热力膨胀阀流动噪声试验研究

为了获得热力膨胀阀的瞬态噪声特性,采用试验方法对不同温包充注、不同阀内结构的膨胀阀的啸叫噪声进行研究。获得了系统开机过程中热力膨胀阀啸叫噪声与温包充注、阀内结构的关系。结果表明:采用交叉充注,低蒸干压力充注,在阀内安装碟形弹簧有利于降低膨胀阀啸叫噪声。     

汽车空调热力膨胀阀容量测试系统的研制

热力膨胀阀在不同工况下的流量特性是影响制冷系统性能的重要因素,因此需要对热力膨胀阀进行制冷剂实流检测。本文研制了制冷量范围为1.7~10 k W的热力膨胀阀容量测试台。该测试台以"膨胀阀进出口的压力值"为测试条件,避免了阀前高压部分设备流动阻力的差异对测量结果的影响。系统的流量测量不确定度为0.5%,控温精度为±0.5℃。在标准工况下取额定容量5.5 k W的H型热力膨胀阀的性能进行了测试,根据温度-开度、开度-流量、温度-流量关系特性分析得到在热力膨胀阀工作区域内,其温度与流量基本成线性比例关系。根据热力膨胀阀增益和滞环的定量分析,判别热力膨胀阀的性能优劣。     

带过热平衡器的空气源热泵热水器设计与性能分析

为了解决空气源热泵热水器的热力膨胀阀在低环境温度下出现的不稳定振荡问题,提出了过热平衡器的理论模型,设计了小型的过热平衡器装置,并进行了实验验证。实验分析结果表明:当空气源热泵热水器的热力膨胀阀在低温环境温度下出现振荡时,接入过热平衡器后其振荡周期明显延长,从59s增加到148s,振荡被抑制,系统COP有所改善。同时,针对过热平衡器的压降计算表明,优化填充材料和丝网的结构,使其压降进一步降低,系统的综合能效和稳定性可望得到进一步提升。     

带旁通节流孔的热力膨胀阀在热泵热水器中的应用分析

针对热泵热水器分别采用带旁通节流孔的热力膨胀阀和普通热力膨胀阀,从系统运行稳定性及除霜性能方面进行对比试验分析,为热泵机组的热力膨胀阀选型提供参考。     

热力膨胀阀对高速列车空调系统性能的影响分析

为了研究热力膨胀阀对高速列车空调系统性能的影响,对有故障的高速列车空调系统进行了膨胀阀静态过热度调节试验,分析了不同静态过热度下空调系统性能。分析和试验表明,增大膨胀阀静态过热度可以有效改善膨胀阀供液不足以及蒸发盘管分液不均的现象,从而提高蒸发压力和蒸发温度,解决空调不制冷的问题。     

有内热源房间空调器制冷系统热力膨胀阀的匹配研究

为了保持热源的降温,应用于有内热源房间的空调器一年四季都需要运行.由于热力膨胀阀特性的限制,空调器在低环境温度下,蒸发器供液不足,使得整机制冷量和COP增幅不高.为了改善整机性能,在焓差实验室对空调器进行了性能测试,得到了-5～35℃环境温度下蒸发压力、冷凝压力、制冷量和COP等热工参数变化.结合热力膨胀阀的型号和特性,研究了热力膨胀阀在变工况条件下与系统其它部件的匹配关系,旨在扩大膨胀阀的工作区间,提高低环境温度下房间空调器的效率.研究表明,兼顾较大范围环境温度变化匹配热力膨胀阀,应扩大50%～100%开度工作区间,缩小100%～120%开度工作区间,降低制冷系统设备、部件和管道阻力,避免两个震荡区进入使用范围.     

热力膨胀阀潜在故障的消除

现有用于制冷系统自动调节供给蒸发器制冷剂流量的热力膨胀阀,普遍存在感温管感受温度的准确性差,调节过程中流量波动大,有时会产生卡跳或啸叫声,膜盒及感温部分一旦泄漏制冷系统将无法工作等隐患。笔者就上述隐患产生的原因进行分析,并从结构上提供技术改进途径,为热力膨胀阀进入家用空调和热泵热水器领域提供保障。     

北美屋顶机设计运行工况下热力膨胀阀选型探讨

热力膨胀阀只能在一个较窄的工况和负荷范围下实现调节过热度的功能。现有一批在北美销售的屋顶机,设计运行工况范围较宽,在室外温度为-17．7℃-51．7℃下,机组都要求能运行。仿真结果表明,对这种运行工况的屋顶机组,用传统方法选出的热力膨胀阀未能在较多工况点充分发挥其控制过热度的作用。在考虑热力膨胀阀的振荡现象的基础上,对选型方法进行改进,并通过实验验证,证明在基于最小负荷比大于30％方法选出的热力膨胀阀能够在较多工况点控制空调机组的过热度,且避免了振荡现象的发生。     

双向MEMS膨胀阀及其在电动大巴热泵系统中的应用

为克服步进电机式的电子膨胀阀在汽车空调上易失步问题,以及热力膨胀阀热惰性不适应变频压缩机的缺点,同时为了满足新能源汽车热泵空调的要求,本文提出一种基于热驱动的双向MEMS膨胀阀,MEMS膨胀阀非步进电机式的驱动方式确保其不会受到汽车振动的影响,同时其线性快速响应速度能够解决热力膨胀阀热惰性的缺点。采用空调的测试标准,利用一台电动大巴热泵系统进行热力膨胀阀和MEMS膨胀阀的对比试验,结果显示,采用MEMS膨胀阀的电动大巴热泵系统能效提升14.7%,同时完成装车试验中行驶200 km无故障的要求。     

热泵除霜特性的实验研究

本文对用热力膨胀阀作为除霜时的节流机构的热泵系统进行了实验研究,包括压力、温度、过热度、制冷量、功率等,最后指出热力膨胀阀更适宜除霜,并与毛细管作了对比,并指出了减小除霜时间的措施。     

Dynamic simulation of a thermostatically controlled counter-flow evaporatorSimulation dynamique d'un évaporateur à détendeur thermostatique avec débit à contre-courant

A numerical model is developed to simulate the transient behaviour of a counter-flow water cooling evaporator controlled by a thermostatic expansion valve (TEV) in a vapour compression refrigeration system. The liquid–vapour slip in the two-phase region of the evaporator is accounted for by a void fraction model (VFM). The thermal capacitance of the TEV is included in the analysis. For the purpose of comparison with predictions of the model, experimental data available are filtered to obtain the best estimate of the mean variation of the liquid–vapour transition plane. The predictions are in good trend-wise agreement with the filtered experimental data. The results of the transient simulations demonstrate the dependence of the stability of the evaporator–TEV system on the characteristics of the TEV, the thermal capacitance of the bulb, thermal conductance between the bulb and wall and on the nature of the input disturbance.     

An experimental and numerical study of hunting in thermostatic-expansion-valve-controlled evaporators

The dynamic behaviour of a thermostatic-expansion–valve (TEV)-controlled dry-evaporator is studied experimentally and numerically. Although the linear model of the TEV together with the distributed model of the evaporator is able to predict the stable dynamic response of the system adequately, it fails to reproduce the hunting behaviour that is observed under certain operating conditions. A scrutiny of the experimental data reveals the possible existence of hysteresis in the system. The distributed model including the experimentally determined input-output characteristics of the TEV is able to reproduce the main features of the hunting oscillations well. The amplitude and frequency of these oscillations depend on the static superheat setting, the heat load of the evaporator and the time constant of the TEV bulb.     

Effects of gap filler and brazing temperature on fracture and fatigue of wide-gap brazed joints

The influence of gap filler content on the fracture, fatigue crack initiation and propagation of AISI 316 stainless steel wide-gap brazed with nickel-based filler metal has been investigated. The brazed joints were found to consist of eutectic, intermetallic compound and solid solution. The volume of solid solution was observed to depend on the gap filler content and brazing temperature. Tensile tests with extra small strain gauge bonded at the centre of the joints showed that the strength and elongation of the brazed joints increased with brazing temperature, and the addition of gap filler was able to improve the load-carrying capacity of the brazed joints only when the brazing temperature was high enough. Fatigue crack initiation and growth under displacement amplitude control were also carried out. Crack closure in the brazed joints was determined by means of back face strain on the compact tension specimen used. The introduction of gap filler was able to increase the fatigue and fracture resistance of the brazed joints when a suitable brazing temperature was used. Crack deflection, branching and uncracked ligament bridging behind the crack tip were observable along the crack paths. Experimental results showed that gap filler was able to enhance the crack closure caused by roughness and ligament bridging.     

Filler dispersion evolution of acrylonitrile–butadiene rubber/graphite nanocomposites during processing

In this work, acrylonitrile–butadiene rubber/expanded graphite compounds with initial fine dispersion of nanosize graphite were prepared by latex compounding method, and then the dispersion evolution of the graphite during subsequent mixing and vulcanization was carefully investigated by using rubber process analysis, X-ray diffraction and transmission electron microscopy. The results showed that a significant filler network was already formed in the initial compounds because of the nanoscale dispersion and the high width/thickness ratio of graphite even at a content of less than 5 phr. During shearing, the graphite dispersion evolution is strongly related to the initial filler network. The filler network as well as the dispersion could also be obviously altered by changing the curing pressure and temperature during vulcanization, suggesting that the initial fine dispersion of graphite in the rubber/graphite nanocomposites could be maintained by reducing shear and by curing at a higher temperature and at a lower pressure.     

Failure behavior of rubber O-ring under cyclic exposure to high-pressure hydrogen gas

This paper presents the effects of hydrogen pressure, ambient temperature and pressure cycle pattern on fracture behavior of O-rings moulded from a peroxide-crosslinked EPDM rubber with white reinforcing filler under cyclic exposure to high-pressure hydrogen gas. By using a developed durability tester which enables the O-rings to expose cyclically high-pressure hydrogen gas, pressure cycle tests were performed at hydrogen pressures ranging from 10 to 70 MPa and ambient temperatures ranging from 30 to 100 °C under two pressure cycle patterns (test frequencies). The cyclic hydrogen exposure caused cracks in the O-rings, and their crack damage became more serious with an increase in the hydrogen pressure and the ambient temperature. The serious crack damage under high temperature is believed to be due to degradation of mechanical properties with increasing ambient temperature. At a hydrogen pressure of 10 MPa, cracks (blisters) caused by bubbles formed from supersaturated hydrogen molecules after decompression were observed. At a hydrogen pressure of 35 MPa or more, a large volume increase of the O-rings was observed by swelling; then, its volume increase induced extrusion fracture of the O-rings in addition to blister fracture. The crack damage also became more serious with a decrease in test frequency. The effect of the test frequency on the crack damage of the O-rings is presumed to be attributed to time-dependent crack growth behavior of the EPDM rubber.     

Adsorption of avermectin on porous hollow silica nanoparticles by supercritical technology

Porous hollow silica nanoparticles with O.D. of approximately 100 nm and a wall thickness of approximately 10 nm were prepared by using inorganic CaCO3 templates. The produced PHSN were employed as a novel carrier to study the adsorption of avermectin in supercritical carbon dioxide by applying different adsorption pressure, adsorption temperature, adsorption time and volume of cosolvent. The results indicated that while increasing adsorption pressure and time always showed a positive effect on the avermectin adsorption until adsorption saturation is reached, both the adsorption temperature and volume of cosolvent require an optimal value for achieving the maximum adsorption. It was found that the optimal adsorption could be obtained at an adsorption pressure of 15 MPa and an adsorption temperature of 313 K for 90 minutes with 5 ml cosolvent. In addition, the desorption behavior of avermectin from the avermectin-loaded PHSN samples showed a sustained style: approximately 60% of avermectin was released in the first 20 minutes, while the other 40% followed a typical sustained desorption pattern and was dissolved out slowly for a time period of 3000 minutes, which is different from the quick and complete desorption from solid SiO2 carriers.     

Analysis of additional leakage resulting from the feeding motion of a vacuum-compatible air bearing stage

A rise in pressure is generated when a vacuum-compatible air bearing stage moves in a vacuum condition. This study analyzed this pressure rise phenomenon theoretically and verified it experimentally. Results indicate that the pressure rise was caused by additional leakage resulting from stage velocity, along with adsorption and outgassing of gas molecules from the guide rail surface. Tilting of the stage had a negligible effect because the tilting time was very short. Additional leakage caused by stage velocity was inevitable if the stage incorporated mechanical movements, but rises in pressure caused by adsorption and outgassing could be suppressed by coating the guide rail surface with titanium nitride, to which gas molecules are less likely to adhere. The results also indicate that the pressure rise ratio increased when the air bearing stage operated under high-vacuum conditions.     

废旧线路板粉料/玻璃纤维增强复合材料研制

以废旧线路板回收处理过程中得到的塑料粉料与玻璃纤维作为增强材料,采用模压成型的方法制备成不饱和聚酯复合材料。研究了模压工艺参数以及废弃物粉末填料配比等对复合材料力学性能的影响规律,并初步展望了废弃物复合材料的应用。结果表明,随着模压温度、压强、模压时间和填料含量的增加,复合材料的弯曲强度先升高后降低;在优化的模压工艺参数条件下,用废弃粉体与短切玻璃纤维作为组合增强体,制得的不饱和聚酯复合材料的力学性能远大于仅用废弃粉体作为增强体的力学性能,其弯曲强度和冲击强度可达150MPa、18kJ/m2。     

Correlating filler transparency with inorganic/polymer composite transparency

The transparency of metal oxide containing polymeric composites was correlated to its filler transparency using a new method based on light microscopy analysis. Filler particles were pressed into filler tablets from which fragments were submerged in different refractive index liquids. Transparencies of different particulate materials with diameters from 0.007 to 1.5 μm were investigated. The transparencies depended on light absorption of the solid, filler particle size and refractive index mismatch of filler and liquid. A correlation between filler transparency and the transparency of filler containing polymers (composites) was established. The method allows to predict the composite transparency for any filler particle size and any filler particle/polymer refractive index mismatch. Manufacturing-caused, batch-wise quality differences in transparency of the same filler material showed similar transparency trends for filler/liquid and filler/polymer transparencies when no quantitative difference was found by nitrogen adsorption, XRD, DRUV–Vis, DRIFTS and SEM analysis.     

A reactive poly(ethylene glycol) layer to achieve specific surface plasmon resonance sensing with a high S/N ratio: the substantial role of a short underbrushed PEG layer in minimizing nonspecific adsorption

A reactive poly(ethylene glycol) (PEG)-brushed layer was constructed on a surface plasmon resonance (SPR) sensor chip using a heterobifunctional PEG possessing an acetal group at one end and a mercapto group at the other end (alpha-acetal-omega-mercapto-PEG). The density of the PEG brushed layer substantially increased with repetitive adsorption/rinse cycles of the PEG on the sensor chip, allowing dramatic reduction of nonspecific protein adsorption. Notably, formation of a short, filler layer of PEG (2 kDa) in the preconstructed longer PEG brushed layer (5 kDa) achieved almost complete prevention of nonspecific protein adsorption. The acetal group located at the distal end of the tethered PEG was converted to an aldehyde group by the acid treatment, followed by the installation of biocytin hydrazide through Schiff base formation. SPR sensing of streptavidin was done with a very high S/N ratio even in a proteinous medium using the biotinylated PEG (5 kDa) tethered chip with an inert filler layer of short PEG (2 kDa). Furthermore, the specific affinity of streptavidin for the biotinylated PEG was highly influenced by the length of the filler PEG and was significantly reduced when the length of the filler PEG was longer than that of the biotinylated PEG. This result clearly revealed the substantial importance of the steric factor on biospecific interaction at the distal end of tethered PEG on the sensor surface.