• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.5 no.3
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• pp.169-177
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• 1976

The importance of surface conditions of nucleate boiling is well recognized and it has been known that the heat transfer to boiling liquid is closely related to the bubble population density. The bubble population density should depend on various factors such as heat flux, surface roughness, surface contamination, properties of liquid, etc. In this paper the effect of surface conditions on heat transfer in nucleate boiling is treated. The experiments were carried out with distilled water boiler, on the horizontal heating surfaces, sintered with various bronze particle, under atmospheric pressure. In addition, experimental investigation for the polished bronze surface was performed. By studing a coefficient Xb defined by eq. (9), which represents the bubble foaming ability of heating surface, generalized fomula on the heat transfer in the nucleate toiling were expressed. The coefficient $X_b$, determined empirically, is not constant and indicates a major influence of the sintered metal surfaces on the $\Delta$, necessary to sustain nucleate boiling at any given heat flux. In this study, the main results are obtained as follows; (1) At low temperature difference, the coefficient $X_b$ of sintered metal surface was found to he higher than the polished surface throughout the full range of experiments. (2) The optimum sintered structure showing the maximum coefficient $X_b$ has been confirmed to exist and it is encountered when particle diameter is $256{\mu}$.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.742-749
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• 2002

This study was performed to clarify the formation procedure of continuous voids in cellular concrete, and to examine the effect of a foaming agent on the manufacture of cellular concrete with continuous voids. By the experiments, it was determined that cellular concrete to be formed with continuous voids is influenced by temperature, viscosity and flowability of cement paste, and stability of air voids, and is formed in accordance with cohesion of air voids. It was also found that separate voids are formed at an added amount of air voids corresponding to 2 ％ or less of the amount of cement, whereas an antifoaming phenomenon occurs when the added amount of air voids exceeds 9 ％ of the amount of cement. In products with respective cement fineness of 3,000, 6,000, and 8,000㎠/g, a higher compressive strength was exhibited at a higher cement fineness. The continuous void ratio depending on a variation in fineness was 38 ％, 52 ％, and 22 ％ in those products, respectively. That is, a highest continuous void ratio was exhibited at a cement fineness of 6,000㎠/g. When the water-cement ratio was reduced from 45％ to 25％, the compressive strength of the cellular concrete was increased from 15 kgf/㎠ to 20 kgf/㎠ Thus, the reduction in water-cement ratio was effective in achieving an increase in strength without any variation in the specific gravity of the cellular concrete.

• Clean Technology
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• v.11 no.4
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• pp.195-204
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• 2005

A new condensation process for manufacturing N-acyl taurates which generates less pollutant and produces more than 60 % yield in comparison with the conventional process has been developed in this work. Its optimum process conditions are at $210{\sim}230^{\circ}C$ of reaction temperature and 6 ~ 9 hour of reaction time when Parasol 123 of petroleum refired oil is employed as process solvent and mixed catalysts of sulfonic acid and phosphoric acid are utilized as process catalyst. And the qualities of N-acyl taurates produced by this new process are similar to or better than those of imported product judging from their acid value, amine value and color. Thus, it can be said that the newly developed process for manufacturing N-acyl taurates in this work is better than the conventional process. The physical properties of N-acyl taurates produced in this work such as surface tension, foaming power, foaming stability, hard water stability, and emulsifying power etc. were compared with those of commercially available anionic surfactants. And the experimental results show that N-acyl taurates shows good physical properties and that they can be alternative to conventional anionic surfactants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.6
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• pp.36-42
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• 2021

With recent developments in the Fourth Industrial Revolution, the manufacturing industry has changed rapidly. Through key aspects of Fourth Industrial Revolution super-connections and super-intelligence, machine learning will be able to make fault predictions during the foam-making process. Polyol and isocyanate are components in polyurethane foam. There has been a lot of research that could affect the characteristics of the products, depending on the specific mixture ratio and temperature. Based on these characteristics, this study collects data from each factor during the foam-making process and applies them to machine learning in order to predict faults. The algorithms used in machine learning are the decision tree, kNN, and an ensemble algorithm, and these algorithms learn from 5,147 cases. Based on 1,000 pieces of data for validation, the learning results show up to 98.5% accuracy using the ensemble algorithm. Therefore, the results confirm the faults of currently produced parts by collecting real-time data from each factor during the foam-making process. Furthermore, control of each of the factors may improve the fault rate.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.3
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• pp.277-285
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• 2007

Porous cordierite beads, of which the average pore size was $130{\mu}m$ and porosity was about 80%, were prepared by the foaming method and then their application as support of the $Pt/{\gamma}-alumina$ catalyst for $NO_x$, reduction with propene was investigated. The pressure drop of a 2 mm porous beads filter was less than that of a 1 mm porous beads filter and the difference in pressure drop between these two increased as the flow rate increased. The catalytic activity of $Pt/{\gamma}-alumina$ washcoated on the porous bead was tested with varying Pt loading $(0.005{\sim}0.1g/cm^3),\;C_3H_6/NO$ mole ratio $(0.5{\sim}8)$, space velocity $(20,000{\sim}30,000h^{-1})$ and oxygen contents (1 and 8). Pt loading of $0.04g/cm^3$ showed the highest activity for $NO_x$ conversion. The $De-NO_x$, test was operated in the temperature range of $200{\sim}400^{\circ}C$ and the best operation temperature of the catalytic filter is about $250^{\circ}C$. As the C/N ratio increased, increase of the $NO_x$, conversion might result from the increase in exhaustion of the amount of oxygen by the reduction of hydrocarbon. $NO_x$ conversion at $20,000h^{-1}$ of space velocity shows a maximum 34% higher conversion than that at $30,000h^{-1}$. On condition that $O_2$ was 5%, space velocity was $20,000h^{-1}$ and the C/N ratio was 8, the $NO_x$ conversion exhibited a maximum of 40% at $250^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.16-23
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• 2009

The porous pellets were prepared from porphyry by slurry foaming method. The effect of sintering temperatures on pore structure of porous porphyry pellets with different extension ratio ($E_R$) was investigated by specific surface area, water absorption and porosity, which changed with sintering temperatures. When the sintering temperatures increased from $975^{\circ}C$ to $1075^{\circ}C$, specific surface area and water absorption of the all samples decreased. In case of the sample with an equal sintering temperature, $E_R=3.0$ pellets had little influence on pore structure compared to the $E_R=2.0$ pellets. As a results, it was shown by SEM that facilitated formation of micro pores at $E_R=2.0$ pellets shrunk increasingly after sintering process. At $E_R=3.0$ and sintering temperature at $1025^{\circ}C$, optimum conditions of the porous porphyry porous pellets was found. Also, Escherichia coli removal efficiency of the silver-containing porphoyry porous pellets was measured for the feasibility as a antibacterial media. The antibacterial activity of prepared silver-containing sample was maintained above 90% for 40 days.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.4
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• pp.110-115
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• 2017

This research was performed to investigate the mechanical performance of lightweight concrete including phase changing material(Low temperature PCM). Micro capsulised PCM consisted of wax type core and melamine based wall. Also, for PCM of one single kind, paraffin wax was inserted into Vermiculite and the surface was coated with melamine resin. Interfacial polymerization is based on the principle that macromolecule reaction takes place on the surfaces between 1-dodecanol(core material) and water (solvent) to form the wall material. Lightweight concrete has compressive strength of 10 MPa, tensile strength of 1.5 MPa, and oven dried density of 1.0kg/liter which included 10%, 20%, or 30% PCM by weight. To do so, this study fabricated light-weight foamed concrete ($1.0kg/m^3$) in pre-foaming method and mixed it with PCM micro capsule of 1-dodecanol and melamine to examine its physical properties.

• Elastomers and Composites
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• v.35 no.2
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• pp.106-114
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• 2000

The foam of ethylene vinyl acetate (EVA)/styrene-vinyl isoprene-styrene triblock copolymer(SVIS) blend was prepared to improve the shock-absorption and compression set characteristics at room temperature. The effects of blowing agent and blend ratio of EVA/SVIS on expansion ratio, cell structure and mechanical properties of the foam were investigated. As the SVIS content increased, the viscosity of blends was increased but the crosslinking rate was slow down, the expansion ratio was decreased. and the specific gravity was increased. At room temperature, the resilience was not affected by increasing the amount of blowing agent. The value of tan ${\delta}$ was increased by increasing the amount of SVIS. As a result, the value of compression set was decreased. This is due to the increased values of specific gravity and crosslinking density of the EVA/SVIS foam.

• Journal of Ocean Engineering and Technology
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• v.36 no.4
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• pp.217-231
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• 2022

Reinforced polyurethane foam (R-PUF), a material for liquefied natural gas cargo containment systems, is expected to have different mechanical properties depending on its stacking position of foaming as the glass fiber reinforcement of R-PUF sinks inside R-PUF under the influence of gravity. In addition, since R-PUF is not a homogeneous material, it is also expected that the coordinate direction within this material has a great correlation with the mechanical properties. So, this study was conducted to confirm this correlation with the one between the mechanical properties and the stacking position. In particular, in this study, R-PUF of 3 different densities (130, 170, and 210 kg/m³) was used, and tensile, compression, and shear tests of this material were performed under 5 temperatures. As a result of the tests, it was confirmed that the strength and modulus of elasticity of the material increased as the temperature decreased. Specifically, the strength and modulus of elasticity in the Z direction, which was the lamination direction, tended to be lower than those in the other directions. Finally, the strength and elastic modulus of different specimens of the material found at the bottom of their lamination compared to the specimens with these properties found at positions other than their lamination bottom were evaluated. Further analysis confirmed that as the temperature decreased, hardening of R-PUF occurred, indicating that the strength and modulus of elasticity increased. On the other hand, as the density of R-PUF increased, a sharp increase in strength and elastic modulus of R-PUF was observed.

• Journal of Korean Society on Water Environment
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• v.22 no.6
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• pp.1101-1106
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• 2006

Many BNR (Biological Nutrient Removal) plants have experienced a bulking problem, mainly due to the growth of filamentous organisms, particularly during the winter months. This study investigated the problem of bulking due to the growth of M. parvicella both at a full-scale municipal wastewater treatment plant and a pilot scale plant located in the C city. The full-scale facility was operated at a flow rate of $51,000m^3/d$, an F/M (Food-to-Microorganism) ratio of 0.12 kgBOD/kgMLVSS/d and an SRT (Solids Retention Time) higher than 25 days, respectively. This plant experienced bulking and foaming problems at low temperatures below $15^{\circ}C$ since it was retrofitted with the BNR system in 2003. The pilot plant employed had an identical process configuration as the full scale one and used the same wastewater source. It was operated at a flow rate of $3.8m^3/d$, temperatures between 10 to $25^{\circ}C$ and SRTs between 10 and 25 days. At full scale, the M. parvicella growth and SVI (Sludge Volume Index) patterns were studied in conjunction with temperature variations. At pilot scale, DO and SRT variations were also explored, in addition to the filamentous bacteria growth and SVI patterns. During the full-scale investigation, over a 3 year period, it was noted that the SVI was maintained within acceptable operational values (i.e. under 160) during the summer months. Moreover settling in the secondary clarifiers was good and was not affected by the presence of M. parvicella. In contrast, at low mean temperatures during winter, the SVI increased to over 300. Overall, as the temperature decreased, the predominance of M. parvicella became apparent. According to this study, M. parvicella growth could be controlled and SVI could drop under 160 by a change in operational conditions which involved an increase in DO concentration between 2 and 4 mg/L and a decrease in SRT to less than 20 days.