基于引射器的双温蒸发CO2热泵系统性能分析

采用高效的热泵系统替代常规锅炉是实现“双碳”目标的有效措施。本文提出采用引射器实现双温蒸发的CO₂热泵系统,以实现余热梯级利用和高效制热。通过窄点分析法,建立了基本CO₂系统、CO₂引射器系统、双温蒸发CO₂引射系统的热力学模型,发现双温蒸发系统存在最优排气压力及最大COP。基于最优工况进行分析,结果表明：在热泵热水器名义工况下,双蒸发器系统COP最高达4.84,比基本CO₂热泵系统提高了9.88%。双温蒸发过程可显著降低吸热过程中的换热不可逆损失,双温蒸发系统蒸发器侧的不可逆性能指数为1.51,比基本CO₂和带有引射器的常规CO₂系统降低了24.50%。     

巡游铁磁体SrRuO3磁性的Preisach描述

测量了巡游铁磁体SrRuO3的零场冷却（ZFC）和加场冷却（FC）的磁化强度随温度的变化关系。以及不同温度下的磁滞回线，考虑了热涨落和自由能壁垒随温度的变化，改进了Preisach模型并对测量数据进行了拟合。数据模拟再现了测量结果的变化规律，包括在不同温度下的磁滞回线和在不同外磁场下的ZFC和FC磁化强度曲线等，对拟合出的巴克豪森跳跃谱进行了讨论。     

Performance of absorption refrigeration cycle at maximum cooling rate

The influence of irreversibility of finite-rate heat transfer on the performance of an absorption refrigerator is investigated using an endoreversible cycle model with continuous flow. The cooling rate is adopted as an objective function for refrigerator optimization. The maximum cooling rate and the corresponding coefficient of performance are derived. The optimal performance with respect to heat transfer areas of the refrigerator is analysed. In addition, certain significant conclusions are reached.     

Oxygen chain disorder and compensation by Ca in Y(1-2-3) cuprates

Several M dopants such as Al, Fe, and Co at the Cu site destroy the superconductivity of YBa₂Cu₃O_6+z . However, superconductivity is restored by substituting Ca at the Y site. Arguments are developed to show that the oxygen chain disorder is not the only cause for destroying the superconductivity. A universal relation seems to exist between the net hole density as a result of Ca substitution andT _c . To stabilize the perovskite structure of YSr₂Cu₃O_6+z , it is necessary to substitute Cu by certain elements. Examples are given on Ti and Re substitution. Again, Ca cosubstitution increasesT _c . Further, the irreversibility line is enhanced by Ca, indicating improved pinning in these materials in spite of the oxygen disorder.     

等焓蒸发过程的不可逆性

通过严格的数学推导,证明等焓蒸发过程是增熵的(△S>0),具有不可逆性,借此揭示了这类科学事实的本质特征.     

Flux Dynamics in Tl2Ba2CaCu2O8 Thin Films

Investigations on flux dynamics of ring-shaped T1₂Ba₂CaCu₂O₈ superconducting thin films have been carried out by measuring the temperature dependent magnetization M(T) during field-cooling (FC) and zero-field-cooling (ZFC) processes. For a given magnetic field, from the magnetization behavior two distinct temperatures, T_kink and T_irr, can be defined. Below T_kink, a clear hysteretic behavior of M(T) is observed leading to a large irreversible signal M = M_FC – M_ZFC. Above T_kink, this irreversible signal, though being very small, is still non-zero until it eventually vanishes at a higher temperature T_irr. Above T_irr, both curves M_FC(T) and M_ZFC(T) merge together and become temperature independent. We attribute the first region ( T< T_kink) to a 3D vortex-glass phase, the second region (T_kink < T < T_irr) to a vortex line liquid state and the third region (T_irr < T < T_c) to a pancake liquid state.     

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.     

Magnetohydrodynamic flow of a micropolar nanofluid in association with Brownian motion and thermophoresis: Irreversibility analysis

This investigation was carried out with the purpose of presenting the flow of micropolar fluid flowing in the microchannel placed parallel to the ground. The prime aim of the work was to study the behavior of micropolar fluid and the response of the microrotation component when the two significant mechanisms namely Brownian movement and thermophoresis are accounted for, as these effects are mainly concerned with the motion of the particles of nano-dimensions. For the flow of micropolar, we account for the extra kinematics variables combined with the classical continuum mechanics namely microinertia moment tensor and gyration tensor. Magnetic effect and suction/injection of the fluid through the channel walls are also facilitated. The influence on the fluid concentration due to the presence of activation energy was accounted in the present examination. On considering all of these effects, equations are carefully modeled and the solution was attained with the aid of Runge–Kutta Fehlberg 4–5th order method using a shooting scheme. The results have deciphered that the presence of material parameter elevates the microrotation component on the upper half of the channel and depletes it at the lower half. The microinertia parameter shows the opposite behavior of the material parameter. Brownian motion parameter is found to enhance the thermal profile and concentration profile. Lesser entropy was generated when the material parameter was high.     

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.