• 한국산업융합학회 논문집
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• 제22권2호
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• pp.191-199
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• 2019

In this paper, dissimilar friction welding were produced using 15 mm diameter solid bar in chrome molybedenum steel(SCM440) to stainless steel(STS316L) to investigate their mechanical properties. Consequently, optimal welding conditions were n=2000 rpm, HP=70 MPa, UP=140 MPa, HT=10 sec and UT=10 sec when the metal loss(Mo) is 8.6 mm. In addition, an acoustic emission technique was applied to evaluate the optimal friction welding condition. AE parameters including the cumulative count, amplitude and energy showed a various changes according to the friction condition. A continuous type waveforms and low frequency spectrum was presented in friction time. On the other hand, a burst type waveform and high frequency spectrum was exhibited in pressing time.

• 대한설비공학회지:설비저널
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• 제14권1호
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• pp.1-11
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• 1985

Solar/absorption cooling system was analyzed and its operating condition was examined. For the system, the optimum size of absorption refrigerator and collector area should be determined. As the temperature of water supplied to the generator increases, the collector efficiency decreases whereas the coefficient of performance of absorption refrigerator increases up to a certain point, and vice versa for decreasing of the temperature of water supplied to the generator . Thus if the reeling load is given, the appropriate operating condition can be determined between the two opposing trends by simulation program. As an example of the simulation, the case of Jejudo province was studied. Under the conditions (such as weather data and prices of components, etc.) given en the sample calculation, the result shows that the optimum temperature of water supplied to the generator turned out to be $80.3^{\circ}C$, and still shows a large economical disadvantage in present stage compared to the case of conventional vapor compression cooling/heating combined heat pump system.

• Advances in Energy Research
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• 제8권4호
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• pp.265-273
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• 2022

In this study, a product gas yield and carbon conversion were measured during the coal pyrolysis. The pyrolysis process occurred under two different atmospheres such as subcritical (45 bar, 10℃) and supercritical CO₂ condition (80 bar, 35℃). Under the same pressure (80 bar), the atmosphere temperature increased from 35℃ to 45℃ to further examine temperature effect on the pyrolysis at supercritical CO₂ condition. For all three cases, a power input supplied to heating wire placed below coal bed was controlled to make coal bed temperature constant. The phase change of CO₂ atmosphere and subsequent pyrolysis behaviors of coal bed were observed using high-resolution camcorder. The pressure and temperature in the reactor were controlled by a CO₂ pump and heater. Then, the coal bed was heated by wire heater to proceed the pyrolysis under supercritical CO₂ condition.

• 열처리공학회지
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• 제8권4호
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• pp.302-317
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• 1995

After initial structure of AISI 9260 steel is changed into pearlite and martensite, one is isothermally annealed at $700^{\circ}C$ below of $A_1$ transformation point and the other is isothermally annealed at the same condition after 3 cycles of heating and cooling between $680^{\circ}C$ and $780^{\circ}C$ of $A_1$ transformation point. Analyzing the changes of microstructure, mechanical properties and fractography of tension test, we obtained result as follows. The fastest spheroidization rate by changes of initial structure and heat treatment cycles is appeared at the heat treatment cycle which is isothermally annealed after 3 cycles of heating and cooling at below and above $A_1$ transformation point for martensite. At the above condition, the perfect spheroidization structure is appeared after 60hrs and after then, globular carbide is being coarsened. The mean diameter of globular carbide is $2.4{\times}10^{-3}mm$ after 90hrs. The changes of tension strength during spheroidization heat treatment follows Orwan function, ${\sigma}_o={\sigma}_i+Gb/l$, where l is interspacing of carbide particles and at the above condition, ${\sigma}_o=70.48+2.5{\times}10^{-3}/l(kg/mm^2)$. Fractography of fracture of spheroidization structure in tension test is appeared as dimple which is ductile rupture type by nucleation and growth of void, size of dimple is larger and deeper with increasing of heat treatment time.

• 한국자동차공학회논문집
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• 제13권2호
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• pp.72-82
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• 2005

The objective of this paper is to describe the optimization of design parameters in a large-sized commercial bus heater system by using CFD(computational fluid dynamics) analysis and Taguchi method. In order to obtain the best combination of each control factor which results in a desired performance of heater system, the parameter design of the Taguchi method is adopted for the robust design considering the dynamic characteristic. The research activity may be divided into four phases. The first one is analyzing the problem, i.e., ascertaining the influential factors. In the second phase the levels were set in such a way that their variation would significantly influence the response. In the third phase the experimental runs were designed. In the final phase the planned runs were carried out numerically to evaluate the optimal combination of factors which is able to provide the best response. In this study, eight factors were considered for the analysis: one with two level and seven with three level combinations comprising the $L_{18}(2^1{\times}3^7)$ orthogonal array. The results of this study can be summarized as follows ; (i)The optimum condition of control factor is a set of <$A_2\;B_1\;C_3\;D_3\;E_1\;F_2\;G_3\;H_2$> where A is shape of the outer fin, B is pitch of the outer fin, C is height of the outer fin, D is the inner fin number, E is the inner fin height, F is length of the flame guide, G is diameter of the heating element and H is clearance between air guide and heating element. (ii)The heat capacity of heated discharge air under the optimum condition satisfies the equation y=0.6M w here M is a signal factor. (iii)The warm-up rate improves about three times, more largely as com pared with the current condition, which results in about 9.2minutes reduction.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1933-1938
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• 2004

Nucleate boiling experiments with constant wall temperature of heating surface were performed using R113 for almost saturated pool boiling conditions. A microscale heater array and Wheatstone bridge circuits were used to maintain a constant wall temperature condition and to measure the heat flow rate with high temporal and spatial resolutions. Bubble images during the bubble growth were taken as 5000 frames a sec using a high-speed CCD camera synchronized with the heat flow rate measurements. The geometry of the bubble during growth time could be obtained from the captured bubble images. The bubble growth behavior was analyzed using the new dimensionless parameters for each growth regions to permit comparisons with previous results at the same scale. We found that the new dimensionless parameters can describe the whole growth region as initial and later respectively. The comparisons showed good agreement in the initial and thermal growth regions. The required heat flow rate for the volume change of the observed bubble was estimated to be larger than the instantaneous heat flow rate measured at the wall. Heat, which is different from the instantaneous heat supplied through the heating wall, can be estimated as being transferred through the interface between bubble and liquid even with saturated pool conditions. This phenomenon under a saturated pool condition needs to be analyzed and the data from this study can supply the good experimental data with the precise boundary condition (constant wall temperature).

• Corrosion Science and Technology
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• 제2권6호
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• pp.283-288
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• 2003

The cathodic protection method is being widely used in marine structural steel, however a high tensile steel like RE 36 steel for marine structural steel is easy to get hydrogen embrittlement due to over protection during cathodic protection as well as preferential corrosion of HAZ(Heating Affected Zone) part. In this paper, corrosion resistance and mechanical properties such as elongation and hydrogen embrittlement were investigated with not only in terms of electrochemical view but also SSRT(Slow Strain Rate Test) method with applied constant cathodic potential, analysis of SEM fractography in case of both As-welded and PWHT(Post-Weld Heat Treatment) of $550^{\circ}C$. The best effect for corrosion resistance was apparently indicated at PWHT of $550^{\circ}C$ and elongation was increased with PWHT of $550^{\circ}C$ than that of As-welded condition. On the other hand. Elongation was decreased with applied potential shifting to low potential direction which may be caused by hydrogen embrittlement, however the susceptibility of hydrogen embrittlement was decreased with PWHT of $550^{\circ}C$ than that of As-welded condition and Q.C(quasi cleavage) fracture mode was also observed significantly according to increasing of susceptibility of hydrogen embrittlement. Eventually it is suggested that an optimum cathodic protection potential range not causing hydrogen embrittlernent is from -770 mV(SCE) to -850 mV(SCE) in As-welded condition while is from -770 mV(SCE) to -875 mV(SCE) in PWHT of $550^{\circ}C$.

• 한국식품위생안전성학회지
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• 제24권3호
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• pp.204-210
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• 2009

대두유에 생마늘, 증숙마늘 및 흑마늘 분쇄물을 농도별로 가하여 $180^{\circ}C$에서 가열하면서 유지의 산패 정도를 비교하였다. 유지의 색도는 가열시간이 경과할수록 높아졌으며, 가열 48시간 후 40 g/100 mL의 마늘 첨가시 생마늘은 1.36, 증숙마늘은 2.99, 흑마늘은 1.99의 색도를 보였다. 아니시딘가는 가열시간이 경과함에 따라 불규칙한 증감을 보이면서 상승하는 경향이었다. 산가는 가열 $12{\sim}48$시간 동안 마늘 첨 가구에서 대조구보다 높았으며, 모든 실험구에서 가열 12시간 후에는 $0.82{\sim}2.04\;mg$/g이었는데, 48시간 후에는 $3.15{\sim}4.30\;mg$/g이었다. 과산화물가는 가열 48시간 후 40 g/100 mL의 흑마늘 첨가시 tocopherol 및 BHT첨가구보다 과산화물 생성이 낮았다. TBA가는 가열 48시간 후 40 g/100 mL의 마늘 첨가시 흑마늘 첨 가구에서 TBA가가 가장 낮았다.

• 생물환경조절학회지
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• 제27권3호
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• pp.269-275
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• 2018

온실 냉난방시스템 설계용 외부기상조건의 분석 기준을 설정하기 위하여 연간 백분위 방식에 의한 냉난방 설계기온을 분석하고, 기존의 계절 백분위 방식에 의한 설계기온과 비교 검토하였다. 우리나라 전 지역을 대상으로 현재 기상청에서 제공하는 기후평년값 기준 30년 간의 매 시각 기상자료를 분석에 사용하였다. 표준기상데이터의 이용이 제한적이기 때문에 전체 기상자료를 이용하여 매년 설계용 기상조건을 구하고, 전체 자료기간의 평균값을 분석에 사용하였다. 연간 백분위 방식으로 1년 기준 총 8,760시간의 백분위수 0.4%, 1%, 2%를 냉방 설계 외기온으로, 99.6%, 99%를 난방 설계 외기온으로 제시하였다. 연간 백분위 방식을 채택할 경우 계절 백분위 방식에 비하여 전체적으로 난방설계 외기온은 6.7~9.6% 상승하는 것으로 나타났으며, 냉방설계 외기온은 0.6~1.1% 하강하는 것으로 나타났다. 동일한 온실 조건에서 최대난방부하는 연간 백분위 방식을 채택할 경우 기존의 계절 백분위 방식에 비하여 약 3.0~3.6% 정도 감소하는 것으로 나타났고, 최대냉방부하에 미치는 영향은 미미한 것으로 분석되었다. 따라서 난방설계 외기온은 연간 백분위 방식으로의 변경에 대하여 고려할 필요가 있지만, 냉방설계 외기온은 두 방법 간의 차이가 거의 없으므로 아직까지 변경할 필요는 없는 것으로 판단된다. 전체적으로 현재의 계절 백분위 방식으로 분석한 설계 외기온을 사용하여도 큰 문제는 없을 것으로 생각되지만, 기후변화의 영향을 고려하여 주기적인 설계용 기상자료의 분석 및 설계기준의 개정이 필요하고, 현재의 기후평년값 기준연도가 바뀌는 2021년 이후에는 이 기간의 기상자료를 분석하여 새로운 설계기준으로 제공해야 할 것이므로, 그 때 연간 백분위 방식에 대한 전문가 그룹의 검토를 통하여 반영할 필요가 있을 것으로 판단된다.

• 대한치과보철학회지
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• 제35권3호
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• pp.566-576
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• 1997

This study was performed to evaluate the tensile strength of solder joint in titanium and the wettability of 14K gold solder on titanium. Two pieces of titanium rod 30 mm in length and 3mm in diameter were butt-soldered with a 14K gold solder using the electric resistance heating under flux-argon atmosphere, the infrared heating under argon atmosphere, and the infrared heating under vacuum-argon atmosphere. A tensile test was performed at a crosshead speed of 0.5 mm/min, and fracture surfaces were examined by SEM. To evaluate the wettability of 14K gold solder on titanium, titanum plates of a $17{\times}17{\times}1mm$ were polished with #80-#2000 emery papers, and the spreading areas of solder 10 mg were measured by heating at 840 * for 60 seconds. The solder-matrix interface regions were etched by the solution of 10% KCN-10% (NH4)2S2O8, and analyzed by EPMA. The results obtained were summarized as follows ; 1. The maximum tensile strength was obtained when the titanium surface was polished with #2000 emery paper and soldered using the electric resistance heating under flux-argon atmosphere. Soldering strengths showed the significant difference between the electric resistance heating and the infrared heating(p<0.05). 3. The fracture surfaces showed the aspect of brittle fracture, and the failure developed along the interfaces of solder-matrix reaction zone. 4. The EPMA data for the solder-matrix interface region revealed that the diffusion of Au and Cu occurred to the titanium matrix, and the reaction zone showed the higher contents of Au, Cu and Ti than others.