• 한국태양에너지학회 논문집
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• 제29권5호
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• pp.35-44
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• 2009

In this study, boiling heat transfer coefficients(HTCs) and critical heat flux(CHF) are measured on a smooth square flat copper heater in a pool of pure water with and without carbon nano tubes(CNTs) dispersed at $60^{\circ}C$. Tested aqueous nanofluids are prepared using multi-walled CNTs whose volume concentrations are 0.0001, 0.001, 0.01, and 0.05%. For dispersion of CNTs, polyvinyl pyrrolidone(PVP) is used in distilled water. Pool boiling HTCs are taken from $10kW/m^2$ to critical heat flux for all nanofluids. Test results show that the pool boiling HTCs of the nanofluids are lower than those of pure water in entire nucleate boiling regime. On the other hand, critical heat flux is enhanced greatly showing up to 200% increase at volume concentration of 0.001% CNTs as compared to that of pure water. This is related to the change of surface characteristics by the deposition of CNTs. This deposition makes a thin CNT layer on the surface and the active nucleation sites of heat transfer surface are decreased due to this layer. The thin layer acts as the thermal resistance and also decreases the bubble generation rate resulting in a decrease in pool boiling HTCs. The same layer, however, maintains the nucleate boiling even at very high heat fluxes and reduces the formation of large vapor canopy at near CHF resulting in a significant increase in CHF.

• Nuclear Engineering and Technology
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• 제42권6호
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• pp.662-669
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• 2010

To develop the manufacturing methods for the blanket first wall (FW) of the International Thermonuclear Experimental Reactor (ITER) and to verify the integrity of the joint, Be/Cu mockups were fabricated and tested at the KoHLT-1 (Korea Heat Load Test facility), a graphite heater facility located at the Korea Atomic Energy Research Institute (KAERI). Since Be and Cu joining is the focus of the present study, the fabricated mockups had a CuCrZr heat sink joined with three Be tiles as an armor material, unlike the original ITER blanket FW, which has a stainless steel structure and coolant tubes. Hot isostatic pressing (HIP) was carried out at $580^{\circ}C$ and 100 MPa for 2 hours as the method for Be/Cu joining. Three interlayers, namely, $1{\mu}mCr/10{\mu}mCu$, $1{\mu}mTi/0.5{\mu}mCr/10{\mu}mCu$, and $5{\mu}mTi/10{\mu}mCu$ were applied as a coating to the Be tiles by a physical vapor deposition (PVD) method. A shear test was performed with the specimens, which were fabricated by the same methods as those used to fabricate the mockups. The average values were 125 MPa to 180 MPa, and the samples with the $1{\mu}mCr/10{\mu}mCu$ interlayer showed the lowest value. No defect or delamination was found in the joints of the mockups by the developed ultrasonic test using a flat-type probe with a 10 MHz frequency and a 0.25 inch diameter. High heat flux (HHF) tests were performed at $1.0\;MW/m^2$ heat flux for each mockup using the given conditions, and the results were analyzed by ANSYS-CFX code. For the test criteria, an expected fatigue lifetime about 1,000 cycles was obtained by analysis with ANSYS-mechanical code. Mockups using the interlayers of $1{\mu}mTi/0.5{\mu}mCr/10{\mu}mCu$ and $5{\mu}mTi/10{\mu}mCu$ survived up to 1,100 cycles over the required number of cycles. However, one of the Be tiles in the other two mockups using the $1{\mu}mCr/10{\mu}mCu$ interlayer was detached during the screening test, and others were detached by discharge after 862 cycles. The integrity of the joints using the proposed interlayers was proven by the HHF test, but the other interlayer requires more study before it can be used for the joining of Be to Cu. Moreover, it was confirmed that the measured temperatures agreed well with the analysis temperatures, which were used to estimate the lifetime and that the developed facility showed its capability of the long time operation.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.205-210
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• 2004

The pulse detonation engine (PDE) has recently expected as a new aerospace propulsion system. The PDE system has high thermal efficiency because of its constant-volume combustion and its simple tube structure. We measured thrust of single-tube pulse detonation rocket (PDR) by two methods using the PDR-Engineering Model (full scale model) for ground testing. The first involved measuring the displacement of the PDR-EM by laser displacement meter, and the second involved measuring the time-averaged thrust by combining a load cell and a spring-damper system. From these two measurements, we obtained 130.1 N of time-averaged thrust, which corresponds to 321.2 sec of effective specific impulse (ISP). As well, we measured the heat flux in the wall of PDE tubes. The heat flux was approximately 400 ㎾/$m^2$. We constructed the PDR-Flight Mode] (PDR-FM). In the vertical flight test in a laboratory, the PDR-FM was flying and keeping its altitude almost constant during 0.3 sec.

• 대한기계학회논문집B
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• 제35권5호
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• pp.503-511
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• 2011

수분류 스프레이 냉각은 $900^{\circ}C$ 이상의 고온에서 강판을 냉각하는데 매우 중요한 기술이다. 본 연구는 냉각수온이 고온 강판의 수분류 스프레이 냉각에 미치는 영향을 고찰하였다. 이 때의 열유속은 시편, 카트리지히터, 열전대의 조합으로 고안된 열유속게이지를 제작하여 엄밀하게 측정되었다. 스프레이는 fullcone 노즐로부터 생성되고 냉각실험은 일정한 스프레이 질량유속과 노즐과 표면 사이의 거리 조건에서 수행되었다. 냉각수온의 효과는 $5^{\circ}C$에서 $45^{\circ}C$까지 다섯 가지의 서로 다른 수온에 대한 수분류 스프레이 냉각의 열전달 현상을 비교 및 평가하였다. 여기서 열유속곡선과 열전달계수는 고온 강판의 냉각공정에서 실제 스프레이 냉각을 위한 기본 데이터로 활용될 수 있다.

• 조명전기설비학회논문지
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• 제29권4호
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• pp.1-10
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• 2015

The light emitting diodes(LED) package of new structure is proposed to promote the reliability and lifespan by maximize heat dissipation occurred on the chip. We designed and fabricated the LED packages mixing the advantages of chip on board(COB) based on conventional metal printed circuit board(PCB) and the merits of Si sub-mount using base as a substrate. The proposed LED package samples were selected for the superior efficiency of the material through the sealant properties, chip characteristics, and phosphor properties evaluations. Reliability test was conducted the thermal shock test and flux rate according to the usage time at room temperature, high-temperature operation, high-temperature operation, high-temperature storage, low-temperature storage, high-temperature and high-humidity storage. Reliability test result, the average flux rate was maintained at 97.04% for each items. Thus, the Si sub-mount based LED package is expected to be applicable to high power down-light type LED light sources.

• 대한설비공학회지:설비저널
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• 제8권3호
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• pp.131-150
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• 1979

Recently only a few correlations between various factors due to the different grades of surface roughness for the nucleate pool boiling have been proposed. The main purpose of this work is to test the validity of these types of correlations between related factors to nucleate pool boiling phenomena. The boiling experiments using distilled water were carried out at the heat flux ranging from $7.4\times10^4\;to\;2.4\times10^5kcal/m^2h$ on the sintered porous metal surface with the cavity diameter of 10, n, 40, 70, $100{\mu}$, respectively, at the atmospheric pressure, To determine the bubble sizes, number of nucleation sites, delay and growth time, frequency of bubble emission and rising velocities of bubbles, the high speed motion picture technique was employed. In the correlation $f{\propto}D_b^n$, where f denotes frequency of bubble emission and $D_b$ departure diameter, n, the power factor of $D_b$, have been found to be from -2 to -10/3. The correlation C in the correlation between heat flux q and density of nucleation sites $\frac{N}{A}$, $q=C(\frac{N}{A})^n$, was appeared to be more crucial than the power factor n. The correlation of the heat flux q to the temperature difference ${\Delta}T$ and the density of nucleation sites$\frac{N}{A}$, was proposed to be $$q-460{\Delta}T^{\frac{5}{4}}=K{\Delta}T{\frac{5}{3}}(\frac{N}{A})^{\frac{2}{3}}$$. The values of heat transfer coefficient obtained in this experiments for the porous sintered metal surface appeared to be very high in comparison with the formerly obtained results for the other surfaces.

• 설비공학논문집
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• 제23권3호
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• pp.194-200
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• 2011

In this work, nucleate pool boiling heat transfer coefficients(HTCs) of pure water are measured on horizontal 26 fpi low fin, Turbo-B and Thermoexcel-E square surfaces of 9.53 mm length. HTCs are taken from 10 $kW/m^2$ to critical heat flux for all surfaces. Test results show that critical heat fluxes(CHFs) of all enhanced surfaces are greatly improved as compared to that of a plain surface. CHFs of water on the 26 fpi low fin surface, Thermoexcel-E surface, and Turbo-B are increased up to 320%, 275%, and 150% as compared to that of the plain surface, respectively. CHF of the Turbo-B enhanced surface is lower than that of the 26 fpi low fin surface due to the surface geometry. The heat transfer enhancement ratios of the Thermoexcel-E surface, low fin surface and Turbo-B enhanced surface are 1.6~2.9, 1.6~2.1, 1.4~1.7 respectively in the range of heat fluxes tested. Judging from these results, it can be said that these types of enhanced surfaces can be used in heat transfer applications at high heat fluxes.

• 대한기계학회논문집B
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• 제24권11호
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• pp.1470-1477
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• 2000

Due to the ozone depletion and global warming potentials, some refrigerants(CFx and HCFCs) have been rapidly substituted. R410A is considered as the alternative refrigerant of R22 for the air-conditioners used a home and in industry. Experiments on the condensation heat transfer characteristics inside a smooth or a micro-fin tube with R410A are performed in this study. The test tubes 7/9.52 mm in outer diameters and 3 m in length are used. Varying the mass flux of the refrigerant and the condensation temperatures, the average heat transfer coefficients and pressure drop are investigated. It is shown that the heat transfer is enhanced and the amount of pressure drops are larger in the microfin tube than the smooth tube. From the heat transfer enhancement coefficient and the pressure penalty factor, it is found that the high heat transfer enhancement coefficients are obtained in the range of small mass flux while the penalty factors are almost equal.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권4호
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• pp.130-136
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• 2008

The refrigerant R-134a flow distributions are experimentally studied for a round header/ten flat tube test section simulating a brazed aluminum heat exchanger. Three different inlet orientations(parallel, normal, vertical) were investigated. Tests were conducted with downward flow for the mass flux from 70 to 130 $kg/m^2s$ and quality from 0.2 to 0.6. In the test section, tubes were flush-mounted with no protrusion into the header. It is shown that normal and vertical inlet yielded approximately similar flow distribution. At high mass fluxes or high qualities, however, slightly better results were obtained for normal inlet configuration. The flow distribution was worst for the parallel inlet configuration. Possible explanation is provided based on flow visualization results.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2006년도 제30회 학술논문발표회 초록집
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• pp.232-232
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• 2006