Assessment of the mixing efficiency of solid mixtures by means of image analysis

When assessing a mixing process, mixing quality is a characteristic parameter. To determine the optimum mixing time, it is necessary to measure the mixing efficiency as a function of mixing time. Mixing efficiency is determined by a sufficient number of sample analyses after certain mixing times. The novel method of image analysis allows to rapidly determine the optimum mixing time without sampling and complex sample analysis being required. In this study the model products have different particle sizes and colors to see a difference between them in the image analysis program. Analyzing a real mixture to find chemical substitutes for all particle components is impossible. The study can help the plant engineer to mark a component of interest for finding the optimum point of stationary equilibrium. In this paper the theory for sampling and comparing multi-component mixtures by image analysis to determine the mixing efficiency will be also described and discussed.     

Prediction of transport properties of composites from equations of elasticity

The mathematically-analogous equations of elasticity were used to predict the transport properties of anisotropic composite films. Composite films of controlled structural and physical characteristics were prepared by embedding impermeable glass ribbons in a cellulose acetate matrix. Simple but approximately-precise equations of composite moduli developed by Halpin and Tsai were used to predict the composite permeability in terms of the permeabilities of the constituent phases and a structure factor which is a measure of the filler reinforcement and signifies the resistance of the filler phase to the diffusive flow in the composite medium. The discrepancy between the theoretical predictions and experimental composite permeabilities has been explained in terms of diffusive flux lines not staying in a single direction. In the case of glass ribbons the diffusive1 flow lines tend to bend away from the ribbons (regions of lower permeabilities). The extent of influence of the filler phase to impede the overall composite permeation is a function of the geometry, orientation and volume fraction of the filler.     

乙炔清净废次钠水循环利用工艺

通过研究新鲜次氯酸钠有效氯含量、pH值等因素对新、废次氯酸钠混合过程及效果的影响,开发了废次氯酸钠溶液循环利用的新工艺。     

Determination of degree of nitration of nitrocellulose by refractometry

Nitrocellulose (NC) films, when dried on a rigid substrate, tend to be biaxial and thus exhibit two refractive indices. The absolute difference between these indices has been found to provide an accurate measure of the degree of nitration of NC. A film of NC is cast from a 1% solution in butyl acetate to provide a film about 0.5 mil thick. The dry film, when placed in an Abbé-3L refractometer, gives two white lines which go to extinction alternately upon rotation of a cap analyzer through the east–west (EW) and north–south (NS) directions. Refractive index measurements are made using the line visible in each direction of the analyzer. The absolute difference between the two indices is related to the degree of nitration through standard curves for various grades of NC. The standard deviation for the proposed method was found to be ±0.01% N.     

Effect of LiF on Hot-Pressing of MgO

Transparent polycrystalline specimens can be fabricated from fine MgO powder with a small LiF addition by a two-step process: hot-pressing and heat-treating. The LiF addition allows MgO to be hot-pressed to near theoretical density at reduced temperatures and stresses. The stress-temperature-time conditions must be designed to attain a hot-pressed density of at least 99.5% of the theoretical density of MgO to obtain a transparent specimen during the subsequent heat treatment used in this study. Possible densification mechanisms are discussed.     

Fingerprinting of fatty acid composition for the verification of the identity of organic eggs

Organic products (such as organic eggs) usually have a higher price than the corresponding conventional products. This makes organic products susceptible to fraud. Administrative controls are conducted to detect this type of frauds. However, an analytical verification of the organic identity of food products would be very useful in this respect. It is unlikely that there is a single compound, or a few compounds, that differ sufficiently between organic and conventional eggs to be used as a marker of organic identity. Instead, fingerprinting of the organic products (that is to say, analyzing a wide range of compounds instead of only a few) might be used as a tool for their verification. Here, we have used the fatty acid composition of egg yolks as a fingerprint to verify the organic identity of eggs. From the fingerprints, chemometric models were built which predict the identity of eggs (organic or conventional) with high success rates.     

A priori characterization of criticity and of dynamic thermal behaviour of a storage of cork powder

The new dispositions of the recent French law, called “Lois Risques” present some difficulties of application to qualify and quantify the new notion of dynamics of a hazardous process such as a thermal runaway. Many steady models predicting the thermal runaway (Semenov, Frank–Kamenetskii, Thomas, etc.) are proposed in literature. Due to their simplifying hypotheses, even if these models are widely used, they do not provide any information on the history of the self-heating of the system enabling to predict the necessary time to urgently react to a drift. The analysis of the transient thermal behaviour turns out to be necessary to complete the previous classical results, to estimate the profile of the adiabatic temperature rise and the time of induction for reaching the maximum adiabatic temperature and thus to better characterize the ability of the system to runaway, whose prediction fiability must be presently improved to respond to the new needs of the hazard study. The present work shows that the consideration of the influence of temperature on the heat transfer parameters and of more realistic boundary conditions during the numerical solution of the heat balances describing the storage behaviour allows us to better predict the criticity and the dynamics of appearance and of evolution of the runaway concerning the example of a cork storage.     

Theory of yield of cohesive powders

In many problems in process technology, the influence of the adhesion forces on the mechanics of fine powders plays a considerable role. The existing knowledge is characterized by intensive experimental and theoretical investigations into the mechanism of adhesion for single particle contacts without consolidation by external forces. On the other hand, the mechanical behaviour of cohesive powders has been investigated mainly on the basis of continuum mechanics.For science and technology, it is useful to combine the particles approach and the continuum approach in order to provide a better understanding of the mechanical properties of cohesive powders. A theoretical model has therefore been developed which takes into account the forces acting in interparticle contacts. The theory especially considers the increase in the adhesion forces transmitted in interparticle contacts with increasing consolidation. Contrary to the commonly used phenomenological view, this theory yields a physically based understanding of the effective yield locus for steady-state flow which is reduced to material properties of the solid particles and is therefore shown to be an invariant of a respective powder.The opinion found in the literature that a single yield locus uniquely belongs to one consolidation locus is shown to be not valid. The microstructural view of a cohesive powder is able to show that, contrary to the continuum mechanical view, in the general case a cohesive powder is mechanically anisotropic due to its loading history.     

Phase properties of mixtures of ceramides

Ceramides have been proposed to have a central role in the function of the stratum corneum. Ceramides also influence the phase properties of model skin lipid mixtures, but the relevance of this to the stratum corneum function is controversial. Because the stratum corneum contains several classes of ceramides, the type of ceramides used in model mixtures of stratum corneum lipid lamellae may be important. Thus, the properties of α-hydroxy fatty acid containing (HFAC) and nonhydroxy fatty acid containing (NFAC) ceramides and their mixtures have been investigated. Ceramides were obtained by the conversion of purified bovine brain cerebrosides. Isolated, anhydrous HFAC underwent an endothermic solid to liquid transition at 92°C. With hydration, an endothermic transition at 71.8°C was observed which was accompanied by a reduction in the birefringence. The enthalpy increased from 66 to 89 J/g with a 20-d storage time. These thermal properties are very similar to those observed with hydroxy fatty acid containing cerebrosides. In contrast, anhydrous nonhydroxy fatty acid containing ceramides underwent a broad endothermic transition over the temperature range of 50–90°C. When hydrated, the initial endothermic transition was interrupted by an exothermic transition that was followed immediately by a second endothermic transition. During these thermal changes, there was a loss of birefringence, and with completion of the second endothermic transition, a nonbirefringent liquid was observed. NFAC samples, stored at 70°C for 5 min, cooled, and then rescanned, displayed only one endotherm at 75°C. The thermal behavior of mixtures of HFAC and NFAC was relatively simple, with a progressive decrease and broadening in the temperature of the phase transition as the proportion of NFAC increased up to weight fractions of NFAC of 0.7. At lower weight fractions, a plateau in thetransition temperature as a function of weight fraction was observed. Even at a weight fraction of 0.1 HFAC, no transition to a nonbirefringent liquid state was observed. The high enthalpic changes observed with mixtures of HFAC and NFAC are consistent with the proposed central role that ceramides have in the mechanical and permeability properties of the skin. Moreover, the marked difference in the properties of these two similar lipids may help to explain some of the properties of the stratum corneum.     

Effect of the mechanical failure of catalyst pellets on the pressure drop of a reactor

The effect of the mechanical failure of catalyst pellets on the pressure drop across a laboratory-scale catalyst packing has been examined by experiment. Results reveal that, along with the mechanical failure of the pellets, there exists a point of maximum curvature around which the slope of pressure drop increases rapidly. This rapid increase is attributed to a mutation of the packing structure, occurring as the amount of failed pellets reaches a certain critical value. The secondary breakage of the pellets contributes much to the mutation of the packing and to the pressure drop. It has been observed that a trilobite catalyst is more susceptible to a mechanical stress than a cylindrical catalyst, and that a catalyst with a smaller diameter is much easier to result in an increase in the pressure drop. The measurement of the pressure drop across a laboratory-scale catalyst packing as the failure of pellets under a mechanical stress has a satisfactory reproducibility, and has a close meaning to the mechanical reliability of a fixed bed converter, and hence is recommended as a method for catalyst assessment. The multi-scale and multi-disciplinary nature of catalyst mechanical reliability is also discussed.     

The determination of the coefficient of dynamic friction of organic powder compacts on steel

A practical experimental model system has been successfully used to study the frictional response of organic powder compacts sliding across a polished steel plate, representative of the die bore of a production compaction system. This system offers a controlled approach to the study of frictional phenomena occurring during compaction and facilitates a more detailed investigation into the fundamental mechanisms of friction than a simple resolution of forces within a punch and die apparatus.For acetylsalicyclic acid sliding on steel, the dynamic friction coefficient was found to be dependent on the displacement and, to a lesser extent, the initial normal load, whereas for PTFE on steel, the dynamic friction coefficient was independent of displacement and load and estimated at 0.09. Thus, soft organic materials exhibit very different frictional characteristics to those of brittle materials. These differences reflect the differing importance and magnitude of the three frictional components, adhesion, shear and ploughing.     

Limits of Existence of a Two-Dimensional Steady-State Structure of a Liquid Film in Combustion-Wave Propagation

A two-dimensional steady-state structure of a film flow of a combustible liquid on a heat-conducting substrate in the case of combustion-wave propagation is considered in the hydrodynamic formulation. The physical mechanism of formation of this structure is analyzed. It is shown that the thermocapillary effect plays an important role. The conclusion is justified that the existence of a two-dimensional regime is possible only for rather low values of the temperature gradient on the film surface. A critical condition is obtained, which determines the transition to a three-dimensional regime. This condition implies that the flow velocity is equal to the velocity induced by the thermocapillary force. If the temperature gradient is higher than a certain critical value, a zone with a reverse flow should appear, in accordance with the two-dimensional model. It is assumed that such a regime cannot exist due to its instability to three-dimensional perturbations. Experiments with a liquid film flowing down due to gravity in the presence of an immovable heat source (without the combustion wave) support the conclusion of the transition to a three-dimensional regular flow structure if the temperature gradient is rather high. The first part of the paper deals with simulation of the film structure for the critical condition satisfied. The second part deals with generalization of the problem to the case of a movable heat source moving with a constant velocity. This formulation of the problem includes the situation with combustion-wave propagation. The mathematical formulation of this problem allows us to assume that the existence of a two-dimensional steady-state regime in this case is limited by the same critical condition. If the temperature gradient on the film surface is higher than the critical value, the two-dimensional steady-state solution does not exist. This concept justified in the present work offers a generic explanation of phenomena observed in liquid films in the presence of local heat sources of various natures.     

尿素联产三聚氰胺的利弊分析

简要介绍520 kt/a氨气提工艺尿素联产30 kt/a三聚氰胺装置的关联情况。从技术与经济两个方面计算和分析了联产三聚氰胺后对原有尿素装置的影响,并与新增50 kt/a小尿素装置对比,说明尿素联产三聚氰胺的技术经济可行性。     

A New Approach to Investigation of vdW Type of Equations of State

A new approach to the investigation ofvdW type of equations of state (EOS) is developed by embedding a vapor pressure equation and a saturated liquid volume equation into vdW type EOS, which resuits in a new function A^s(T). The A^s(T) possesses the properties of an attractive parameter A(T), and if an EOS is accurate in the whole PVT space, then its numerical wahie equal8 A(T). As a useful tool for investigating EOS, the A^s(T) has been used to make comparisons among RKS, PRSVII, PT and ALS EOS, and to indicate where the shortcomings of the EOS are coming from. Based or. the A^s(T), a possible way to develop at real predictive equation of state is also suggested.     

Experimental validation of a theoretical analysis of the range of operation of catalyst poisons

A formula to calculate theminimum quantity of material necessary to poison or promote a supported metal catalyst, based on theoretical criteria of poisoning range, has recently been proposed (R.W. Joyner and J.B. Pendry, Catal. Lett. 1 (1988) 1). This paper reports experimental tests of this formula for chlorine, sulphur and iodine poisoning of a Pd/C catalyst for the hydrogenation of cyclohexene. For chlorine and sulphur a significant excess of poison is required compared to the estimate, while the results for iodine are in excellent agreement with the calculation. The theory is also compared with a number of literature studies of sulphur poisoning and appears to have wide validity.     

过碳酸钠洗涤性能和稳定性能影响因素的研究

过碳酸钠 (PC)是一种碳酸钠与过氧化氢的络合物 ,其特点是对环境无污染。作者以洗涤剂中含有过碳酸钠为前提 ,从洗涤剂最常见的原料对PC的活性与稳定性能的影响方面进行了研究 ,通过实验证明Na2 CO3 、Na2 SO4 、十二烷基苯磺酸钠 (LAS)、三聚磷酸钠 (STPP)、MgSO4 、Na2 SiO3 、四乙酰乙二胺 (TAED)对PC的活性和稳定性都有影响。发现Na2 CO3 对过碳酸钠漂白的促进作用在过碳酸钠质量浓度低的时候尤其明显 ;随着Na2 SO4 、LAS用量的增加 ,白度值上升 ,在达到一定值后白度下降 ;而STPP恰恰相反 ,质量浓度增大 ,白度增大 ,当STPP质量浓度达到一定值时 ,作用反而更显著 ;MgSO4 很敏感 ,在窄区间有一峰值 ;Na2 SiO3 的用量在 2 5 %以内时 ,白度升高的趋势很强 ;TAED对PC起活化作用且和温度有关。最后设计出一个配方与标准粉比较去污比值是 2 2 1。     

Aging and loss of flocculation activity of aqueous polyacrylamide solutions

There is a rapid and a slow stage in the decrease of reduced specific viscosity versus time (aging) for a solution of a high intrinsic viscosity polyacrylamide in water. The rapid stage is irreversible and has a fairly high temperature coefficient. Results of the latter type are usually associated with a weak-link scission mechanism, but they can also be reconciled with a disaggregation mechanism. A disaggregation mechanism is also indicated for the rapid stage by an increase in the first-order rate contant with a decrease in the polymer concentration or an increase in the shear rate and by the absence of the rapid stage during the aging of the same sample in formamide. Chemical changes in the polymer are suspected as being responsible for the RSV change during the slow stage in the aging of the high intrinsic viscosity polyacrylamide and also in the aging of a polyacrylamide of low intrinsic viscosity. The aging of the polyacrylamide of high intrinsic viscosity is paralleled by a decrease in the ability of the polymer to increase the subsidence of kaolin suspensions. This decrease in the flocculation activity is attributed to a weakening of the interparticle bridging by a change from a strong adsorption of the bridging polymer to two particles to a strong adsorption of the bridging polymer to one particle but weak adsorption of the bridging polymer to the other particle.     

注塑机拉杆三角螺纹端卸载槽的多目标优化

针对注塑机拉杆三角螺纹在近卸载槽处发生早期断裂的问题，在用ANSYS软件对近卸载槽处三角螺纹进行有限元分析的基础上，就拉杆三角螺纹端卸载槽的几何特性建立参数优化模型，以控制三角螺纹在近卸载槽附近的最大应力、卸载槽的最大应力以及卸载槽加工量最小化为统一的目标函数。通过对拉杆在单向拉伸力作用下的多目标优化，可使拉杆三角螺纹牙根在卸载槽处的最大应力降低55％，在偏载作用下，其最大应力降低21．4％。在单向拉伸力作用下，拉杆卸载槽的最大应力比平均单向拉伸应力提高26．5％，使卸载槽能够较好地发挥其卸载的作用。     

Co-carbonization of solvent fractions of hydrogenated and alkylated SRC pitches in studies of formation of needle-cokes

The optical texture of cokes from two SRC pitches of different coking properties, from co-carbonizations of these materials and of hydrogenated and alkylated products has been studied. The objective, relative to formation of needle-cokes, is to correlate the optical texture of cokes with the chemical structure of the pitch materials using both benzene-soluble (BS) and insoluble (BI) fractions of the pitches. Hydrogenation improved the compatibility of the BS fraction of the inferior SRC pitch (No. 2) with the BI fractions of the two pitches (non-hydrogenated) using a ratio of only 1 to 9. Before hydrogenation, a ratio of BS to BI of 8 to 2 did not give a needle-coke. In contrast, alkylation destroyed the compatibility of the BS fraction of the superior SRC pitch (No. 1) with the BI fraction (non-alkylated) using a ratio of 6 to 4, and which gave a needle-coke before alkylation. Hydrogenation of the alkylated material restored the compatability. The relevance of these studies to industrial carbonization processes is discussed in terms of chemical treatment and the hydrogen economy.