依据微扰理论用链转子方程计算流体的热力学性质

本文综述了状态方程式的统计热力学基础,应用统计热力学的标准方法由配分函数导出状态方程,并用链转子方程编制了Fortran计算程序,在ACOS—4型计算机上计算了超临界气体、亚临界液体及小分子和大分子流体混合物的热力学性质。     

描述流体临界区性质的状态方程及标度律方法

针对Ｐｅｎｇ—Ｒｏｂｉｎｓｏｎ状态方程及Ｆｏｘ提出的标度变换方法，作者提出了两点修正．修正后的Ｆｏｘ方法可以移动计算所得的临界点，并满足过渡区的理论要求．对１５种纯流体的近临界区（０．９８＞Ｔｒ＞０．８３）的汽、液两相密度及饱和蒸汽压的计算结果表明，所提出的方法较原始Ｆｏｘ方法更为合理地描述了流体在临界区附近的性质，同时可实现从远离临界区向临界区的平滑过渡     

用Lennard—Jones和Kihara位能模型预测真实流体的PVT性质

分别采用Ｌｅｎｎａｒｄ－Ｊｏｎｅｓ（Ｌ－Ｊ）和Ｋｉｈａｒａ位能模型并结合顺序解析法计算了径向分布函数，然后代入统计热力学所给出的严格理论状态方程来预测真实流体的ＰＶＴ性质。位能模型参数由纯流体的临界温度性质确定。计算结果表明，该方法可用于预测较度广的压力、温度范围内的非极性和弱极性纯流体的ＰＶＴ性质。讨还上于正己烷时，近临界区除外，由Ｌ－Ｊ模型预测的饱和液体体积的相对平均误差一般小于５％。对于分子     

用Lennard-Jones和Kihara位能模型预测真实流体的PVT性质

分别采用ＬｅｎｎａｒｄＪｏｎｅｓ（ＬＪ）和Ｋｉｈａｒａ位能模型并结合顺序解析法计算了径向分布函数,然后代入统计热力学所给出的严格理论状态方程来预测真实流体的ＰＶＴ性质。位能模型参数由纯流体的临界温度性质确定。计算结果表明,该方法可用于预测较宽广的压力、温度范围内的非极性和弱极性纯流体的ＰＶＴ性质。当分子尺寸小于正己烷时,近临界区除外,由ＬＪ模型预测的饱和液体体积的相对平均误差一般小于５％。对于分子尺寸更大的流体,需用三参数Ｋｉｈａｒａ位能模型来提高预测精度     

涨落在理想气体系统中的应用

理想气体系统是热力学研究的一种典型模型,通过研究理想气体系统,可以得到真实气体的一些主要性质.用统计物理学观点和热力学基本关系式,研究理想气体系统中宏观物理量的涨落及涨落关联函数,进而说明热力学系统宏观量的涨落与热力学系统的状态方程有关.     

立方型及CPA状态方程对极性缔合物质预测能力的评价

采用22种极性缔合物质的热力学性质评价CPA、SRK、PR和PR-Sun状态方程的预测能力，比较仅采用蒸气压、同时采用蒸气压和液体体积两种方法回归CPA状态方程参数的准确性。结果表明，CPA-1和CPA-2状态方程对蒸气压预测结果的平均相对偏差（ARD）均小于0.50%，对蒸发焓预测结果的ARD分别为8.30%和8.24%,CPA-2状态方程对液体体积的预测结果明显优于CPA-1状态方程，其ARD为1.90%。CPA-1和CPA-2状态方程对缔合物质热力学性质的预测结果优于立方型状态方程，且以蒸气压和液体密度同时回归的CPA模型参数优于仅以蒸气压回归的参数。     

非经典近临界流体相态行为的研究

对近年来发展起来的非经典近临界相态研究从工程实用的角度作了系统的综述.对这一相平衡领域前沿课题的研究动态及趋势作了讨论.指出近临界区流体相态还远未成熟.经典的状态方程仍占主导地位.但是随着非经典近临界理论的飞速发展,其在工程实际中将会得到应用.     

新的应用于氧和氮的全区域状态方程

建立了一个新的全区域状态方程，将其表示成温度和密度函数的亥姆霍兹自由能形式。新状态方程克服了以前状态方程不能全区域计算热物理性质的缺陷，尤其在临界区的数学困难，它是截至目前唯一能够适应于液相区、气相区、饱和区、临界区的热力性质计算的全区域方程，并将其应用于氧和氮的热力性质呈现．本文给出的氧的状态方程能精确适用于温度低至三相点、温度高达３００Ｋ，密度高达３倍临界密度的宽广范围；氮的状态方程温度高达３５０Ｋ，新方程式不仅能准确呈现温度、密度、压力关系式，而且还能满意地给出其它导出热力性质，诸如比热容和音速，最后，给出了新状态方程与实验数据的比较偏差。     

非经典近临界流体相态行为的研究

对近年来发展起来的非经典近临界相态研究从工程实用的角度作了系统的综述，对这一相平衡领域前沿课题的研究动态及趋势作了讨论。指出近临界区流体相态还远未成熟，经典的状态方程仍占主导地位。但是随着非经典临界理论的飞速发展，其在工程实际中将会得到应用。     

链状方阱流体的状态方程研究

为研究链状分子物质（如烷烃等）及其混合物的热力学性质,应用Ｗｅｒｔｈｅｉｍ的热力学微扰理论,在链状硬球流体状态方程的基础上,发展得到了链状方阱流体的状态方程。它可以表示成三部分：硬球贡献、方阱吸引势能贡献和成键贡献。在计算成键对压缩因子的贡献时,考虑到了成键对组成链的原子之间径向分布函数的影响。用得到的状态方程计算不同链长的链状方阱流体的压缩因子,其结果与分子模拟数据符合较好。     

氨水混合物的相平衡和热力性质计算

Reynolds W.所推荐的纯水和纯氨的状态方程和比热容方程可获得高精度的纯水和纯氨热力性质的计算值。应用溶液理论获得了具有较高精度的、适用于动力循环分析的氨水混合物热力性质的计算方法。其中液相热力性质的计算精度比Sayed和Tribus的高10倍以上。     

Direct measurement of critical Casimir forces

When fluctuating fields are confined between two surfaces, long-range forces arise. A famous example is the quantum-electrodynamical Casimir force that results from zero-point vacuum fluctuations confined between two conducting metal plates. A thermodynamic analogue is the critical Casimir force: it acts between surfaces immersed in a binary liquid mixture close to its critical point and arises from the confinement of concentration fluctuations within the thin film of fluid separating the surfaces. So far, all experimental evidence for the existence of this effect has been indirect. Here we report the direct measurement of critical Casimir force between a single colloidal sphere and a flat silica surface immersed in a mixture of water and 2,6-lutidine near its critical point. We use total internal reflection microscopy to determine in situ the forces between the sphere and the surface, with femtonewton resolution. Depending on whether the adsorption preferences of the sphere and the surface for water and 2,6-lutidine are identical or opposite, we measure attractive and repulsive forces, respectively, that agree quantitatively with theoretical predictions and exhibit exquisite dependence on the temperature of the system. We expect that these features of critical Casimir forces may result in novel uses of colloids as model systems.     

Breakdown of intermediate-range order in liquid GeSe(2) at high pressure.

Studies of liquids with tetrahedral coordination, particularly during compression or quenching, have indicated the existence of distinct phases in the liquid state, distinguishable by density and local structure. In systems that exhibit critical phenomena in the supercooled state, anomalous behaviour of the compressibility is also anticipated above the critical point, as revealed by simulations of water. Liquid GeSe(2) is a potentially attractive system for studying both types of phenomena, given its two-dimensional tetrahedral structure and anomalous physical properties (including a density minimum near its melting point). Here we report in situ X-ray diffraction measurements of solid and liquid GeSe(2) at high temperature and high pressure, revealing that the structure of the liquid is sensitive to pressure and that anomalous compressibility is expected. During compression of liquid GeSe(2), the connectivity of the liquid changes from two- to three-dimensional, leading to a breakdown of the intermediate-range order. The gradual change in structure above the melting line may develop to a first-order liquid-liquid transition in the supercooled regime.     

Thermally fluctuating superconductors in two dimensions

In many two-dimensional superconducting systems, such as Josephson-junction arrays, granular superconducting films, and the high-temperature superconductors, it appears that the electrons bind into Cooper pairs below a pairing temperature (T(P)) that is well above the Kosterlitz-Thouless temperature (T(KT)) the temperature below which there is long-range superconducting order). The electron dynamics at temperatures between T(KT) and T(P) involve a complex interplay of thermal and quantum fluctuations, for which no quantitative theory exists. Here we report numerical results for this region, by exploiting its proximity to a T = 0 superconductor-insulator quantum phase transition. This quantum critical point need not be experimentally accessible for our results to apply. We characterize the static, thermodynamic properties by a single dimensionless parameter, gamma(T). Quantitative and universal results are obtained for the frequency dependence of the conductivity, which are dependent only upon gamma(T) and fundamental constants of nature.     

一个新的二甲醚气液相密度方程

为了获得二甲醚的气液相密度,在对二甲醚PVT实验数据进行文献调研的基础上,基于对比态原理运用准牛顿优化算法得到了一个6参数的用于计算二甲醚气相和液相密度的方程.气相和液相方程适用于温度从三相点温度至临界温度,压力最大达到70 MPa.新方程计算的二甲醚气液相密度值与实验数据比较后表明:两者的气相密度平均绝对偏差的范围从低温区的0.1％到临界点附近的1％;两者的液相密度平均绝对偏差的范围从低温区的0.1％到临界点附近的3％.     

Observation of scale invariance and universality in two-dimensional Bose gases

The collective behaviour of a many-body system near a continuous phase transition is insensitive to the details of its microscopic physics; for example, thermodynamic observables follow generalized scaling laws near the phase transition. The Berezinskii-Kosterlitz-Thouless (BKT) phase transition in two-dimensional Bose gases presents a particularly interesting case because the marginal dimensionality and intrinsic scaling symmetry result in a broad fluctuation regime and an extended range of universal scaling behaviour. Studies of the BKT transition in cold atoms have stimulated great interest in recent years, but a clear demonstration of critical behaviour near the phase transition has remained elusive. Here we report in situ density and density-fluctuation measurements of two-dimensional Bose gases of caesium at different temperatures and interaction strengths, observing scale-invariant, universal behaviours. The extracted thermodynamic functions confirm the existence of a wide universal region near the BKT phase transition, and provide a sensitive test of the universality predicted by classical-field theory and quantum Monte Carlo calculations. Our experimental results provide evidence for growing density-density correlations in the fluctuation region, and call for further explorations of universal phenomena in classical and quantum critical physics.     

二甲醚热力学性质的计算

利用现有的二甲醚气相状态方程、饱和气液密度方程、蒸气压方程、理想气体定压比热容等方程,计算得到了二甲醚的饱和液体熵和饱和气体熵.从气相维里方程出发,结合Clapeyron方程计算得到了二甲醚的饱和蒸发焓.采用偏差函数法及陈则韶教授提出的饱和液体焓推算公式,计算出了二甲醚的饱和气液焓和临界焓值.最后,开发了二甲醚热力学性质的计算程序,并得到了从235 15K至临界点的二甲醚饱和热力学性质表,计算结果的精度在±2%内,可为工程实际应用提供服务.