气体轴承特性模拟及实验验证

针对某30 kW微型燃气轮机用静压气体轴承,开展轴承刚度、承载力及轴系临界转速特征的数值与实验研究。通过离散化可压缩雷诺方程,采用数值迭代方法,获取轴承内气膜压力分布和气膜刚度特性;采用有限元方法,研究转子-轴承系统的模态特性与临界转速;在气体轴承支撑的微型燃气轮机试验台上,采用时域振动信号和不平衡响应曲线等振动测试分析方法,获取轴系的气膜临界转速特性。研究结果表明:研究的该静压气体轴承,其转速在30 000 r/min内动压效应相对于静压效应可以忽略;轴承气膜刚度随着偏心率增大而增大,但当偏心率超过0. 8时,由于出现"静态不稳定区域"导致气膜刚度下降。数值模拟和实验都证实了转子在6 000 r/min和9 000 r/min附近出现了由气膜刚度引起的锥动临界特征。     

Fe2O3-Al纳米铝热剂与超细RDX复合物的制备与性能

采用溶胶-凝胶方法,制备出了纳米铝热剂nano-Fe2O3-Al,并获得了其与超细RDX的复合含能材料nanoFe2O3-Al/SFRDX。采用BET法、SEM、XRD综合表征了nano-Fe2O3-Al的结构,采用TG/DSC联用技术测试了nano-Fe2O3-Al的热性能,结果表明气凝胶铝热剂的反应温度更低;nano-Fe2O3-Al的静电火花感度测试结果表明纳米铝热剂对静电十分敏感。对nano-Fe2O3-Al/SFRDX在无约束条件和密闭条件下的燃烧行为进行了研究,高速相机照片法发现在无约束条件下,nanoFe2O3-Al燃烧高达300 m/s,且nano-Fe2O3-Al/SFRDX具有在无约束条件下由燃烧转为爆轰的趋势。     

不同方法测定两种表面活性剂的临界胶束浓度

采用电导法及表面张力法分别测定了十二烷基硫酸钠(阴离子表面活性剂)和十二烷基三甲基氯化铵(阳离子表面活性剂)的临界胶束浓度,两种实验方法测得十二烷基硫酸钠的临界胶束浓度约为7.0×10-3mol·dm-3,十二烷基三甲基氯化铵的临界胶束浓度约为1.60×10-2mol·dm-3,两种方法所得结果一致。     

三相气升式环流反应器内上升区相含率轴向分布与循环液速的研究

常温常压下,在三相气升式内环流反应器中,将硅铝球、石英砂和瓷球分别与空气、水组成三相物系,考察了细颗粒与大颗粒物系中上升区相含率轴向分布规律、固体装载率和颗粒粒径对该规律的影响,以及各物系中上升区循环液速随表观气速的变化规律。结果表明:随轴向高度的增加,瓷球物系中上升区固含率εsr先增大后减小;硅铝球物系中εsr减小;石英砂物系中εsr均匀分布。随轴向高度的增加,瓷球物系中上升区气含率εgr增大;硅铝球物系中εgr减小;石英砂物系中εgr先增大后减小。固定表观气速,各轴向位置处的上升区气含率随固体装载率、颗粒粒径的增大而增大。当固体装载率相同时,各物系中上升区循环液速随表观气速的增大而增大。     

Continuous flow characterization of solid biomass in a reciprocating/rotating scraper tube: An experimental study

The performance of reciprocating/rotating scrapers has been assessed in a visualization study of the continuous flow hydrodynamics of air‐fluidized solid biomass under varying conditions of air flow rate and scraping velocities. A combination of low air flow rates and high scraping velocities results in more uniform flow of both types of biomass investigated. Power consumed by the reciprocating action of the scrapers increases with the scraping velocity but typically represents no more than 20% of the overall power consumption at the highest air flow rate applied. We also demonstrate that rotation of the scrapers superimposed on their reciprocating action gives higher flow rate of biomass and better mixing within the bulk solid compared to reciprocating action alone. The application of the reciprocating/rotating scraper technology described in this study represents a viable step forward in developing a continuous, large‐scale process for the microwave‐assisted decomposition of solid biomass to produce bio‐oils. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3732–3738, 2014     

Distribution of large biomass particles in a sand‐biomass fluidized bed: Experiments and modeling

The axial distribution of large biomass particles in bubbling fluidized beds comprised of sand and biomass is investigated in this study. The global and local pressure drop profiles are analyzed in mixtures fluidized at superficial gas velocities ranging from 0.2 to 1 m/s. In addition, the radioactive particle tracking technique is used to track the trajectory of a tracer mimicking the behavior of biomass particles in systems consisting of 2, 8, and 16% of biomass mass ratio. The effects of superficial gas velocity and the mixture composition on the mixing/segregation of the bed components are explored by analyzing the circulatory motion of the active tracer. Contrary to low fluidization velocity (U = 0.36 m/s), biomass circulation and distribution are enhanced at U = 0.64 m/s with increasing the load of biomass particles. The axial profile of volume fraction of biomass along the bed is modeled on the basis of the experimental findings. © 2014 American Institute of Chemical Engineers AIChE J, 60: 869–880, 2014     

Production of aromatics by catalytic fast pyrolysis of cellulose in a bubbling fluidized bed reactor

Catalytic fast pyrolysis of cellulose was studied at 500°C using a ZSM‐5 catalyst in a bubbling fluidized bed reactor constructed from a 4.92‐cm ID pipe. Inert gas was fed from below through the distributor plate and from above through a vertical feed tube along with cellulose. Flowing 34% of the total fluidization gas through the feed tube led to the optimal mixing of the pyrolysis vapors into the catalyst bed, which experimentally corresponded to 29.5% carbon aromatic yield. Aromatic yield reached a maximum of 31.6% carbon with increasing gas residence time by changing the catalyst bed height. Increasing the hole‐spacing in the distributor plate was shown to have negligible effect on average bubble diameter and hence did not change the product distribution. Aromatic yields of up to 39.5% carbon were obtained when all studied parameters were optimized. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1320–1335, 2014     

Effect of gas properties on the onset of flooding in small diameter inclined tubes

This work concerns the effect of gas phase properties on incipient flooding in counter-current gas–liquid two-phase flow in small diameter inclined tubes (D < 10 mm). The aim is to propose generalized correlations that can be used to predict incipient flooding in small diameter tubes. Experiments were performed in a 7 mm glass tube and at two inclination angles, i.e. 30 and 60° from the horizontal, using water as liquid phase and atmospheric air, He and CO₂ as gas phase. Previously proposed correlations for flooding prediction ( Pantzali et al., 2008) were suitably adjusted to incorporate the effect of gas phase properties. It has been proved that the flooding curves calculated using the proposed correlations are in good agreement with both the results of the present study and relevant literature data.     

Applying fractography and fracture mechanics to the energy and mass of crack growth for glass in the mirror region

The mirror region following the fracture initiation site is considered by applying fracture mechanics principles along with experimental observations of the crack velocity at the formation of the mirror mist boundary. Several issues regarding this crack growth in glass are addressed after considering the terminal velocity of crack growth and the mirror mist boundary information on silicate glasses. A strain energy release rate criterion is applied to estimate the kinetic energy of an advancing crack in glass at the mirror/mist boundary. This energy is then utilized to estimate the effective mass of the crack at the mirror/mist boundary. It is compared with material volumes in the vicinity of the crack.