• Corrosion Science and Technology
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• v.12 no.1
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• pp.7-11
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• 2013

High velocity oxy-fuel (HVOF) spray coating of WC-metal powder (powder) was carried out to improve the resistances of friction, wear and corrosion of magnetic bearing shaft material Inconel718 (In718) of turbo blower. A micron sized WC-metal powder (86.5% WC, 9.5% Co 4% Cr) was coated onto In718 surface using HVOF thermal spraying. During the spraying, the binder metals and alloy such as Co, Cr and Co-Cr alloy were molten and a small portion of WC particles were partially decomposed to $W_2C$ and free carbon at above its decomposition temperature of $1250^{\circ}C$. The free carbon and excessively sprayed oxygen formed carbon oxide gases, resulting a porous coating of porosity of $2.2{\pm}0.3%$. The surface hardness of substrate increased approximately three times from 400 Hv of In718 to $1260{\pm}30Hv$ of the coating The friction coefficients of the coating were approximately $0.33{\pm}0.03$ at $25^{\circ}C$ and $0.26{\pm}0.03$ at $450^{\circ}C$. These values were smaller than those of In718 substrate at both temperatures due to the lubrication from the free carbon and the cobalt oxide debris. The corrosion resistance of the coating was higher than that of In718 both in salt water of 3.5% NaCl and acid of 1 M HCl solutions, on the contrary, it was lower in base solution of 1 M NaOH. According to this study, the HVOF WC-metal powder coating is recommended for the durability improvement of magnetic bearing shaft of turbo blower.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.60-66
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• 2010

Zinc has a number of characteristics that make it well suited for use as a coating to protecting iron and steel products from corrosion. Its excellent corrosion resistance in most environments accounts for its successful use as a protective coating on a variety of products and in many exposure conditions. The excellent field performance of zinc coatings results from their ability to form dense, adherent films that corrode at a rate that ranges from 1% to 10% of the corrosion rate of ferrous materials, depending on the environment. Recently, EU RoHS and EU ELV prohibited the use of materials that adversely affect the environment, such as Pb, Hg, Cd, and $Cr^{+6}$. In this study, environmentally-friendly, Cr-free solutions (epoxy solution, acrylic solution, and urethane solution S-700) and organic/inorganic solution with Si; LRO-317) were used to evaluate the corrosion resistance of zinc-coated steel subjected to a saltwater spray for 72 hours. The coating of urethane solution (S-700) was best among the three kinds of solution with heat treatment during five minutes at $190^{\circ}F$. Test specimens with S-700 and LRO-317 coating were heat treated in a drying oven at 170, 180, 190, 200, and $210^{\circ}C$ for five minutes. The results show that the optimum corrosion resistance was $190^{\circ}C$ in EGI and $170^{\circ}C$ in HDGI, respectively.

• Journal of Hydrogen and New Energy
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• v.31 no.2
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• pp.210-222
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• 2020

Hydrogen is evaluated as one of new energy sources that can overcome the limitations and pollution problems of conventional fossil fuels. Although hydrogen is free from CO₂, attention is required in NOx emission and flame stability in order to use hydrogen in existing gas fuel system. This study investigates the differences in operating characteristics and its problems to be modified when the hydrogen is used as fuel for existing domestic boilers and new heat recover boilers with water spray. When the hydrogen is used in domestic boilers, the efficiency is about 6-7% lower than methane due to higher partial vapor pressure in the exhaust gas at usual operating conditions above 60℃ in combustion chamber outlet temperature. On the other hand, the heat recovery boiler with water spray (HR-B/WS-X) is expected to achieve up to 95% efficiency, which is 12% more efficient than conventional boilers. It can also significantly reduce NOx emission by lowering the flame temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.3
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• pp.237-243
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• 2015

In this study, the effects of the mixing ratio of emulsified fuel on the droplet evaporation and spray behavior characteristics were analyzed. A surfactant comprising span 80 and tween 80 mixed at a 9:1 ratio was used for the emulsified fuel. The fuel and surfactant were mixed at a ratio of 3:1 for the emulsified fuel. In addition, considering the mixing ratio of the surfactant, the mixing ratio of $H_2O_2$ in the emulsified fuel was set as EF (emulsified fuel)0, EF2, EF12, EF22, EF32, and EF42. To observe the evaporation characteristics, droplets of the emulsified fuel were dropped on a heating plate and observed using scattered light and a Schlieren system. In addition, to analyze the effect of the $H_2O_2$ mixing ratio, the behavior characteristics of the evaporative free spray were investigated in the mixing ratio range of EF0 to EF22 using a constant volume chamber with heaters. Consequentially, it was found that in the case of EF22, the free spray development of the emulsified fuel was faster than that of EF0 (diesel only) because of the promotion of the evaporation due to the phase change in the peroxide contained in the emulsion fuel.

• Korean Journal of Food Science and Technology
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• v.40 no.3
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• pp.303-310
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• 2008

This study was performed to verify the effects of encapsulation against oil oxidation. Thiobarbituric acid (TBA) values of samples were compared during storage at $60^{\circ}C$, indicating that the encapsulated avocado oil had lower TBA values than the free avocado oil. Microcapsules consisting of a whey protein isolate (WPI)-only wall system had slightly improved oxidative stability; however, spray-dried particles containing a high proportion of maltodextrin (MD) clearly offered better protection from oxidation than the other forms of encapsulation. The chlorophyll (Chl) content of the encapsulated avocado oil was higher than that of the free oil sample. When compared to the control, all wall systems protected the change of the chlorophyll content storage. No large differences were observed between the encapsulated powders according to the various wall materials. The color of the encapsulated oil changed from green to yellowish-green, indicating the formation of pheophytin from chlorophyll. The yellowish color of the oil correlated with a reduced total Chl content. In conclusion, encapsulation with spray drying for avocado oil could lead to improved stability during storage with respect to oxidation and the preservation of chlorophyll.

• Journal of ILASS-Korea
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• v.26 no.2
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• pp.88-95
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• 2021

This study aims to investigate the influence of the droplet volume on the evaporation characteristics of the sessile droplet. In particular, the effect of the free convection in the vapor domain on the evaporation rate was analyzed through the numerical simulation. The commercial code of the ANSYS Fluent (V.2020 R2) was used to simulate the heat transfer in the liquid-vapor domain. Moreover, we used the diffusion model to estimate the evaporation rate for the different droplet volume under the room temperature. It was found that the evaporation rate significantly increases with the droplet volume because of the larger surface area for the mass transfer. Also, the effect of free convection on the evaporation rate becomes significant with an increment of droplet volume owing to the increase in the droplet radius corresponding to the characteristic length of the free convection.

• Corrosion Science and Technology
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• v.6 no.2
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• pp.68-73
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• 2007

The toxicity of chromium that is used to impart corrosion resistance to galvanized steel created environmental and health-related concerns and generated a great deal of interest in developing chrome-free treatment coatings. In the present work, organic-inorganic composite coatings were used to coat electrogalvanized steel (EG) sheets for corrosion protection without degrading its weldability property. The new coatings composed of specially modified polyurethane dispersion hybridized with silicate and unique inorganic-organic inhibitors were developed during this work. It was found that about $1{\mu}m$ thickness of coating layer is secure enough in corrosion resistance of flat and formed part even after alkaline degreasing. Overall chemical resistances including fingerprint resistance and paint adhesion property were satisfied with the test specification of Sony technical standard of SS-00260-2002. Therefore, it is concluded that the newly developed chrome-free product can replace the conventional chromated product.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.2
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• pp.61-66
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• 2011

The purpose of this paper is to design a hydraulic actuator to operate under high pressure conditions. The flow characteristics under design conditions of hydraulic actuator were numerically conducted by commercial fluid dynamic code(ANSYS CFX V11). The numerical analysis was performed by transient technique according to the variation of stroke times, which was changed from 0 to 1 second by interval of 0.01. Turbulence model, $k-\omega$ SST was selected to secure more accurate prediction of hydraulic oil flow. The ICEM-CFD 11 and CFXMesher, reliable grid generation software was also adapted to secure high quality grid necessary for the reliable analysis. According to the simulation results, the flow rate which was supplied to the hydraulic actuator was 30.4l/min. These results are in good agreement with design results within 3.5% error.

• Proceedings of the Korean Magnestics Society Conference
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• 2013.12a
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• pp.89-89
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• 2013

Rare earth (RE) - transition metal based high energy density magnets are of immense significance in various engineering applications. $Nd_2Fe_{14}B$ magnets possess the highest energy product and are widely used in whole industries. Simultaneously, composite alloys that are cheap, cost effective and strong commercially available have drawn great attention, because rare-earth metals are costly, less abundant and strategic shortage. We designed rare-earth free alloys and fabrication process and developed novel route to prepare $Nd_2Fe_{14}B$ powders by wet process employing spray drying and reduction-diffusion (R-D) without the use of high purity metals as raw material. MnAl-base permanent magnetic powders are potentially important material for rare-earth free magnets. We have prepared the nano-sized MnAl powders by plasma arc discharge and micron-sized MnAl powders by gas atomization. They showed good magnetic property, compared with that from conventional processes. $Nd_2Fe_{14}B$ powders with high coercivity of more than 10 kOe were successfully synthesized by adjusting R-D step, followed by precise washing system. It is considered that this process can be applied for the recycling of RE-elements extracted from ewaste including motors.

• Biotechnology and Bioprocess Engineering:BBE
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• v.3 no.1
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• pp.35-39
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• 1998

An enzymatic process was developed to produce protein hydrolysater form defatted soya protein. Various unit operations were tried, and the effects of pre- and post-treatments on the product characteristics such as degree of hydroylsis (DH), free amino acid content (%FAA) and average molecular weight (MW) were investigated. The use of acid washes showed no difference in %DH. Increasing pH during pre-cooking gave lower %DH. Alkaline cooking made too much insoluble protein, thus the protein yield was too small. A better hydrolysis with more acceptable taste was obtained when the combination of Neutrase/Alcalase/Flavourzyme was used in place of Alcalase/Flavourzyme combination; Untoasted defatted soya was more effective on the proteolysis than toasted one. The MW of the evaporated and spray dried product was higher than that of undried product, due to precipitation of low-solubility components. When ultrafiltration and the product concentration carried out the product separation by reverse osmosis, the solubility and the taste of the product were improved. The difference between enzyme hydrolysate and acid hydrolysate was significant in free amino acid composition, especially in tyrosine, phenylalanine, glutamine and asparagine.