• 대한기계학회논문집B
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• 제27권5호
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• pp.668-676
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• 2003

The effect of nozzle height on heat transfer of a hot steel plate cooled by an impinging liquid jet is not well understood. Previous studies have been based on the dimensionless parameter z/d. To test the validity of this dimensionless parameter and to investigate gravitational effects on the jet, stagnation velocity of an impinging liquid jet were measured and the cooling experiments of a hot steel plate were conducted for z/d from 6.7 to 75, and an inverse heat conduction method is applied for the quantitative comparison. Also, the critical instability point of a liquid jet was examined over a range of flow rates. The experimental velocity data for the liquid jet were well correlated with the dimensionless number 1/F $r_{z}$$^2$based on distance. It was thought that the z/d parameter was not valid for heat transfer to an impinging liquid jet under gravitational forces. In the cooling experiments, heat transfer was independent of z when 1/F $r_{z}$$^2$< 0.187(z/d = 6.7). However, it was found that the heat transfer quantity for 1/F $r_{z}$$^2$=0.523(z/d = 70) is larger 11% than that in the region for 1/F $r_{z}$$^2$=0.187. The discrepancy between these results and previous research is likely due to the instability of liquid jet.uid jet.

• 공업화학
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• 제7권1호
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• pp.34-42
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• 1996

합성에메랄드[$(BeO)_3(Al_{2-x}Cr_xO_3)(SiO_2)_6$]단결정을 flux법에 의하여 육성하였다. 출발물질로 BeO, $Al_2O_3$와 $SiO_2$ 시약을 화학양론비로 혼합하여 사용하였다. 에메랄드 단결정의 성장 조건은 다음과 같다. 온도범위 ; $1150{\sim}900^{\circ}C$, 냉각속도 ; 2, 4, $10^{\circ}C/hr$, 융제 : $Li_2CO_3$, $V_2O_5$, 첨가제 ; $Cr_2O_3$. 에메랄드 단결정의 크기는 2, 4, $10^{\circ}C/hr$의 냉각속도에 의존하였다. 얻어진 에메랄드 단결정을 동정하였고, 그 결과는 다음과 같다. 즉, 결정계 ; 육방정계, 격자상수 ; a=0.921nm, c=0.917nm, 결정의 크기 ; 최대 $0.80{\times}0.95mm^2(c{\times}m)$, 방위 ; c(1000), $m(10{\bar{1}}0)$.

• 청정기술
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• 제13권4호
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• pp.281-286
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• 2007

본 연구에서는 폐열회수형 환기장치(전열교환기)로부터의 휘발성 유기화합물이 측정되었다. KS 냉방 및 난방표준조건하에서 휘발성유기화합물의 초기 배출특성을 연구하기 위하여 폐열회수 환기장치로부터 2종류의 열교환소자(L형과 M형)가 평가되었다. 휘발성 유기화합물은 다양한 풍량 변화와 운전시간 변화에 대하여 측정되었다. 본 연구의 분석방법 및 기기상의 한계로 인하여 농도가 비교적 큰 물질만을 살펴보니 페열회수 환기장치에서는 acetic acid, 2-butanone (MEK), 2-(methylthio)ethylamine, toluene, styrene 및 x-acids (Ion 57) 등의 6종의 휘발성 유기화합물이 배출됨을 확인하였다. 배출된 휘발성 유기화합물의 농도는 운전조건에 대해서는 크게 영향을 받지 않았다. 높은 작동온도 때문에 휘발성 유기화합물의 농도는 난방조건보다는 냉방조건에서 더 크게 나타났다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1995년도 춘계학술대회논문집; 전남대학교, 19 May 1995
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• pp.196-201
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• 1995

The broadband and discrete sources of sound in small cooling fans of propeller type and centrifugal type were investigated to understand the turbulent vortex structures from many bladed fans using ANSI test plenum for small air-moving devices (AMDs). The noise measurement method uses the plenum as a test apparatus to determine the acoustic source spectral density function at each operating conditions similar to real engineering applications based on acoustic similarity laws. The characteristics of fans including the head rise vs. volumetric flow rate performance were measured using a performance test facility. The sound power spectrum is decomposed into two non-dimensional functions: an acoustic source spectral distribution function F(St,.phi.) and an acoustic system response function G(He,.phi.) where St, He, and .phi. are the Strouhal number, the Helmholtz number, and the volumetric flow rate coefficient, respectively. The autospectra of radiated noise measurements for the fan operating at several volumetric flow rates,.phi., are analyzed using acoustical similarity. The rotating stall in the small propeller fan with a bell-mouth guided is mainly due to a leading edge separation. It creates a blockage in the passage and the reduction in the flow rate. The sound power levels with respect to the rotational speeds were measured to reveal the mechanisms of stall and/or surge for different loading conditions and geometries, for example, fans installed with a impinging plate. Lee and Meecham (1993) studied the effect of the large-scale motions like impinging normally on a flat plate using Large-Eddy Simulation(LES) and Lighthill's analogy.[ASME Winter Annual Meeting 1993, 93-WA/NCA-22]. The dipole and quadrupole sources in the fans tested are shown closely related to the vortex structures involved using cross-correlations of the hot-wire and microphone signals.

• 한국정밀공학회지
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• 제7권1호
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• pp.37-52
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• 1990

In this study, the characteristics of cooling and rolling during strip casting process is obtained in comparison with the experimental and analytical results. The prupose of this study is to effectively analyze the thermal and mechanical deformation of roller applying the results of the heat transfer and the pressure distribution to boundary conditions. And then the relation between strip thickness and roll deformation is shown. The second purpose is to obtain the proper condition of the continuous casting for stainless steel. The summary and conclusions can be made on the basis of the results obtained by the theories and experiments. a) The strip casting condition for the fine surface quality of tin-alloy as-cast material was obtained in accordance with the velocity of roll rotation and initial roll gap. b) The experimental condition that the dimension of the cast strip thickness coincide with that of the initial roll gap was according to the experimental result of continuous casting by twin-roll type. c) The thermoelastic finite element model to calculate the roll deformation is represented. Thermoelastic model prediction for the roll deformation are in good agreement with the experimental results considering the thermal expansion of the roll. d) The higher cooling rates were obtained by a twin-roller quenching technique. Also quenched microstructure of the rapidly solidified shell was verified. e) The magnitude of roll deformation due to the thermal expansion and roll separating force is quantit- atively represented in the analysis of continuous casting for stainless steel.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.302-310
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• 2011

A fluid in an enclosure can be heated by electric heating, chemical reaction, or fission heat. In order to remove the volumetric heat of the fluid, the walls surrounding the enclosure must be cooled. In this case, a natural convection occurs in the pool of the fluid, and it has a dominant role in heat transfer to the surrounding walls. It can augment the heat transfer rates tens to hundreds times larger than conductive heat transfer. The heat transfer by a natural convection in a regular shape such as a square cavity or semi-circular pool has been studied experimentally and numerically for many years. A pool of an inverted triangular shape with 10 degree inclined bottom walls has a good cooling performance because of enhanced boiling critical heat flux (CHF) compared to horizontal downward surface. The coolability of the pool is determined by comparing the thermal load from the pool and the maximum heat flux removable by cooling mechanism such as radiative or boiling heat transfer on the pool boundaries. In order to evaluate the pool coolability, it is important to correctly expect the thermal load by a natural convection heat transfer of the pool. In this study, turbulence models with modifications for buoyancy effect were validated for unsteady natural convections by volumetric heating. And natural convection in the triangular pool was evaluated by using the models.

• 멤브레인
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• 제21권3호
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• pp.236-246
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• 2011

본 연구에서는 기공의 크기가 $0.4{\mu}m$의 소수성 막인 폴리에틸렌 100가닥으로 모듈을 제작하여 직접접촉식과 동반기체식 막증류 과정에서 막의 양단의 온도차, 공급수의 염분농도, 그리고 냉각수/동반기체의 유량에 대해서 투과수의 플럭스를 측정하였다. 이론적으로는, 동반기체식 막증류는 직접접촉식 막증류 공정의 막의 투과측 표면과 냉각수 사이에 동반 기체층이 추가된 것으로 간주하였다. 이 동반기체층은 새로운 저항층과과 동반기체의 이동중 상변화된 수증기가 손실되는 것이 투과유속을 30% 정도 감소시키게 된다. 물질수지식을 이용하여, 기존의 식과는 다르게 보정계수(${\omega}$)를 넣어 직접접촉식 막증류와 동반기체식 막증류의 이론값을 실험값과 비교 분석하였다.

• 한국재료학회지
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• 제12권12호
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• pp.897-903
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• 2002

Morphological evolution and growth mechanism at the solid/liquid interface during solidification were investigated in the Ni-base superalloy GTD111M by directional soldification and quenching(DSQ) technique. The experiments were conducted by changing solidification rate(V) and thermal gradient(G) which are major solidification process variables. High thermal gradient condition could be obtained by increasing the furnace temperature and closely attaching the heating and cooling zones in the Bridgeman type furnace. The dendritic/equiaxed transition was found in the G/V value lower than $0.05$\times$10{^3}^{\circ}C$s/$\textrm{mm}^2$, and the planar interface of the MC-${\gamma}$ eutectic was found under $17 $\times$ 10{^3}^{\circ}C$ s/$\textrm{mm}^2$. It was confirmed that the dendrite spacing depended on the cooling rate(GV), and the primary spacing was affected by the thermal gradient more than solidification rate. The dendrite lengths were decreased as increasing the thermal graditne, and the dendrite tip temperature was close to the liquidus temperature at $50 \mu\textrm{m}$/s.

• 한국식품과학회지
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• 제35권6호
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• pp.1233-1236
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• 2003

미백복숭아의 신선도를 연장시키기 위하여 수확후 예냉처리가 행해졌다. 복숭아에 대한 예냉 시험 결과 $25.9^{\circ}C$에서 $5^{\circ}C$까지 3시간 이내에 냉각이 가능하였으며 풍량과 정압을 증가시킬수록 냉각속도는 증가하였다. 복숭아의 호흡속도와 에틸렌발생속도는 $20^{\circ}C$의 경우 $7^{\circ}C$에서의 4배 빠르게 나타났다. 예냉처리한 복숭아는 $7^{\circ}C$와 $20^{\circ}C$에 저장한 경우 무예냉처리구에 비해 당도, 감모율, 비타민 C, 외관등에서 30% 이상 우수한 상품성을 유지하였다.

• 한국재료학회지
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• 제9권9호
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• pp.883-889
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• 1999

직경이 각각 4,6,8,12 및 15mm인 순Al 또는 Al-(1,2,3wt%) Cu합금 내부냉금이 95mm ø$\times$200mm H 크기의 흑연주형 중심부에 설치되었다. 이 내부냉금과 같은 조성의 용융금속이 $750^{\circ}C$의 주입온도에서 주형에 주입되었고, 냉각속도, 응고조직 및 성분편석이 분석되었다. 주괴직경/내부냉금직경의 비가 8까지 증가될수록 결정립도, 2차수지상간격 및 성분편석이 현저하게 감소됨이 확인되었다. 그러나 이 비가 8이상이 되면, 미용해 내부냉금이 발생되고, 내부냉금의 효과는 급속히 감소되었다. 순Al 및 Al-(1,2,3wt%)Cu 합금에서 최대 내부냉금 효과를 얻을 수 있는 적정 주괴직경/내부냉금직경의 비는 $750^{\circ}C$주입온도에서는 8이었다.