• 항공우주시스템공학회지
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• 제15권5호
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• pp.1-7
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• 2021

Ti-6Al-4V 티타늄 합금은 무게 대비 우수한 강도와 고온 강도 특성 때문에 수요가 증가하고 있지만 상온에서 낮은 성형성 때문에 고온으로 성형을 해야 한다. 현재 진행된 고온 성형 연구는 하부 금형을 가열하여 시편을 가열하는 방식이기 때문에 제약이 많다. 기존 고온 성형 방식과 다르게 제품을 국부적으로 가열할 수 있는 고주파 유도가열을 적용한다면 가공의 효율성을 높일 수 있을 것으로 예상된다. 또한 공정 기술 개발 시 신뢰도 높은 해석 기법으로 미리 공정을 시뮬레이션한다면 시간과 비용을 절약할 수 있다. 본 논문에서는 고주파 유도가열을 이용하여 Ti-6Al-4V 합금을 가열하였고 실험 결과와 전자기-열전달 연동 해석 결과를 비교하여 해석의 신뢰도를 판단하였다.

• 한국기계가공학회지
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• 제21권1호
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• pp.28-33
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• 2022

The heating roller of an actual pulse output device (POD) production facility is composed of a steel roller and a rubber roller. The time to reach a specific temperature and the temperature distribution on the roller surface were analyzed and compared according to the change in the number of cartridge heaters inside the heating roller. In this analysis, a steady-state thermal analysis of a steel roller was performed for the cases of a 5-cartridge heater and 9-cartridge heater. Finite element analysis was applied with reference to the surface temperature data of the heating roller during operation and the calorific value of the cartridge heater. Using the 9-cartridge heater, faster target temperature achievement and more uniform temperature distribution were confirmed than for the 5-cartridge heater.

• 태양에너지
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• 제12권1호
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• pp.59-71
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• 1992

본 연구는 주거용건물에서의 난방용에너지 소비량절감 및 실내환경의 쾌적도 향상을 목적으로, 잠열재 용기의 축열 및 방열특성을 파악한 후, 잠열저장패널을 이용한 바닥난방공간의 실내온도분포를 분석하였다. 잠열저장패널의 특성을 구명하기 위해서는 패널의 가열시간에 따른 잠열재의 융해 및 응고특성에 대해 실험 분석하고 실험건물을 이용하여 잠열저장패널을 설치한 실내공간의 온도분포에 대해 실험 분석하였다.

• Journal of Biosystems Engineering
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• 제35권2호
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• pp.108-115
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• 2010

This study was conducted to estimate the optimum temperature and required time for soil sterilization when heated water was circulated through underground heating pipes in the greenhouse which solar heat was influenced to the temperature of soil during the summer day. Two different types of heating pipes were used for the experiment. One was a polyethylene pipe(XL) and the other was a corrugated ring shaped stainless steel pipe(STS). The results of the studies were summarized as follows; By measuring the thermal characteristics of the XL and STS, it was examined that the average temperature differences of the inlet and outlet were $8.5^{\circ}C$ and $13.3^{\circ}C$, the average flowrates were 15.3 L/min and 5.6 L/min, and the average radiation powers were 9.1 kW and 4.1 kW, respectively. As results of the regression analysis of underground temperatures, when average soil temperature was$35^{\circ}C$, an average water temperature was $80^{\circ}C$, and XL was used, it was estimated that the possible heat transfer distance, the required time for heat transfer and heat flux to reach the underground temperature of $60^{\circ}C$ were 300 mm, 230 hours, and $7.57kW/m^2$, respectively.

• Design & Manufacturing
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• 제16권1호
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• pp.27-35
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• 2022

Thermoforming is a plastic manufacturing process that applies a force to stretch a film of heated thermoplastic material over an engineered mold to create a 3-dimensional shape. After forming, the shaped part can then be trimmed and finished to specification to meet an end-user's requirements. The process and thermoplastic materials are extremely versatile and can be utilized to manufacture parts for a very wide range of applications. In this study, based on K-BKZ nonlinear viscoelastic model, thermoforming process analysis was performed for an interior room-lamp. The predicted thickness was minimum at the corner of a molded film, and maximum at the center of the bottom. By using the Taguchi method of design of experiments, the effects of process conditions on residual stresses were investigated. The dominant factors were the liner thickness and the film heating time. As the thickness of the liner increased, the residual stress decreased. And it was found that the residual stress decreased significantly when the film heating temperature was higher than the glass transition temperature. A thermoforming mold and a trimming mold were manufactured, and the spring back was investigated through experiments. The dominant factors were film heating time, liner thickness, and lower mold temperature. As the film heating time and liner thickness increased, the spring back decreased. In addition, it was found that the spring back decreased as the lower mold temperature increased.

• 한국주조공학회지
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• 제18권5호
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• pp.450-461
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• 1998

The optimal reheating conditions to apply the thixoforging and semi-solid die casting process were investigated by changing the reheating time, the holding time, the reheating temperatures, the capacity of the induction heating system, and the adiabatic material size. In the case of solid fraction fs=50% (for semi-solid die casting), the microstructure of SSM (specimen size:$d76{\times}l90$) at the condition of the first elevating time of 4 min, holding time of 1 min and holding temperature of $350^{\circ}C$, the second elevating time of 3 min, holding time of 3 min and holding temperature of $575^{\circ}C$, the third elevating time of 1 min, holding time of 2 min and holding temperature of $584^{\circ}C$, capacity of Q=8.398KW is obtained with globular microstructure and finest. In addition, in the case of solid fraction fs=55% (for thixoforging), the SSM (specimen size:$d76{\times}l90$) at the condition of the first elevating time of 4 min, holding time of 1 min and holding temperature of $350^{\circ}C$, the second elevating time of 3 min, holding time of 3 min and holding temperature of $570^{\circ}C$, the third elevating time of 1 min, holding time of 2 min and holding temperature of $576^{\circ}C$, capacity of Q=12.04KW is obtained with the finest globular microstructure. We saw that the most important factor in a three-step reheating process is the final holding time.

• 대한기계학회논문집B
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• 제26권10호
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• pp.1427-1435
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• 2002

The main aim of the present article is numerically to investigate the micro-scale heat transfer phenomena in a silicon microstructure irradiated by picosecond-to-femtosecond ultra-short laser pulses. Carrier-lattice non-equilibrium phenomena are simulated with a self-consistent numerical model based on Boltzmann transport theory to obtain the spatial and temporal evolutions of the lattice temperature, the carrier number density and its temperature. Especially, an equilibration time, after which carrier and lattice are in equilibrium, is newly introduced to quantify the time duration of non-equilibrium state. Significant increase in carrier temperature is observed for a few picosecond pulse laser, while the lattice temperature rise is relatively small with decreasing laser pulse width. It is also found that the laser fluence significantly affects the N 3 decaying rate of Auger recombination, the carrier temperature exhibits two peaks as a function of time due to Auger heating as well as direct laser heating of the carriers, and finally both laser fluence and pulse width play an important role in controlling the duration time of non-equilibrium between carrier and lattice.

• 공업화학
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• 제22권2호
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• pp.214-218
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• 2011

마이크로파 가열 방법과 기존의 가열 방법을 이용하여 석탄회로부터 제올라이트 A를 합성하였다. 반응시간, sodium aluminate의 양, 반응 온도 등이 제올라이트 A의 결정화에 미치는 영향에 대해 연구하였다. $80{\sim}100^{\circ}C$의 범위에서 제올라이트 A의 합성에 필요한 반응 시간은 3~6 h이었으며, 6 h 이상이 되면 결정화도가 오히려 감소하였다. 제올라이트 A의 합성에 필요한 sodium aluminate의 양은 $90^{\circ}C$ 이상에서는 합성용액의 $SiO_2/Al_2O_3$의 비가 0.44~1.05에서 최적이었으며, $80^{\circ}C$에서는 더 많은 양이 필요하였다. 마이크로파 가열 방법은 기존의 가열 방법에 비해 초기 결정화 속도는 약간 증가하였으나, 충분히 결정화되는데 필요한 반응시간은 서로 비슷하였다. 따라서 마이크로파 가열에 의한 석탄회로부터 제올라이트 A의 합성에 미치는 영향은 크지 않다는 것을 알 수 있었다.

• 한국의류산업학회지
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• 제12권4호
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• pp.500-507
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• 2010

In this study, physical properties were studied by using latent stretching yarn in order to develop the texturing yarn technique for super bulky yarn, which is better in bulkiness and handle than natural wool and also adds property of synthetic fiber to natural wool. In order to obtain textured conditions by analysing basic properties for manufacturing DTY yarn with super bulky property, DTY 50d/12 after spinning latent yarn spined POY 80d/12 was obtained under the two conditions of (i) false twist(T/M) level 3 in DTY texturing and (ii) draw ratio level 4 in draw texturing. For DTY texturing yarn, Elongation rate increased as the heat treatment time and temperatures increased. In addition, shrinkage became higher as false twist was higher, so that elongation rate became lower. When annealing became longer in time and higher in temperature, initial modulus increased. In addition, as the count of false twist increased, the initial modulus showed higher values. For draw texturing yarn, under the conditions of heat temperature 180 and heating time 30 minutes, shrinkage rate in draw ratio 1.55 and 1.6 draw ratio was 7%, and that in 1.65 and 1.7 draw ratio was 8.5%. High draw ratio samples' tenacity was much influenced by heating time and temperature, but low draw ratio samples' tenacity was influenced not by treated time, but by treated temperature.

• Journal of Acupuncture Research
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• 제18권6호
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• pp.171-187
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• 2001

Objective : Moxibustion has been proved efficacious for many diseases, but isn't widespread in the clinics due to a danger of skin burning, the smoke produced while burning a moxa combustion and so on. Therefore, another type of moxa that can be resolved these troubles is required. To improve the effect of moxibustion and develop the new thermal stimulating treatment, the performance of commercial moxibustion widely used are studied systematically and found out quantitatively. Methods : We have selected two types (small-size moxa A(sMA), small-size moxa B (sMB)) among small-size moxaes used widely in the clinic. We examined combustion time, various temperatures, temperature gradient in each period during a combustion of moxa. Results : 1. The combustion time in the preheating period appeared somewhat longer in sMA than in sMB. 2, The combustion time in the heating period appeared longer in sMA by 26% than in sMB. 3. The average temperature in the heating period was $37.6{\sim}37.8^{\circ}C\;in\;sMA\;and\;36.2{\sim}36.8^{\circ}C$ in sMB and the maximum temperature measured at a center of contact surface in sMA was $48.6^{\circ}C$, higher by over $2.8^{\circ}C$ than that of sMB moxibustion. 4. The average ascending temperature gradient in the heating period was $0.08{\sim}0.1^{\circ}C/sec$ in both moxaes, and the average ascending temperature gradient of heating period in sMB appeared larger. The maximum ascending temperature gradient appeared higher in sMB, and the time reaching maximum ascending temperature gradient appeared much earlier in sMA than in sMB. 5. The combustion time in the retaining period was around 100 sec in sMA and around 275 sec in sMB. 6. The average temperature in the retaining period was $42.2{\sim}46.0^{\circ}C\;in\;sMA\;and\;39.3{\sim}41.4^{\circ}C/sec$ in sMB. The minimum temperature in the retaining period was over $38.80^{\circ}C$ in sMA but just $34.7^{\circ}C$ in sMB. 7. The average descending temperature gradient in sMA was $-0.050{\sim}0.067^{\circ}C/sec$ and in sMB was $-0.030{\sim}0.037^{\circ}C/sec$ 8. The combustion time in the cooling period appeared longer over two times in sMA than in sMB, and the time which the cooling period (minimum temperature) finished at appeared later in sMB by 55 sec. 9. We classified the combustion process that the measured temperature rose over body heat($37^{\circ}C$) into the effective combustion period. The effective combustion time was 233.3 sec in sMA and 300.4 sec in sMB respectively, and was longer by about 29% in sMB. The average temperature and maximum temperature in the effective combustion time appeared higher in sMA. The time taken until the maximum temperature was reached was 225.1 sec in sMA and 244.5 sec in sMB, faster by about 20 sec in sMA. The maximum ascending temperature gradient during the effective combustion period appeared larger about 1.4 times in sMB, but the time when the maximum ascending temperature gradient happened was faster in sMA. Conclusion : It appears that sMB, compared with sMA, is proper if necessary to apply the long time and weak stimulus, because of the gentle stimulus during the relatively longer time. In contrast, sMA that the symmetrical combustion happened is proper if necessary to apply the short time and strong stimulus.