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991.
超缓凝砂浆是由水泥、复合缓凝剂、水和砂经适当配比而形成的,该种砂浆可塑性能的研究是其在工程上应用的重要依据。试验测定了A,B,C三种不同配比的缓凝砂浆静态塑性指数.分析了温度、龄期、复合缓凝剂的掺量及不同水泥品种对缓凝砂浆的缓凝时间的影响。结果表明:(1)三种缓凝砂浆各温度下的静态塑性指数都随龄期的增长而增大.说明缓凝砂浆在缓凝早期塑性指数小,触变性能好;(2)缓凝时间随复合缓凝剂的增加增长,随温度的升高缓凝时间会延长。(3)缓凝砂浆的凝结时间与水泥品种也有较大关系,同配比下早强型水泥凝结时间短,抗硫酸盐水泥凝结时间长。 相似文献
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995.
用吊片法和自制改进的最大泡压法分别测定了全氟庚氧基全氟亚乙基磺酸钾(C9FK)溶液的平衡和动态表面张力,计算得出该种表面活性剂形成胶束的标准热力学函数△Hmθ、△Smθ、△Gmθ分别为16.98 kJ/mol、218.29 J/mol·K、-48.22 kJ/mol。结合Word-Tordai方程,计算得到在不同条件下的表观扩散系数Da和吸附势垒Ea。实验证明,增大表面活性剂的浓度、降低温度、以及无机盐(NaCl)的加入都会使扩散系数减小,吸附势垒增大,从而不利于吸附的进行。当表面活性剂的浓度小于等于1×10-6 mol/L时,该体系属于扩散控制模型,而浓度大于 1×10-6 mol/L时,在吸附初期(t→O)属于扩散控制,后期均属于混合控制模型。 相似文献
996.
Anglique Lonard Silvia Blacher Pierre Marchot Jean‐Paul Pirard Michel Crine 《加拿大化工杂志》2005,83(1):127-131
The knowledge of internal moisture profiles which develop during drying is essential for model validation purposes, but they are difficult to determine experimentally. This paper shows that X‐ray microtomography, together with image analysis, provides an accurate, non destructive and easy to use technique to determine moisture profiles. Results reported concern the drying of wastewater sludges whose management is becoming a real environmental challenge. An analysis of the development of moisture gradients at the sample external wall shows an influence of drying operating conditions. Finally, mass diffusion coefficients are estimated from the knowledge of both the moisture gradients and the drying flux. 相似文献
997.
By poly(A-B) we denote a chain with repeating sequence -A-B-, such as polyoxymethylene. Here A and B stand for a single atom, e.g., -O-, or a group of atoms, e.g., -CH2-. All n bond vectors are of the same length, l, as are all bond dipole moment vectors, m. The manner in which the characteristic ratio of the dipole moment, Dn≡〈μ2〉0/nm2 approaches its asymptotic limit is related quantitatively to the behavior of subchains of various sizes in poly(A-B). Illustrative numerical calculations with rotational isomeric state (RIS) models for several polymers are consistent with the predictions. The approach of Dn to its asymptotic limit is sensitive to longer subchains than is the approach of the characteristic ratio of the end-to-end distance, Cn≡〈r2〉0/nl2, to its asymptotic limit, due to the differences in the connectivity of the bond vectors (head-to-tail) and the bond dipole moment vectors (head-to-head, tail-to-tail). 相似文献
998.
Experiments were performed in a shear cell device under four different solid fractions. The glass spheres with a mean diameter of 3 mm were used as granular materials. The motions of the granular materials were recorded by a high-speed camera. By using image processing technology and a particle tracking method, the average and fluctuation velocities in the streamwise and the transverse directions could be successfully measured and analyzed. Three bi-directional stress gages were used to measure the normal and shear stresses along the upper boundary. The effective viscosity of the granular material flow can be calculated. By tracking the movements of particles continually, the curves of the mean-square diffusive displacements versus time were plotted and were used to determine the self-diffusion coefficients from the slopes of the curves. The fluctuations and the self-diffusion coefficients in the streamwise direction were much higher than those in the transverse direction. The fluctuations were found to increase with the solid fraction, but the diffusion coefficients were greater in a more dilute flow system. 相似文献
999.
The time series of heat-transfer film coefficient for an evaporator with a vapor-liquid two-phase boiling flow were forecasted by the chaotic prediction or the local nonlinear short-term prediction. The forecasting method was based on the phase space reconstruction theory and a mathematic model in the form of datum driving had been developed to carry out the prediction. The signals of heat-transfer film coefficients predicted by this method were compared with those obtained from the experimental measurements. Different from the previous work, the comparisons in this work were done both from the point of view of the time trajectory and from the point of view of macroscopic or general characters. Besides the time-averaged statistics characteristics, such as the average value, average deviation and standard deviation, the power spectrum, phase plane map and chaotic invariants including the correlation dimension and Kolmogorov entropy had been calculated and been compared for the time series obtained both from the experimental measurement and from the forecast. The comparison for each parameter between the value calculated from the time series measured and that estimated from the time series forecasted by the chaotic forecast method shows satisfactory agreement. The limited length in time with an accuracy prediction indicates that the system is chaotic. The agreement of the comparison of the general parameter indicates that the chaotic prediction is effective for the estimations of the heat transfer characteristics of the two-phase flow boiling system and that the chaotic prediction method may be a potential tool for the effective thermo-fluid control for such evaporators. 相似文献
1000.
Techniques are presented for determination of activity coefficients of binary systems from unsteady state evaporation and growth of single microdroplets in controlled environments. A high-precision light scattering method based on resonances observed in light scattering by microdroplets was used to determine the size and composition of a microdroplet as functions of time. The techniques were validated through data on growth of glycerol microdroplets in slowly developing water vapor concentration fields and evaporation of microdroplets, containing volatile dimethylphthalate (DMP) and nonvolatile dioctylphthalate (DOP), in vapor-free atmospheres. When the water vapor concentration in the surrounding gas changes slowly a glycerol droplet maintains a dynamic equilibrium with the water vapor; thus the activity coefficient of water was determined from knowledge of the droplet composition and the water vapor saturation ratio in the gas phase. The activity coefficients of DMP were determined on the basis that the instantaneous evaporation rate of a DMP-DOP microdroplet in a vapor-free atmosphere is equal to the product of the activity of DMP and the evaporation rate of a pure DMP droplet. The activity coefficient values obtained from microdroplet experiments are highly reproducible and agree with data available in the literature. 相似文献