Calculation of second virial coefficients and gaseous viscosities of the refrigerants HFC-32 (CH2 F2), HFC-23 (CHF3), and HCFC-22 (CHC1F2)

The second virial coefficients of refrigerants HFC-32 (CH₂F₂), HFC-23 (CHF₃), and HCFC-22 (CHC1F₂) have been correlated on the bisis of site site model potential and have been compared with experimental results. The molecular interactions consisted of repulsion dispersion and electrostatic parts. From the site site potentials adjusted to the experimental second virial coefficients, spherically averaged potentials have been determined and a subsequent calculation of gaseous viscosity has been carried out. Agreement between measured and calculated values of second virial coellicients and gaseous viscosity is satisfactory. Calculated values of second virial coefficients and gaseous viscosity beyond available experimental data, therefore. can be assumed as a reliable extrapolation to lower and higher temperatures.     

Bubble-point pressures and liquid densities of binary R-125 + R-143a System

Bubble-point pressures and saturated-liquid densities of the binary R-135 (pentafuoroethane) + R- 143a ( 1, 1, 1-trifluoroethane) system have been measured for several compositions at temperatures from 280 to 330 K by means of a magnetic densimeter coupled with a variable-volume cell mounted with a metallic bellows. The experimental uncertainties of the temperature, pressure. and density measurements and the composition determination were estimated to be within ±15 mK, ±13 k Pa, ±0.2%, and ±0.1 wt%, respectively. The purities of the samples used throughout the measurements are 99.98 wt% for R-125 and 99.0 mol % for R- 143a. Based on the present data, the thermodynamic behavior of the vapor-liquid equilibria of this binary refrigerant mixture has been evaluated by using the Peng-Robinson equation for the bubble-point pressures, and the modified Hankinson-Brobst-Thomson equation for the saturated-liquid densities. This was done to identify the optimized binary interaction parameters.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

A prediction method for thermal conductivity of alternative refrigerants in the liquid phase

A prediction method for the thermal conductivity of halocarbon refrigerants in the saturated liquid state in the reduced temperature range 0.3 to well above 0.9 is presented in this paper. The aim of the method is to present a very simple calculation of the transport property useful for engineering purposes. The method determines thermal conductivity as a sole function of the reduced temperature and requires the knowledge of a parameter dependent upon easily available physical constants characteristic of each compound. The method is validated against experimental data available in the literature, giving average absolute deviations which are usually less than 5%, with maximum absolute deviations generally less than 10%. An extension of the method to estimate thermal conductivity of binary mixtures is also presented, along with a comparison with the few experimental data available in the literature.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

ODS替代品生产及发展动向

国内外主要的ODS替代品有HFC—134a、120系列产品、HFC-32、HFC-152a等。其中HFC-134a广泛用于汽车和冰箱行业,全球生产能力达到19.4万t/a,我国市场消费量已经超过1000t/a。目前国内还没有开展全面的ODS替代工作,所以用量不大,几乎全部依赖进口。随着2010年停用ODS期限的临近,国内应从市场调研、产品开发等各方面做好建设ODS替代品项目的工作。     

Estimating the virial coefficients of small polar molecules

We adapt existing models for estimating the second and third virial coefficients of small molecules to the halogenated methanes and ethanes. We compare the results with the abundant new, high-qualityPVT data resulting from the search for alternative refrigerants. The present model provides an accurate method for calculating densities, and therefore it should provide reliable thermodynamic properties and fugacity coefficients. We give equations and parameters useful for estimating the properties of pure refrigerants and their mixtures when noPVT data are available.Nomenclature B Second virial coeficient - B ₁₂ Mixture cross second virial - B _h Second virial of a hard sphere fluid - _i (T) Temperature function, second virial, Eq. (7) - C Third virial coefficient - C ₁₁₂,C ₁₂₂ Mixture cross third virials - C _h Third virial of a hard sphere fluid - N Avogadro's number Virial Coefficients P _c Critical pressure - P _c12 Characteristic critical pressure of a binary mixture - T _c Critical temperature - T _c12 Characteristic critical temperature of a binary mixture - T _r Reduced temperature,T/T _c - Parameter measuring polar contribution toB, Eq. (3) - b Volume of a hard sphere molecule - f ^(f) Polynomials determining temperature dependence of the nonpolar part ofB - k ₁₂ Binary interaction parameter for mixtures, Eq. (9a) - _c Critical volume - _e Molecular polarizability - Dipole moment - _R Reduced dipole moment, Eq. (4) - _R12 Mixture reduced dipole moment, second virial - _R112, _R122 Mixture reduced dipole moment, third virial - Pitzer acentric factor - ₁₂ Mixture acentric factor - (r) Intermolecular potential - _c Critical density (1/_c)     

超市制冷系统与未来发展

分析了几种超市制冷系统的特点,得出超市制冷系统应向着占地小,耗能少,对环境污染小的方向发展,采用自然制冷工质,不仅节约能源而且保护环境,是未来的发展方向。     

制冷系统仿真中的工质热力性质计算程序

制冷系统仿真中必然用到工质热力性质计算程序,本文针对制冷系统中常用到的9种工质进行了热力性质分析,利用VB6.0编写了其计算程序模块,并在实际的制冷仿真系统中得到了应用,最终通过动力实验平台的测试,证实计算程序是合理的.     

A numerical investigation of flow boiling of non-azeotropic and near-azeotropic binary mixtures

The flow and heat transfer characteristics of binary refrigerant mixtures in a heated horizontal tube were investigated numerically. The pressure drop, temperature profile, and heat transfer coefficient for non-azeotropic and near-azeotropic mixtures of different bulk compositions were obtained. It is found that the non-linear physical properties of the mixtures strongly affect the pressure drop characteristics. Both the fluid properties and mass transfer resistance are responsible for the heat transfer characteristics. The mass transfer resistance has a more significant influence on the nucleate boiling than the convective evaporation for non-azeotropic mixtures, while the resistance can be neglected for near-azeotropic mixtures.     

可燃制冷剂标准修订进展

阐述了全球各主要地区制冷剂及系统关于可燃性的安全标准的修订情况,并介绍了各国对于HCs类易可燃性制冷剂的应用态度。各国对弱可燃制冷剂的态度有所松动,但对于HCs类易燃制冷剂的应用仍有较大分歧。     

CFCs,HCFCs类制冷工质的替代评述与展望

从环保,经济性和使用安全性角度分析了各自的特点和局限性。指出环境不友好的过渡性替代物的应用会走技术改造的弯路,造成巨大的经济损失。并指明:只要采取适当措施就可以使用环境性能经济性能都很好的碳氢类物质作为现在的和未来的制冷剂。未来的制冷剂将不会使用氟利昂。