基于均匀设计法的碳纳米管纳米流体稳定性

研究碳纳米管质量分数、分散剂质量分数、pH值和超声振荡时间对碳纳米管纳米流体稳定性的交互影响和定量影响.配置12个碳纳米管纳米流体样品,测定各样品的Zeta电位值.样品的4因素取值通过均匀设计法确定,稳定性用Zeta电位表征.采用二次多项式逐步回归法处理数据,建立碳纳米管纳米流体稳定性与4个因素之间的回归模型.由模型分析可知,该4因素对碳纳米管纳米流体稳定性的影响是相互约束的.当超声振荡时间>3.411 h时,碳纳米管纳米流体的稳定性与碳纳米管质量分数正相关;当超声振荡时间<3.411 h时,碳纳米管纳米流体的稳定性与碳纳米管质量分数负相关.

Influence factors on thermal conductivity of ammonia-water nanofluids

In order to investigate the mechanism of nanoparticles enhancing the heat and mass transfer of the ammonia-water absorption process,several types of binary nanofluids were prepared by mixing Al2O3 nanoparticles with polyacrylic acid(PAA),TiO2 with polyethylene glycol(PEG 1000),and TiN,SiC,hydroxyapatite(noodle-like) with PEG 10000 to ammonia-water solution,respectively.The thermal conductivities were measured by using a KD2 Pro thermal properties analyzer.The influences of surfactant and ammonia on the dispersion stabilities of the binary nanofluids were investigated by the light absorbency ratio index methods.The results show that the type,content and size of nanoparticles,the temperature as well as the dispersion stability are the key parameters that affect the thermal conductivity of nanofluids.For the given nanoparticle material and the base fluid,the thermal conductivity ratio of the nanofluid to the ammonia-water liquid increases as the nanoparticle content and the temperature are increased,and the diameter of nanoparticle is decreased.Furthermore,the thermal conductivity ratio increases significantly by improving the stabilities of nanofluids,which is achieved by adding surfactants or performing the proper ammonia content in the fluid.

Vane Shear Strength Based Stability Analysis of Slopes in Unconsolidated Soft Clay

In-situ vane shear test is frequently performed to determine shear strength for slope stability analysis in Tianjin New Harbor.However,the soil shear strength varies with the shear plane orientation.A possible means to reduce the effect of directional dependency of shear strength is to convert the in-situ vane shear strength into undrained shear strength parameters.A method of converting in-situ vane shear strength into undrained shear strength parameters is presented.The shear strength parameters determined for all of the in-situ vane shear strengths are subjected to statistical regression analysis to take into consideration the possible effect of non-homogeneity in the soft clay deposit.Using the regressed shear strength parameters,slope stability analyses are performed for five existing soil slopes.The results of stability analyses indicate that the safety factors obtained from the converted parameters reflect the state of the slopes analyzed much better than those obtained from in-situ vane shear strength and laboratory consolidated-undrained and unconsolidated-undrained strength parameters.It is concluded that the presented methsod of determining undrained shear strength parameters for in-situ vane shear strength is effective.

The Lotka-Volterra Competition System with Discrete and Distributed Time Delays

In this paper, the Lotka-Volterra competition system with discrete and distributed time delays is considered. By analyzing the characteristic equation of the linearized system, the local asymptotic stability of the positive equilibrium is investigated. Moreover, we discover the delays don＇t effect the stability of the equilibrium in the delay system. Finally, we can conclude that the positive equilibrium is global asymptotically stable in the delay system.

Thermal convection driven by a heat-releasing scalar component

In this paper,we investigate the thermal convection flow which is driven by a heat-releasing concentration field.Different from our previous work on the internally heated double diffusive convection(IHDDC),in the current internally heated Rayleigh-Bénard convection(IHRBC),the fluid density depends solely on the temperature field and the concentration field only serves as the internal heat source.Linear stability analyses reveal that the most unstable mode is always the stationary one.The critical Rayleigh number,which measures the strength of the unstable driving force,decreases with the Schmidt number(the ratio between the viscosity and the molecular diffusivity of concentration field),but increases with the Prandtl number(the ratio between the viscosity and the thermal molecular diffusivity).Fully developed flows are then studied by three-dimensional direct numerical simulations.The unifying model developed for IHDDC can also be used to describe the transport properties for the current flow.The characteristic widths are smaller for the plumes descending from the top plate than those ascending from the bottom one.