• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1195-1204
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• 1992

The natural convection from upward and downward facing horizontal isothermal plate immersed in water is studied numerically. The temperature of the plate is from 0.0 .deg. C to 8.0 .deg. C and the ambient water temperature is from 1.0 .deg. C to 10.0 .deg. C. Numerical results are presented for the velocity profiles, temperature profiles, local heat transfer coefficients, and average Nusselt numbers over the entire flow fields. Flow patterns are shown in the upward and downward facing surfaces at different ambient water temperatures. For the upward facing surface, there are upflow and unsteady flow. And the regions of the ambient water temperatures which give rise to the upflow are more extensive as the temperatures of the isothermal surface become more distant from the density extremum temperature. For the downward facing surface, only the downflow region is shown. For the upward facing horizontal isothermal surface, the average Nusselt number(= N $u_{1}$$^{*}$) is 28.86(Ra)$^{0.01}$. And for the downward facing surface, the average Nusselt number(= N $u_{2}$$^{*}$) is $C_{2}$(Ra)$^{0.2}$ and the values of $C_{2}$ are enlarged in the range of 0.785 .leq. $C_{2}$ .leq. 1.250 as increasing of the temperatures of the isothermal surface.ace.ace.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.847-864
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• 1988

The main purpose of this study is to investigate the local velocity acceleration in a boundary layer diffusion flame over a flat plate. In order to know the effect of separation on the local velocity acceleration, two typical cases, flows with and without separation, are considered. For these cases, flow visualization using paraffine smoke tracers has been made. Mean velocity and r.m.s. value of fluctuating velocity are measured by using a laser Doppler velocimeter. In addition, measurements of time-mean concentration and time-mean temperature have been made. Time-mean density profiles have been obtained from the data of concentration and temperature. The obtained results are summarized as follows : (1) In the case without separation, the local velocity acceleration is clearly observed near the visible flame zone for all flow conditions. On the while, in the case with serration, the local velocity acceleration is observed only at low free stream velocity and high fuel injection velocity. As increasing the free stream velocity or decreasing the fuel injection velocity, it is not distinctly observed in the mean velocity profile. (2) The r.m.s. value of fluctuating velocity is significantly decreased by combustion in the case with separation. But in the case without separation, the r.m.s. value is increased near the visible flame zone in comparison with cold flow. In both cases, the peak value of r.m.s. appeared just at the visible flame zone, where the mean velocity gradient is not too high.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1033-1040
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• 2011

The premixed burner is a very strong candidate for using household boiler burner system because it has high efficiency, low emission and can be used in compact boiler system. Usually, household boiler burner systems use a Bunsen burner, which consists of an inner rich premixed flame and fuel burned completely by a secondary air supply. It has a relatively long flame length and operates in a high excess of air, so it is difficult to fit such a burner into a high efficiency compact boiler. In this paper, the characteristics of a premixed combustion burner for surface media such as metal fiber, ceramic, and SUS fin were evaluated. In particular, the flow velocity over the burner surface for the cold flow characteristics of the surface material were measured and adjusted. The combustion tests were carried out by taking pictures of the flame and measuring the flame temperature. The amounts of CO and NO were measured and the characteristics of the surface burner materials, combustion chamber, and heat exchangers were evaluated for various excess air ratios and heating values.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.592-600
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• 2012

Conventional methods for preparing ceramic bodies, such as cold isostatic pressing, gypsum-mold slip casting, and filter pressing are not completely suitable for fabricating large and thick ceramic plates owing to disadvantages of these processes, such as the high cost of the equipment, the formation of density gradients, and differential shrinkage during drying. These problems can be avoided by employing a pressure-vacuum hybrid slip casting approach that considers not only by the compression of the aqueous slip in the casting room (pressure slip casting) but also the vacuum sucking of the dispersion medium (water) around the mold (vacuum slip casting). We prepared the alumina formed bodies by means of pressure-vacuum hybrid slip casting with stepwise pressure loading up to 0.5 MPa using a slip consisting of 40 vol% solid, 0.6 wt% APC, 1 wt% PEG, and 1 wt% PVA. After drying the green body at $30^{\circ}C$ and 80% RH, the green density of the alumina bodies was about 56% RD. The sintered density of an alumina plate created by means of sintering at $1650^{\circ}C$ for 4 h exceeded 99.8%.This method enabled us to fabricate a $110{\times}110{\times}20$ mm alumina plate without cracks and with a homogeneous density, thus demonstrating the possibility of extending the method to the fabrication of other ceramic products.

• Journal of the East Asian Society of Dietary Life
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• v.18 no.4
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• pp.633-640
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• 2008

In this study, the effects of feeding citrus byproducts on various qualities of pork during cold storage were investigated, such as water holding capacity, drip loss, meat color, storage stability, rancidity, and antioxidant activity. Pork samples (195 days old, $115{\pm}3\;kg$, female) used for the experiment was divided into three groups: T0(pigs not fed citrus byproducts), T1(pigs fed 3% and 5% citrus byproducts during growth and the finishing period, respectively), and T2(pigs fed 6% and 10% citrus byproducts). The loin used for the experiment was obtained from 5 pigs of each group, vacuum packaged, and then stored at $3^{\circ}C$ for 4 weeks. There was no difference among T0, T1, and T2 for pH, water holding capacity, or drip loss. As for the meat color of the loin, T1 and T2 showed higher redness($a^*$ value) during early chilling but showed higher yellowness($b^*$ value) during late chilling. T1 and T2 showed higher electron donating ability and lower volatile basic nitrogen, total plate count, and TBA values than T0, regardless of the chilling period. Thus, feeding citrus byproducts improves the storage stability of chilled pork in terms of rancidity and antioxidant activity.

• KSBB Journal
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• v.23 no.5
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• pp.403-407
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• 2008

Recently, Candida antarctica lipase B (CalB) draws attention from industries for various applications for food, detergent, fine chemical, and biodiesel, because of its characteristics as an efficient biocatalyst. Since many industrial processes carry out in organic solvent and at high temperature, CalB, which is stable under harsh condition, is in demand from many industries. In order to reform CalB promptly, the expression system which has advantages of ease to use and low cost for gene libraries screening was developed using E. coli. The E. coli strains, Rosettagami with competence for enhanced disulfide bond formation, Novablue, and $DH5{\alpha}$, were exploited in this study. To obtain the soluble CalB, the pCold I vector expressing the cloned gene at $15^{\circ}C$ and the chaperone plasmids containing groES/groEL, groES/groEL/tig, tig, dnaK/dnaJ/grpE, and dnaK/dnaJ/grpE/groES/groEL were used for coexpression of CalB and chaperones. The colonies expressing functional lipase were selected by employing the halo plate containing 1% tributyrin, and the CalB expression was confirmed by SDS-PAGE. E. coli Rosettagami and $DH5{\alpha}$ harbouring groES/groEL chaperones were able to express soluble CalB effectively. From a facilitative point of view, E. coli $DH5{\alpha}$ is more suitable for further mutation study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.585-592
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• 2011

The enhancement of the cold-start capability of polymer electrolyte fuel cells is of great importance in terms of the durability and reliability of fuel-cell vehicles. In this study, vanadium oxide films deposited onto the flat surface of metallic bipolar plates were synthesized to investigate the feasibility of their use as an efficient self-heating source to expedite the temperature rise during startup at subzero temperatures. Samples were prepared through the dip-coating technique using the hydrolytic sol-gel route, and the chemical compositions and microstructures of the films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and field-emission scanning electron microscopy. In addition, the electrical resistance hysteresis loop of the films was measured over a temperature range from -20 to $80^{\circ}C$ using a four-terminal technique. Experimentally, it was found that the thermal energy (Joule heating) resulting from self-heating of the films was sufficient to provide the substantial amount of energy required for thawing at subzero temperatures.

• The Korean Journal of Food And Nutrition
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• v.29 no.6
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• pp.849-859
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• 2016

Edible insects have gained recognition worldwide as complementary protein sources. Recently, four edible insects were newly allowed to be used as food materials in Korea: the mealworm (Tenebrio molitor), the cricket (Velarifictorus asperses), the white-spotted flower chaffer beetle larva (Protaetia brevitarsis seulensis), and the rhinoceros beetle larva (Allomyrina dichotoma). In this study, we evaluated the oxidative stabilities of these four edible insects during cold storage. The insects were sacrificed by blanching for 3 minutes in boiling water. The blanched insects were then stored at $4^{\circ}C$ in an incubator for 42 days. The color values, titratable acidity, peroxide values, acid values, TBARS, contents of VBN, and total plate counts of the insects were measured at days 0, 2, 4, 7, 10, 14, 21, 28, 35, and 42, respectively. Blanching decreases oxidative stresses during storage. At day 0, the white-spotted flower chaffer beetle larva showed the highest values for acid value, TBARS, VBN, and microbial counts. Most of the oxidative indicators were significantly changed at day 14 in all four insects, possibly related with the growth on all microbial plates. Based on microbial safety and the oxidative stabilities of lipids and proteins, optimal storage conditions for the cricket, the white-spotted flower chaffer beetle larva, and the rhinoceros beetle larva were 10~14 days at $4^{\circ}C$. Likewise, the mealworm showed rapid oxidation after day 14, but poor qualities were not observed until day 28.

• Laser Solutions
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• v.1 no.1
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• pp.24-29
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• 1998

A new wide laser beam optical system for the laser materials processing has been developed with a polygonal mirror. It consists of polygonal mirror and cooling part that prevents the surface of rotating polygonal mirror from damage by heat. The polygonal minors have been designed and made as 24 and 30 facets in pyramid type. This system provides a uniform linear laser heat source with the surface scanning width from 15 to 50mm according to the scanning height To examine the wide laser beam, He-Ne laser is used. Also, Acryl is used to confirm the laser beam pattern by bum-pattern print To analyze the energy distribution of the wide laser ben empirical values and theoretical values are compared and discussed. To improve the efficiency of the wide laser beam optical system, methods are suggested by the optical theories. For larger area processing like turbine blade, drawing blade, cold roller and guide plate, optimal overlapping locations have been calculated and analyzed by geometric and optical theories.

• Korean Journal of Poultry Science
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• v.24 no.1
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• pp.9-15
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• 1997

This experiment was carried out to investigate the effects on shelf-life of chilling and packing methods of cold chicken breast and thigh meats. Deboned chicken breast and thigh meats were packed by either vacuum or atmosphere packing method, and stored at -2˚C for 1, 3, 7, 11, 15, and 20 days. The thiobarbituric acid(TBA) values of all treatments were significantly increased as the storage period extended(P<0.05), however, TBA values of all treatments were remark-ably decreased at 15 days. TBA values of immersion chilled and vacuum-packed thigh meats were increased, but no difference between atmosphere and vacuum-packing methods was found. The volatile basic nitrogen(VBN) values at 1 day of storage were low, but they were increased as the storage period extended. The VBN values at 20 days after storage were from 12.25~19.28 mg %. Total bacterial counts tended to increase in all treatments, however, no significant difference was found in any treatment. Total plate counts of breast meat were higher than those of thigh meat as the storage period extended.