Autothermal reactors with internal heat exchang—I Numerical and experimental studies in the multiple steady-state region

Detailed numerical and experimental studies in the multiple steady-state region of an autothermal reactor with internal countercurrent heat exchange were conducted. The mildly exothermic water-gas shift reaction was used in the studies. In this distributed-parameter system multiple steady states were found experimentally. Although significant radial and longitudinal temperature gradients exist, one-dimensional (radially-lumped) simulations predict mean behavior quite well. For two-dimensional simulations, Legendre polynomial trial functions give faster convergence than Jacobi polynomials when using orthogonal collocation methods. Inflections in the radial temperature gradients were measured near the hot spot although not predicted by the simulations. Significant temperature jumps at the inner wall upstream of the hot spot were also measured. Production of hydrogen could be conducted at surprisingly mild conditions if the reactor could be controlled in a stable mode essentially identical to the middle unstable steady state.     

Modelling of diffusion-limited,homogeneous reactions in supported liquid-phase catalysts

A model is proposed for describing mass transfer of gaseous reactants and products in supported liquid-phase catalysis. It is based on the dusty-gas equation and incorporates the pore-size distribution of the dry support as well as the nonuniform liquid-phase distribution. Experimental testing was conducted with three separate liquids and for various loadings in an α-alumina support. With each having a contact angle of less than 90° on the alumina, the dispersion patterns of the three liquids were essentially the same. Nonsoluble gases were used in the experiments.     

Dimensional Changes in CFRP/PMI Foam Core Sandwich Structures

A sandwich structure was observed from the beginning of life—starting at the vacuum assisted manufacturing process up to several environmental in service conditions. Strain variations due to curing process at the manufacturing, well as thermal fluctuations and humidity environments in service were detected and reviewed by their influence on the overall dimensional stability. The CFRP/PMI foam core sandwich structure was checked for an application as a primary structure in commercial aviation with its specific environmental requirements.     

Nanoparticle Accumulation in Angiogenic Tissues: Towards Predictable Pharmacokinetics

Nanoparticles are increasingly used in medical applications such as drug delivery, imaging, and biodiagnostics, particularly for cancer. The design of nanoparticles for tumor delivery has been largely empirical, owing to a lack of quantitative data on angiogenic tissue sequestration. Using fluorescence correlation spectroscopy, the deposition rate constants of nanoparticles into angiogenic blood vessel tissue are determined. It is shown that deposition is dependent on surface charge. Moreover, the size dependency strongly suggests that nanoparticles are taken up by a passive mechanism that depends largely on geometry. These findings imply that it is possible to tune nanoparticle pharmacokinetics simply by adjusting nanoparticle size.     

Physical solubility of hydrogen sulfide in several aqueous solvents

The solubility of hydrogen sulfide in several aqueous solutions was measured over the temperature range 25°C to 60°C. The solvents investigated in this work include 0 to 50% aqueous solutions of polyethylene glycol, ethylene glycol, methyldiethanolamine and diethanolamine. The amine solutions used in this work were neutralized by the addition of hydrochloric acid in order to suppress the hydrogen sulfide reaction (H₂S → H⁺ + HS^?) so that only the physical solubility of hydrogen sulfide would be measured. The solubility data determined in this work are expressed in terms of Henry's law. The Henry's law constants found in this work were correlated well by a particularly simple empirical formula based on the molecular weight of the solvent.     

Mapping a Single Assignment Programming Language to Reconfigurable Systems

This paper presents the high level, machine independent, algorithmic, single-assignment programming language SA-C and its optimizing compiler targeting reconfigurable systems. SA-C is intended for Image Processing applications. Language features are introduced and discussed. The intermediate forms DDCF, DFG and AHA, used in the optimization and code-generation phases, are described. Conventional and reconfigurable system specific optimizations are introduced. The code generation process is described. The performance for these systems is analyzed, using a range of applications from simple Image Processing Library functions to more comprehensive applications, such as the ARAGTAP target acquisition prescreener.     

Modification of the dusty-gas equation to predict mass transfer in general poruos media

Volume-mean correction factors are used in the dusty-gas equation to account for heteroporosity effects on isobaric and nonisobaric mass transfer in general porous media. Using conventional information on pore-size distribution, the modified equation maintains reliance on the original dusty-gas constants for characterizing the porous structure. The modified equation was tested with experimental data for a binary helium-nitrogen system in macroporous α-alumina and microporous γ-alumina.     

从密炼机供应商的观点看白炭黑胶料的混炼

轮胎性能方面的新进展已经导致在轮胎胶料中用白炭黑替代炭黑。使用白炭黑胶料制造轮胎可降低轮胎滚动阻力,减少燃料消耗,提高防滑性能和安全性能。在轮胎胶料中,作为补强填充剂的炭黑被白炭黑部分或全部替代。与炭黑相比,白炭黑本身并不致使胶料性能更好。作为一种化学配合剂添加的硅烷被用作白炭黑与聚合物之间的偶联剂。混炼期间,硅烷与白炭黑反应,并生成以后可在硫化过程中与聚合物键合的活性反应点。由于在混炼过程中发生化学反应,因此密炼机的作用是一个胶料温度必须非常精确控制的化学反应器。除了让填充剂分散于胶料中以外,还必…     

Concentration forcing in ammonia synthesis—I Controlled cyclic operation

Qualitative and quantitative arguments are made, based on accepted reaction mechanisms, that the Haber synthesis of ammonia should provide enhanced production, compared to steady state operation, when operated in a controlled cyclic mode (concentration forcing). In the study reported here, the potential for such an enhancement was examined experimentally at several temperatures and pressures. The observed trends are explained in terms of phenomenological steps. For conditions of low temperature and pressure, at which most detailed kinetic studies have been conducted, appreciable production enhancement is observed. However, for conditions of current industrial operation using conventional ammonia catalysts, steady state should provide greater production than concentration forcing operation.When using cyclic operation, the relaxed steady state approximation provides a convenient basis for comparing experimental production of ammonia with that predicted by phenomenological models. This comparison indicates a failure of the models of Temkin, Brill, and Ozaki, Taylor, and Boudart to describe the observed kinetics of ammonia synthesis during high-frequency, concentration-cycling operation.