• 대한기계학회논문집A
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• 제30권7호
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• pp.865-872
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• 2006

High frequency induction welding is widely employed for longitudinal seam welding of small scale tubes and pipes because of its relatively high processing speed and efficiency. This research is aimed at understanding the variables that affect the quality of the high frequency induction welding. The welding variables include the welding frequency, weld speed, V-angle and tube thickness. Temperature distribution of the tube is calculated through three dimensional coupled electromagnetic and thermal FE analysis. The skin and proximity effects are considered in the electromagnetic analysis. The influence of the impeder is also analyzed. The effects of the operating welding variables on the temperature distribution are investigated quantitatively by exhibiting the heat affected zone (HAZ). The results explain the mechanism of significant enhancement of welding efficiency when the impeder is used. The proper welding conditions without the overheated edge are obtained through FE analysis.

• 한국전산유체공학회지
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• 제15권1호
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• pp.17-23
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• 2010

Performance improvements of the heat recovery steam generator(HRSG) can be achieved by improving the flow distribution of exhaust gases for a various type of different equipments. A number of design parameters are systematically investigated and their effects on an index of velocity deviation established. The parameters include the three shape of the transition duct and the wide range of the guide vane angles. The numerical results clearly reveal feature of the flow pattern in the transition duct, velocity deviation and pressure drop at tube bank part.

• 설비공학논문집
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• 제14권3호
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• pp.231-239
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• 2002

Experiments on the single phase cooling heat transfer and pressure drop with microfin tubes were performed using water as a test fluid. Experimental data were obtained in the range of Reynolds number 3000 ~40000 and Prandtl number 4-6. The data of microfin tubes presented the characteristics of rough surface tube in pressure drop and heat transfer Experimental data were compared with the heat transfer and friction factor correlations of smooth tubes. Heat transfer enhancements of microfin tubes were lower than pressure drop penalty factors. The helix angle is more significant parameter in both of the pressure drop and heat transfer than the relative roughness. The correlations of Nusselt number and friction factor were suggested for the tested microfin tubes. Maximum deviations between correlations and experimental data were within $\pm15$% for Nusselt number and $\pm10$% for friction factor.

• 소성∙가공
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• 제23권8호
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• pp.507-512
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• 2014

The objective of the current investigation is to establish techniques in micro pattern forming operations of polymeric circular tubes by using hydrostatic pressing. This method was developed and successfully applied to the micro pattern forming on polymeric plates. The key idea of the new technique is to pressurize multiple vacuum-packed substrate-mold stacks above the glass transition temperature of the polymeric substrates. The new process is thought to be a promising micro-pattern fabrication technique for two reasons; first, (hydro-) isostatic pressing ensures a uniform micro-pattern replicating condition regardless of the substrate area and thickness. Second, multiple curved substrates can be patterned at the same time. With the prototype forming machine for the new process, micro prismatic array patterns, 25um in height and 90 degrees in apex angle, were successfully made on the PMMA circular tubes with diameters of 5~40mm. These results show that this process can be also used in the micro pattern forming process on curved plates such as circular tube.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.557-560
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• 2006

The contact angle of a meniscus and a droplet can be controlled by using electrowetting phenomena. We investigated the dynamic aspect of electrowetting for an oil-electrolyte interface formed inside a closed glass tube. A step input voltage is applied and the subsequent motion of the interface is recorded by a high-speed camera. A kind of capillary instability is observed near the three-phase contact line, which could degrade the reliability of device utilizing electrowetting such as electrowetting liquid lens. The dynamics of interface motion for different input voltages and the fluid viscosities are analyzed and discussed based on the experimental results.

• 대한기계학회논문집A
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• 제30권6호
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• pp.662-669
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• 2006

The pneumatic muscle actuator consists of an air bellows tube with two end-flanges. The air bellows tube is made from rubber layers and flexible sheathing formed from nylon 6 fibers. This structure can be stretched or compressed to convert the radial expansive forces into contractile forces. We performed the finite element analysis and the performance test of pneumatic muscle actuator. Also, the pneumatic muscle actuator was manufactured and tested by home-made tester. The results of FEA was similar with performance test below the maximum error of 42 %.

• 설비공학논문집
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• 제14권6호
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• pp.525-531
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• 2002

The effects of different surface hydrophilicity on frosting and defrosting characteristic were experimentally investigated. Mass of frost and water hold-up was measured. Results showed that no significant difference in the frost mass was found between the two different surfaces while the water hold-up of heat exchanger court be reduced by the enhancement of surface hydrophilicity. Also, the defrosting efficiency m hydrophilic surface was improved by 76%. It was expected that hydrophilic heat exchanger could provide the improvements in both thermal-hydraulic performances and system reliability during frost/defrost operating in refrigeration systems.

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2001년도 춘계학술대회 논문집
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• pp.100-105
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• 2001

The present paper is to present the results of studied of pressure drop in annuli with corrugated and spirally fluted inner tubes for the turbulent flow regime. To understand the underlying physical phenomena responsible for heat transfer enhancement, flow mechanism documented elsewhere are combined with pressure drop measurements to confirm the friction factors obtained from the annuli with the grooved inner tubes for the Reynolds number of 1000 to 8000. Friction factors were found to be functions of trough depth, pitch and angle, and the annulus radius ratio. friction factor increases in the spirally fluted tubes were larger than those in the corrugated tubes.

• 대한기계학회논문집B
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• 제32권5호
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• pp.392-399
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• 2008

Accurate measurement of speed and altitude of flying vehicles in air data system remains a critical technical issue. A highly reliable Pitot-static probe is required to obtain air data such as total pressure and static pressure. In this study, an analysis of the characteristics of flowfield around the Pitot-static probe was performed by using a Navier-Stokes CFD code. In addition, for the purpose of finding an optimal configuration, a technique based on the response surface method is applied to the problem with design parameters including shape of the nose section and cone angle. It is shown that the optimal configuration fulfills the MIL specification in wider range of high angles of attack.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 B
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• pp.942-944
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• 2005

In this study, eddy current signals from various anomalous defects in the heat exchanger tube are predicted af their signal slope characteristics no analyzed. The signal changes due to frequency increase are also observed. Based in the accumulated knowledge, the analysis of superimposed signal is attempted which includes the effects of support plate. Both differential and absolute bobbin probe signals are analyzed. For the prediction of signals, axisymmetric finite element modeling is used and this leads us to the utilization of slope angle analysis of the signal. Results show that differential signals are useful to locate the position of defect under the support plate and absolute signals no easy to predict and analyze even though they no superimposed signals. Combined use of these two types of signals will accomplish a reliable inspection.