用于脉动热管的二元混合工质热力特性探讨

脉动热管是一种新型传热元件。工质种类的选取影响脉动热管的运行与传热,因此应根据脉动热管的用途及相应的温度范围选择适当的工质。提出选取二元混合工作介质(简称混合工质)作为脉动热管的工作介质。分析二元混合工质的露点温度或泡点温度与工质的种类、配比、压力之间的关系,以选取适合脉动热管传热特性的二元混合工质热力参数,得到选取混合工质的相应方法及注意事项。     

强非共沸工质R1234yf/R170/R14系气液相平衡的模拟

超额吉布斯自由能-状态方程法(G~E-EoS)是继传统的状态方程法和活度系数法之后预测气液相平衡的一个新思路。本文采用PRWS-UNIFAC-PSRK模型对R161/R1234yf、R32/R125/R134a及强非共沸工质R1234yf/R170/R14系的气液相平衡数据进行计算。结果表明:R161/R1234yf系压力和气相组分质量分数的计算值与实验值的偏差在±1.5%和±0.02以内,优于REFPROP9.0软件的计算结果,而R32/R125/R134a系的偏差分别在±4%和±0.02以内。根据计算结果及三维相平衡图发现,R1234yf/R170/R14在质量分数比为0.4/0.2/0.4附近时体系的温度滑移现象最为明显,最大的滑移温度达到72.5 K;且R1234yf组分的质量分数越大,泡点温度与露点温度越高。     

三元混合制冷剂R32+R161+R1234yf气液相平衡实验研究

本文研究了含R1234yf的三元混合制冷剂的气液相平衡性质和模型,利用基于液相单相循环法搭建的气液相平衡实验装置,对温度范围为283.15～323.15 K的三元混合制冷工质R32+R161+R1234yf进行了实验研究,共得到45组实验数据。同时采用Peng-Robinson-Stryjek-Vera(PRSV)状态方程结合Wong-Sandler(WS)混合法则和Non-Random Two-Liquid(NRTL)活度系数模型,在前期工作得到的二元混合工质的模型参数的基础上,对三元混合工质气液相平衡性质进行推算。最后将模型推算结果与实验数据进行对比,结果表明系统压力平均绝对偏差AAD_p为0.34%,系统组分R32和R161的气相摩尔分数平均绝对偏差AAD_y_1和AAD_y_2分别为0.002和0.001。     

基于最小熵增法编程确定非共沸混合工质组分比

以非共沸混合工质在蒸发器中沿程温度分布变化所导致传热不可逆熵增为目标函数,建立混合工质与冷媒水在蒸发器中的稳态换热模型;以换热温差最小值为基准,编程分析计算,得出二元混合工质R290/R600在不同组分比下的相对熵增,选取其中最小值对应组分比为最佳组分比.     

多元氮─氟里昂混合工质工作机理分析

在分析二元氮－氟里昂混合工质的汽液固相平衡的基础上，揭示了二元氮－氟里昂混合工质“冰堵”的机理，并且分析了二组元高沸点氟里昂工质的共晶点，证明了多元混合工质可以有效地防止固相的析出。在此基础上，分析了三元混合工质的节流特性以及成分配比的影响，最后计算了四元氮－氟里昂混合工质的理论制冷量，并与纯氮和氮－烃类混合工质作了比较。结果表明，此类工质是一类可以替代氮－烃类多元混合工质的不可燃的安全工质。     

多元氮—氟里昂混合工质工作机理分析

在分析二元氮－氟里昂混合工质的汽液固相平衡的基础上，揭示了二元氮－氟里昂混合工质“冰堵”的机理，并且分析了二组元高沸点氟里昂工质的共晶点，证明了多元混合工质可以有效地防止固相的析出。在此基础上，分析了三元混合工质的节流特性以及成分配比的影响，最后计算了四元氮－氟里昂混合工质的理论制冷量，并与纯氮和氮－烃类混合工质作了比较。结果表明，此类工质是一类可以替代氮－烃类多元混合工质的不可燃的安全工质。     

R236fa/R32制冷系统冷凝温度和蒸发温度的确定方法

根据泡露点的特性使用3种计算非共沸混合工质冷凝温度和蒸发温度的计算方法,建立应用于R236fa/R32混合工质制冷系统设计计算和性能测试的计算模型,并通过对该混合工质制冷系统的变组分试验,对制冷系统的性能测试数据进行对比分析。结果表明泡露点法不适用于大滑移温度混合工质的计算,中点法和平均值法均适用。相对于平均值法,采用中点法计算最准确,但计算过程最复杂。     

烃露点分析在天然气标准气体制备中的应用

基于Peng-Robinson物性方程对天然气在不同组分组成条件下的烃露点进行模拟计算,并根据计算结果绘制了天然气的气液组成相平衡图。对比GB/T 5274-2008称量法制备气体标准物质中的饱和蒸汽压估算法,通过对相图中烃露点线的分析,可以准确地预测天然气在特定压力和温度条件下组分出现冷凝液化的可能性,可有效保证标气配制量值的可靠性。     

采用非共沸混合工质机械过冷的跨临界CO_2制冷循环性能分析

本文提出了非共沸混合工质机械过冷跨临界CO_2制冷循环。在最优排气压力和最优过冷度下循环取得最大COP。最大COP、最优排气压力和过冷度与混合制冷剂的温度滑移密切相关。当选取合理温度滑移的混合工质作为机械过冷循环的制冷剂时,可明显提升CO_2制冷循环能效,降低排气压力。与基本CO_2制冷循环相比,在蒸发温度为-40℃、环境温度为35℃时,采用R32/R152a(40/60)循环总COP可提升46.53%,CO_2排气压力可降低2.758 MPa。总COP的提升程度受混合制冷剂的温度滑移影响显著,推荐机械过冷循环使用温度滑移合理的混合制冷剂。在温暖和炎热的气候地区及冷冻冷藏等低温应用领域,采用非共沸混合制冷剂机械过冷跨临界CO_2制冷循环整体性能的提升更加显著。     

二元氮－氟里昂低温混合工质的最佳配比分析

从高技术应用的要求出发，论述了纯质及氮－烃类混合工质的不足，用ＰＲ方程分析了成分配比对二元氮－氟里昂混合工质节流循环特性的影响，指出合理的成分配比对二元氮－氟里昂混合工质是十分必要的。并以不同温度下的△Ｈ＿Ｔ为目标函数，优化计算了一些二元氮，氟里昂低温混合工质的最佳成分配比。     

Thermodynamic Properties for R-404A

An 18-coefficient modified Benedict–Webb–Rubin equation of state has been developed for R-404A, a ternary mixture of 44% by mass of pentafluoroethane (R-125), 52% by mass of 1,1,1-trifluoroethane (R-143a), and 4% by mass of 1,1,1,2-tetrafluoroethane (R-134a). Correlations of bubble point pressures, dew point pressures, saturated liquid densities, and saturated vapor densities are also presented. This equation of state has been developed based on the reported experimental data of PVT properties, saturation properties, and isochoric heat capacities by using least-squares fitting. These correlations are valid in the temperature range from 250 K to the critical temperature. This equation of state is valid at pressures up to 19 MPa, densities to 1300 kg·m^–3, and temperatures from 250 to 400 K. The thermodynamic properties except for the saturation pressures are calculated from this equation of state.     

Thermodynamic Properties of Mixtures of R-32, R-125, R-134a, and R-152a

A mixture model explicit in Helmholtz energy has been developed that is capable of predicting thermodynamic properties of refrigerant mixtures containing R-32, R-125, R-134a, and R-152a. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the compressibility (or real gas) contribution, and the contribution from mixing. The contribution from mixing is given by a single equation that is applied to all mixtures used in this work. The independent variables are the density, temperature, and composition. The model may be used to calculate thermodynamic properties of mixtures, including dew and bubble point properties and critical points, generally within the experimental uncertainties of the available measured properties. It incorporates the most accurate published equation of state for each pure fluid. The estimated uncertainties of calculated properties are ±0.25% in density, ±0.5% in the speed of sound, and ±1% in heat capacities. Calculated bubble point pressures are generally accurate to within ±1%.     

A Generalized Model for the Thermodynamic Properties of Mixtures

A mixture model explicit in Helmholtz energy has been developed which is capable of predicting thermodynamic properties of mixtures containing nitrogen, argon, oxygen, carbon dioxide, methane, ethane, propane, n-butane, i-butane, R-32, R-125, R-134a, and R-152a within the estimated accuracy of available experimental data. The Helmholtz energy of the mixture is the sum of the ideal gas contribution, the compressibility (or real gas) contribution, and the contribution from mixing. The contribution from mixing is given by a single generalized equation which is applied to all mixtures studied in this work. The independent variables are the density, temperature, and composition. The model may be used to calculate the thermodynamic properties of mixtures at various compositions including dew and bubble point properties and critical points. It incorporates accurate published equations of state for each pure fluid. The estimated accuracy of calculated properties is ±0.2% in density, ±0.1 % in the speed of sound at pressures below 10 MPa, ±0.5% in the speed of sound for pressures above 10 MPa, and ±1% in heat capacities. In the region from 250 to 350 K at pressures up to 30 MPa, calculated densities are within ±0.1 % for most gaseous phase mixtures. For binary mixtures where the critical point temperatures of the pure fluid constituents are within 100 K of each other, calculated bubble point pressures are generally accurate to within ±1 to 2%. For mixtures with critical points further apart, calculated bubble point pressures are generally accurate to within ±5 to 10%.     

蛋白质气泡有限变形研究

根据粘弹性材料有限变形的应变能密度函数、Maxwell模型的松弛函数及气泡的变形梯度张量,推导出蛋白质气泡有限变形的应力方程。并结合气泡的平衡方程,得到气泡在动态压力作用下有限变形时内径相对变化率随时间变化的表达式。运用该表达式,通过数值模拟方法,对蛋白质气泡有限变形的非线性特性、径向变形随气泡内外压力差、膜的厚度以及膜的粘性的变化规律进行了计算分析。结果表明:在不同载荷作用下,蛋白质气泡径向变形不但具有明显的非线性特性,而且气泡变形达到平衡时的变形大小和时间也不相同。增加气泡膜的厚度和膜的粘性既可以延长气泡变形达到平衡的时间,又可以大大增强气泡承受载荷的能力。     

以PR方程为基础的氧—氮—氩系统气液平衡计算及在空分操作中应用

综合分析了多组分相平衡理论特点,介绍利用Peng—Robinson(PR)立方型状态方程进行氧—氮—氩系统气液平衡计算的方法(泡点、露点和闪蒸计算),对该计算方法的准确性进行分析和验证,并举例分析了空分设备的运行工况。     

Targeted Nanoparticle Thermometry: A Method to Measure Local Temperature at the Nanoscale Point Where Water Vapor Nucleation Occurs

An optical nanothermometer technique based on laser trapping, moving and targeted attaching an erbium oxide nanoparticle cluster is developed to measure the local temperature. The authors apply this new nanoscale temperature measuring technique (limited by the size of the nanoparticles) to measure the temperature of vapor nucleation in water. Vapor nucleation is observed after superheating water above the boiling point for degassed and nondegassed water. The average nucleation temperature for water without gas is 560 K but this temperature is lowered by 100 K when gas is introduced into the water. The authors are able to measure the temperature inside the bubble during bubble formation and find that the temperature inside the bubble spikes to over 1000 K because the heat source (optically‐heated nanorods) is no longer connected to liquid water and heat dissipation is greatly reduced.     

Pseudo-Pure Fluid Equations of State for the Refrigerant Blends R-410A, R-404A, R-507A, and R-407C

Pseudo-pure fluid equations of state explicit in Helmholtz energy have been developed to permit rapid calculation of the thermodynamic properties of the refrigerant blends R-410A, R-404A, R-507A, and R-407C. The equations were fitted to values calculated from a mixture model developed in previous work for mixtures of R-32, R-125, R-134a, and R-143a. The equations may be used to calculate the single-phase thermodynamic properties of the blends; dew and bubble point properties are calculated with the aid of additional ancillary equations for the saturation pressures. Differences between calculations from the pseudo-pure fluid equations and the full mixture model are on average 0.01%, with all calculations less than 0.1% in density except in the critical region. For the heat capacity and speed of sound, differences are on average 0.1% with maximum differences of 0.5%. Generally, these differences are consistent with the accuracy of available experimental data for the mixtures, and comparisons are given to selected experimental values to verify accuracy estimates. The equations are valid from 200 to 450 K and can be extrapolated to higher temperatures. Computations from the new equations are up to 100 times faster for phase equilibria at a given temperature and 5 times faster for single-phase state points given input conditions of temperature and pressure.     

HFCs混合制冷剂热力性质的研究

为了利用PR方程和Huron-Vidal混合规则对三元混合制冷剂的热力性质进行精确计算，通过对10组二元HFCs混合制冷剂的汽液相平衡实验数据进行热力学关联，得出了相应的NRTL模型参数，由优选得到的过量Gibbs自由能NRTL模型的相互作用系数预测了构成R407C和R404A的三元混合制冷剂R32／R125／R134a以及R125／R143a／R134a的汽液相平衡，结果表明，泡点压力实验值和计算值的算术平均相对偏差小于0．42％，各组分的汽相组成实验值和计算值基本吻合。最后还应用相关热力性质分别对R32／R125和R407C进行了理论制冷循环分析计算并和其他模型的计算结果进行了比较。     

Numerical investigation of temperature increment effect on bubble dynamics in stagnant water and Al2O3 nanofluid column

Formation, growth, and detachment of injected air bubble from a submerged needle in stagnant liquid at the different temperature of fluid, investigated numerically. Experiments have been done for validation of numerical simulation results. The injection flow rate of air was varied between 600 and 1200?mL/h in experimental study. Bubble formation, growth, and detachment information were obtained using high speed camera and visual photography technique. Young–Laplace equation that was derived from the force balance on the bubble, was utilized in numerical simulation. A novel method was used for solution of Young–Laplace equation. The bubble diameter, instantaneous contact angle, volume, and other characteristics of bubble were studied at different temperature of operating condition. Also, the enhancement of temperature in Al₂O₃ nanofluid with 0.01% volume concentration (φ?=?0.01%) was compared with deionized water results. The results reveal that by increasing the Al₂O₃ nanofluid and the deionized water temperature, the diameter, volume, and center of gravity of bubble decrease; however, the instantaneous contact angle increases. Meanwhile, the size of bubble at Al₂O₃ nanofluid is larger than of that in deionized water at same temperature. Also, the bubble aspect ratio is almost senseless to temperature increment in both deionized water and Al₂O₃ nanofluid. Eventually, the variation of operating temperature and adding of nanoparticle to the deionized water have significant influence on behavior of growing bubble.