• Journal of the Korean Wood Science and Technology
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• v.16 no.1
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• pp.3-8
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• 1988

This study was carried out to examine the effect of pretreatment of veneer with aluminum sulfate solution for the manufacture of the kapur plywood on the reduction of urea resin spread. The results were as follows: 1. Specific gravities of plywoods made of the kapur veneers ranged from 0.83 to 0.84 and their moisture contents based on air dry weight showed from 10.6% to 11.4%. These met the Korean Industrial Standards. 2. In the case of dry shear strength for the 3rd class plywood, 40% reduction- spread met K S as well as normal urea resin spread. pH of the aluminum sulfate solution gave better result at pH 4.5 and pH 6 than at pH 3. For the manufacture of the 2nd class plywood, hot and cold water-wet shear strength show the best results at the following conditions; such as 20% reduction spread, pH 4.5 of aluminum sulfate solution and all veneer treatment.

• Journal of ILASS-Korea
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• v.13 no.3
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• pp.134-142
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• 2008

In the case of heavy duty diesel engines, the Urea-SCR system is currently considered to reduce the NOx emission as a proved technology, and it is widely studied to get the high performance and durability. However, the nozzles to inject the urea-water solution into the exhaust pipe occur some problems, including the nozzle clogging, deposition of urea-water solution on the inner wall of the exhaust pipe, resulting in the production of urea salt. In this study, a swirl-type twin-fluid nozzle to produce more fine droplets was used as a method to solve the problems. The effect of the nozzle cap geometry, including the length to diameter ratio ($l_o/d_o$) and chamfer, on the spray characteristics were investigated experimentally. The length to diameter ratio of nozzle cap were varied from 0.25 to 1.125. The chamfer angle of the nozzle cap was constant at 90o. The mean velocity and droplet size distributions of the spray were measured using a 2-D PDA (phase Doppler analyzer) system, and the spray half-width, AMD (arithmetic mean diameter) and SMD (Sauter mean diameter) were analyzed. At result, The larger length to diameter ratio of nozzle cap were more small SMD and AMD. The effect of the chamfer did increase the radial velocity, while it did not affect the atomization effect.

• Journal of ILASS-Korea
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• v.25 no.4
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• pp.196-203
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• 2020

Nowadays, urea SCR technology is considered as the most effective NOx reduction technology of diesel engine. However, low NOx conversion efficiency under low temperature conditions is one of its problems to be solved. This is because injection of UWS (Urea Water Solution) is impossible under such a low temperature condition due to the problem of insufficient of urea decomposition and urea deposits. In several previous studies, it has been reported that appropriate control of the amount of ammonia adsorbed on SCR catalyst can improve the NOx conversion efficiency under low temperature conditions. In this study, we tried to find out how much the NOx conversion efficiency increases with respect to the amount of ammonia adsorbed on the catalyst, and what the temperature conditions that the ammonia slip occurs. This study shows the results of 8 times repeated WHTC test with a diesel engine, in which UWS was injected with NH3/NOx mole ratio of '1'. Through this study, it was found that 13% of the NOx conversion efficiency of WHTC increased while the θ (ammonia adsorption rate) increased from "0%" to "22%". In addition, it is found that in cases of high θ value, the significant improvement of NOx conversion efficiency at low temperatures presented during the beginning period of WHTC and at high temperature and transient conditions presented during last part of WHTC test. The NH3 slip occurring condition was 250℃ of catalyst temperature and 10% of θ, and the amount of NH3 slip increased as the temperature and θ are increased.

• Bulletin of the Korean Chemical Society
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• v.6 no.3
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• pp.128-131
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• 1985

A series of copolymer membranes of 2-hydroxyethylmethacrylate (HEMA) with selected hydrophobic monomers were prepared without crosslinking agents. The equilibrium water content, the partition coefficient, and the permeability of the solutes such as urea, methylurea, 1,3-di-methylurea, and acetamide via these membranes were measured. The partition coefficient data show that as the hydrophobicity of solutes increased, the partition of solutes were dictated by hydrophobic interaction between solute and polymer matrix. Diffusion coefficients obtained in these experiments decrease as the water content of polymer membrane decreases. This decrease is blunt as the excess heat capacities, ${\phi}C^0_p$ (excess) in aqueous solution at infinite dilution of solute increases. To investigate the relationship between water content and diffusion coefficient, the results of the diffusion experiments were examined in light of a free-volume model of diffusive transport. The remarkable increase of urea mobility in the polymer network containing relatively larger bulk water can be considered as water structure breaking effect.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.368-377
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• 2013

The Urea-SCR system commercialized shows a remarkable performance to reduce NOx emission in heavy duty diesel engines. However, Urea-water solution injected upstream a mixer, which is set up inside a exhaust pipe to promote exhaust gas-atomized droplet mixing, bumps up against the wall of a exhaust pipe as the droplets flow downstream through the exhaust gas. The urea deposited on the wall of the exhaust pipe is changed into the Urea-salt, resulting in the decreased life-time of the SCR catalysts. Therefore, the development of the urea deposition avoidance technologies is being treated as an important issue of the Urea-SCR systems. An experimental study was carried out to investigate the effects of the wall flow characteristics around the mixer-housing assembly with the variation of the mixer housing surrounding and supporting the mixer, which is designed to increase the wall flow and then to reduce droplet deposition. The flow characteristics was investigated by using a hot-wire anemometry for 2-D simplified duct model, and the housing tilt angles and the position of the mixer were changed : angle of $0^{\circ}$, $1^{\circ}$, $2^{\circ}$, $3^{\circ}$, and mixer positions of 0L, 0.5L, 1L. The results showed that the wall flow onto the exhaust pipe was improved with changing the tilt angle of the mixer housing, and the wall flow improved more when the position of the mixer was on 1L.

• Asian-Australasian Journal of Animal Sciences
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• v.3 no.2
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• pp.75-83
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• 1990

An experiment was conducted with three ruminally and intestinally cannulated non-lactating cows of Finnish Ayrshire breed, to assess the ruminal degradation characteristics of oat (Avena sativa), rye (Secale cereale) and rice (Oryza sativa) straw by the nylon bag technique, and the subsequent post-ruminal degradation of their rumen-undegraded residues by using the mobile bag technique, respectively. The straw samples were untreated or treated with aqueous $NH_3$ or with urea solution in cold or hot water. The untreated straw samples were milled or chopped, and the treated straw samples were chopped. The constant values a, b, and c were computed according to the exponential equation, where a = intercept of degradation curve at time 0, b = potentially degradable material, c = rate of degradation of band (a+b) = maximum potential degradability (asymptote). It was found that nitrogen contents of chemically treated straw were markedly increased by both $NH_3$ and urea treatments. Milling the samples attributed to a remarkable loss at 0 h incubation time as compared to chopping of the respective samples. However, chemical treatment markedly improved the b value and the subsequent (a+b) values for dry matter, organic matter, neutral-detergent fiber, and acid-detergent fiber of the samples. Furthermore, temperature of the water used in the urea solutions was considered essential, since urea in hot water rather than in cold water seemed to enhance the overall degradability. The disappearance of rumen-incubated straw residues from the mobile bags ranged from 4.5 to 9.6% for the parameters measured. On average, the OM disappearance from bags was clearly higher for the residues of urea treated straw compared to those of ammonia treated straw, but the disappearance of NDF tended, however, to be higher on the ammonia treatment.

• The Korean Journal of Physiology
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• v.7 no.1
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• pp.23-31
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• 1973

Numerous factors concern with the absorption of substances through the membrane of the gastrointestinal tract. To simplify the experimental condition, present work has been restricted to observe the disappearance rate of substance from the intestinal loop which was made in the jejunum, 70 cm apart from the pylorus of the adult rabbit. The purpose of the study is to clarify the absorption of urea through the jejunal wall is solely attributable to the concentration difference between the luminal fluid and plasma, and to observe the effect of adding red pepper upon the rate of absorption. The rabbits were anesthetized with nembutal, 35mg/kg I.V. Jejunal loop was made by ligating at 2 spots, 70 cm and 80cm apart from the pylorus. After rinsing with normal saline solution through the polyethylene tubing inserted from the end of the loop, 8 ml of test solution was placed through the same tubing. The test solution contained 200 mg% of urea and 150mg% of polyethylene glycol(M.W. 4,000) in normal saline solution. Right after placing the test solution the first specimen was taken through the tubing, and successive samplings were performed at 5, 10, 20, and 30 minutes. Logarithm of the difference of urea concentration between the luminal fluid and plasma was plotted against time elapsed after the onset of the experiment. If straight line is revealed, it would verify the nature of transport mechanism as diffusion, obeying the Fick's principle. The concentration of polyethylene glycol (PEG) was also measured in order to examine the change in the volume. PEG was used as the marker substance because it is not absorbable in the intestinal tract. Consequently the concentration of PEG relates inversely to the volume of the loop. Instantaneous concentration of urea in the loop times the volume will give the amount of urea remaining in the luminal fluid. The change in the amount of any substance is directly relate to the volume of the compartment and differs from the change in the concentration which is independent of the volume. After completion of the experiment without red pepper, it was added in the test solution and was centrifuged after thorough mixing. Supernatant of the mixture was placed in the loop and similar sampling were performed with the same time intervals that of previous run in order to observe the effects of the red pepper on the passive transport of the water soluble small substance, urea. The results obtained were as follows: 1. Logarithm of the concentration difference of urea between the luminal fluid and plasma was diminished exponentially as time elapsed. The decay constant in the experiment without red pepper was 0.0563/min. By adding red pepper in the test solution as much as the concentration rose to 4,000 mg% and 8,000 mg%, the decay constants were lowered to 0.0493/min and to 0.0506/min, respectively. The time interval by which the concentration difference dropped to one half of the initial value was prolonged. Without red pepper the half concentration time was 13.30 minutes, and by adding extract of red pepper, 15.31 minutes and 15.71 minutes were revealed. 2. The profile of the diminishing rate of tile amount of urea was quite different from that of the concentration because of the change in the volume of the loop during the observed period. 3. By adding the extract of red pepper, it slowed down the rate of absorption of urea in the intestinal loop, suggesting an increase in the diffusional barrier. 4. Larger dosage of red pepper brought an increase in the secretion of intestinal fluid with concomitant expansion of the luminal volume, and the retardation of the absorption of urea was noticed. This effect was largely dependent on the sensitivity of the individual animal to the red pepper, extract. The amount of urea remained after 10 minutes interval was 55.5% of the initial amount in the experiment without red pepper. On the other hand it was not consistent after administration of red pepper, showing 50.6% and 66.5% of the initial figures by adding 400 mg and 800 mg of red pepper in the test solution, respectively. It was postulated that symptom of diarrhea often encountered by taking a hot (red pepper) food might be attributable to the increase of secretion and the retardation of absorption in the intestinal tract.

• Textile Coloration and Finishing
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• v.2 no.3
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• pp.36-42
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• 1990

The effect of urea and its derivatives, which are known as structure breakers of water, in the dyeing of silk with acid dyes was investigated. Without ureas the maximum dye uptake was observed at $60^{\circ}C$ when dyed with Milling Cyanine 5R, but in the presence of ureas the maximum dye uptake was decreased and its temperature also shifted to lower regin in the order of urea >N-methyl urea > N,N-dimethyl urea>tetramethyl urea. These tendencies were more marked in the dyeing of silk fiber with Orange II, a typical levelling type acid dye. These can be interpreted as the decrease in the hydropholic interaction between fiber molecules which results in the broadening of the inter micelie spacing. The increased partition coefficient of dye molecules in the bath by the action of ureas also contributes to dyeing results, and it can be seen from the spectral characteristics of dyes in aqueous urea solution.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.6
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• pp.1020-1033
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• 2015

In order to design a compact urea selective catalytic reduction system, numerical simulation was conducted by computational fluid dynamics tool. A swirl type static mixer and a mixing chamber were considered as mixing units in the system. It had great influence on flow characteristics and urea decomposition into ammonia. The mixer caused flow recirculation and high level of turbulence intensity, and the chamber increased residence time of urea-water-solution injected. Because of those effects, reaction rates of urea decomposition were enhanced in the region. When those mixing units were combined, it showed the maximum because the recirculation zone was significantly developed. $NH_3$ conversion was maximized in the zone due to widely distributed turbulence intensity and high value of uniformity index. It caused improvement of $NO_x$ reduction efficiency of the system. It was possible to reduce 55% length of the chamber and connecting pipe without decrease of $NO_x$ reduction efficiency.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.4
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• pp.174-178
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• 2008

Nano-crystalline slaked lime was synthesized using design of experiment. In order to synthesize slaked lime, calcium chloride $(CaCl_2)$ and urea were used as starting materials. Calcium chloride solution and urea solution were mixed and heated in vessel that calcium carbonate was precipitated during heating. Precipitates were filtered, washed several times using D.I.water and ethanol and finally dried in oven. Slaked lime $(Ca(OH)_2)$ has been fabricated by the hydration of calcined $CaCO_3$. Design of experiment (Taguchi method) was used to optimize parameter, to minimize noise factors of experiment and to statistically analyze the results. Slaked lime having about 50 nm in optimized crystallite size could be obtained by calcination of $CaCO_3$ at $1000^{\circ}C$ for 0.5 h and hydration with D.I water containing ethanol and oxalic acid.