• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.3
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• pp.223-232
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• 1995

Abstract Urea($(NH_2)_2CO$) and THAMP (Tris(hydroxymethyl) aminomethane phosphate) are new organic nonlinear optical materials (NLO) for the device application such as the frequency conversion of laser radiation. The single crystals of urea and THAMP have been grown by the falling temperature method and the temperature difference method. The crystal growth parameters were presented associated with the molphology of the grown crystals. Based on the solubility measurements, methanol was a suitable solvent for the growth of urea. The solubilities of urea have a positive temperature coefficient and the heat of solution of urea was estimated to be -2.58 kcal/mol. The grown crystals of urea have the preferential growth habit in the z-axis. Additives such as $NH_4_H_2PO_4$, KCL, $H_3PO_4$, $CaCl_2{\cdot}2H_2O$, $C_2H_5OH$ were used for the favourable growth in the x - and y-axis and the preventive growth in the z-axis. The moleratio of THAM and H3P04 for the solution of THAMP was 1 : 1. The solubilities of THAMP have a positive temperature coefficient. The heat of solution was estimated to be - 1.70 kcal/ mol.

• 한국연소학회:학술대회논문집
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• 2014.11a
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• pp.235-236
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• 2014

An experimental study has been carried out to investigate a thermal decomposition of urea solution at relative low temperature with a lab-scaled exhaust pipe. The conversion efficiency of reductant considered with both ammonia and HNCO related with the urea injection quantity, inflow gas velocity and temperature. The conversion efficiency of ammonia was larger than that of HNCO under all experimental conditions unlike the theoretical thermolysis reaction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.2
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• pp.177-182
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• 2015

The NOx emissions from diesel engines and industrial boilers are a major cause of environmental pollution. The selective catalytic reduction of urea is an aftertreatment technology that is widely used for the reduction of NOx emissions. The objective of this study was to investigate the characteristics of the thermal decomposition of a urea aqueous solution using laboratory-scale experimental equipment under conditions similar to those of marine diesel engines. A 40 wt. urea aqueous solution was used in this study. It was found that the total conversion rate varied with the inflow gas conditions and flow rates of the urea aqueous solution. In addition, there were conversion rate differences between NH3 and HNCO. At inflow gas temperature conditions of $210^{\circ}C$ and $250^{\circ}C$, the $NH_3$ conversion rate was found to be higher than that of the HNCO, depending on the residence time.

• Journal of the Korean Chemical Society
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• v.24 no.3
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• pp.209-217
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• 1980

The relative viscosities and osmotic coefficients of solutions of urea, 1,3-dimethyl-urea(DMU), acetamide(AA), and propionamide (PA) in dimethylsulfoxide(DMSO), water, methanol, and in ethanol have been measured at 25 and $45^{\circ}$C by viscometry and osmometry. Viscosity increment in nonaqueous solutions decreased with increasing of the partial molal volumes of the solutes, but in aqueous solution the result was inversed. Viscosity increment of aqueous solution was smaller than that of aqueous DMU solution, but that of nonaqueous urea solution was larger than that of DMU. Amides, however, showed similar viscosity increment in any solvent.Osmotic coefficients of aqueous solution of urea were larger than those of DMU. In the nonaqueous solutions urea exhibited larger deviation from Raoult's law than DMU. The results indicated that urea molecules break water-structure in water, self-associate in DMSO, and showed larger solute-solvent interaction in alcohols than DMU. It can be also confirmed that amides break alcohol structure to a greater extent than any other solutes.

• Journal of Plant Biology
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• v.5 no.2
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• pp.6-12
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• 1962

For the comparison with the previous paper (4) the present report deals with the absorption and metabolism of urea and other nitrogen ions in barley seedling absorbed through root. 1. The amount of nitrate in barley treated with urea reach it peak on the 8th day. NO3 on the 4th, NH4 on the 6th or 8th, respectively. 2. The ammonia content in urea group reaches its peak on the 6th day but other groups on the 4th day. The present data in the urea group show to shorten 4 days compared with that of the previous paper(4). 3. the content of total amide from the present data aare gradully increased on all of the groups during this experiment. These are agreement with the result of the previous paper (4). 4. the alcohol solution nitrogen in the urea gorup shows the similar tendency to the NaNO3 group but reaches it peak 2 days later than in the (NH4)2SO4 group. 5. The content of total nitrogen in the urea series has the lowest amount at the beginning while the richest from the 4th day after. These would be explained on that the absorption of urea is delayed and the PH in the urea solution does not change, so called "physiological neutrality". The author should like express his sincere thanks to Prof. M.J.Lee of Seoul National University for his valuable advices.e advices.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.7
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• pp.531-540
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• 2009

In this study, thermo-gravimetric analysis(TGA) was used to investigate the effect of urea concentration and heating rate on the ammonia($NH_3$) formation process from urea solution. A newly designed pipe nozzle was inserted through a 1,000 N${\ss}$(C)/h oil firing boiler to compare the DeNOx efficiencies between the upward and downward nozzle. This experiment reveals the effect of path which an urea droplet goes through. Urea solution showed the same TGA graph without regard to the presence of oxygen. Heating rate had a great influence on the weight loss trend. But the concentration of urea solution between 10% and 40% did not affect so much the thermal decomposition temperature. Therefore, heating rate is more important factor on the thermal decomposition of urea than the concentration of urea solution. Three nozzles located at different positions showed similar DeNOx efficiencies such as 68.1%, 71.8%, 70.8% at the same temperature. Even though urea solution was injected for the same zone, the injection direction made much difference in DeNOx efficiency. A upward nozzle showed 68.1% and downward nozzle 9.5%. This results illustrate the importance of heating rate.

• Journal of Korean Society for Atmospheric Environment
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• v.32 no.5
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• pp.526-535
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• 2016

Recently, fine dust in atmosphere have been considerably issued as a harmful element for human. Nitrogen oxide ($NO_x$) exhausted from diesel engines and power plants has been disclosed as a main source of secondary production of fine dust. In order to prevent exhausting these nitrogenous compounds into atmosphere, a treatment system with selective catalytic reduction (SCR) catalyst with ammonia as a reductant has been used in various industries. Urea solution has been widely studied to supply ammonia into a SCR catalytic reactor, safely. However, the conversion of urea solution to ammonia has several challenges, especially on a slow conversion velocity. In the present study, a fast urea conversion system including a plasma burner was suggested and designed to evaluate the performances of urea conversion and initial operation time. A designed lab-scale facility has a plasma burner, urea nozzle, mixer, and SCR catalyst which is for hydrolysis of isocyane. Flow rate of methane that is a fuel of the plasma burner was varied to control temperatures in the urea conversion facility. From experimental results, it is found that urea can be converted into ammonia using high temperature condition of above $400^{\circ}C$. In the designed test facility, it is found that ammonia can be produced within 1 min from urea injection and the result shows prospect commercialization of proposed technology in the SCR facilities.

• Asian-Australasian Journal of Animal Sciences
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• v.4 no.1
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• pp.91-97
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• 1991

Twenty five 75% Holstein Friesian cross bred bullocks fed rice straw (Oryza sativa) of long form, were fed with the following five treatments. 1. Rice straw, untreated (RS) 2. RS + water (1:1), stored for 24 hours (WRS) 3. RS (100 kg) + urea solution (4 kg urea/100 litre water) and dried (USRS) 4. RS (100 kg) + urea solution (as in 3) stored in wet condition for 24 hours (UWRS) 5. RS (100 kg) + urea solution (as in 3) stored in pit for 21 days (UTRS). Potential digestibility of treatments of RS was evaluated by monitoring (in vitro) Simulating Rumen like Fermentation (SRLF). The results indicated that Dry Matter Intake (DMI), digestibility of nutrients, N utilization were of the order UTRS > UWRS > USRS > WRS and RS (p < 0.05 to p < 0.01). SRLF index was high (255.84) for UTRS and least (145.58) for USRS. It was intermediary (199.66) for UWRS. The acetyl content (AC) of UTRS with higher hemicellulose (HCE) digestibility (80.8%) was low compared to UWRS, USRS, RS and WRS. The acetate content was of the order UTRS < UWRS < USRS < WRS and RS thereby indicating that reduction in acetyl content was an index of positive response of urea-treatment of RS. In addition, the ratio of HCE/AC in faeces of UTRS was 0.87 as against the ratios (2.26-2.48) observed in other treatments recording reduction in AC due to urea-treatment. Among the treatments, USRS only supplemented N while UTRS in addition to utilization N, increased the digestibility of structural carbohydrates. Reduction in treatment time from 21 days to 1 day (UWRS) resulted in improvements similar to those of UTRS.

• Journal of the Korean Applied Science and Technology
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• v.22 no.2
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• pp.168-174
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• 2005

Aluminum tri-butoxide was mixed with the water/ethanol solution and then chloroplatinic acid was added to the solution. The solution was dried at $100^{\circ}C$ for 15hrs to remove the solvent and water then it was calcined at $500^{\circ}C$. The catalyst was activated with a gas mixture. During the activation, the temperature was increased from $150^{\circ}C$ to $500^{\circ}C$. The necessary amount of urea was dissolved in 50mL water and injected. Aqueous urea solution was then mixed with the feed gas stream. At low temperatures, nitrogen containing compounds of urea decomposition are used as reductants in the reducton of $NO_X$. However at high temperatures the nitrogen containing compounds are oxidized to NO and $NO_2$ by oxygen instead of being used in the reduction. The activity of the catalyst was dependent on urea concentration in the feed stream when there was not adequate water vapor in the feed. The maximum conversion was shifted from $250^{\circ}C$ to $150^{\circ}C$ when water concentration was increased from 2 to 17%. It seems that the maximum temperature shifts to lower temperatures because the hydrolysis rate of HNCO increases with water, resulting in higher amounts of $NH_3$.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.5
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• pp.818-826
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• 2004

The spray-induced mixing characteristics and thermal decomposition of aqueous urea solution into ammonia have been studied to design optimum sizes and geometries of the mixing chamber in SCR(Selective Catalytic Reduction) system. The cold flow tests about the urea-injection nozzle were performed to clarify the parameters of spray mixing characteristics such as mean diameter and velocity of drops and spray width determined from the interactions between incoming air and injected drops. Discrete particle model in Fluent code was adopted to simulate spray-induced mixing process and the experimental results on the spray characteristics were used as input data of numerical calculations. The simulation results on the spray-induced mixing were verified by comparing the spray width extracted from the digital images with the simulated Particle tracks of injected drops. The single kinetic model was adopted to predict thermal decomposition of urea solution into ammonia and solved simultaneously along with the verified spray model. The hot air generator was designed to match the flow rate and temperature of the exhaust gas of the real engines The measured ammonia productions in the hot air generator were compared with the numerical predictions and the comparison results showed good agreements. Finally, we concluded that the design capabilities for sizing optimum mixing chamber were established.