Influence of melt superheat on breakup process of close-coupled gas atomization

In close-coupled gas atomization（CCGA）, the influences of melt superheat on breakup process are fundamental to obtain desired or finer powder. Based on a series of Cu atomization experiment under different superheating conditions, the influences of melt superheat on breakup process were studied. Experimental results indicate that as the melt superheat is increased to 150, 200, 250 and 300 K, the mean particle size （D50） decreases consequently to 34.9, 32.3, 30.9 and 19.7 μm. Theoretical analysis reveals that the primary breakup and secondary breakup processes are close coupled, and the melt superheat radically influences the melt properties, and plays a crucial role on governing the filming process of primary breakup and the atomization modes of secondary breakup. There exists a strong nonlinear decrease of contact angle of melt to nozzle orifice wall when the superheat is increased fi＇om 250 K to 300 K, leading to a marked fall of the film thickness formed in primary breakup, and D50 of copper powders is therefore sharply reduced. However, the log-normal distribution feature of particle size has not been substantially improved.     

Effect of electrolysis superheat degree on anticorrosion performance of 5 Cu/（10NiO-NiFe2O4） cermet inert anode

5Cu/(10NiO-NiFe2O4) cermet inert anodes were prepared by cold-pressing and sintering process, and the effect of superheat degree of melting K3AlF6-Na3AlF6-AlF3 on their anticorrosion performance was studied under electrolysis conditions. The results show that, the fluctuation of cell becomes small with increasing of superheat degree, which is helpful to inhibit the formation of cathodic encrustation; the concentration of impurities from inert anode in bath goes up to certain degree, but it is far smaller than those in traditional high-temperature bath. Increasing the superheat degree of melting K3AlF6-Na3AlF6-AlF3 has unconspicuous effect on the contents of impurities in cathodic aluminum. The total mass fractions of Fe, Ni and Cu in aluminum are 15.38% and 15.09% respectively under superheat degree of 95 and 195 ℃. From micro-topography of anode used view, increasing the superheat degree can aggravate corrosion of metal Cu in inert anode, and has negative influence on electrical conductivity of electrode to some extent.     

过热度对电脉冲孕育处理Al-5%CU合金凝固组织的影响

研究了不同的过热度对电脉冲孕育处理Al-5％Cu合金凝同组织的影响。实验结果表明：不同的过热度下对Al-5％Cu合金进行电脉冲处理，合金凝同组织均得到一定程度的细化，但过热度不同时细化效果不同。一定温度范围内．熔体温度为740℃时，电脉冲孕育处理细化的效果最好，并分析了过热度影响电脉冲孕育处理Al-5％Cu合金凝同组织的机制。     

熔体过热处理对定向凝固界面形态及稳定性的影响

介绍了固液界面形态及稳定性的判据,即成分过冷理论和绝对稳定理论;简述了国内熔体过热处理的研究;详细阐述了熔体过热处理影响定向凝固界面形态及稳定性的现象及理论研究.并对今后熔体过热处理在定向凝固技术中的研究方向作了展望.     

低过热度浇注ZL101铝合金半固态组织研究

采用低过热度浇注技术制备半固态ZL101铝合金,研究了冷却强度、保温时间、浇注温度对铸造显微组织的影响。研究结果表明,在液相线附近,冷却强度大,晶粒细小;随着保温时间的延长,晶粒变大,形状变得圆整,结晶组织均匀;浇注温度越高,晶粒越粗大;铸锭中心部位组织比边缘部位组织粗大,且均匀,球化明显。低过热度浇注可以获得理想的ZL101铝合金半固态浆料。半固态坯料重熔加热温度为585℃,保温30min,α-Al相逐渐变成球状,此时,晶粒平均等级圆直径为42.6μm,晶粒平均圆度为2.13。     

大容器水沸腾换热特性测试系统开发

沸腾换热是传热学中的重要内容,为了更好地研究大容器水的沸腾换热现象,开发了大容器水沸腾换热特性测试系统。阐述了大容器沸腾换热的传热学原理,并在此基础上完成了测试系统的研制,在.NET开发平台下运用面向对象的设计方法开发了相应的测控软件,对测试结果进行了分析。     

Casting structure of pure aluminum by electric pulse modification at different superheated temperatures

Electric pulse modification （EPM） is a novel technique that reduces grain size by altering the structure of a melt. It was investigated that the response of the casting structure of high pure aluminum to EPM in different superheated melts. The results indicate that the grain refining effect of a given pulse electric field holds an optimal temperature range, moreover, a lower or higher superheated temperature will both disadvantage the improvements of casting structure. It essentially lies in the cooperative action between the distorted absorption of clusters and the activated capability of atoms in the aluminum melt.     

空调性能最佳状态点的匹配研究

为了匹配空调性能的最佳状态点,本文选用1台制冷量为5.15 k W的空调机组,实验研究了空调系统的充注量、过冷度和蒸发器出口过热度对系统制冷量及能效的影响,并提出了SH-Q、SC-EER、SC-Q、SH-EER理论匹配曲线,通过曲线匹配出空调系统的最佳状态点。实现最佳状态点匹配的途径可分为两部分:1)首次充注制冷剂充注量,根据匹配曲线找到系统最适宜的蒸发过热度和冷凝过冷度; 2)根据蒸发过热度及冷凝过冷度,调整充注量和节流强度,匹配出空调系统制冷能效的最佳状态点。实验研究了蒸发过热度为0～18℃、过冷度为0～9℃时空调性能的变化规律,根据匹配曲线得到系统匹配的最佳状态点,即最适宜的过热度、过冷度分别为1.3℃、6℃,对应的制冷能效为2.94,与实验区间最小值2.64相比增加了11.4%。     

控制钢液过热度提高连铸坯质量与产量

连铸浇钢控制合理的过热度,可以获得低倍质量好,等轴晶粒高的连铸坯,提高连铸产量,降低拉漏率。     

Homogeneous non-equilibrium two-phase choked flow modeling

The estimation of the release conditions is critical input to subsequent risk assessment accident analysis. To this respect a new homogeneous non-equilibrium two-phase model is proposed to simulate the depressurization from stagnation conditions leading to the bubbly flow regime. The proposed model, being intermediate between HEM (homogeneous equilibrium) and HFM (homogeneous frozen) models, presents no discontinuity in the liquid phase depressurization path gradient and therefore no discontinuity in sound speed. The proposed model is successfully validated against the NASA hydrogen critical flow experiments and compared against predictions from both HEM and HFM, using hydrogen physical properties from NIST. An increase of the pressure difference between stagnation and the intersection of isentropic with saturation line leads to increase of the choked mass flux, decrease of the throat to stagnation pressure ratio, decrease of the liquid superheat and decrease of the vapor quality. The proposed model was found to overestimate the experimental throat mass fluxes by no more than 10% and underestimate the experimental throat to stagnation pressure ratios by no more than 50%, while predicted liquid superheat values range from 3.8 to 11% of the saturation temperature. Deviations between models were found to increase for low values of the pressure difference parameter, where non-equilibrium effects become more important. Under these conditions the throat mass flux is underestimated by maximum 20% by HEM and overestimated up to 32% by HFM, while the throat to stagnation pressure ratio is overestimated by up to 72% and underestimated by 80% respectively.