普通电渣炉的全密闭气氛改造及其对典型钢种的影响

随着电渣钢品质的不断提升,普通电渣炉亟须进行全密闭气氛保护的升级改造,从而解决电渣重熔过程元素烧损、增氧、增氢、氢气孔等问题。采用新型的电渣炉气氛改造技术,分别用5 t和2 t电渣炉对GCr15SiMn轴承钢和GH2132高温合金进行传统气氛保护电渣炉和新型电渣炉的对比试验。冶炼过程中实现了结晶器内氧分压低至1×10^-6。试验数据显示,传统气氛保护电渣炉冶炼下,GH2132中Ti收得率低,仅为88%;GCr15SiMn轴承钢电渣重熔过程中增w[O]量大,可达5×10^-6。而在新型气氛保护改造中,GH2132中的Ti收得率高达96%;重熔过程轴承钢增w[O]控制在3×10^-6以内,电渣锭中w[O]稳定控制在10×10^-6以内,其电渣锭效果媲美气保电渣炉。以上炉内氧分压和电渣锭检测结果表明,电渣炉气氛改造后,可有效解决传统气氛保护改造技术下,往复的热浪涌出和负压吸气导致的结晶器内氩气保护不稳定,从而造成电极表面氧化,氧化皮掉入渣中引起的熔渣氧势升高和电渣锭增氧的问题;尤其对于GH2132高Ti低Al型高温合金,普通电渣炉加入脱氧剂Al条件下,无法避免Ti的烧损,只能导致电渣锭增Al。     

An experimental investigation of sootshell formation in microgravity droplet combustion

Spherically symmetric droplet combustion experiments were performed at the NASA Glenn Research Center (GRC) 2.2 second drop tower in Cleveland, OH in an effort to better understand the mechanism leading to sootshell formation. Rapid insertion of a blunt plunger was used to remove the symmetric sootshell that formed during the period of quasi-steady burning. This allowed for the observation of sootshell re-formation. Soot particles were formed near the flame front and migrated towards the droplet to ultimately reside at the sootshell location. These experiments helped to bring about a better understanding of soot transport in microgravity droplet combustion.     

化肥塑料编织袋灼烧残渣率的测定方法

介绍了一种化肥塑料编织袋灼烧残渣率的测定方法。样品通过灰化、灼烧得到残渣,最后计算出残渣率,以此作为衡量化肥塑料编织袋质量指标之一。     

Turbulent burning rates of methane and methane-hydrogen mixtures

Methane and methane-hydrogen (10%, 20% and 50% hydrogen by volume) mixtures have been ignited in a fan stirred bomb in turbulence and filmed using high speed cine schlieren imaging. Measurements were performed at 0.1 MPa (absolute) and 360 K. A turbulent burning velocity was determined for a range of turbulence velocities and equivalence ratios. Experimental laminar burning velocities and Markstein numbers were also derived. For all fuels the turbulent burning velocity increased with turbulence velocity. The addition of hydrogen generally resulted in increased turbulent and laminar burning velocity and decreased Markstein number. Those flames that were less sensitive to stretch (lower Markstein number) burned faster under turbulent conditions, especially as the turbulence levels were increased, compared to stretch-sensitive (high Markstein number) flames.     

Effects of nano-scale additives on the linear burning rate of nitromethane

This paper examines the effects of various nanoparticle additives on the combustion behavior of nitromethane, using a pressure-based method recently demonstrated by the authors to measure the linear burning rates of liquid monopropellants and heterogeneous mixtures with high precision. The linear burning rates of these mixtures were measured in a constant-volume system at chamber pressures ranging from 3 to 14 MPa, all without direct observation of the burning front. Nano-scale aluminum was used to increase the overall energy density of the mixture, fumed silica powder was used to increase the mixture thickness and encourage aluminum suspension, and nano-scale titania was also included based on its previous use as a burning rate modifier in solid propellants. The silica loading was varied from 1% to 3% by weight, aluminum was varied from 5% to 13.5% by weight, and titania was added at 1% by weight. The use of fumed silica yielded increased burning rates compared to those of neat nitromethane, and the pressure exponent of the burning rate curve shifted from lower to higher than the nitromethane baseline as more silica was added. This increased pressure sensitivity for mixtures containing 3% silica by weight was previously unobserved in similar studies by other groups and may be an effect of the higher specific surface area of the currently used silica. The subsequent addition of aluminum led to even faster burning rates and higher pressure exponents for all but one mixture. The addition of titania also led to elevated burning rates, with dramatically increased pressure sensitivity and rate inconsistency for chamber pressures above approximately 8 MPa but a decreased pressure sensitivity for the same mixture below 8 MPa. These changes in combustion behavior that accompanied titania were diminished by the presence of aluminum and completely negated in mixtures also containing fumed silica.     

Effect of packing density on flame propagation of nickel-coated aluminum particles

The combustion-wave propagation of nickel-coated aluminum particles is studied theoretically for packing densities in the range of 10–100% of the theoretical maximum density. Emphasis is placed on the effect of packing density on the burning properties. The energy conservation equation is solved numerically and the burning rate is determined by tracking the position of the flame front. Atomic diffusion coefficients and reaction rate of isolated nickel-coated aluminum particles are input parameters to the model. The burning behaviors and combustion wave structures are dictated by the heat transfer from the flame zone to the unburned region. Five different models for the effective thermal conductivity of the mixture are employed. The impact of radiation heat transfer is also assessed. As a specific example, the case with a particle size of 79 μm is considered in detail. The burning rate remains nearly constant (<1 cm/s) up to a packing density of 60%, and then increases sharply toward the maximum value of 11.55 cm/s at a density of 100%. The Maxwell–Eucken–Bruggeman model of thermal conductivity offers the most accurate predictions of the burning rate for all loading densities.