非均匀水流量对热力膨胀阀控制稳定性的影响

为研究热力膨胀阀(TEV)的控制失稳机理,采用TEX2型外平衡式TEV进行实验,在7组非均匀水流量率的情况下,实现TEV控制从稳定到振荡的动态变化.结果表明:当支路2的水流量F2从36.9%递减至27.0%,TEV流量控制特性稳定,蒸发器换热量仅衰减了3.4%;当F2从27.0%降至9.1%,总出口的制冷剂状态由过热变为带液,其出口温度由稳定变波动,且波动幅度持续增大,此时TEV的流量控制失稳,蒸发器换热量衰减了14.1%.支路1过热蒸汽的显热不足以提供支路2带液量完全蒸发所需的潜热,混合后总出口的过热度小于热力膨胀阀的MSS曲线要求的最小过热度,进而导致热力膨胀阀的持续振荡.实验结果可为多流路制冷系统中换热器的设计提供参考.     

市场经济：拉大差距，还是机会均等

市场经济的精髓是机会均等。市场经济必须做到起点平等、过程公正、规则公平，它不是人为地拉大分配差距而是凭个人的能力和勤劳参与公平竞争并自然而然形成分配差距的一种制度安排。要防止和纠正打着改革和市场经济的旗号谋私利而拉大的分配差距。要打破职称职务导向的旧的不尽合理的人力资源管理文化．推行个人能力和工作业绩导向的新的公平合理的人力资源管理文化。但市场经济不是最好的，它最终将被一种完美的人本经济模式所取代。     

气液固三相流化床局部相含率轴径向分布

应用开发的微电导探针测试技术,对小尺寸颗粒玻璃珠（粒径分别为0.48、0.80、1.25 mm）和1.45 mm苯乙烯树脂为固相,空气和水分别为气相和液相的三相流化床的各相局部含率进行了同时测定.在较宽操作条件下,获得了一系列局部相含率实验数据.通过对实验数据研究发现：在充分发展段,局部固含率在r/R=0.75～0.85范围内有一个极大值,床层截面平均气含率随表观液速的变化存在一个极小值.在气体分布器区,在距气体分布器轴向一定距离范围内,三相局部含率的径向分布存在明显的不对称分布.随着轴向距离的增加,局部气含率径向不对称分布逐渐消失,最终过渡到对称分布,而局部固含率的径向不对称分布消失得不明显.     

Experimental study on the two phase flow behavior in PEM fuel cell parallel channels with porous media inserts

In this study, the air–water two phase flow behavior in PEM fuel cell parallel channels with porous media inserts was experimentally investigated using a self-designed and manufactured transparent assembly. The visualization images of the two phase flow in channels with porous media inserts were presented and three patterns were summarized. Compared with the traditional hollow channel design, the novel configuration featured less severe two phase flow mal-distribution and self-adjustment to water amount in channels, although a higher pressure drop was introduced due to the porous media inserts. The dominant frequency of pressure drop signal was found to be a diagnostic tool for water behavior in channels. The novel flow channel design with porous media inserts may become a solution to the water management problem in PEM fuel cells.     

Propane combustion in non-adiabatic microreactors: 2. Flow configuration in posted microreactors

The aim of this paper is to analyze cross-flow operation in a microreactor with posted catalytic inserts for Pt-catalyzed propane combustion under fuel-lean conditions. The insert consists of 150 posts arranged in-line in six rows. The posts are static pillar-like structures in the flow channel, which act as static mixers and provide higher catalytic surface area. Computational Fluid Dynamics (CFD) simulations are used to compare the post microreactors for axial- and cross-flow configurations. In cross-flow case, where the bulk flow is in transverse direction across the six rows of posts, significant flow mal-distribution is observed. Tapering of the inner walls of the microreactor solid structure, at an angle of 5.766°, is proposed for obtaining more uniform flow distribution. For the cross-flow microreactors with tapered inner walls (referred to as “tapered-post”), the flow distribution becomes more uniform as the flow rate is decreased. The axial- and tapered-post microreactors show similar propane conversion for a wide range of operating conditions. Tapered-post microreactors have lower pressure drop and more uniform wall temperatures because the reaction zone is spread over the entire length of the catalytic insert. We also show that tapered-post microreactors have lower heat losses, and therefore are more stable towards device extinction. Consequently, the primary advantages of tapered-post microreactors are better thermal management and ability to operate at more fuel-lean conditions.     

CFD simulation and experimental study of liquid flow mal-distribution through the randomly trickle bed reactors

A numerical model for liquid mal-distribution in randomly trickle bed reactors has been investigated and the results are compared with the experimental data. A CFD model based on the three-phase Eulerian approach is developed and a two-fluid model is utilized to perform the inter-phase momentum exchanges. Furthermore, radial distribution of the bed porosity is considered adjacent to the reactor wall. Two different types of liquid inlet distributors have been used in order to study the accuracy of the CFD model. To validate the CFD model, the simulation results are compared with the experimental data and the results from the porous media concept in which the permeability model has been applied to implement the inter-phase momentum exchange. Experimental results have been obtained on an industrial trilobe catalyst under a trickling flow regime in a pilot scale reactor setup. Co-current liquid and gas streams have entered to the reactor through a mono or multi orifice distributor. Results of the developed CFD model have found more accurate than that of the porous media concept when compared with the experimental data.     

气-液-固三相流化床气体分布器区局部相含率和床层膨胀比的实验研究

在内径150 mm,高4 350 mm的三相流化床中,分别以空气、水和0.48 mm、1.25mm的玻璃珠及1.45 mm的苯乙烯树脂为气相、液相和固相,应用开发的微电导探针测试技术同时测得三相局部含率,并对气体分布器区的局部相含率和床层膨胀比(H/H0)进行了实验研究,考察了固体颗粒的粒径、密度及表观液速和气速对床层膨胀比的影响。研究发现,在距气体分布器轴向一定距离范围内,三相局部含率的径向分布存在明显的不对称分布;随着轴向距离的增加,局部气含率的径向不对称分布逐渐消失,局部固含率的径向不对称分布变化不明显;床层膨胀比随表观气速和液速的增大而增大;较低密度颗粒系统的H/H0开始增加缓慢,后来增加很快;较高密度颗粒系统的H/H0开始迅速增加,后来增加缓慢。     

Gas–liquid two-phase flow patterns in parallel channels for fuel cells

Two-phase flow in horizontal parallel channels has been experimentally investigated under fuel cell related operating conditions. Pronounced hysteresis is observed in the pressure drop versus flow characteristic curve when starting from either flooded or dry conditions. When gas is introduced into channels initially filled with water (flooded initial condition), both gas and liquid tend to flow predominantly in one channel at low gas or liquid flow velocities. As the gas flow velocity increases, even distribution of gas and liquid flow in both channels is observed, accompanied with a sudden decrease in the pressure drop. On the other hand, even gas and liquid flow distribution between both channels is found at comparatively lower gas flow velocities when starting with dry-gas flow conditions with liquid introduced into channels filled with gas (stratified flow regime). The flow regimes of this system are visualized in plots of the pressure drop against gas and liquid flow velocities. However, this phenomenon tends to vanish at high gas and liquid flow velocities, suggesting that high gas and liquid flow velocities are required to ensure even flow distribution in parallel channels. The hysteresis points appear at the same level of the pressure drop, reflecting intrinsic characteristics of the parallel channels used in this study. These results have important implications for PEM fuel cell operational strategies. In order to avoid reactant mal-distribution in parallel flow channels in the flow field in the two-phase flow regime, fuel cells should be operated at sufficiently high gas flow velocities.     

蒸汽发生器汽水分离器负荷不均匀性分析

应用三维稳态热工水力软件GENEPI,对CPR1000蒸汽发生器管束区及汽水分离器区域进行热工水力分析,得到了管束区和汽水分离器入口的热工水力参数分布。结果表明,汽水分离器区域的负荷不均匀性明显,中间及热侧的汽水分离器承受的负荷较高,分析数据为汽水分离器及干燥器湿度分析提供输入数据和设计依据。对比了不同汽水分离器局部阻力系数下的结果,表明汽水分离器局部阻力系数对其负荷不均匀性有一定的影响,系数越大,流量越均匀。