Critical evaluation and thermodynamic optimization of Mg–Ga system and effect of low pressure on phase equilibria

A complete literature review and critical evaluation of the Mg–Ga binary system are presented. All stable phases known in this system were thermodynamically modeled in the framework of CALPHAD. Liquid phase was modeled using the Modified Quasichemical Model in the pair approximation which takes into account short-range ordering. α-(Mg) solid solution of hcp structure was modeled as a substitutional solution. All intermetallic phases Mg₅Ga₂, Mg₂Ga, MgGa, MgGa₂, Mg₂Ga₅, as well as Ga-rich phase, were treated as stoichiometric compounds. Gas phase was assumed to behave as an ideal solution. Thermodynamic optimization was carried out by evaluating enthalpic and entropic contributions to the Gibbs free energy of all phases independently. It showed that the optimized model parameters along with the model equations could reproduce the available and reliable experimental data in the Mg–Ga system. Representation of partial excess Gibbs free energy of Mg in Ga-rich liquid was improved compared to the previous thermodynamic modeling. Low pressure phase equilibria in this system were analyzed using the developed thermodynamic model, and it was compared with a recent observation of an Mg nanopillar fabricated by Ga⁺ ion beam in a focused ion beam (FIB), followed by in-situ heating in a transmission electron microscope (TEM). Reported surface melting of Mg nanopillar in the TEM column pressure (~10⁻¹⁰ bar) is attributed to the fact that decreasing pressure enhanced sublimation of Mg from the Mg nanopillar significantly, leaving Ga-rich liquid.     

变新风量的最小焓差控制

基于焓值理论,得出影响焓差的关键因素是相对湿度和干球温度。将夏季工况下测试房间的空气参数绘入焓湿图中,依据上述理论分析不同空气状态下的焓值控制参数。利用最小焓差控制与新风量调节过程相结合的方法,使进入空气处理机组前的空气更加接近舒适区域并且减小表冷器的换热量。测试表明,变新风量最小焓差PID控制的效果优于定新风量PID控制,并且减少了表冷器换热量。在舒适性方面,测试房间的空气状态参数也稳定在焓湿图的舒适区域内。     

Comprehensive first-principles study of transition-metal substitution in the γ phase of nickel-based superalloys

In order to elucidate the role of various M-alloying additions in the fcc-type γ phase of nickel-based superalloys, we have performed a comprehensive and systematical computation on all 3d-, 4d- and 5d-M alloying additions substituting in the Ni lattice using the same standard of the first-principles calculations within the framework of the density functional theory. The results show that the substitution enthalpies of Sc, Ti, V, Mn, Fe, Co, Zn, Zr, Nb, Hf, Ta, and Pt are negative, while the others elements have positive substitution enthalpies. To further explore the contributions of various factors to the substitution enthalpy, we have attempted to divide the substitution enthalpy into two parts. The first one is the mechanical deformation energy caused by the atomic volume change because of the M-alloying additions substituting in fcc Ni and the other one is the chemical and magnetic energy through electronic hybridizations and local magnetic interactions. It is found that the substitution enthalpy is a consequence of the balancing of these two contributions. Furthermore, we have attempted to correlate their mechanical deformation energies with metallic atomic radii of substitutional M-alloying addition with respect to Ni, and the chemical and magnetic energies with transferred charges between M-alloying addition and Ni, which are indeed associated with the so-called electronegativity difference.     

含缔合组分二元混合物超额焓计算

基于缔合溶液理论和正规溶液理论,作者提出了简化缔合模型(SAM)。用SAM计算包括醇-烃、醇-酮和醇-醇等在内的各类含缔合组分的61个二元混合物的超额焓,平均均方根偏差和百分误差分别为21.4J/mol和2.12％。     

Bukn还原型硫辛酸抗氧化活性的理论研究

硫辛酸是一种强抗氧化剂,本文运用量子化学计算,模拟了还原型硫辛酸即二氢硫辛酸(DHLA)和谷胱甘肽(GSH)在真空、水和四氯化碳3种溶剂环境中发生氧化反应的过程,来研究它们在这3种溶剂条件下的抗氧化活性。以GSH作对比,分析得出DHLA上的巯基抗氧化活性较强,且其作用机理为2个S-H键同时发生断裂。此外,通过对比分析真空和溶剂环境中的键解离焓、质子解离焓和HOMO、LUMO能级差值,发现溶剂环境极性越大,越容易发生电子转移反应:极性越小,越易发生自由基反应。     

一种新颖的供热管网隐性气体泄漏检测系统设计

供热管网由于管线距离长、高空架设结构不统一,导致其隐性热量泄露严重且很难发现;设计了一种新颖的供热管网隐性泄漏检测系统;采用光离子传感器PID-A1,通过热电偶的阻值随燃烧热量来影响初始电压的变化进而对管线隐性泄露气体进行反映并检测,采用HUAWEICM无线模块.完成全部PID-A1检测数据的无线接收、发射、基带信号处理和音频信号处理并传递数据到OPA4340数据采集模块,采用高速数字信号处理MCU芯片AT89C58实时处理采集到的数据,最终实现了供热管网隐性气体泄漏的检测;软件设计通过直接焓值法优化数据MCU处理模块的中央控制器运算性能,采用最小二乘法增强热量采集温度的效率和精度,确保检测系统的低功耗和高效率;最后进行仿真实验,实验结果表明:文中系统的节能量比传统系统平均节能120 J,并且运算效率优于传统系统,提高22％左右,检测误差在2％以内,说明文中系统具有很强的可用性和推广价值.     

利用神经网络推算二元混合物体系的过量

以第一组分的摩尔分数和第二组分分子中碳原子数目的差异来表证二元分子体系，利用具有三层拓扑结构的神经网络模型，推算了２８个体系的过量焓，其中内插１６个体系，外推１２个体系，所有体系的相对误差均在５％左右，最大相对误差为７．６８％，最小相对误差为２．２９％。     

基于LabVIEW 8.0测定纯液体蒸发焓的虚拟仪器

将常规的数字温度仪与压力计通过串行口和计算机连接,构建基于LabVIEW 8.0测定纯液体蒸发焓的虚拟仪器,实现实验数据的动态采集、实时显示、自动绘制p～T曲线并显示曲线方程、自动数据处理和写成结果报告等。应用结果表明:基于LabVIEW构建的测定纯液体蒸发焓的虚拟仪器,免除人工操作的繁琐和人为误差,测定乙醇和苯蒸发焓的相对误差分别为0.86%、-2.97%,提高了测量结果的准确度,且具有界面友好,操作简便和功能易扩展等诸多优点。     

Thermodynamic assessment of TbCl3–MCl (M=Na,K, Rb,Cs) binary systems

The phase diagrams of TbCl₃–MCl (M=Na, K, Rb, Cs) binary systems were reassessed by CALPHAD method. The liquid phase has been described by the associate model with main 3Na⁺+TbCl₆³⁻ associate. The Gibbs energies of formation of solid compounds were calculated and compared with previous data. The entropy of mixing of the liquid phase has been used for the interpretation of structure of this phase.     

An implicit enthalpy scheme for one-phase Stefan problems

A compact finite-difference scheme to solve one-phase Stefan problems in one dimension is described. Numerical experiments indicate that the moving interface is obtained withO(t) accuracy when 3–4 iterations per time step are used to solve the nonlinear implicit scheme. The scheme can be adapted to ADI methods in higher dimensions.     

Machine learning aided high-throughput first-principles calculations to predict the formation enthalpy of σ phase

The σ phase is a topologically close-packed phase and can significantly influence the performance and properties of materials. Accurate prediction the formation enthalpy of the σ phase is crucial for the development of high-performance materials. First-principles calculations based on density functional theory (DFT) have been employed to study the formation enthalpy of the σ phase, but this approach requires a amount of computational resources and time. In this study, we propose a machine learning (ML) method to predict the formation enthalpy of the σ phase. This method employs a first-principles dataset containing 1342 configurations of the binary σ phases for model training and testing. Among the algorithms used, the Multi-Layer Perceptron algorithm demonstrated the highest predictive accuracy, with the mean absolute error (MAE) of 22.881 meV/atom, which is comparable to the existing ML prediction model based on first-principles calculations. The trained model was then utilized to predict the formation enthalpy of the 1177 untrained ternary configurations, achieving a significant reduction in computational time of over 59% compared to traditional first-principles calculations. Furthermore, the model was validated for lattice parameters prediction, achieving the MAE of 0.073 Å and 0.048 Å for the a and c, respectively. A Graphical User Interface (GUI) was developed. Finally, we predicted the formation enthalpy of all the possible ternary configurations, which is comparable to the MAE of DFT-calculations itself.     

基于焓差法的空调机性能测试方法的研究

文中针对空调机制冷、制热量测试的要求,研究开发了基于焓差法的空调机制冷量或制热量的测控系统,该系统可对室内、外实验室的各种传感器状态进行实时监测.在Visual C 6.0的环境下,通过对数据采集卡的编程实现了传感、变送器与工控机的数据通讯以及对实验室空气状态的测量、控制.文中详述了风洞式焓差法的基本原理和计算方法,介绍了测控系统的硬件结构、功能和特点及软件设计.应用结果表明,该测控系统运行稳定可靠,测试精度高,具有一定的实用性和推广价值.     

电厂性能计算实用化问题分析

本文总结了电厂性能计算所面临的实用化问题,在分析的基础上提出相应的解决方案。     

BENSON法预测标准生成焓的改进与程序实现

本工作改进、扩充了Ｂｅｎｓｏｎ－Ｂｕｓｓ的基团加和法计算有机化合物标准生成焓的方案,完成了化学结构特征的计算机识别,扩充了Ｂｅｎｓｏｎ的碎片库,改良了旁式校正方法,建立了原子属性库、碎片库、环校正库、顺式校正库。将该方法实现成微机上运行的Ｗｉｎｄｏｗｓ应用软件。对７０４个化合物的预测值与实验值进行相关性分析,相关性系数为０．９７５。改进后的Ｂｅｎｓｏｎ法比其它基团加和法有明显的优越性。     

直流锅炉机组参数自适应模糊PID控制

针对某765MW联合循环直流锅炉-汽轮发电机组．文中给出了机组输出功率和焓值的并行模糊PID控制系统结构．研究了模糊控制器参数的自适应在线整定方法。首先．分析了联合循环直流锅炉-汽轮发电机组的数学模型,然后,在作者前期工作的基础上,给出了并行模糊PID控制器参数的自适应整定方法．最后．与基本并行模糊PID控制系统进行了仿真对比分析。仿真结果表明．本文所叙述的参数自适应模糊PID控制系统对于降低控制系统振荡,缩短调节时间等方面．其控制效果更优于基本并行模糊PID控制系统。