• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.483-488
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• 2003

Frictional heating in brakes causes thermoelastic distortion of the contacting bodies and hence affects the contact pressure distribution. The resulting thermo-mechanical coupling can cause thermoelastic instability (TEI) if the sliding speed is sufficiently high, leading to non-uniform heating called hot spots and low frequency vibration known as hot judder. The vibration of brakes to the known phenomenon of frictionally-excited thermoelastic instability is estimated studying the interface temperature and pressure evolution with time. A simple model has been considered where a layer with half-thickness ${\alpha}$ slides with speed V between two half-planes which are rigid and non-conducting. The advantage of this properly simple model permits us to deduce analytically the critical conditions for the onset of instability, which is the relation between the critical speed and the growth rate of the interface temperature and pressure. Symmetrical component of pressure and temperature distribution at the layer interfaces can be more unstable than antisymmetrical component. As the thickness ${\alpha}$ reduces, the system becomes more apt to thermoelastic instability. Moreover, the evolution of the system beyond the critical conditions has shown that even if low frequency perturbations are associated with low critical speed, it might be less critical than high frequency perturbations if the working sliding speed is much larger than the actual critical speed of the system.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2850-2855
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• 2008

Very High Temperature Reactor (VHTR) has been selected as a high energy heat source for a nuclear hydrogen generation. The VHTR heat is transferred to a thermo-chemical hydrogen production process through an intermediate loop. Both Process Heat Exchanger and sulfuric acid evaporator provide the coupled components between the VHTR intermediate loop and hydrogen production module. A small scaled Compact Nuclear Hydrogen Coupled Components test loop is developed to simulate the VHTR intermediate loop and hydrogen production module. Main objective of the loop is to screening the candidates of NHDD (Nuclear Hydrogen Development and Demonstration) coupled components. The operating condition of the gas loop is a temperature up to $950^{\circ}C$ and a pressure up to 6.0MPa. The thermal and fluid dynamic design of the loop is dependent on the structures that enclose the gas flow, especially primary side that has fast gas velocity. We designed and constructed a small scale sulfuric acid experimental system which can simulate a part of the hydrogen production module also.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2738-2743
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• 2008

We conducted a study by computational simulation about the effects of frost thickness on the pressure drop and heat transfer characteristics as whole heat exchanger configuration changes. In order to perform the analysis for validation, we assumed that frost properties have constant values and the frost layers that are formed on the fin and tube surfaces are uniform. In order to find the constant thermal conductivity of frost layer, a variety of frost thermal conductivities are performed in our work and compared with the results by Lee et al. [4] and Yang et al. [5] proposed many experimental data about the 2-rows and 2-columns finned tube heat exchanger. The numerical results agreed well with the experimental data when frost conductivity is 0.07W/mK. After the validation had performed, we applied this procedure to the finned tube heat exchanger of domestic refrigeration and investigated the thermo-hydraulic characteristic of the heat exchanger affected by frost thickness according to the inlet velocities and temperatures of air considering the configuration change such as fin pitch.

• Corrosion Science and Technology
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• 제10권2호
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• pp.43-46
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• 2011

Zinc consumption in a continuous galvanizing line is one of the highest operating cost items in the facility and minimizing zinc waste is a key economic objective for any operation. One of the primary sources of excessive loss of zinc is through the formation of top dross and skimmings in the coating pot. It has been reported that the top skimmings, manually removed from the bath, typically consist of more than 80% metallic zinc with the remainder being entrained dross particles ($Fe_2Al_5$) along with some oxides. Depending on the drossing practices and bath management, the composition of the removed top skimmings may contain up to 2 wt% aluminum and 1 wt% iron. On-going research efforts have been aimed at in-house recovery of the metallic zinc from the discarded top skimmings prior to selling to zinc recycling brokers. However, attempting to recover the zinc entrapped in the skimmings is difficult due to the complex nature of the intermetallic dross particles and the quality and volume of the recycled zinc is highly susceptible to fluctuations in processing parameters. As such, an efficient method to extract metallic zinc from top skimmings has been optimized through the use of a specialized thermo-mechanical process enabling a continuous galvanizing facility to conserve zinc usage on-site. Also, through this work, it has been identified that filtration of discrete dross particles has been proven effective at maintaining the cleanliness of the zinc. Future efforts may progress towards expanded utilization of filters in continuous galvanizing.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.278-283
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• 2003

A generation rate of sludge in Korea had increased dramatically about 200 % for a decade. A requirement for high efficiency dewatering system being possible to produce the low water content cake have suggested due to the appearanceof commercial and social problems about handling of dewatered cake. The conventional dewatering system with mechanical compression device was not suitable to produce the low water content cake and didn'tcope with lots of requirements. Therefore, this paper was to develop the high efficient filter press with the compressive and heating forces through the heating plate to be built between membrane filter plates. It is possible to produce the low water content cake and improve the dewatering rate, so this equipment positively coped with several types of problems related to the sludge dewatering. The plate heated by heat transfer materials such as steam, hot water and thermo-oil made the sludge make the residual moisture within the cake to discharge easilyand to improve the dewatering efficiency of equipment. The pilot scale experiment with 500kg of cake production showed that the dewatering efficiency determined by the final water content and dewatering velocity was improved 30% more than the conventional dewatering equipment.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.85-86
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• 2006

A theoretical model is applied to the analysis of thermomechanical properties of $Al-SiC_p$ FGMs in this study. Functionally graded $Al-SiC_p$ composites ($Al-SiC_p$ FGMs) consisted with 10 layers gradually changing volume fractions of Al and $SiC_p$ were fabricated using the pressureless infiltration technique. $Al-SiC_p$ FGMs plates of total thickness of 3mm, 5mm and 7mm with fairly uniform distribution and compositional gradient of $SiC_p$ reinforcement in the Al matrix throughout the thickness was successfully fabricated. The curvature of $Al-SiC_p$ FGM plates was measured to check the internal stress distribution predicted via a theoretical model for the analysis of thermo-mechanical deformation. The evolution of curvature and also internal stresses in response to temperature variations could be predicted for the different combinations of geometric thickness of FGM plates. Theoretical prediction of thermally induced stress distribution makes it possible to design FGM structures without any critical failure during the usage of them.

• 한국연소학회지
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• 제21권2호
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• pp.29-37
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• 2016

This study described the experimental investigations of combustion instability in a model gas turbine combustor. Strong coupling between pressure oscillations and unsteady heat release excites a self-sustained acoustic wave, which results in a loud and annoyed sound, and may also lead to a structural damage to the combustion system. In this study, in order to examine the combustion instability phenomenon of a dual swirling combustor configuration, the information of heat release and pressure fluctuation period with respect to the variation in both thermal power and combustor length was collected experimentally. As a result, the fundamental acoustic frequency turned out to increase with the increasing thermal power without respect to the combustor length. The frequency response to the combustor length was found to have two distinct regimes. In a higher power regime the frequency significantly decreases with the combustor length, as it is expected from the resonance of gas column. However, in a lower power regime it is almost insensitive to the combustor length. This insensitive response might be a result of the beating phenomenon between the interacting pilot and main flames with different periods.

• 한국자동차공학회논문집
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• 제12권1호
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• pp.114-121
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• 2004

Frictional heating in brakes causes thermoelastic distortion of the contacting bodies and hence affects the contact pressure distribution. The resulting thermo-mechanical coupling can cause thermoelastic instability (TEI) if the sliding speed is sufficiently high, leading to non-uniform heating called hot spots and low frequency vibration known as hot judder. The vibration of brakes to the known phenomenon of frictionally-excited thermoelastic instability is estimated studying the interface temperature and pressure evolution with time. A simple model has been considered where a layer with half-thickness$\alpha$slides with speed V between two half-planes which are rigid and non-conducting. The advantage of this properlysimple model permits us to deduce analytically the critical conditions for the onset of instability, which is the relation between the critical speed and the growth rate of the interface temperature and pressure. Symmetrical component of pressure and temperature distribution at the layer interfaces can be more unstable than antisymmetrical component. As the thickness $\alpha$ reduces, the system becomes more apt to thermoelastic instability. For perturbations with wave number smaller than the critical$m_{cr}$ the temperature increases with m vice versa for perturbations with wave number larges than $m_{cr}$ , the temperature decreases with m.

• International Journal of Aeronautical and Space Sciences
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• 제3권1호
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• pp.95-104
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• 2002

Numerical solution of the full Navier-Stokes equation as well as the energy equation has been obtained for the unsteady natural convection in a rectangular enclosure. One side wall was maintained at very high temperature simulating fires. Especially the effect of surface radiation was taken into account. While the enclosed air was assumed to be transparent, the internal walls directly interacted one another through the surface radiation. Due to a significant temperature difference in the flow field, the equation of state was used instead of the Boussinesq approximation. It was found that the rapid heating of the adiabatic ceiling and floor by the incoming radiation from the hot wall made the evolution at thermo-fluid field highly unstable in the initial period. Therefore, the secondary cells brought about at the floor region greatly affected the heat transfer mechanism inside the enclosure. The heat transfer rate was augmented by the radiation, resulting in requiring less time for the flow to reach the steady state. At the steady state neglecting radiation two internal hydraulic jumps were clearly observed in upper/left as well as in lower/right comer. However, the hydraulic jump in the lower/right comer could not be observed for the case including radiation due to its high momentum flow over the bottom wall. Radiation resulted in a faster establishment of the steady state phenomena.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.242-242
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• 2007

To verify the applicability of High Temperature Superconducting (HTS) cable system into the real grid, the HTS cable system with the specification of 22.9 kV, 1250 A, 100 m long was installed in the second quarter of 2006, and the long term field test has been in progress at the KEPCO's Gochang power testing yard. Apart from the conventional power cable, HTS cable system requires sufficient thermo-mechanical strength to endure a large temperature difference. To date, the KEPCO HTS cable system was cooled down and warmed to the room temperature several times to investigate the influence of thermal cycles experimentally. Dielectric properties, critical current dependance and heat losses were evaluated at each step of thermal cycle. The test results showed that thermal cycle did not induce the degradation of dielectric properties, and the critical current decreased to 5 % of the initial value.