Thermal conductivity of gaseous fluorocarbon refrigerants R 12, R 13, R 22, and R 23, under pressure

The thermal conductivity of four gaseous fluorocarbon refrigerants has been measured by a vertical coaxial cylinder apparatus on a relative basis. The fluorocarbon refrigerants used and the ranges of temperature and pressure covered are as follows: R 12 (Dichlorodifluoromethane CCl₂F₂): 298.15–393.15 K, 0.1–4.28 MPa R 13 (Chlorotrifluoromethane CClF₃): 283.15–373.15 K, 0.1–6.96 MPa R 22 (Chlorodifluoromethane CHClF₂): 298.15–393.15 K, 0.1–5.76 MPa R 23 (Trifluoromethane CHF₃): 283.15–373.15 K, 0.1–6.96 MPaThe apparatus was calibrated using Ar, N₂, and CO₂ as the standard gases. The uncertainty of the experimental data is estimated to be within 2%, except in the critical region. The behavior of the thermal conductivity for these fluorocarbons is quite similar; thermal conductivity increases with increasing pressure. The temperature coefficient of thermal conductivity at constant pressure, (/T) _p , is positive at low pressures and becomes negative at high pressures. Therefore, the thermal conductivity isotherms of each refrigerant intersect each other in a specific range of pressure. A steep enhancement of thermal conductivity is observed near the critical point. The experimental results are statistically analyzed and the thermal conductivities are expressed as functions of temperature and pressure and of temperature and density.     

Energy performance evaluation of R1234yf,R1234ze(E), R600a,R290 and R152a as low-GWP R134a alternatives

In 2014, the Directive 517/2014 was introduced by European Parliament to reduce the use of high-GWP greenhouse gases in the European area in order to limit global climate change in accordance with the objectives marked by the EU Research and Innovation programme Horizon 2020. These restrictions affect the large majority of artificial refrigerants among which R134a is included due to its relatively high GWP₁₀₀ (1301). The widely used of R134a in the refrigeration and air conditioning fields reveals the need to identify new low-GWP alternatives. Accordingly, in this work five low-GWP R134a possible choices have been tested and compared in an identical refrigerating facility equipped with a hermetic compressor, under the same operating conditions.The refrigerants used in this analysis are: R290 and R600a (HCs); R134a and R152a (HFCs), and finally, R1234yf and R1234ze(E) (HFOs). All of them have been assayed without changes in the facility, that is, as direct drop-ins. The results obtained from the experimental tests are presented and commented in this work from the energetic point of view.     

R1234ze(E)在多元醇脂油中溶解度的实验研究

R1234ze(E)(1,1,1,3-四氟丙烯)是当下具有较强替代潜能的环保制冷剂之一。本文搭建了溶解度测试实验系统,对R1234ze(E)在两种多元醇脂油中的溶解度进行测试,测试的温度范围为40～80℃,压力范围为0.123～0.360 MPa。采用PR状态方程和MHV2混合规则及NRTL活度系数模型对实验结果进行关联计算,得到不同温度下的交互系数及计算值与实验值的平均相对误差。结果表明:R1234ze(E)在两种多元醇脂油中的溶解度均随着温度的升高而降低,且R1234ze(E)在两种多元醇脂油中的平衡压力与溶解度之间存在立方函数关系。在两种多元醇酯油中,计算值与实验值的平均相对误差分别为1.68%和1.11%,可较好的描述R1234ze(E)在两种多元醇酯油中的相平衡行为。     

Thermodynamic properties for the alternative refrigerants

Models commonly used to calculate the thermodynamic properties of refrigerants are summarized. For pure refrigerants, the virial, cubic, Martin-Hou, Benedict-Webb-Rubin, and Helmholtz energy equations of state and the extended corresponding states model are discussed. High-accuracy formulations for 16 refrigerants are recommended. These models may be extended to mixtures through the use of mixing rules applied either to the parameters of the equation of state or to some property of the mixture components. Mixtures of a specific composition may also be modeled as a pseudo-pure fluid. Five mixture models, employing four distinct approaches, have been compared by a group working under the auspices of the International Energy Agency. These comparisons show all five models to be very capable in representing mixture properties. No single model was best in all aspects, but based on its combination of excellent accuracy and great generality, we recommend the mixture Helmholtz energy model as the best available.Experimental data are essential to both fit the adjustable parameters in property models and to assess their accuracy. We present a survey of the data available for mixtures of the HFC refrigerants R32, R125, R143a, R134a, and R152a and for mixtures of the natural refrigerants propane, butane, isobutane, and carbon dioxide. More than 60 data references are identified. Further data needs include caloric data for additional mixtures, comprehensive pressure-density-temperature data for additional mixture compositions, and improved accuracy for vapor-liquid equilibria data.     

Equations of State for the Ozone-Safe Refrigerants R32 and R125

Equations of state for gaseous and liquid difluoromethane (R32) and pentafluoroethane (R125) were developed. The coefficients of the equations were determined using experimental density data and heat capacities c _v and c _s. The equations satisfy Maxwell's rule. The equations describe the thermodynamic properties of R32 and R125 at temperatures from 140 to 433 K and from 178 to 480 K, respectively, and at pressures up to 70 MPa within the experimental uncertainties. In particular, the root-mean-square deviations of the calculated values of density from the most reliable experimental data are equal to 0.10% for R32 and 0.12% for R125.     

Measurements of PρT properties,vapor pressures,saturated densities,and critical parameters for R 1234ze(Z) and R 245fa

Pressure-density-temperature (PρT) properties, vapor pressures, and saturated liquid and vapor densities for refrigerants R 1234ze(Z) (cis-1,3,3,3-tetrafluoroprop-1-ene; CF₃CHCHF) and R 245fa (1,1,1,3,3-pentafluoropropane; C₃H₃F₅) were measured with two types of isochoric methods. Pressure was measured with a digital quartz pressure transducer. Temperature was measured with 25 Ω standard platinum resistance thermometer on the ITS-90 temperature scale. Density was calculated from the mass of sample and the inner volume of pressure vessel. By using the present vapor pressure data, new vapor pressure correlations for R 1234ze(Z) and R 245fa have been formulated. In addition, the critical temperature T_c, critical density ρ_c, and critical pressure P_c were directly determined on the basis of direct observation of the meniscus disappearance.     

Fluid-phase-equilibrium prediction of fluorocompound-containing binary systems with the predictive E-PPR78 model

In order to reduce the overall emissions of greenhouse gases and to be in compliance with the current environmental regulations, a new class of refrigerants has appeared. Such refrigerants are generally multi-component systems that contain a fluorocompound mixed with CO₂ and/or an alkane. In order to design processes involving such blends or to implement a product-design approach aimed at identifying new refrigerant mixtures, an equation of state (EoS) able to predict the properties of fluorocompound-containing systems is required. In order to reach this goal, it was decided in this study to add six fluorinated groups to the Enhanced-PPR78 model which combines the Peng–Robinson EoS and a group contribution method aimed at estimating the binary interaction parameters, k_ij(T), involved in Van der Waals one-fluid mixing rules.     

Thermodynamic properties of R32 + R134a and R125 + R32 mixtures in and beyond the critical region

A parametric crossover equation of state for pure fluids is adapted to binary mixtures. This equation incorporates scaling laws asymptotically close to the critical point and is transformed into a regular classical expansion far away from the critical point. An isomorphic generalization of the law of corresponding states is applied to the prediction of thermodynamic properties and the phase behavior of binary mixtures over a wide region around the locus of vapor-liquid critical points. A comparison is made with experimental data for pure R32, R 125 and R 134a, and for R32 + R 134a and R 125 + R32 binary mixtures. The equation of state yields a good representation of thermodynamic property data in the range of temperatures 0.8T_c(x) ≤ T ≤ 1.5T_c(x) and densities 0.35 ?_c(x) ≤ ? ≤ 1.65?_c(x).     

The effect of Pt nanoparticles loading on H2 sensing properties of flame-spray-made SnO2 sensing films

SnO₂ nanoparticles loaded with 0.2–2 wt% Pt have successfully been synthesized in a single step by flame spray pyrolysis (FSP) and investigated for gas sensing towards hydrogen (H₂). According to characterization results by X-ray diffraction, nitrogen adsorption, scanning/high resolution-transmission electron microscopy and analyses based on Hume-Rothery rules using atomic radii, crystal structure, electronegativities, and valency/oxidation states of Pt and Sn, it is conclusive that Pt is not solute in SnO₂ crystal but forms nanoparticles loaded on SnO₂ surface. H₂ gas sensing was studied at 200–10,000 ppm and 150–350 °C in dry air. It was found that H₂ response was enhanced by more than one order of magnitude with a small Pt loading concentration of 0.2 wt% but further increase of Pt loading amount resulted in deteriorated H₂-sensing performance. The optimal SnO₂ sensing film (0.2 wt% Pt-loaded SnO₂, 20 μm in thickness) showed an optimum H₂ response of ∼150.2 at 10,000 ppm and very short response time in a few seconds at a low optimal operating temperature of 200 °C. In addition, the response tended to increase linearly and the response times decreased drastically with increasing H₂ concentration. Moreover, the selectivity against carbon monoxide (CO) and acetylene (C₂H₂) gases was also found to be considerably improved with the small amount of Pt loading. The H₂ response dependence on Pt concentration can be explained based on the spillover mechanism, which is highly effective only when Pt catalyst is well-dispersed at the low Pt loading concentration of 0.2 wt%.     

Vapour-liquid equilibrium of ternary mixtures of the refrigerants R125, R143a and R134a

Apart from ternary mixtures of R32 with R125 and R134a, similar mixtures with R143a instead of R32 are discussed as alternatives to the widely used refrigerants R22 and R502. In the present work, the phase equilibrium of such ternary mixtures is described by simple cubic equations of state which are based only on experimental data for the pure substances and for a nearly equimolar mixture of every binary system.In addition to previous experimental investigations the critical properties and the saturation pressure were measured for pure R143a and for nearly equimolar mixtures of the binary systems and . The temperature ranged from −70°C up to the respective critical point. The validity of the resulting equations of state for ternary mixtures of R125, R143a and R134a is confirmed by comparison with experimental results of the vapour-liquid equilibrium for a mixture with about 17mol% of R125 and R143a, respectively, and about 66mol% of R134a.     

Saturated Liquid Densities for 33 Binary Refrigerant Mixtures Based on the ISM Equation of State

In this work, the ISM equation of state based on statistical-mechanical perturbation theory has been extended to liquid refrigerant mixtures by using correlations of Boushehri and Mason. Three temperature-dependent parameters are needed to use the equation of state: the second virial coefficient, B₂(T), an effective van der Waals covolume, b(T), and a scaling factor, α (T). The second virial coefficients are calculated from a correlation based on the heat of vaporization, ΔH_vap, and the liquid density at the normal boiling point, ρ_nb. α(T) and b(T) can also be calculated from second virial coefficients by a scaling rule. The theory has considerable predictive power, since it permits the construction of the PVT surface from the heat of vaporization and the liquid density at the normal boiling point. The equation of state was tested on 33 liquid mixtures from 12 refrigerants. The results indicate that the liquid densities can be predicted to at most 2.8% over a wide range of temperatures, 170–369 K.     

Viscosity of saturated liquid fluorocarbon refrigerants from 273 to 353 K

Viscosity measurements were carried out on saturated liquid fluorocarbon refrigerants using an improved capillary viscometer for 11 kinds of fluorocarbon refrigerants; CCl₃F (R11), CCl₂F₂ (R12), CHClF₂ (R22), CBrF₃ (R13B1), CH₃CHF₂ (R152a), CCl₂FCClF₂ (R113), CHCl₂CF₃ (R123), CHClFCClF₂ (R123a), CH₃CF₃ (R143a), CClF₂CCl₂F₂ (R114), and CH₂FCF₃ (R134a), in the temperature range from 273 to 353 K. An equation is given to represent the viscosity as a function of temperature.     

Isochoric Heat Capacity Measurements for 0.5 H2O+0.5 D2O Mixture in the Critical Region

The isochoric heat capacity C _V of an equimolar H₂O+D₂O mixture was measured in the temperature range from 391 to 655 K, at near-critical liquid and vapor densities between 274.05 and 385.36 kgm^–3. A high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter was used. The measurements were performed in the one- and two-phase regions including the coexistence curve. The uncertainty of the heat-capacity measurement is estimated to be ±2%. The liquid and vapor one- and two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from the experimental data for each measured isochore. The critical temperature and the critical density for the equimolar H₂O+D₂O mixture were obtained from isochoric heat capacity measurements using the method of quasi-static thermograms. The measurements were compared with a crossover equation of state for H₂O+D₂O mixtures. The near-critical isochoric heat capacity behavior for the 0.5 H₂O+0.5 D₂O mixture was studied using the principle of isomorphism of critical phenomena. The experimental isochoric heat capacity data for the 0.5 H₂O+0.5 D₂O mixture exhibit a weak singularity, like that of both pure components. The reliability of the experimental method was confirmed with measurements on pure light water, for which the isochoric heat capacity was measured on the critical isochore (321.96 kgm^–3) in both the one- and two-phase regions. The result for the phase-transition temperature (the critical temperature, T _{C, this work}=647.104±0.003 K) agreed, within experimental uncertainty, with the critical temperature (T _{C, IAPWS}=647.096 K) adopted by IAPWS.     

Double effects of atomic hydrogen anneal on the microstructure of hydrogenated amorphous silicon films

Hydrogenated amorphous silicon (a-Si:H) films have been deposited with pure silane and then annealed with atomic hydrogen at lower temperature (T_s=170 °C) in a novel, hot wire assisted microwave electron cyclotron resonant chemical vapor deposition system (HW-MWECR-CVD). The experimental results showed that the total hydrogen concentration (C_H) in the film decreased with H₂ flux increase in the atomic hydrogen anneal (AHA) step, but it does not obviously change, keeping at about 3% when H₂ flux increased to a higher value. This is due to double effects of AHA, the crystallization effect at lower substrate temperature and the rehydrogenation effect in low hydrogen concentration films. Furthermore, it was proposed that with increasing R(R=1/{F_hydrogen/(F_silane+F_hydrogen)}, in which F_silane is the silane gas flux in first film synthesis stage and F_hydrogen is the hydrogen gas flux during the annealing step, respectively.), polyhydrides such as SiH_x (x=2 or 3) turn into monohydrides SiH, which results in reducing the network defects, improving the film microstructure and decreasing the optical band gap from 1.644 to 1.557 eV.     

Modeling of Gas Solubility Data for HFCs–Lubricant Oil Binary Systems by Means of the SRK Equation of State

The Soave–Redlich–Kwong (SRK) equation of state (EOS) is used to describe vapor-liquid (VLE) and vapor-liquid-liquid (VLLE) equilibria of mixtures containing environmentally friendly refrigerants (hydrofluorocarbons, HFCs) and lubricant oils (polyalkylene glycols, PAGs and polyol esters, POEs) at high pressures. For refrigerants, pure component parameters are used as they were found in refrigerant properties computer program Version 6.0 of REFPROP. For the PAG and POE oils, they are either predicted by group contribution methods or obtained from thermodynamic data. Extension to mixtures is performed by using the conventional quadratic mixing rule with only one parameter for each binary pair. The binary parameters are regressed from VLE experimental data available in the literature and subsequently used for prediction of VLLE. All results of the calculations are discussed, and the necessary parameters for prediction of thermodynamic properties of these types of mixtures for the SRK EOS are presented. The computations were performed using phase equilibria software (PE2000).     

Thermal conductivity of the new refrigerants R134a,R152a,and R123 measured by the transient hot-wire method

Thermal-conductivity measurements are reported for the new refrigerants R134a, R152a und R123. Transient hot-wire experiments were performed which cover both the liquid and vapor states at temperatures and pressures ranging from?=?20°C to 90°C and fromp=0.1 bar to 60 bar respectively. The results are correlated with density and temperature. In addition temperature dependent correlations are presented for (i) saturated liquid, (ii) saturated vapor, (iii) ideal gas (which equals approximately vapor state at ambient pressure). Finally the results are compared with data from the literature and also with the thermal conductivities of R12 and R11.     

Solubility of Carbon Dioxide in Pentaerythritol Tetrabutyrate (PEC4) and Comparison with Other Linear Chained Pentaerythritol Tetraalkyl Esters

Carbon dioxide (CO₂) is one of the most promising natural refrigerants that can be employed as an alternative to hydrofluorocarbons (HFC), due to its low global warming potential (GWP). Nevertheless, CO₂ presents several technical problems when employed as a working fluid in refrigeration systems. In particular, the selection of the most suitable lubricant for each application is far from being resolved. The thermodynamic behavior of a CO₂+lubricant system must be well-known for a correct oil selection. This work is part of a research project to study the solubility of CO₂ in commercial oils and their precursors. Here, solubility measurements of CO₂ in pure pentaerythritol tetrabutyrate (PEC4) between 243 K and 343 K are presented and compared with miscibility data of CO₂ in pentaerythritol tetrahexanoate (PEC6) and pentaerythritol tetraoctanoate (PEC8). The experimental data were correlated with a thermodynamic model based on a cubic equation of state with Huron–Vidal mixing rules and the UNIQUAC equation for the excess Gibbs energy at infinite pressure.     

A single crystal X-ray diffraction study of R[UO2(C2H5COO)3] (R = K or NH4)

A single crystal X-ray diffraction study of R[UO₂(C₂H₅COO)₃] [R = K (I) or NH₄ (II)] was performed. Both compounds crystallize in the cubic system, unit cell parameters for I: a = 11.4329(3) Å (at 100 K), space group P2₁3, Z = 4; for II: a = 11.60503(7) Å (at 123 K), space group P2₁3, Z = 4. The structures of crystals of I and II contain complex anions [UO₂(C₂H₅COO)₃]^? belonging to crystal-chemical group AB ₃ ⁰¹ of uranyl complexes (A = UO ₂ ²⁺ , B⁰¹ = C₂H₅COO^?). These anions are linked in a framework by electrostatic interactions with outer-sphere cations R and by hydrogen bonds (in case of II). The effect of the kind of carboxylate ion on structural features of R[UO₂L₃] (L is propionate or acetate ion) is discussed.