范德瓦耳斯气体直线过程的若干讨论

首先对各种范德瓦耳斯气体在同一条确定直线过程中的温度转换点和吸放热转换点进行求解,随后绘制出温度以及吸放热特性对斜率和体积的依赖关系三维图,最终找到了影响温度和吸放热转换点的因素.     

论理想气体p-V图中负斜率直线过程

本文通过对理想气体p-V图中负斜率直线过程温度及吸、放热变化的综合讨论，使我们对该过程有一个全面、清晰的认识，以开拓我们对热学过程讨论的方法及思路．     

也谈直线过程的吸放热和循环效率的计算

分析了p-V图上具有负斜率的直线过程的吸放热以及含有直线过程的循环效率的计算.     

热力系统最佳效率输出功率与两换热器优化方法

本文介绍了外不可逆内可逆循环热力系统的输出功率、效率、工质等效吸/放热温度,吸/放热率与高/低温换热器总传热系数比值的关系,给出了无量纲的关系式和功率-效率关系图,以及在选定最佳效率后提高输出功率与增加总传热系数比值关系的作图设计法,为优化传热与热力循环耦合的热力系统优化设计和运行调节提供了理论参考。     

理想气体吸放热的判断和计算

根据热力学系统热容量和温度的变化,找出系统吸放热之间的转换点,计算了系统吸收或放出的热量。     

用温度计测量酒精的体积膨胀系数

温度计毛细管中酒精的长度变化ΔL1与温度改变ΔT1成正比,通过拟合ΔL1-ΔT1获得斜率S1,由已知毛细管的横截面积A1和酒精初始体积V1,计算得到酒精的体积膨胀系数.对于毛细管的横截面积和酒精初始体积未知的温度计,可以更换不同量程和精度的温度计,拟合ΔL2-ΔT2获得斜率S2,拟合ΔL1-ΔL2获得斜率S3,由S2,S3,V1和A1计算得到酒精的体积膨胀系数.     

利用光栅光谱仪研究乙醇汽油溶液的吸收特性

利用WGD-8A型多功能光栅光谱仪测量了不同汽油体积含量的乙醇汽油溶液对波长为300.0～430.0 nm光的吸收光谱,分析了乙醇汽油吸光度和汽油浓度的关系,在稀溶液吸光度的朗伯-比尔定律基础上,进一步研究了2种高浓度混合溶液吸光度的计算方法,并得出了入射光波长为377.0,382.0,391.5,410.9 nm时乙醇汽油的吸光度与汽油体积浓度的关系式.     

对多方过程定义的讨论及对p=f(v)过程的分析

本文对一些教科书中多方过程的定义进行了讨论，并对ｐ＝ｆ（ｖ）过程的吸、放热情况作了具体分析．     

热特性参数可变时双曲线型截面环肋传热的最优尺寸

本文研究了当热特性参数可变时双曲线型截面环肋传热的最优化。应用不变嵌入原理,确定了双曲线型环肋在一定体积下传递最大传热量的最优几何尺寸,同时还对两个主要的物理参数,即导热系数变化参数α和放热系数变化指数m对最优几何尺寸的影响进行研究。所得结果对工程设计具有现实指导意义。     

电加热式平板微热管阵列相变蓄热器蓄放热性能研究

本文提出了一种基于相变蓄热技术和平板微热管阵列技术的电加热式蓄热器,阐明了该装置的结构形式和工作原理,并对其单独蓄/放热与同时蓄/放热过程的热特性进行了研究。该新型电蓄热器采用12支带有百叶窗翅片的平板微热管阵列作为传热元件,蓄热器内填充18 kg的67#工业石蜡。蓄热工况采用不同加热功率(0.2～2.0 kW)对该电蓄热器进行加热,放热时控制放热流体体积流量(20～120 m³/h)和放热流体温度(15～27?C)进行放热。实验结果表明：在不同的运行模式下,该新型电蓄热器运行高效稳定,在单独蓄放模式下,测试结果显示装置的蓄、放热效率可达到99%和89%。     

A mathematical model of hotspot condensed phase ignition in the presence of a competitive endothermic reaction

We consider the propagation of a combustion front resulting from the gasless combustion of a condensed state fuel. The propagation of the front, essentially a premixed laminar flame, is supported by an exothermic reaction subject to possible heat loss through a competitive endothermic reaction. The dynamics of the endothermic process inducing the heat loss strongly depend on the temperature and the local fuel concentration. Through an analysis based on high activation energy, the steady-state values of the final burnt temperature as well as the burning velocity are obtained, and the control parameters are identified. Using a linear perturbation method, we assess the stability of the propagating front and obtain a condition for oscillatory behaviour. The critical parameter values for the transition from steady to oscillatory burning speeds are identified. The results represent a generalization of those obtained by Matkowsky and Sivashinsky to include the effects of heat loss induced by a competitive endothermic reaction.     

Effects of endothermic chain-branching reaction on spherical flame initiation and propagation

A theoretical model is developed to describe the spherical flame initiation and propagation. It considers endothermic chain-branching reaction and exothermic recombination reaction. Based on this model, the effects of endothermic chain-branching reaction on spherical flame initiation and propagation are assessed. First, the analytical solutions for the distributions of fuel and radical mass fraction as well as temperature are obtained within the framework of large activation energy and quasi-steady assumption. Then, a correlation describing spherical flame initiation and propagation is derived. Based on this correlation, different factors affecting spherical flame propagation and initiation are examined. It is found that endothermicity of the chain-branching reaction suppresses radical accumulation at the flame front and thus reduces flame intensity. With the increase of endothermicity, the unstretched flame speed decreases while both flame ball radius and Markstein length increases. Endothermicity has a stronger effect on the stretched flame speed with larger fuel Lewis number. The Markstein length is found to increase monotonically with endothermicity. Furthermore, the endothermicity of the chain-branching reaction is shown to affect the transition among different flame regimes including ignition kernel, flame ball, propagating spherical flame, and planar flame. The critical ignition power radius increases with endothermicity, indicating that endothermicity inhibits the ignition process. The influence of endothermicity on ignition becomes relatively stronger at higher crossover temperature or higher fuel Lewis number. Moreover, one-dimensional transient simulations are conducted to validate the theoretical results. It is shown that the quasi-steady-state assumption used in theoretical analysis is reasonable and that the same conclusion on the effects of endothermic chain-branching reaction can be drawn from simulation and theoretical analysis.     

An isothermal titration calorimetry study of the interactions between an oxyphenylethylene/oxyethylene diblock copolymer and sodium dodecyl sulfate

Interactions between the diblock copolymer S₁₅E₆₃ and the surfactant sodium dodecyl sulfate (SDS) have been investigated by isothermal titration calorimetry (ITC) in the temperature range 10–40°C. At 20°C, the block copolymer is associated into micelles with a hydrodynamic radius of 11.6?nm, which is composed of a hydrophobic styrene oxide (S) core and a water-swollen oxypolyethylene (PEO) corona. The copolymer/surfactant system has been studied at a constant copolymer concentration of 0.25?wt% and over a wide range of surfactant concentration, from 7.5?×?10^?6 up to 0.3?M. The titration calorimetric data for SDS in the temperature range 10–20°C presents a first endothermic increase indicating the formation of mixed copolymer rich-surfactant micelles. From that point, important differences in the ITC plots for surfactant titrations in the presence and in the absence of the copolymer are present. A shallow second endothermic peak is assigned to the interaction between SDS molecules and copolymer molecules resulting from the beginning of micelle disruption. An exothermic peak indicates the end of this disruption where only SDS micelles attached to single copolymer monomers are present, as shown by DLS in a previous paper. At higher temperatures in the range 25–40°C, the first endothermic maximum is not totally shown because interactions between surfactant and block copolymer start at very low SDS concentrations. Moreover, the second endothermic peak is absent and the exothermic minimum is less pronounced as a consequence of the increased micellization of the block copolymer.     

Magnetically tunable atom-exchange process involving ultracold weakly bound Feshbach molecules

Chemical reactions at ultracold temperatures have attracted great interest in recent years. The atom-exchange reaction between an atom and a weakly bound Feshbach molecule near overlapping Feshbach resonances presents a simple and ideal example of the controlled ultracold chemistry. The energy released in the reaction can be tuned to be very small and thus the reaction products can be trapped and detected, allowing the study of state-to-state reaction dynamics. The reaction can be tuned from the exothermic regime to the endothermic regime, which allows to study the threshold behavior of an endothermic reaction. In this paper, we review the recent progress in studying the atom-exchange reaction involving Feshbach molecules in ultracold atomic gases.     

Analysis of Multiple Melting of High-Speed Melt Spun Polylactide Fibers Based on Kinetic Modeling

Multiple melting behavior of high-speed melt-spun polylactide (PLA) fibers was investigated by temperature modulated differential scanning calorimetry (TMDSC) in the heating process with various modulation periods in the calorimeter. In the case of the as-spun PLA fibers taken-up at 1 km/min, a melting endothermic peak and a recrystallization exothermic peak appeared at the same peak temperature of 151°C in the reversing and non-reversing heat flows (RHF and NRHF), respectively, whereas at 168°C, an endothermic peak was observed in both the RHF and NRHF. On the other hand, the as-spun PLA fibers taken-up at a high-speed of 6 km/min showed the melting in both the RHF and NRHF, but the recrystallization behavior was not obvious in the NRHF at the shorter modulation period conditions. The obtained data were analyzed based on the kinetic modeling of melting proposed by Toda et al. The real and imaginary parts of the complex apparent heat capacity in the melting region showed a strong modulation period dependence for both the low- and high-speed spun fibers. The endothermic heat flow of melting was separated by extrapolating the frequency to zero. For the PLA fibers spun at 1 km/min, a set of melting and recrystallization peaks in the RHF and NRHF appeared even for the melting at 168°C. In other words, the simultaneous occurrence of melting and recrystallization was confirmed through this extrapolation. For the 6 km/min PLA fibers, the presence of an exothermic heat of recrystallization was clearly confirmed at a peak temperature of 164°C.     

Assessment of competing mechanisms of the abstraction of hydrogen from CH4 on Li/MgO(0 0 1)

First-principles calculations based on the density functional theory (DFT)-pseudopotential method with plane wave basis sets are used to study the energetics of H abstraction from CH₄ on the Li-doped MgO(0 0 1) surface. Experimental work has led to the proposal of two competing mechanisms for the reaction: either direct interaction of CH₄ with an O⁻ hole state bound to the Li dopant, or interaction of CH₄ with a surface F-centre whose charge state is modified by the presence of the dopant. The calculations are performed in periodically repeated slab geometry, with attention given to system-size errors. For direct interaction with the hole state, the calculations indicate that the reaction is weakly endothermic, by about 0.2 eV, but for the F-centre mechanism it is endothermic by over 1 eV. Even allowing for likely DFT errors of a few tenths of an electron volt, this gives strong evidence against the F-centre mechanism.     

AIM Study on the Reaction of CH2SH Radical with Fluorine Atom

采用MP2(Full)/6-311G(d,p)、QCISD(T)/6-311++G(2df,p)和B3LYP/6-311G(d,p)方法研究了CH2SH自由基与F原子的反应．F原子通过进攻自由基上的C原子或S原子形成三种不同的反应通道．计算结果表明F原子进攻自由基上的C原子生成CH2S和HF为主要的反应通道．对反应进程中若干关键点进行了电子密度拓扑分析,找到了该反应的结构过渡区(结构过渡态)和能量过渡态．计算结果表明,对于比较显著的吸热或放热反应,其结构过渡区范围很小,对于吸热或放热不太显著的反应,结构过渡区范围较大.     

聚天门冬氨酸水凝胶对Zn2＋的吸附行为

以聚丁二酰亚胺为原料,以戊二醛为交联剂制备聚天门冬氨酸水凝胶.研究了聚天门冬氨酸水凝胶对Zn2＋的吸附性能.结果表明：聚天门冬氨酸水凝胶对Zn2＋的吸附满足Langmuir等温方程,且吸附行为为吸热过程,聚天门冬氨酸水凝胶对Zn2＋的吸附能力较强.     

吸收式制冷循环系统的热力学分析

从热力学观点讨论了工作温度对于制冷循环系统性能的影响。分析了与循环时间有关的温度效率和熵产数。对于一个相对较短的循环时间,吸收/解吸收热量转换器的温度效率在200秒后可以达到92%。熵产数Ns由在一个循环系统内生成的不可逆性参数和热量转换器流体有效性参数之间的比率决定。结果显示,在使用一个30℃冷源的情况下高级吸收式循环系统的熵产数Ns在热水温度是45℃至55℃之间时是相对较小的,而对于传统循环,在使用相同冷源温度的情况下,热水温度在65℃到75℃之间时,Ns是相对较小的。