新一代制冷剂HFO-1234yf的热物性模型

基于Peng-Robinson通用状态方程,采用基团贡献原理以及多项式拟合方法,建立了符合精度要求的新型LGWP制冷剂HFO-1234yf的热物性模型,并对模型进行了验证,利用数学软件对模型进行编程求解,得到了较为全面的HFO-1234yf制冷剂的热物性数据。将HFO-1234yf制冷剂与R134a及R417A制冷剂的热物性能进行了对比,结果显示HFO-1234yf的饱和蒸汽压力与定压比热容和R134a的表现相似,二者的饱和蒸气压均低于R417A,HFO-1234yf制冷剂与R134a和R417A相比,其饱和状态焓值较低,这将导致HFO-1234y系统运行时的性能系数不高。该模型能为HFO-1234yf制冷剂在汽车空调以及固定式空调制冷设备上的应用提供理论依据。     

新一代制冷剂HFO-1234yf的热物性模型

基于Peng-Robinson通用状态方程,采用基团贡献原理以及多项式拟合方法,建立了符合精度要求的新型LGWP制冷剂HFO-1234yf的热物性模型,并对模型进行了验证,利用数学软件对模型进行编程求解,得到了较为全面的HFO-1234yf制冷剂的热物性数据.将HFO-1234yf制冷剂与R134a及R417A制冷剂的热物性能进行了对比,结果显示HFO-1234yf的饱和蒸汽压力与定压比热容和R134a的表现相似,二者的饱和蒸气压均低于R417A,HFO-1234yf制冷剂与R134a和R417A相比,其饱和状态焓值较低,这将导致HFO-1234y系统运行时的性能系数不高.该模型能为HFO-1234yf制冷剂在汽车空调以及固定式空调制冷设备上的应用提供理论依据.     

基于COSMO-RS的单工质气液相平衡热物性计算方法

本文对基于真实溶剂似导体模型(COSMO-RS)的单工质制冷剂气液相平衡热物性的模拟精度进行了研究。研究结果表明,调节分子的表面面积比例因子可以改善模型精度。将制冷剂单工质分为无机物、碳氢化合物(HCs)和氢氟烃类化合物(HFCs)3类,在最佳比例因子参数下,模拟值与NIST实验值的相对误差,无机物CO_2和NH_3分别在±3%和±1%以内,HCs和HFCs在±2%以内。在此基础上,分析各类工质的尺寸因子参数的变化规律,并拟合出各类单工质的饱和蒸气压方程,为新型单工质的气液相平衡热物性预测提供了新方法。     

氨制冷系统在新时期的再认识

针对制冷剂现状着重从氨的热力学性能、物理性质、环保及毒笥等方面分析了扩大氨制冷剂在新时期应用的可行性。     

HFC-161混合物替代R502的理论研究

提出一种新型制冷剂HFC-161/125/143a(质量百分比10/45/45)用于替代制冷剂R502.新制冷剂环境性能良好,ODP值为0,GWP值为3466,GWP值小于R502及其常用替代制冷剂R404A和R507.采用Refprop软件计算了HFC-161混合物的基本热物理性质,以及低温工况和变工况下的理论循环性能,并与制冷剂R502、R404A、R507的相关数据进行对比.结果表明:新制冷剂的运行压力、压比、COP值、单位容积制冷量与R502相当,温度滑移小于R502常用替代物R404A,是一种性能优良的制冷剂R502的替代物.     

溴化锂水溶液的比焓分析

从溴化锂水溶液的热物理性质出发，分析了国内外有关溴化锂水溶液的比焓值数据，合理地解释了国内外溴化锂水溶液比焓值不同的原因，提出了一种简单的转换国内外溴化锂水溶液比焓值数据的公式，并显示了较好的吻合性，为今后借鉴国外有关的比焓数据提供了方法。并根据这一方法，对国外有关的高温高浓度区域的比焓值数据进行了转换，可为三效和四效溴化锂吸收式制冷机的开发和研制提供比焓值数据。     

兼容电池热管理的热泵系统研究与探索

本文通过台架试验和整车试验,验证不同制冷剂在汽车空调上的性能表现,给汽车空调制冷剂选择提供建议。通过对比分别充注R134a和R410A制冷剂的汽车热泵热管理系统在不同环境下的整车试验、焓差试验的性能和低温制热量等可知R410A性能更佳,环境适用性更广,更能应对复杂的整车环境;考虑环保因素也同步研究了物性同R410A相似但GWP值更低的制冷剂R32和XL41等以适应未来市场需求;考虑更好的低温适应性和低温性能的提升,研究了低温增焓热泵系统,其环境温度越低性能提升越大,试验数据表明汽车空调能效在-20℃,低温增焓方式可提升38%。考虑电动汽车热泵运行环境和经济性要求,本文给出最佳设计方案。     

冷库氨制冷剂在系统安装及使用中的问题

目前，在中、大型冷库系统中，采用氨作制冷剂仍占据98％以上。其主要原因．一是氨制冷剂具有其它制冷剂无法替代的优点，如：具有较好的热力性质和热物理性质，特别是目前，冷库的使用温度一般在-60℃～0℃之间的较为多数。对氨制冷剂在此范围内使用，发挥其优点及特性更加明显。目前，国际社会环保意识越来越高，对消耗破坏臭氧层物质或对环境造成热效应的R12、R13、R502等等氯氟烃类制冷剂停止使用，故此派生出许多新制冷剂虽然大部分新制冷剂可以满足要求，但由于价格及其他要求，远远不能使我国迅速利用到工程上。针对目前我们的国情及实力，大型空调及分体空调小冷库基本采用R22及410A。而大中型冷库系统均基本采用氨。除有传热效果好，流动阻力小外，更重要的是氨对臭氧层破坏（ODP值）程度和使全球变暖（CWP值）的值均为零，所以使得发展中国家及发达国家大中型制冷装置中，使用氨作制冷剂的已占80～90％。正因氨的广泛及大量使用，氨的负面问题就应引起高度重视。     

HFC-32制冷剂饱和液体热力性能参数计算模型

制冷剂简单有效的热力性能参数计算模型对制冷循环的仿真是十分必要的.提出了HFC-32制冷剂饱和液体的蒸汽压和密度关联式计算模型;在HFC-32的GMA液体状态方程基础上,利用Helmholtz偏离函数和Maxwell关系式推导出了HFC-32饱和液体的焓、熵和比热容的计算模型;上述各模型均不存在迭代,保证了模型的计算精度和稳定性.将建立的各模型在饱和液体(275 ～ 335K,0.862～4.095MPa)范围内与REFPROP7计算值进行对比,结果表明,所有热力性能参数计算模型的相对平均误差不超过0.776％,最大误差小于4.464％,证明了所建立模型的可靠性.     

超临界态二氧化碳流体热力学性质的分子动力学模拟北大核心CSCD

采用恒温恒压(NPT)系综分子动力学模拟方法,模拟预测了超临界态区间内(温度600—900 K,压力30—100 MPa)CO_(2)流体的热力学特性(密度和比定压热容),同时对比研究了4种典型的半经验型力场的预测性能。结果表明:4种力场在超临界态热力区间内对CO_(2)流体的密度和比定压热容特性均具有较好的预测精度,其中密度的预测偏差在3%以内,而比定压热容的预测偏差在1%以内。相比单点粗粒化SAFT-γ力场,具有更多参数自由度的全原子力场对超临界区间内流体热物性的预测并不具有显著优势,这表明其力场参数对于超临界态物性的预测而言并非最优解。EPM2和Zhang力场对CO_(2)流体密度和比定压热容的预测偏差均随温度的升高而减小,表明此两种力场可用于更高温度工况下热力学特性的模拟预测。     

Prediction of Transport Properties of Liquid Ammonia and Its Binary Mixture with Methanol by Molecular Simulation

Transport properties of ammonia and of the binary mixture ammonia + methanol are predicted for a broad range of liquid states by molecular dynamics (MD) simulation on the basis of rigid, non-polarizable molecular models of the united-atom type. These models were parameterized in preceding work using only experimental vapor-liquid equilibrium data. The self- and the Maxwell-Stefan (MS) diffusion coefficients as well as the shear viscosity are obtained by equilibrium MD and the Green-Kubo formalism. Non-equilibrium MD is used for the thermal conductivity. The transport properties of liquid ammonia are predicted for temperatures between 223 K and 473 K up to pressures of 200 MPa and are compared to experimental data and correlations thereof. Generally, good agreement is achieved. The predicted self-diffusion coefficient as well as the shear viscosity deviates on average by less than 15 % from the experiment and the thermal conductivity by less than 6 %. Furthermore, the self- and the MS transport diffusion coefficients as well as the shear viscosity of the liquid mixture ammonia + methanol are studied at different compositions and compared to the available experimental data.     

Thermal Conductivity Modeling of Pure Refrigerants in a Three-Parameter Corresponding States Format

The potential of the corresponding states (CS) principle for modeling a pure fluid thermal conductivity surface is studied here. While for thermodynamic properties and for viscosity, successful results have been previously obtained by directly applying an improved three-parameter CS method, significant difficulties were encountered while trying to extend this method to thermal conductivity and, in particular, it fails if applied without separately dealing with the dilute-gas term, and the residual and critical enhancement contributions. These last two parts are also combined in the excess term. It is shown that the dilute-gas term cannot be expressed in such a format, and it has necessarily to be individually modeled for each target fluid. On the contrary, the excess contribution can be described through a specific conductivity scaling factor that can be individually determined from a single saturated liquid conductivity experimental value. The model for the excess part is set up in a three-parameter CS format on two reference fluids, in the present case, methane and R134a, for which dedicated thermal conductivity equations are available, and it has a predictive character. The models for the dilute-gas and for the excess contributions are then combined to give the final TC model. The model has been successfully validated for two homologous families of refrigerant fluids obtaining an AAD of 3.67% for 3332 points for haloalkanes and an AAD of 2.87% for 354 points for alkanes.Paper presented at the Sixteenth European Conference on Thermophysical Properties, September 1–4, 2002, London, United Kingdom.     

Diagrams of entropy for ammonia–water mixtures: Applications to absorption refrigeration systems

The objective of this work is to calculate the entropy of ammonia–water mixture as a function of temperature, pressure, concentration, and other thermodynamic properties associated to absorption process, to support energy and exergy analysis of absorption refrigeration systems. This calculation is possible because a novel mathematical modelling was developed for this attempt. This determination will allow simulation and optimisation of absorption refrigeration systems, giving major importance in determining the values of thermodynamic properties of ammonia–water mixtures, such as enthalpy and entropy. A mathematical modelling for thermodynamics properties calculation at liquid and vapour phases of ammonia–water system is developed. The studies were based on the enthalpy vs. concentration diagram obtaining the enthalpy in the liquid phase corresponding at a temperature range from 80 °C to −40 °C. The mixtures enthalpy values were calculated for ammonia (h_1c) and water (h_2c) by using a non-linear regression program. The evaluation of thermodynamic properties in this work was discretised by formulating appropriate equations for each type of substance. However, thermodynamic properties of mixtures can be determined based on data from simple substances and mixing laws, or from an equation of state that considers the mixture concentration. The consistency of experimental data indicates the most suitable method to be used in entropy calculation.     

A Rigorous Thermodynamic Property Model for Fluid-Phase 1,1-Difluoroethane (R-152a)

A new thermodynamic property model for the Helmholtz free energy with rational third virial coefficients for fluid-phase 1,1-difluoroethane (R-152a) was developed. The model was validated by existing experimental data for temperatures from the triple point to 450 K and pressures up to 60 MPa. Reasonable behavior of the second and third virial coefficients was confirmed from intermolecular potential models. The estimated uncertainties are 0.1% in density for the gaseous and liquid phases, 0.4% in density for the supercritical region, 0.05% in speed of sound for the gaseous phase, 2% in speed of sound for the liquid phase, and 1% in specific heat capacities for the liquid phase. From the reasonable behavior of the ideal curves and the third virial coefficients, the model can be assumed reliable in representing the thermodynamic properties not only at states with available experimental data but also at states for which no experimental data are available.     

常用制冷工质热力性质计算数据库的开发

建立了包括湿空气、R22、R21、R12、Rll、R134a、NH3、H2O的热力性质计算数据库系统，其中热力性质计算包括温度、压力、密度、比焓、比熵、比容、汽化潜热。对R11、R12、R21、NH3、R134a的热力性质计算公式进行了修正，计算结果与文献中的数据进行比较，结果显示：数据库中除R134a和湿空气外，其他丁质的计算误差均小于0．8％，此外R22的热力性质计算程序已在制冷循环仿真模型中得到应用。     

A basis for the development of new ammonia–water–sodium hydroxide absorption chillers

Adding NaOH to ammonia/water improves the separation of ammonia in the generator and reduces both chiller driving temperature and rectification losses. In this paper the main disadvantages for the implementation of these new mixtures are addressed: a) few experimental data or reliable correlations of the fluid mixture properties exist; b) selection of an adequate system for separating the hydroxide; and c) evaluation of potential corrosion problems. Our results show that the separation of NaOH from an ammonia/water solution with a maximum approximate mass fraction of 0.05 (5% weight) is viable when reverse osmosis is used with membranes BW30 and SW30HR LE. Cycle simulation using experimental data to calculate the vapour–liquid equilibrium properties shows that the COP is approximately 20% higher than with a conventional ammonia/water chiller working under the same conditions and using a hydroxyl separation efficiency of 99% for NaOH, which is feasible according to the experimental tests.     

Extension of the implicit curve-fitting method for fast calculation of thermodynamic properties of refrigerants in supercritical region

The implicit curve-fitting method has been used for fast and stable calculations of thermodynamic properties of subcritical refrigerants, and it has to use the saturated liquid or vapor state as the reference state. In order to extend the application range of this method in supercritical region, an isothermal state in the supercritical region is used as the reference state, and the implicit equations for supercritical refrigerants in this state and out of this state are established, respectively. The new calculation method can be used in the entire supercritical region. With the new method, thermodynamic properties of supercritical CO₂ and R410A are predicted and compared with REFPROP 8. It shows that the total mean relative deviations of the fast calculation formulae from REFPROP 8 are less than 1%, while the mean calculation speeds of the fast calculation formulae are more than 100 times faster than those of REFPROP 8.     

Saturated Humidity, Entropy, and Enthalpy for the Nitrogen-Water System at Elevated Temperatures and Pressures

A model is used to calculate saturated thermophysical properties (humidity, entropy, and enthalpy) of a nitrogen-water mixture at elevated temperatures and pressures. In the model, a modified Redlich–Kwong equation of state is used to calculate fugacity coefficients for the vapor phase, and the liquid phase follows Henry's law. The model has been investigated by comparing the calculated results with the available experimental data. The comparison shows that the model can be used to calculate saturated thermodynamic properties for the nitrogen-water mixture reliably up to 523.15 K and 300 bar.     

Thermodynamic property representation for the R-32/125 binary system by a new cubic equation of state

Thermodynamic properties of the R-32/125 binary system are modeled by a new cubic equation of state which was developed and applied to the pure R-32 and R-125 in a previous paper by the present authors. The essential thermodynamic properties such as PVTx properties, vapor-liquid equilibrium, enthalpy, entropy, isobaric specific heat, and speed of sound are well represented by the new model simultaneously for the liquid phase, the gas phase, and the two-phase region of the R-32/125 binary system. The developed model is valid for the entire range of compositions, and a pressure-enthalpy diagram for a R-32/125 mixture with 50 mass% of R-32 is illustrated as an example. The new model was also compared with other reported models in refrigeration cycle calculations.     

A Rational Helmholtz Fundamental Equation of State for Difluoromethane with an Intermolecular Potential Background

A new fundamental thermodynamic equation of state for difluoromethane was developed by considering the intermolecular potential behavior for improving the reliability in the gaseous phase. Reliable second and third virial coefficients are introduced in accordance with the principle of a unified relation of the intermolecular potential energy and the fundamental equation of state. The fundamental equation of state is able to provide reliable thermodynamic properties even at low temperatures or in the region near saturation where precise and accurate experimental data are not available. The estimated uncertainties of calculated properties from the equation of state are 0.07% in density for the liquid phase, 0.1% in pressure for the gaseous phase, 0.35% in pressure for the supercritical region, 0.07% in vapor pressure, 0.2% in saturated-liquid density, 0.7% in saturated-vapor density, 0.01% in speed of sound for the gaseous phase, 0.7% in speed of sound for the liquid phase, and 0.6% in isochoric specific heat for the liquid phase. The equation is valid for temperatures from the triple point to 450 K and pressures up to 72 MPa.