%

A microporous platinum/fullerenes (Pt/C 60) counter electrode was prepared by using a facile rapid thermal decomposition method,and the quantum-dot sensitized solar cell (QDSSC) of Pt/C 60-TiO 2-CdS-ZnS and Pt/C 60-TiO 2-CdTe-ZnS was fabrication.The technique forms a good contact between QDs and TiO 2 films.The photovoltaic performances of the as-prepared cells were investigated.The QDSSCs with Pt/C 60 counter electrode show high power conversion efficiency of 1.90% and 2.06%,respectively (under irradiation of a simulated solar light with an intensity of 100 mW cm 2),which is comparable to the one fabricated using conventional Pt electrode.

Analyses of thermodynamic performance for the endoreversible Otto cycle with the concepts of entropy generation and entransy

In this paper, the endoreversible Otto cycle is analyzed with the entropy generation minimization and the entransy theory. The output power and the heat-work conversion efficiency are taken as the optimization objectives, and the relationships of the output power, the heat-work conversion efficiency, the entropy generation rate, the entropy generation numbers, the entransy loss rate, the entransy loss coefficient, the entransy dissipation rate and the entransy variation rate associated with work are discussed. The applicability of the entropy generation minimization and the entransy theory to the analyses is also analyzed. It is found that smaller entropy generation rate does not always lead to larger output power, while smaller entropy generation numbers do not always lead to larger heat-work conversion efficiency, either. In our calculations, both larger entransy loss rate and larger entransy variation rate associated with work correspond to larger output power, while larger entransy loss coefficient results in larger heat-work conversion efficiency. It is also found that the concept of entransy dissipation is not always suitable for the analyses because it was developed for heat transfer.