UNIFAC基团贡献法预测混合制冷剂的气液相平衡

将UNIFAC基团贡献法成功地应用于HFCs混合制冷剂的气液相平衡热力学性质的预测.根据资料拟合得到了CH₂、CF₂、F三个主基团的相互作用参数, 用拟合的基团相互作用参数预测了新工质对R32/R227ea、R227ea/R134a和R152a/R227ea及三元混合制冷剂R32/R125/R134a的气液相平衡数据,并与实验进行了对比,两者基本吻合.本工作为今后HFCs混合制冷剂替代和制冷系统研究提供了极有推广价值的物性计算方法和数据,满足了新工质工程设计的要求.     

含HFO混合体系气液相平衡的理论模型评价

HFO类新型环保工质具有很低的全球变暖潜能,但受限于热工性能且具有可燃性。含HFO的混合工质可实现优势互补,具有良好的应用前景。气液相平衡是混合物最基本的热力性质,其理论模型极为重要。选取PR状态方程,vdW、HV、WS三种混合规则和NRTL、Wilson两种活度系数模型,构建了PR-vdW、PR-HV-NRTL、PR-WS-NRTL和PR-WS-Wilson共4套理论模型,对HFC+HFO、HC+HFO、CO₂+HFO类二元体系气液相平衡的计算性能进行了比较和评价,并进一步分析了模型对含超临界组元体系的计算效果和对三元体系相平衡预测能力。结果表明PR-vdW模型计算性能稳定,对大多数体系计算性能优良;PR-WS-NRTL模型和PR-WS-Wilson模型性能优秀,但预测混合体系临界轨迹线和三元相平衡时稳定性不够好,PR-HV-NRTL模型预测三元相平衡时性能良好。     

R32+R1234yf+R1234ze（E）混合制冷剂气液相平衡实验研究

基于液相循环法搭建的气液相平衡实验装置,在263.15~323.15 K温度范围内,实验测量了R32+R1234yf和R1234yf+R1234ze（E）二元混合物以及R32+R1234yf+R1234ze（E）三元混合物的气液相平衡数据,利用PRSV状态方程结合WS混合法则和NRTL活度系数模型进行关联拟合,获得二元混合工质的交互参数,并在其基础上预测了三元混合工质气液相平衡性质。计算结果与实验数据对比表明,二元体系R32+R1234yf和R1234yf+R1234ze（E）的压力平均绝对偏差分别为0.71%和0.20%,气相摩尔分数平均绝对偏差均约为0.0016,三元体系R32+R1234yf+R1234ze（E）的压力平均绝对偏差为0.82%,系统组分R32和R1234yf的气相摩尔分数平均绝对偏差均约为0.007。     

CO2混合工质的气液相平衡的混合规则对比与预测研究

CO₂混合工质兼顾高效和环境友好的特点,在新一代热功转化循环中受到广泛关注。混合工质气液相平衡性质是循环分析与计算的基础。为了提高CO₂混合工质气液相平衡数据的计算精度,采用PR状态方程结合三种混合规则（vdW、MHV1、WS）,对7种CO₂+HFCs/HFOs及4种CO₂+HCs混合工质的气液相平衡性质进行了计算。结果表明,对CO₂+HCs混合工质,vdW混合规则可达较好的结果;对CO₂+HFCs/HFOs混合工质,在亚临界区三者计算精度相近,但在超临界区,WS混合规则对计算精度提升明显。最后,提出了一种差值模型预测CO₂混合工质气液相平衡性质,预测的AARD(p)值为2.03%,AAD(y)值为0.0120,预测精度较高。     

混合制冷剂比定压热容的理论推算

利用状态方程,采用余函数法对混合制冷剂的比定压热容进行了推算。根据热力学普遍关系式推导了用通用性好、精度高的Peng-Robinson状态方程推算实际流体比定压热容的计算公式。以混合制冷剂HFC152a/HCFC22、HFC152a/HFC32和HFC134a/HFC152a为例,计算了其比定压热容,并与实验数据进行了比较。结果表明:液态HFC152a/HCFC22在温度区间303.15—353.15 K总平均偏差为12.90%;液态HFC152a/HFC32在温度区间313.15—353.15 K的总平均偏差为17.91%;气态HFC134a/HFC152a在温度区间298.15—423.15 K总平均偏差为2.93%。该法可以用于混合工质的比定压热容的理论推算。     

含HFO二元混合工质汽液相平衡性质研究

为了提高环保替代混合制冷工质相平衡数据的计算精度,文中收集了公开发表的7种HFOs/HFCs及6种HFOs/HCs 2类二元混合工质的气液相平衡性质实验数据,分别采用PR方程+VDW混合法则、PR方程+MHV1混合法则+Wilson模型对2类混合工质的气液相平衡性质进行了非线性优化,结果表明:对于HFOs/HFCs,PR+MHV1+Wilson模型计算值与实验结果的压力平均相对偏差为0. 28%,汽相组分的平均绝对偏差为0. 003 5,PR+VDW模型的结果分别为0. 30%和0. 003 6;对于HFOs/HCs,PR+MHV1+Wilson模型计算值与实验结果的压力平均相对偏差为0. 25%,汽相组分的平均绝对偏差为0. 003 7,PR+VDW模型的结果分别为0. 55%和0. 004 8。可见:相比于PR+VDW模型,PR+MHV1+Wilson模型对HFOs/HFCs混合工质的汽液相平衡性质计算精度提升有限,对HFOs/HCs类工质则可显著提升计算精度。     

强非共沸工质R134a/R23/R14汽液相平衡和压焓图的构建及应用

基于PR状态方程,分模块模拟计算了三级自动复叠制冷系统中R134a/R23/R14三元混合工质的热物理特性参数,得到非共沸混合工质的汽液平衡数据、两相组分,并利用干度计算焓熵值,构建了典型配比下混合工质的压焓图和汽液相平衡图。二元R134a/R23和R32/R134a混合工质的泡点压力和气相组分的计算值与实验测试值的误差分别小于1.3%、1.2%和1.0%、2.4%;三元R32/R125/R134a混合工质95%的计算值与实验值的偏差在±5%之内,表明该模型能满足工程计算需要。利用理论模型,结合实验系统,对R134a/R23/R14三级自动复叠制冷系统进行详细的组分等热物性分析,并在空间压焓图上进行了详细表述。     

二氧化碳混合工质临界参数计算模型对比研究

二氧化碳(CO₂)混合工质是具有应用潜力的动力循环工质,临界参数作为CO₂混合工质的关键基础热物性,对其进行准确地计算和预测具有重要意义。采用4种不同类型的计算模型,分别针对CO₂+HFC、CO₂+HFO和CO₂+HC三类二元混合工质的临界温度和临界压力进行了推算,并与公开发表的实验数据和REFPROP数据库计算结果进行对比,分析讨论了各种计算方法对各类CO₂混合工质的适用性。结果表明,Li方法形式简单,混合物临界温度的计算式仅与纯质组分的临界温度及临界体积有关,可用于CO₂+HFC和CO₂+HFO混合工质临界温度的快速推算。对于CO₂+HC混合工质,RK方法计算偏差最小,该类混合物临界参数实验数据点数和套数较多,因此可直接通过RK方法回归得到关联式进行应用。     

非共沸混合工质管内流动凝结换热系数的分析与计算

对非共沸混合工质R32 /R134a的管内流动凝结局部换热系数进行了理论分析和计算 .计算表明 ,非共沸混合工质的管内流动凝结换热系数总是低于具有等同物性的纯工质的换热系数 ,其换热系数下降的程度不仅受浓度的影响 ,还受干度的影响 .对混合工质R32 /R134a而言 ,换热系数的极小值出现在R32质量分数为10 %～ 30 %的区域内     

1-丁基-3-甲基咪唑磷酸二丁酯+甲醇/乙醇+水三元工质溶液混合焓的测量及预测

采用绝热量热法测量了由离子液体1-丁基-3-甲基咪唑磷酸二丁酯([bmim][DBP])分别与CH₃OH、C₂H₅OH和H₂O所组成的3个二元工质溶液体系[bmim][DBP](1)+ CH₃OH(2)/C₂H₅OH(2)/H₂O(2),以及2个三元工质溶液体系[bmim][DBP](1)+ CH₃OH(2)/C₂H₅OH(2)+ H₂O(3)在298.15 K和常压下的摩尔混合焓H_m^E。利用Gibbs-Helmholtz方程和NRTL活度系数模型,对每个二元溶液体系摩尔混合焓的实验数据进行关联,获得模型方程中的组分作用参数。摩尔混合焓的模型拟合值与实验值的平均相对偏差分别为1.81%、1.44%和0.72%。在此基础上预测了2个三元工质溶液体系的摩尔混合焓。结果表明:三元工质溶液体系的摩尔混合焓在实验浓度范围内均为负值,混合为放热过程。表明三元工质溶液具有成为吸收制冷循环新工质溶液的基本特征;采用NRTL模型预测2个三元溶液体系摩尔混合焓的计算值与实验值的平均相对误差分别为2.31%、2.49%。     

High pressure vapor-liquid equilibria and critical loci for the HFC125-HFC134a system

We measured vapor-liquid equilibria (VLE) ranging from 303.75 to 363.15 K and the critical locus for the system of pentafluoroethane (HFC125)-1,1,1,2-tetrafluoroethane (HFC134a). The critical locus exhibited type I behavior by van Konynenberg and Sccot. Correlating the VLE data with an extended BWR equation of state, we found the optimum binary interaction parameter for this system 1.0081 and estimated coefficients of performance (C.O.P.) as a mixture refrigerant. As a result of the correlation, we found that the HFC125-HFC134a system is a potential alternative refrigerant when mole fraction of HFC125 is lower than 0.6. Calculations showed a 4.9% saving energy in the cycle compared with chlorodifluoromethane (HCFC22), for a composition of 30 mole percent HFC125. This paper was presented at The 5th International Symposium on Separation Technology-Korea and Japan held at Seoul between August 19 and 21, 1999.     

混合制冷工质核态沸腾的传热研究

Heat transfer coefficients in nucleate pool boiling were measured on a horizontal copper surface for refrigerants, HFC-134a, HFC-32, and HFC-125, their binary and ternary mixtures under saturated conditions at 0.9MPa. Compared to pure components, both binary and ternary mixtures showed lower heat transfer coefficients.This deterioration was more pronounced as heat flux was increased. Experimental data were compared with some empirical and semi-empirical correlations available in literature. For binary mixture, the accuracy of the correlations varied considerably with mixtures and the heat flux. Experimental data for HFC-32/134a/125 were also compared with available correlated equation obtained by Thome. For ternary mixture, the boiling range of binary mixture composed by the pure fluids with the lowest and the medium boiling points, and their concentration difference had important effects on boiling heat transfer coefficients.     

Isobaric vapor–liquid equilibria for mixtures of tetrahydrofuran, 2-propanol, and 2,2,4-trimethylpentane at 101.3 kPa

Vapor–liquid equilibrium (VLE) at 101.3 kPa have been determined for a ternary system (tetrahydofuran + 2-propanol + 2,2,4-trimethylpentane) and its constituent binary systems (tetrahydrofuran + 2-propanol, tetrahydrofuran + 2,2,4-trimethylpentane, and 2-propanol + 2,2,4-trimethylpentane). The activity coefficients of liquid mixtures were calculated from the modified Raoult's law. Thermodynamic consistency tests were performed for all VLE data. The VLE data of the binary mixtures and ternary mixtures were correlated using the Margules, Wilson, NRTL, and UNIQUAC activity-coefficient models. The models with their best-fitted interaction parameters of the binary systems were used to predict the ternary vapor–liquid equilibrium. All VLE data are also used to calculate the reduced excess molar Gibbs free energy g^E/RT and the deviations in the boiling point ΔT. The calculated quantities of g^E/RT and ΔT were fitted to variable-degree polynomials in terms of liquid composition.     

甲醇-甲基丙烯酸甲酯-水三元系汽液平衡和液液汽平衡的研究(Ⅱ)三元系部分

本工作测定了25、35、45、55和60℃时甲醇-甲基丙烯酸甲酯-水三元系互溶区蒸汽压以及部分互溶区的液液平衡和蒸汽压数据.用各对二元系修正的UNIQUAC模型参数推算得到的三元系相平衡数据与实验值符合良好,表明这些模型参数可作为对该三元系进行由低压至常压的相平衡计算基础数据.     

High pressure vapor-liquid equilibria for the HFC125-HFC152a system

We measured vapor-liquid equilibria (VLE) for the system of pentafluoroethane (HFC125)-difluoroethane (HFC152a) over the temperature range from 268.15 K to 373.15 K. Fitting VLE data obtained to an extended BWR equation of state, binary interaction parameters were correlated as a linear function of temperature. Applying the equation of state including the binary interaction parameters to refrigeration cycle, estimation of coefficient of performance (COP) revealed about 13.3 % energy-saving against chlorodifluoromethane (HCFC22), when the mole fraction of HFC125 is 0.44. As the condition of COP estimation, we assumed that temperature changes of out-side fluids were from 285.15 down to 280.15 K and 305.15 up to 310.15 K with 3 K in minimum temperature difference, respectively.     

ON THE COMPOSITION-DEPENDENT INTERACTION PARAMETERS IN EQUATIONS OF STATE

Composition-dependent interaction parameters have been applied to the calculation of vapor-liquid equilibria (VLE) in mixtures containing components of different chemical nature. Binary VLE have been correlated and ternary VLE have been predicted from binary data using five different mixing rules. Binary data can be accurately correlated for systems with moderate deviations from ideality using mixing rules with two binary parameters. For very strongly nonideal mixtures three binary parameters are needed. For the prediction of ternary VLE from binary information only the mixing rules of Panagiotopoulos and Reid (1986) and Schwartzentruber et al. (1987) are reliable. For most systems the quality of predicting ternary data is comparable to the quality of correlating binary data. Significant deviations are noted only for strongly nonideal systems close to phase separation. In these cases it is recommended to use models incorporating association in an explicit form. KEYWORDS Equations of state Mixing rules Multicomponent Vapor-liquid equilibria.     

甲苯-苯甲醛-苯甲酸体系汽液平衡的研究

本文在600×1.333×10~2Pa和400×1.333×10~2Pa压力下分别测定了甲苯-苯甲醛-苯甲酸三元体系及其三个二元体系的汽液平衡数据。用点检验法对二元数据进行了热力学一致性检验,并用Margules、wilson、NRTL和UNIQUAC方程作热力学关联。预测了三元汽液平衡关系,与实测值吻合结果令人满意。