• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.05a
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• pp.268-271
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• 2007

A sandwich tube is a structured material that has two inner and outer circular tubes and light material between them. In this paper, a sandwich tube with a pyramidal truss core is introduced. Fabrication method and example made by brazing are shown. The behavior of the sandwich tube under lateral loading is predicted by analytical and numerical method. Comparative study between the sandwich and the monocoque tube is performed at a point of view such as strength and weight saving. As a result, proposed tube is appropriate for application to lightweight structural material

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1876-1881
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• 2007

The micro plated heat exchangers were designed to transfer more heat/volume or mass than previous heat exchangers within the context of the design constraints specified. The increase of the surface-to-volume ratio results in an increase of the interfacial area. This enhances considerably the performance of a heat exchanger. This can be an important component in a wide range of applications fuel cell, aerospace, automotive, electronic system and home heating, etc). In this study, the performance evaluation of micro plated heat exchangers under the counter flows with straight and S-shaped channel are carried out. The pressure drop as well as inlet and outlet fluid temperature were measured at steady state under various operating conditions and the total heat transfer rate were also calculated.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.229-234
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• 2007

Microscale heat transfer and microfluidics have become increasingly important to overcome some very complex engineering challenges. The use of very small passages to gain heat transfer enhancement is a well documented method for achieving high heat flux dissipation. As the passage size is decreased, the heat transfer performance increases but the pressure drop increases sharply when the passage size is reduced. In this study, the performance evaluation of micro plated heat exchangers under the counter flows with straight, V-shaped and Y-shaped channel are carried out.

• International Journal of Korean Welding Society
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• v.1 no.1
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• pp.71-77
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• 2001

The characteristics of the fume generation in a flux cored arc welding were investigated using the fume collection chamber developed. The Korean Standard concerning the method for the evaluation of the fume generation rate(FGR) was updated by the evaluation method obtained through this study. It was found that the effect of humidity in the test environment should be considered and the automatic welding method had to be employed for the purpose of the exact evaluation of the fume generation rate. The results showed that the fume generation rate was influenced by the welding parameters. The important factors were the welding current arc voltage, travel speed, and contact tip to work distance(CTWD) that affected the heat input as well as the torch angle and the shielding gas flow rate that influenced the shielding effect. The fume generation rate increased as the heat input increased and the shielding effect decreased. It was also observed that the effect of the welding current is much grater than the other welding parameters.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.6
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• pp.384-389
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• 2015

In this paper, we fabricated ceramic body and sapphire wafer in order to develop a hydraulic pressure sensor with high sensitivity and high temperature stability. The sapphire wafer was adopted with a membrane of capacitance ceramic pressure sensor. The capacitance value of the sensor for the finite element analysis(FEM) showed a linear pressure characteristics. Membrane was processed with a diameter of 32.4 mm and a thickness of 1 mm by using alumina powders. Ceramic body was processed with a diameter 32.4 mm and a thickness 5 mm. The capacitance pressure sensor was made with high heat treatment of the ceramic body and the sapphire wafer. Initially capacitance of the pressure sensor was 50 pF and a capacitance of 110 pF was measured from 5 bar pressure. Output voltage of 5 V was appeared at 5 bar pressure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.11
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• pp.767-774
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• 2008

This paper presented the heat transfer and pressure drop characteristics for micro plate heat exchanger with straight channel. The metal sheets for straight channel are manufactured by chemical etching and fabricated micro plate heat exchangers by using the vacuum brazing of bonding technology. The performance experiments are performed within the Reynolds numbers range of 15$\sim$250 under the same flow rate conditions for hot and cold sides. The inlet temperature of hot and cold water are conducted in the range of $30^{\circ}C{\sim}50^{\circ}C$ and $15^{\circ}C{\sim}25^{\circ}C$, respectively. Heat transfer rate and pressure drop are evaluated by the Reynolds numbers and mass flow rates as the inlet temperature variations of the hot and cold sides. Correlations of Nusselt number and friction factor are suggested for micro plate heat exchanger with straight channel using the results of performance experiment.

• Korean Journal of Materials Research
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• v.11 no.12
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• pp.1020-1027
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• 2001

Powder type Ag system insert metals were manufactured by mechanical alloying method. Alloying method was the ball milling process using zirconia ball media, and all alloying variables were constant except the milling time. The milling times were selected 24, 48 and 72 hours. The insert metals made by milling method were observed using scanning electron microscope and x-ray analyses. And also, the evaluation of wettability and microstructures of the insert metals were conducted to investigate the characteristics of the brazed joint. The wettability of the insert metals made by milling of 48 hours, was the best condition. And the insert metals contained Cd shows good wettability, however, there was the oxides residue on the brazing test specimen. The microstructures of the manufactured and the commercial insert metals were almost same displaying the Cu- rich proeutectic and Ag-rich eutectic. Further, there were some porosities. The 48 hours alloyed insert metal was exhibited the most sound brazed joint without containing porosity due to the superior wettability and good alloying condition.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.2
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• pp.81-87
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• 2017

The pipe connection process using a clamping ring is used for joining small pipes in the refrigerator and air-conditioner industries instead of the brazing process, which induces inevitable thermal deformation in the pipes. However, few studies have been carried out on the process to select optimal parameters in joining pipes, and studies on the relation between the process parameters of the connection and connecting force of the joint have not been conducted. In this study, the connection process of pipes with the clamping ring was modeled using the finite element method (FEM) and analyzed to obtain the contact stress distribution between the pipes with which the connecting force of the joint was estimated. Considering the characteristics of pipe connection, the process was modeled and simulated in a two-dimensional axisymmetric solution domain. With the numerical model, the effect of ring shape on the connection was studied by adding a projection to the end of a ring or changing the length of a ring. The results of the analyses revealed that the contact stress distribution could be predicted with the suggested model. The effect of the ring shape was also presented. The effect of any combination of process parameters could be easily estimated through the related analyses.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.2
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• pp.311-316
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• 2008

Powder type Ag system insert metals were manufactured by ball milling process. The variables of milling process were constant except the milling time. The milling times were selected for 24, 48 and 72 hours. The insert metals made by milling process were evaluated by performing scanning electron microscope, DSC(differential scanning calorimetry) analyses, spreading test and further in terms of wettability test. The selected insert metals that have the good characteristics compared to commercial insert metals were applied to make the brazed joints. The characterizations of those brazed joints were also conducted by microstructural observations. The results indicated that milling time of 48 hours for making powder type insert metals was the best condition showing the good spreadibility, low wetting angle. The brazed joints that applied the 48 hours milled insert metal were very sound condition indicating the stable microstructure in spite of containing small amount of porosity and the microhardness value of the joint was about 138VHN.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.4
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• pp.249-254
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• 2018

We researched about a bulk metallic glass system as an additive to an Ag paste for high temperature thermoelectric modules. Bulk metallic glass (BMG) ribbons were produced by using a rapid solidification process (RSP) under a cooling rate condition higher than $10^{\circ}C/sec$. We investigated BMG characteristics of the ribbons by means of x-ray diffraction (XRD) and differential scanning calorimetry (DSC) in order to evaluate the glass transition temperature ($T_g$) and the recrystallization temperature ($T_x$) lower than $400^{\circ}C$. A milling process was also developed to apply the BMG ribbons to a commercial Al paste as an additive for lower sintering temperature.