多种不可逆性对太阳能空间动力系统性能的影响

考虑太阳能空间动力系统中的主要不可逆因素对其循环性能的影响,应用有限时间热力学理论计算系统在不同约束条件下的最大效率,确定太阳能集热器的最佳工作温度,并对其它有关的性能参数进行优化分析,从而获得一些有意义的新结论。     

Entropy generation and thermoeconomic analysis of the wire-and-tube condenser

In this work, entropy generation analysis of an air-cooled natural draft wire-and-tube condenser commonly used in the domestic refrigerator is carried out to investigate geometrical and operating parameters. The Bejan number formulation is used for the analysis because of its ability to relate the heat transfer to pressure drop entropy generation. The analysis also incorporates thermoeconomics by combining the second law of thermodynamics with economic principles. The analytical study is carried out by varying geometrical parameters of the condenser such as tube outer diameter, wire diameter, number of wire pairs, number of tube rows, tube pitch, wire pitch and refrigerant (R134a) properties such as mass velocity, saturation temperature and dryness fraction. The behaviour of entropy generation due to heat transfer and pressure drop, Bejan number and thermoeconomic variables such as relative cost difference and exergoeconomic factor are analysed. These results are used in obtaining the values of condenser dimensions leading to better performance.     

用热力学第二定律分析换热器内传热过程

用热力学第二定律分析不同流形换热器的不可逆性与冷热流体的热容比及换热器的传热单元数（换热器面积）之间的关系。     

回转窑内铁矿氧化球团焙烧过程的能量和分析

在对铁矿氧化球团回转窑系统的平衡测试的基础上,对其进行了能量和的分析。能量分析表明,窑体表面散热是能量损失的主要部份。分析表明,燃烧不可逆损是火用损的主要部份。系统的燃烧不可逆损失较大。建议减小助燃空气或压缩空气等非预热空气的供应量的方法降低之。烟气中的含氧量对球团的氧化过程,存在着一定的影响。考察了烟气中氧含量对损的影响。对该参数的优化,可以使损最小化。在满足球团矿焙烧工艺所需氧气含量的前提下,可以适当降低烟气中的含氧量。本文的研究对回转窑内铁矿氧化球团焙烧过程的能量流和火用流有了更进一步的认识。研究结果可以进一步应用于"链-回-环"系统的过程优化,进一步提高系统的经济效益。     

Electrochemical behavior of a silicon monoxide and Li-powder double layer anode cell

A new technique for synthesizing double layer anodes with silicon monoxide and Li powder has been developed to reduce the initial capacity loss of silicon monoxide anodes. Double layer anode (DLA) cells are fabricated using Li emulsified powders on a Cu foil and silicon monoxide powders on a Cu mesh collector and their electrochemical behaviors are studied. The DLA cells show reduced initial irreversibility and enhanced coulombic efficiency. The coulombic efficiency of the first cycle of the DLA cell is over 100% and its capacity remains as 700 mAh g⁻¹ up to 20 cycles. SEM observation shows that the Li-powder layer in DLA compensated for the initial irreversible loss and vanished after several cycles.     

针束型回热器熵产率的分析

回热器是热声装置的关键部件,在多种具有规则流道的回热器结构中,针束型结构是综合性能最优的结构.针对针束型回热器参数优化问题,建立了以最小熵产率为目标的优化模型,研究基于不可逆性的回热器参数优化方法.通过分析工质在回热器内振荡时由于与固壁的换热和黏性扩散导致的热动力学上不可逆性,对工质在针束型回热器内运动时的熵产率进行了理论分析和数值计算.计算获得了回热器截面分布和截面平均熵产率表达式,分析了针束型回热器中不同位置截面分布熵产率的变化规律,分析了温度梯度对截面平均熵产率的影响,获得了给定特征尺寸截面平均熵产率最小时的最优频率和最优阻抗比.     

Entropy generation on MHD flow of a Casson fluid over a curved stretching surface with exponential space-dependent heat source and nonlinear thermal radiation

The present model concentrates on entropy generation on a steady incompressible flow of a Casson liquid past a permeable stretching curve surface through chemical reaction and magnetic field effects. The exponential space-dependent heat source cum heat and mass convective boundary conditions are accounted for. The resulting nonlinear boundary layer model is simplified by the transformation of similarity. Chebyshev spectral technique is involved for obtaining numerical results of the converted system of the mathematical models. Behavior of the determining thermo-physical parameters on the profiles of velocity, temperature, concentration, skin friction, heat, mass transfer rate, rate of entropy generation, and finally the Bejan number are presented. The major point of the present investigation show that the curvature term weakens the mass transfer profile as the fluid temperature reduces all over the diffusion regime. A decrease in heat generation strengthens the species molecular bond, which prevents free Casson particle diffusion. Furthermore, the mass transfer field diminishes in suction and injection flow medium.     

不可逆性对热机功率效率的影响

从静态和动态两方面定性定量地讨论了各种不可逆性对热机功率效率的影响，给出了各种不可逆循环模型Ｐ－η特性曲线的物理解释，指出了提高热机效率功率的具有实用价值的途径．     

Collective pinning behavior of intergranular Josephson vortices and the intergranular irreversibility line of high-Tc superconducting ceramics

The supercurrent-transport properties of YBa₂Cu₃O₇ (Y123) polycrystalline bulk sintered samples with random grain orientation were thoroughly investigated. The dissipation process in these materials occurs due to intergranular flux motion, rather than by weak-link quenching. It was found that the model which takes into consideration collective creep of intergranular vortices is self-consistent in describing the low-voltage-level current-voltage characteristics and the intergranular irreversibility line of high-T _c superconducting ceramics.