• Membrane Journal
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• v.6 no.4
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• pp.203-212
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• 1996

The operating parameters influencing on limiting flux was investigated in the ultrafiltration of PVA, and a new model, which is based on the Amiar model using the concept of heat transfer coefficient, was devised to overcome the limitation of gel-layer model. Using polysulfone plate-unit membrane (MWCO=20,000) and hollow-fiber membrane (MWCO= 30,000), ultrafiltration characteristics of PVA was examined with the variation of operating parameters such as cross flow velocity, transmembrane pressure, temperature, and PVA concentration. According to experimental results, the ultrafiltration of PVA through polysulfone membrane is mainly controlled by well-known phenomena of concentration polarization caused by gel-layer formation. On the contrary, in hollow fiber membrane was observed upward limiting flux which can not be explained by gel-layer model. New model was applied to predict the upward limiting flux behavior with partial satisfaction. The application of new model including viscosity correction factor, however, revealed that PVA ultrafiltration is closely related to the viscosity of permeating fluid.

• Solar Energy
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• v.15 no.3
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• pp.127-140
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• 1995

This experimental study was carried out to examine the heat transfer characteristics of a 2-dimensional impinging air jet on a flat plate with a set of square rods. The objectives of the study were to investigate the flow and heat transfer characteristics caused by the square rods. Experiment was carried out first without using the rods to establish the baseline heat transfer performance. Then, rods of different widths and clearances were installed to cause the turbulence on the fluid flow. When rods are installed in front of the plate, the acceleration of the flow and the turbulence generation due to the rods and reattachment of the flow seem to contribute to the observed heat transfer augmentation and the heat transfer augmentation increases as the clearance decreases. With wider individual rod the heat transfer coefficient is higher, which is due to the increased acceleration and development of the eddies just before the rods.

• Korean Journal of Food Science and Technology
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• v.31 no.1
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• pp.54-61
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• 1999

A study was conducted to find a rapid thawing method which prevents excessive drip loss and local overheating. Effects of thawing methods (conventional thawing vs. 2,450 and 915 MHz microwave thawing) on thawing time, temperature profile, drip loss, water holding capacity, total color difference and total aerobes were investigated. Samples were thawed at 4, 28 and $50^{\circ}C$ in a refrigerator or an oven for the conventional thawing methods the convertional thawing methods. Power levels of 5, 10 and 15 kW were used for 915MHz microwave thawing. Cotreatment of 915 MHz microwave and convectional heating $(120^{\circ}C)$ was tested. 915 MHz microwave accelerated the thawing rate, and showed significant effects on penetration depth, drip loss, water holding capacity and total aerobes. Cotreatment of 915 MHz microwave and convection heating was appeared to be a suitable thawing process for the food industry.

• Journal of the Korean Applied Science and Technology
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• v.31 no.1
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• pp.83-91
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• 2014

In this study, we synthesized two different silica monoliths by using sol-gel, solvent exchange, surface modification, ambient pressure drying processes, and surfactant-based templating technique followed by calcination process. All of the prepared two silica monoliths showed crack-free appearance with fairly good transparency, and furthermore were confirmed to have extremely high porosity, specific surface area, and mean pore size below 30 nm. The silica aerogel sample exhibited finer and more homogeneous nano-sized pore structure due to spring back effect caused by surface modification, which resulted in better thermal insulation performance. Based on measured thermal conductivities and theoretical relationship, multi-layered glass window system in which silica monolith prepared in this study was inserted as a middle layer was revealed to have superior thermal insulation performance compared to conventional air-inserted glass window system.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.4
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• pp.328-334
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• 2015

Building insulation materials use for the purpose of energy saving. Insulation materials can be classified inorganic and organic insulation materials. Inorganic insulation is used for fire resistive performance parts and organic insulation is used for thermal performance parts. Meanwhile, organic insulation is due to toxic gas emission in fire. Inorganic insulation is too heavy and low thermal performance than organic materials. This study is focused on evaluation of the physical properties of inorganic foam material using industrial by-products such as waste glass powder and fly ash. From the test result, inorganic foam materials for the applicability of fire-resistance and insulation light-weight materials.

• Journal of the Korean Chemical Society
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• v.55 no.2
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• pp.157-162
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• 2011

In the present study, we developed a portable GC module for real-time, quantitative determinations of gas mixtures in air sample. Capillary or packed column was coiled together with a heater wire and thermocouple in a small case. Together with the small and light weight sensors and valves as well as the rechargeable carrier gas canister, which permits collection and separation of samples, this system can determine the components of complex mixtures of air contaminants at low concentrations with a duty cycle of 10 min. When measured the various samples with a FID and TCD, the system showed, for a capillary column, a good resolution (R=8.3), high sensitivity, reproducibility, and linear dynamic range greater than three orders of magnitude. These results indicate that the portable GC module is expected to be used for a wide range of applications, particularly for in situ environmental monitoring, chemical processes, and regulation of contaminant emission.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.5
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• pp.744-752
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• 2000

The influence of arrangement and length of discrete ribs on heat/mass transfer and friction loss is investigated. Mass transfer experiments are conducted to obtain the detailed local heat/mass transfer information on the ribbed wall. The aspect ratio (width/height) of the duct is 2.04 and the rib height is one tenth of the duct height, such that the ratio of the rib height to hydraulic diameter is 0.0743. The ratio of rib-to-rib distance to rib height is 10. The discrete ribs were made by dividing each continuous rib into 2, 3 or 5 pieces and attached periodically to the top and the bottom walls of the duct with a parallel orientation The combined effects of rib angle and length of the discrete ribs on heat/mass transfer ae considered for the rib angles $({\alpha})\;of\;90^{\circ}\;and\;45^{\circ}$. As the number of the discrete ribs increases, the uniformity of the heat/mass transfer distributions increases. For $(\alpha})=90^{\circ}$, the heat/mass transfer enhancement with the discrete ribs is remarkable, while the heat/mass transfer performances are slightly higher than that of the transverse continuous ribs due to the accompanied high friction loss penalty. For $(\alpha})=90^{\circ}$, the average heat/mass transfer coefficients and the heat/mass transfer performances decrease slightly with the discrete ribs compared to the case of the angled continuous ribs.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1089-1095
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• 2011

Numerical simulation is performed for nucleate boiling on a micro-finned surface, which has been widely used to enhance heat transfer, by solving the equations governing the conservation of mass, momentum, and energy in the liquid and vapor phases. The bubble motion is determined by a sharp-interface level-set method, which is modified to include the effect of phase change and to treat the no-slip and contact-angle conditions, as well as the evaporative heat flux from the liquid microlayer on immersed solid surfaces such as micro fins and cavities. The numerical results for bubble formation, growth, and departure on a microstructured surface including fins and cavities show that the bubble behavior during nucleate boiling is significantly influenced by the fin-cavity arrangement and the fin-fin spacing.

• Journal of the Korean Recycled Construction Resources Institute
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• v.3 no.2
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• pp.165-170
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• 2015

Pipe-rack structures supporting high temperature and pressure are of great importance to ensure the safety of the operation of the plants. If some damage occurred in the pipe-rack structure, the facilities not only bring damage to the commercial property, but also result in economic losses. Specially, since pipe-rack structures are exposed to various environmental conditions, it is essential to evaluate the thermal behavior of the structure caused by environmental conditions for the appropriate design and maintenance of the pipe-rack structure. Thus, based on a selected, typical pipe-rack structure, a thermal-stress coupled analysis was conducted to evaluate the temperature distributions and thermal stresses of the structure. For this, this study accounted for the operating condition of the pipe and the effect of environmental conditions, Yeosu in South Korea and Saudi Arabia in the Middle East. The results of the study showed the need for accounting for a variance in the environmental factors to evaluate the thermal behavior of the pipe-rack structure along with the working condition of pipe.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.418-425
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• 2011

In this study, a high energy ball milling process was introduced in order to improve the densification of direct nitrided AlN powder. The sintering behavior and thermal conductivity of the AlN milled powder was investigated. The mixture of AlN powder and 5 wt% $Y_2O_3$ as a sintering additive was pulverized and dispersed by a bead mill with very small $ZrO_2$ bead media. The milled powders were sintered at $1700^{\circ}C-1800^{\circ}C$ for 4 h under $N_2$ atmosphere. The results showed that the sintered density was enhanced with increasing milling time due to the particle refinement as well as the increase in oxygen contents. Appropriate milling time was effective for the improvement of thermal conductivity, but the extensive millied powder formed more fractions of secondary phase during sintering, resulted in the decrease in thermal conductivity. The AlN powder milled for 10min after sintering at $1800^{\circ}C$ revealed the highest thermal conductivity, of 164W/$m{\cdot}K$ in tne densified AlN sintered at $1800^{\circ}C$.