摘要:

This study investigated the effects of dissolved oxygen ( DO) concentration and flow conditions on the conversion rates and pathways of nitrogenous compounds in an pilot open channel. Ammonium sulfate and glucose were added externally as the substrates in the investigation. The experimental results showed that under conditions of constant flow velocity and DO concentration above 1 mg/1, the removal rates of total nitrogen (including nitrite, nitrate and ammonium nitrogens) varied linearly with the removal rates of ammonium nitrogen. Comparison of the removal rate for each individual nitrogenous component reveals the following order of removal rates: ammonium nitrogen>total nitrogen>nitrate nitrogen> nitrite nitrogen. Moreover, the nitrite concentration was found to increase in all tests and the nitrate concentration was increased only when the DO concentration was within the range of 3 to 5 mg/l. In contrast, when the DO concentration was less than 1 mg/l, all nitrogenous compounds were removed and the following order of removal rates of nitrogenous compounds was observed: total nitrogen>nitrate nitrogen>nitrite nitrogen>ammo‐nium nitrogen. The results indicated that the conversion pathways of nitrogenous compounds can be divided into four different types depending on the DO concentration level. The test results also revealed that an increase in the flow velocity significantly influenced the conversion rates of nitrogenous compounds. While a V‐shaped relation of the removal rates of total nitrogen vs the Reynolds numbers was observed for low DO below 1.5 mg/1, an inverted V‐shaped relation occurred at high DO above 5 mg/1.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670477

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Electric arc method was employed in this work to investigate the fullerene synthesis under various operating conditions. An elaborate apparatus was designed for the experimental studies. For fullerene separation and purification, a modified Soxhlet extraction column packed with alumina or alumina/granular activated carbon (GAC) was utilized. The fullerene‐containing soot was generated from ultra‐pure graphite rods in a quartz reactor in the absence of oxygen and under partial vacuum conditions. Helium, argon and nitrogen were employed as the purging gases in the electric arc system. Among these three working inert gases, helium was found to be the best in terms of fullerene yield. The helium flow rate was observed to have lesser effect on the fullerene yield than the operating pressure maintained in the reactor. The fullerene production by the present electric arc apparatus was found to consist of over 90% C60and C70with the remainder being other minor fullerene components. The Soxhlet extraction column packed with alumina/GAC offered efficient separation of C60from C70and other minor fullerene components. It was also observed in the experiments that fullerene yield, and thus the C60production, is considerably enhanced as the current input is increased.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670478

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Iterative dynamic programming (IDP) introduced by Luus has been recognized as a powerful method for solving a wide variety of nonlinear optimal control problems. Based on backward stagewise operation, the original IDP computational scheme performs the evaluation of the optimal control associated with each state node in a backward manner, starting from the last stage. In this paper, we present an improved scheme for carrying out the IDP computation which yields the same result as the backward IDP. The proposed scheme performs the control evaluation in a forward‐backward manner and thus can save computing time by eliminating the determination of optimal controls for inaccessible state nodes.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670479

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Several non‐acid amines including diethylenediamine (DEDA), trimethylenediamine (TEDA), monoethanolamine (MEA), diethanol‐amine (DEA) and triethanolamine (TEA), were examined in order to understand their suitability for being used as complex agents in the reaction with ammonium hydroxide to form ionized complex agents in the sol preparation from zirconyl chloride octahydrate. Only DEA and TEA amongst the non‐acid complex agents could produce the sol of the precursor of zirconium oxide, by reaction of zirconyl chloride octahydrate (ZrOCl2• 8H2O) and TEA (or DEA) in ammonia solution. The reaction mechanism of sol formation, which includes sequential hydrolysis and condensation, has been proposed here. A tetranuclear complex molecule ([Zr4(OH)8(OH2)16)8+]) is first produced in the aqueous solution via hydrolysis, and a larger complex molecule ([Zr4(OH)8(OH2)16–2n]8+(HN(R‐O‐)22‐)nand [Zr4(OH)8–2n(OH2)16]8+(HN(R‐O‐)22‐)nfor DEA, and [Zr4(OH)8(OH2)16–3n]8+(N(R‐O‐)33‐)nand [Zr4(OH)8–3n(OH2)16](N(R‐O‐)33‐)nfor TEA) is subsequently generated via condensation. The viscosity of the sol and average size of the sol particles, which have been observed to be affected by the reaction conditions, can be explained by the proposed mechanism. The effects of reaction conditions, such as temperature, molar ratio of ZrOCl2/H2O, amount of ammonia, and agitation speed, on the viscosity of the sol and average size of the particles have been investigated.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670480

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study investigated composite yarn on a 4‐roller drafting system with the goal of improving the cross‐sectional structure of polyester filament/rayon fiber (P/R) composite yarn. We found that a 4‐roller drafting system with 2 double aprons is beneficial for controlling the filament spread width, as well as improving the mixing efficiency of spreaded polyester filaments and drafted rayon fibers in the nip of the front roller. Consequently, this arrangement will yield a composite yarn with better blend uniformity. The results revealed that the fraction of the uniform distribution type and the wrapping type could increase up to 34.0% and 19.5% respectively.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670481

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This work investigates the constant‐pressure consolidation characteristics of three different sludge samples, with particular emphasis on the ternary consolida. The Terzaghi‐Voigt rheological model modified by Chang and Lee (1998) is also applied to interpret the data and, in doing so, to evaluate the model parameters. Experimental results indicate that the ternary consolidation stage commonly found in sludge contains a large amount of bound water. In addition, consolidation pressure and polymer conditioning markedly affects the moisture distribution. Results obtained from conventional analysis are also compared with those of the modified model.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670482

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study investigated the effects of spinning conditions such as traveller, twist multiplier, front top roller pressure and hardness on the physical properties of 19.7 tex Polyester/Rayon (P/R) composite yarns. Results showed that a traveller of #1/0, twist multiplier of 2.8, front top roller pressure of 18 kgf and hardness of 70° are the optimum spinning conditions. This combination results in the best mixing of spreaded polyester filaments and drafting rayon fibers in the nip of the front rollers, arranging them in the best dispersion to form a P/R composite yarn with better quality and good blend uniformity. The results also showed that the 19.7‐tex composite yarn spun in this study is superior to the world 5 % for standards of uniformity and hairiness. This indicates that the quality of P/R composite yarn has been remarkably improved.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670483

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

First principles quantum mechanical calculations based on the local‐density‐functional (LDF) theory have been used to investigate the electronic, structural, and defect properties of transition‐metal aluminides and silicides. Three examples are given to show the predictive capability of modern LDF calculation: (1) interfacial properties of two‐phase Ti‐Al alloys, (2) point defect structure of NiAl and FeAl, and (3) elastic constants and coefficient of thermal expansion (CTE) of Mo5Si3. Emphasis is placed on the effect of interfaces on the planar fault energies in Ti‐Al, the interaction between vacancies in B2 aluminides, and the interplay between bonding and the anisotropy in CTE in Mo5Si3. We show that first principles calculation not only yields results in excellent agreement with experiments (if available), but offers information on electronic structure from which a clearer understanding of atomic‐level interactions that govern alloy behavior can be made.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670484

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The along‐wind response of a surface‐mounted elastic fence under the action of wind was investigated numerically. In the computations, two sets of equations, one for the simulation of the unsteady turbulent flow and the other for the calculation of the dynamic motion of the fence, were solved alternatively. The resulting time‐series tip response of the fence as well as the flow fields were analyzed to examine the dynamic behaviors of the two.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670485

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study numerically and experimentally investigates the properties of pressure, temperature and mass flow rate of air discharged from a number of nozzles drilled on a blow pipe. In addition to deriving a set of equations to express the physical phenomena, this study also uses measurement equipment to measure the indispensable data used in the above equations. Consequently, the theoretical and experimental works complement each other. According to the results, the mass flow rate of the air pulse discharged from a nozzle depends on the position and diameter of the nozzle on the blow pipe. Furthermore, the direction of the discharged air pulse is not perpendicular to the blow pipe and has an inclined angle which also depends on the position of the nozzle on the blow pipe. Employing the model proposed herein, a uniform mass flow rate discharged from each nozzle can be obtained by adjusting the sizes of the nozzles on the blow pipe.

ISSN:0253-3839    

DOI:10.1080/02533839.1999.9670486

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor