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排序方式: 共有803条查询结果,搜索用时 76 毫秒
81.
The results of an experimental investigation of staggered tube bundle heat transfer to upward and downward moving vertical foam flow are presented in this article. It was determined that a dependency exists between tube bundle heat transfer intensity on foam volumetric void fraction, foam flow velocity and direction, and liquid drainage from foam. In addition to this, the influence of tube position of the bundle on heat transfer was investigated. Experimental results were summarized by criterion equations, which can be applied in the design of foam type heat exchangers. 相似文献
82.
Cellulase could not be selectively collected from fermentation broth by simple foam fractionation, because of the presence
of other more surface-active compounds. A new approach of affinity foam fractionation was investigated for improvement. A
hardwood hydrolysate (containing cellulose oligomers, substrates to cellulase) and two substrate analogs, i.e., carboxymethyl
cellulose (CMC) and xylan hydrolysate, were added before the foaming process. The substrates and substrate analogs were indeed
found to bind the cellulase selectively and form more hydrophobic complexes that partition more readily onto bubble surfaces.
In this study, the effects of the type and concentration of substrate/analog as well as the presence of cells at different
growth stages were examined. The foam fractionation properties evaluated included foaming speed, foam stability, foamate volume,
and enrichment of filter paper unit (FPU) and individual cellulase components (i.e., endoglucanases, exoglucanases, and β-glucosidases).
Depending on the broth and substrate/analog employed, the foamate FPU could be more than fourfold higher than the starting
broth FPU. Addition of substrate/analog also deterred the enrichment of other extracellular proteins, resulting in the desired
cellulase purification in the foamate. The value of E/P (enzyme activity-FPU/g/L of proteins) in the foamate reached as high
as 18, from a lactose-based fermentation broth with original E/P of 5.6. Among cellulase components, exoglucanases were enriched
the most and β-glucosidases the least. The study with CMC of different molecular weights (MW) and degrees of substitution
(DS) indicated that the CMC with low DS and high MW performed better in cellulase foam fractionation. 相似文献
83.
Propagation of sound and weak shock waves in gas-liquid foams is investigated theoretically and experimentally. An original
physical model is developed to describe the evolution of small perturbations in a foam of polyhedral structure. The model
developed takes into account both peculiarities of interface heat transfer in foam and liquid motion through the system of
Plateau-Gibbs borders which results in the appearance of an additional hydrodynamic dissipative force. The Rayleigh equation
analog, which takes into account the latter phenomenon, is obtained. Structure and dynamics of weak shock waves are investigated.
A vertical shock tube was constructed and used to measure the parameters of weak shock wave propagation in gas-liquid foams
of polyhedral structure. Spectral analysis of the data obtained shows that there are weak dispersion and strong dissipation
of the initial signal. Comparison of the evolution of experimental and theoretical profiles permits to conclude that the suggested
model allows to describe the peculiarities of acoustical perturbations in gas-liquid foam more precisely than it follows from
the standard models.
Received 15 September 1993 / Accepted 27 December 1993 相似文献
84.
V. Dzhunushaliev 《Foundations of Physics》2002,32(7):1069-1090
An approximate model of a spacetime foam is presented. It is supposed that in the spacetime foam each quantum handle is like to an electric dipole and therefore the spacetime foam is similar to a dielectric. If we neglect of linear sizes of the quantum handle then it can be described with an operator containing a Grassman number and either a scalar or a spinor field. For both fields the Lagrangian is presented. For the scalar field it is the dilaton gravity + electrodynamics and the dilaton field is a dielectric permeability. The spherically symmetric solution in this case give us the screening of a bare electric charge surrounded by a polarized spacetime foam and the energy of the electric field becomes finite one. In the case of the spinor field the spherically symmetric solution give us a ball of the polarized spacetime foam filled with the confined electric field. It is shown that the full energy of the electric field in the ball can be very big. 相似文献
85.
Preconcentration Systems Using Polyurethane Foam/Me-BDBD for Determination of Copper in Food Samples
Valfredo Azevedo Lemos Daniel Rodrigues Vieira Cleber Galvão Novaes Marcelo Eça Rocha Moacy Selis Santos Regina Terumi Yamaki 《Mikrochimica acta》2006,153(3-4):193-201
A new reagent, 6-[2′-(6′-methyl-benzothiazolylazo)]-1,2-dihydroxy-3,5-benzenedisulfonic acid (Me-BDBD), was synthesised and
used in on-line and off-line systems for copper preconcentration by solid-phase extraction. Spectrophotometry and Flame Atomic
Absorption Spectrometry (FAAS) were the detection techniques. Polyurethane foam loaded with Me-BDBD packed in a minicolumn
was used as sorbent in both systems. The spectral characteristics of Me-BDBD were investigated. The optimum pH values for
maximum sorption of the metal are between 7.0 and 8.5. Copper was desorbed with 0.05 and 0.50 mol L−1 hydrochloric acid solutions, for on-line and off-line systems, respectively. The effects of several foreign substances on
the adsorption of copper are reported. The enrichment factors obtained were 7 (on-line) and 26 (off-line) for the systems.
The proposed procedures allowed the determination of copper with detection limits of 3.4 and 1.4 μg L−1 (0.85 and 0.35 μg per gram of sample) for on-line and off-line systems, respectively. The precision of the procedures was
also calculated: 3.2 (on-line) and 1.9% (off-line). The validation of the procedures was carried out by analysis of certified
reference material. The copper contents in corn and rice flour and black tea samples were determined by applying the proposed
procedures. 相似文献
86.
The present work describes a novel method for the incorporation of Nile blue A into polyurethane foam matrix. This foam material was found to be very suitable for the extraction of metal ions from aqueous solutions. The characterization of Nile blue A grafted foam and the effect of halide concentration, pH, shaking time, extraction isotherm and capacity have been investigated. This foam material was found to be suitable for the separation and preconcentration of iron (III), zinc (II), cadmium (II) and mercury (II) from waste water. The extraction was accomplished in (15-20) minutes. Iron was separated from acid medium (2-4 M HCl), zinc from (3-5 M HCl), cadmium from (4-6 M HCl) as thiocyanate complexes and mercury was separated from (1-2 M HCl) as chloride. 相似文献
87.
A stable chelating sorbent was synthesized by covalently linking 4-hydroxytoluene or 4-hydroxyacetophenone with the polyurethane foam (PUF) through -NN- group. The synthesized chelating sorbents were characterized by IR and UV/vis measurements. The modified foams show excellent stability towards various solvents. Factors influencing the extraction process of Zn(II), Pb(II), Cd(II) and Hg(II) were studied and evaluated as a function of pH of metal ion solution and equilibration shaking time. The values of sorption capacity of metal ions (μg g−1) were determined with the two types of bonded foams. The two phenolic bonded foams were studied comparatively. The potential applications of the two newly synthesized foams for the removal and separation of the examined metal ions from two natural water samples (drinking tap water and Qaroun lake water at Fayoum City, Egypt) were investigated. Precision (assessed as a relative standard deviation, R.S.D.) was also evaluated and found to be ≤7.3% (N = 5) with a detection limit under 0.46 μg L−1. 相似文献
88.
Metal foams: A survey 总被引:37,自引:0,他引:37
The current state-of-the-art in the development of cellular metal foams is reviewed, with focus on their fabrication, mechanical/thermal/acoustic properties, and potential applications as lightweight panels, energy absorbers, heat exchangers, and acoustic liners. Foam property charts with scaling relations are presented, allowing scoping and selection through the use of material indices. 相似文献
89.
β-Glucosidase was covalently immobilized alone and coimmobilized with cellulase using a hydrophilic polyurethane foam (Hypol®FHP 2002). Immobilization improved the functional properties of the enzymes. When immobilized alone, the Km for cellobiose of β-glucosidase was decreased by 33% and the pH optimum shifted to a slightly more basic value, compared to the free enzyme. Immobilized β-glucosidase was extremely stable (95% of activity remained after 1000 h of continuous use). Coimmobilization of cellulase and β-glucosidase produced a cellulose-hydrolyzing complex with a 2.5-fold greater rate of glucose production for soluble cellulose and a four-fold greater increase for insoluble cellulose, compared to immobilized cellulase alone. The immobilized enzymes showed a broader acceptance of various types of insoluble cellulose substrates than did the free enzymes and showed a long-term (at least 24 h) linear rate of glucose production from microcrystalline cellulose. The pH optimum for the coimmobilized enzymes was 6.0. This method for enzyme immobilization is fast, irreversible, and does not require harsh conditions. The enhanced glucose yields obtained indicate that this method may prove useful for commercial cellulose hydrolysis. 相似文献
90.