三元混合工质R407C热力参数模型分析

R407C是替代R22的一种极具前景的新工质，采用Peng—Robinson型方程对新工质R407C的热力学性质进行了全面的计算，并根据实验数据拟合出新工质的迁移特性计算公式。根据计算结果给出了新工质R407C的压焓图和温-熵图。计算关联式具有较高的精度，热力学参数计算误差小于l％，迁移特性参数误差小于4％。本文的研究结果为新工质R407C的系统分析和计算提供了准确、可靠的热力学性质和热物理性质分析计算结果。     

R407C组分质量误差对压缩机性能测试——流量计法的影响

对于混合工质R407C,在生产、储存、运输、分馏时其组分HFC-32／HFC-125／HFC-134a浓度难以严格达到23％／25％／52％。针对上述问题,本文讨论了R407C各组分浓度误差小于5％时对压缩机性能实验——流量计法的影响,从而提高测试结果的精度。     

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。     

流程布置对R407C冷凝器性能的影响

本文基于传热单元法，建立了冷凝器的分布参数模型。以R407C为工质，运用该模型详细分析了四种不同流程布置两排管冷凝器的换热和流动特性，并与以R22为工质的冷凝器进行了性能比较。结果表明：采用R407C为工质时，四种流程布置中，无论是随着管内冷媒流量的变化，还是随着冷凝器迎风面风速的变化，逆流布置换热效果都是最好，换热量比顺流高约5％-40％，压降比顺流高约3％-10％，其次是错流布置，顺流布置最差。在与以R22为工质的冷凝器性能比较中，无论是随着管内冷媒流量的变化，还是随着迎风面风速的变化，R407C冷凝器换热量都比R22冷凝器高约3％-5％，压降低约5％-10％，是其理想的替代产品。     

汽车空调制冷系统中应用R407C的分析

本文对混合工质R407C与R12的物理和热力性质进行了比较分析，并针对汽车空调制冷系统的特点，对两种工质在变工况下进行了制冷系统的理论循环分析，阐明了在汽车空调制冷系统中使用R407C的可行性。     

《制冷空调新工质-热物理性质的计算方法与实用图表》出版

由上海交通大学丁国良教授、张春路副教授等编著的《制冷空调新工质-热物理性质的计算方法与实用图表》已由上海交通大学出版社出版。本书所选工质包含了原CFC工质的主要替代物,包括R134a、R152a等HFC类纯工质,R600a、R290、CO2等自然工质,以及R407C、R410A等混合工质。本书内容包括两大部分:(1)     

汽车空调系统采用工质R407C的性能结构探讨

提出了汽车空调制冷剂对环境的污染问题,并对此具体论述了制冷系统采用混合工质R407C替代氟利昂-22的必要性和可行性,从而根据新工质特性,研究探讨出满足公交车空调冷量要求的空调系统.     

混合工质R407C温度滑移的验证

本文通过实验验证了非沸混合工质R407C的温度滑移的特性,并由此提出了R407C使用在家用空调器中系统设计优化的基本思想。     

R407C组分质量误差对压缩机性能测试——流量计法的影响

对于混合工质R407C,在生产过程中其组分HFC32/HFC125/HFC1348浓度难以严格达到23%/25%/52%,并且由于试验装置的泄露,其组分的浓度也会有所偏差.针对上述问题,讨论了R407C各组分浓度误差小于5%时对压缩机性能实验-流量计法的影响,从而提高测试结果的精度.     

非共沸工质在毛细管中的流动特性研究

本文对非共沸工质R407C在毛细管中的流动特性进行了系统的研究.通过能量、动量、质量方程,分别就过冷区和两相区作了理论求解,并将计算结果全部绘制成了曲线.     

Flexural properties and dynamic mechanical properties of glass fibre-epoxy composites

The viscoelastic behaviour of glass fibre (GF)-epoxy composites was studied by flexural tests and dynamic mechanical measurements. In relation, the influence of surface treatment of GF on viscoelastic behaviour was also examined. Using the results of flexural tests under a variety of constant temperature and strain rate, master curves of flexural strength () and flexural strain () were obtained for matrix epoxy and GF composites. The magnitudes of the master curves were different between matrix epoxy and GF composites. The fracture mode was influenced by temperature, strain rate, and G F surface treatment. The magnitude of storage modulus and effectiveness of adhesion at the GF-matrix interface were also influenced by GF surface treatment. Relationship between the results of flexural strain and loss modulus were considered for GF composites.     

Effective thermal properties of viscoelastic composites having field-dependent constituent properties

This study introduces a micromechanical model for predicting effective thermal properties (linear coefficient of thermal expansion and thermal conductivity) of viscoelastic composites having solid spherical particle reinforcements. A representative volume element (RVE) of the composites is modeled by a single particle embedded in the cubic matrix. Periodic boundary conditions are imposed to the RVE. The micromechanical model consists of four particle and matrix subcells. Micromechanical relations are formulated in terms of incremental average field quantities, i.e., stress, strain, heat flux and temperature gradient, in the subcells. Perfect bonds are assumed along the subcell’s interfaces. Stress and temperature-dependent viscoelastic constitutive models are used for the isotropic constituents in the micromechanical model. Thermal properties of the particle and matrix constituents are temperature dependent. The effective coefficient of thermal expansion is derived by satisfying displacement and traction continuity at the interfaces during thermo-viscoelastic deformations. This formulation leads to an effective time–temperature–stress-dependent coefficient of thermal expansion. The effective thermal conductivity is formulated by imposing heat flux and temperature continuity at the subcells’ interfaces. The effective thermal properties obtained from the micromechanical model are compared with analytical solutions and experimental data available in the literature. Finally, parametric studies are also performed to investigate the effects of nonlinear thermal and mechanical properties of each constituent on the overall thermal properties of the composite.     

Predicting fracture and fatigue crack growth properties using tensile properties

The safe-life assessment of components requires information such as the plane stress (K_c), plane strain (K_Ic), part-through fracture toughness (K_Ie), and the fatigue crack growth rate properties. A proposed parametric/theoretical approach, based on an extended Griffith theory is used to derive fracture toughness properties and generate fatigue crack growth rate data for a range of alloys. The simplicity of the concept is based on the use of basic, and in most cases available, uniaxial stress-strain material properties data to derive material fracture toughness values. However since the methodology is in part based on an empirical relationship a wide ranging validation with actual data is required. This paper uses steel, aluminum and titanium based alloys from a pedigree database to quantify material properties sensitivity to the predictions for K_Ic and K_c and the subsequent estimation of ΔK_th threshold and the Paris constants, C and n values. A sensitivity analysis using experimental scatter bounds show the range of da/dN predictions can be achieved. It is found K_Ic/ΔK_th ratios designated as α has a range of 5-25 irrespective of tensile ductility, ε_f, and is insensitive to it. The value of ΔK_th for all the alloys considered was found to be proportional to the final elongation, ε_f, and an empirical relationship describing ΔK_th as a function of ε_f was established. Furthermore it is suggested that, with the knowledge of appropriate tensile properties and the estimated range of K_Ic/ΔK_th ratios for the different alloys applying this method could be an appropriate tool that can be used to conservatively predict fracture and fatigue in similar alloy categories. Thus helping to reduce costs and optimize the number of experimental tests needed for alloy characterizations.     

Mechanical properties of

The ultimate values for compressive strength, Young's modulus, and toughness of cylindrical specimens of unitary aspect ratios and uniform grain-size distributions were extrapolated for hydroxyapatite (HAP) to 70 MPa, 9.2 GPa, and 0.36 J cm-3, and for tricalcium phosphate (TCP), to 315 MPa, 21 GPa, and 2.34 J cm-3. For total volume porosities of 50%, the corresponding values were determined: for HAP, 9.3 MPa, 1.2 GPa, 0.042 J cm-3, for TCP, 13 MPa, 1.6 GP, 0.077 J cm-3. Porosities of HAP specimens ranged from 3%–50%; TCP from 10%–70%. Two pore-size distributions were employed. Exponential dependencies of the mechanical properties were found upon porosity (p0.0001). No differences in measured mechanical properties, as determined in compression, could be attributed to pore size. The superiority of TCP increases with density and suggests that a larger or more selective pore-size distribution could be effectively employed in TCP biological implants. This work also suggests the dominant role of secondary calcium phosphates in increasing compressive strengths. © 1999 Kluwer Academic Publishers     

Synthesis and properties

Poly(D,L lactic acid) was prepared by bulk polymerization of D,L lactide, both under atmospheric pressure and in vacuum. The obtained polymeric products were characterized in terms of molecular weight, Mw, melting point, calorimetric response and swelling behaviour. All products were amorphous. Their molecular weights were determined by viscosimetry and ranged from 2×103 to 9×104. Similarly, the melting points ranged from 90 to 210°C. Swelling experiments, with specimens immersed in buffer solutions, showed that hydrolytic degradation started in a few days for the low Mw material, whereas for the higher molecular weight products it took much longer and probably followed a two-stage mechanism. This study suggests that the high molecular weight material could be an interesting carrier for the preparation of controlled release products, in cases where prolonged delivery is necessary. © 1999 Kluwer Academic Publishers     

Free-volume properties of epoxy composites and its relation to macrostructure properties

Some characteristics of epoxy composites are discussed based on the results of positron annihilation lifetime spectroscopy (PALS), electrical and mechanical measurements. The effect of different types and wt% of fillers such as aluminium oxide (Al₂O₃), titanium oxide (TiO₂) and silicon carbide (SiC) on the epoxy structure and hence free volume, physical, electrical, and mechanical properties is presented. The results showed that the electrical properties are improved at high wt% of filler, while mechanical properties are improved at low wt% of filler. Furthermore, a similar trend is observed for all fillers but with a systematic shift to high influence when Sic added to cured epoxy. On the other hand, adding SiC as a filler on epoxy improved the resistance to water absorption.The role of PALS as a sensitive probe for changes in microstructure of epoxy composites is confirmed during the correlation between the free-volume parameters and the other measurements.     

Water-based epoxy materials: properties of curing agents and film-forming properties

The structural changes of polyamino-amide and polyamino-imidazoline, used as curing agents for water-based epoxy materials (WBEM), have been examined under various conditions of storage. Additionally, epoxy emulsion stabilization and film-forming in WBEM needed special research to set the limits of material utility. Infrared analysis, potentiometric titration and viscometric data obtained for some curing agents for WBEM, commercial polyamino-amide and the derived polyamino-imidazoline compounds, prove that during prolonged storage (from 1 to 140 days) these products can hydrolyse to yield free amines and carboxyl groups. The reaction mechanisms are suggested. The results include considerations for further development of epoxy compositions and a study of film-forming properties.