• 설비공학논문집
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• 제13권8호
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• pp.674-681
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• 2001

An experiment is conducted to investigate the effect of the inclination angle on convective boiling heat transfer of a uniformly heated tube. The test section used is a stainless steel tube with10.7mm in inner diameter. The hating length is 3m and is heated directly by an AC current. The test fluid is R-113. Experiment are carried out with mass flow rates of 300, 500 and $700\;kg/m^{2}s$, and heat fluxes varying from 5 to 65 kW/$m^2$. The inclination angles of the tube are $0^{\circ},\;5^{\circ},\;11^{\circ}\;and\;25^{\circ}$. the circumferential temperature variation at low quality region and the location of dryout at high quality region are mainly observed. Circumferential anisothermality occurring at low mass flow rate and low quality conditions is gradually reduced with the increase in the inclination angle and finally disappears at the inclination angle of $25^{\circ}$. Critical quality where dryout is initiated is seriously influenced by the inclination angle. Wall temperature after critical quality is also affected by the inclination angle.

• 한국응용과학기술학회지
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• 제8권2호
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• pp.145-151
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• 1991

Hazadous properties were evaluated for Alkyl nitrates such as hexyl nitrate, decyl nitrate, dodecyl nitrate and 2-methyl pentyl nitrate, 2-hexyl ethyl nitrate. The thermochemical properties such as heat of vaporization, boiling point, flash point and kinetic parameter for aliphatic nitrate were measured to determine the hazadous properties of these compounds. The boiling points and heat of vaporization increase as the increase of alkyl chain length in alkyl nitrates. Flash point is a linear function of boiling point as same as alkanes. The rate equation in isothermal decomposition are 1/2 order and compensation effect is found between logarithm of frequency factor the activation energy, then the decomposition preceeds with simlar reaction mechanism for each nitrate.

• Nuclear Engineering and Technology
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• 제56권1호
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• pp.265-274
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• 2024

The current research focuses on the development of a numerical approach to forecast strongly subcooled flow boiling of FC-72 as the refrigerant in various vertical minichannel shapes for high-heat-flux cooling applications. The simulations are carried out using the Volume of Fluid method with the Lee phase change model, which revealed some inherent flaws in multiphase flows that are primarily due to an insufficient interpretation of shearlift force on bubbles and conjugate heat transfer against the walls. A user-defined function (UDF) is used to provide specific information about this noticeable effect. The influence of shape and the inlet mass fluxes on the flow patterns, heat transfer, and pressure drop characteristics are discussed. The computational results are validated with experimental measurements, where excellent agreements are found that prove the efficiency of the present numerical model. The findings demonstrate that the heat transfer coefficient decreases as the mass flux increases and that the constriction design improves the thermal performance by 24.68% and 10.45% compared to the straight and expansion shapes, respectively. The periodic constriction sections ensure good mixing between the core and near-wall layers. In addition, a slight pressure drop penalty versus the thermal transfer benefits for the two configurations proposed is reported.

• Journal of Mechanical Science and Technology
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• 제17권8호
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• pp.1171-1184
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• 2003

An experimental study on critical heat flux (CHF) has been performed in an internally heated vertical annulus with non-uniform heating. The CHF data for the chopped cosine heat flux have been compared with those for uniform heat flux obtained from the previous study of the authors, in order to investigate the effect of axial heat flux distribution on CHF. The local CHF with the parameters such as mass flux and critical quality shows an irregular behavior. However, the total critical power with mass flux and the average CHF with critical quality are represented by a unique curve without the irregularity. The effect of the heat flux distribution on CHF is large at low pressure conditions but becomes rapidly smaller as the pressure increases. The relationship between the critical quality and the boiling length is represented by a single curve, independent of the axial heat flux distribution. For non-uniform axial heat flux distribution, the prediction results from Doerffer et al.'s and Bowling's CHF correlations have considerably large errors, compared to the prediction for uniform heat flux distribution.

• 한국식품과학회지
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• 제6권2호
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• pp.70-74
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• 1974

한우(韓牛)의 round muscle과 오징어 근육(筋肉)을 여러 가지 조리조건(調理條件)으로 처리(處理)하여 pepsin에 의한 in vitro 소화율(消化率)과 소화과정중(消化過程中)의 amino태(態) N, 유기용매(有機溶媒) 처리(處理)가 소화율(消化率)에 미치는 영향(影響)을 AOAC에 의한 semi-micro Kjeldahl법(法)으로 실험(實驗)한 결과(結果)는 다음과 같다. 1. 소화율(消化率)은 우육(牛肉)에서 autoclaving, frying, raw, freezing, roasting, boiling, dry heating의 순서이며 오징어육(肉)에서는 raw, autoclaving, boiling, freezing, frying, dry heating, roasting의 순서로 높았다. 2. Amino태(態) N는 우육(牛肉), 오징어육(肉) 공(共)히 소화율(消化率)이 높은 순서로 비례해서 증가(增加)한다. 3. 우육(牛肉)과 오징어육(肉)의 raw condition에서 ether처리(處理)가 소화율(消化率)에 거의 영향을 미치지 않는다.

• 대한기계학회논문집B
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• 제29권5호
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• pp.643-652
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• 2005

Saturated nucleate pool boiling experiments for binary mixtures, which are consisted of refrigerant R11 and R113, were performed with constant wall temperature condition. Results for binary mixtures were also compared with pure fluids. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant temperature of the heating surface and to obtain heat flow rate measurements with high temporal and spatial resolutions. Bubble growth images were captured using a high speed CCD camera synchronized with the heat flow rate measurements. The departure time for binary mixtures was longer than that for pure fluids, and binary mixtures had a higher onset of nucleate boiling (ONB) temperature than pure fluids. In the asymptotic growth region, the bubble growth rate was proportional to a value between $t^{\frac{1}{6}}$ and $t^{\frac{1}{4}}$. The bubble growth behavior was analyzed to permit comparisons with binary mixtures and pure fluids at the same scale using dimensionless parameters. There was no discernable difference in the bubble growth behavior between binary mixtures and pure fluids for a given ONB temperature. And the departure radius and time were well predicted within a ${\pm}30{\%}$ error. The minimum heat transfer coefficient of binary mixtures occurred near the maximum ${\mid}y-x{\mid}$ value, and the average required heat flux during bubble growth did not depend on the mass fraction of R11 as more volatile component in binary mixtures. Finally, the results showed that for binary mixtures, a higher ONB temperature had the greatest effect on reducing the heat transfer coefficient.

• Journal of Advanced Marine Engineering and Technology
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• 제32권5호
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• pp.707-716
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• 2008

The objective of this study was to analyze the effect of mixed fuel composition and mass fraction on spray inner structure in evaporating transient spray under the variant ambient conditions. Spray structure and spatial distribution of liquid phase concentration were investigated using a thin laser sheet illumination technique on the three component mixed fuels. A pulsed Nd:YAG laser was used as a light source. The experiments were conducted in a constant volume vessel with optical access. Fuel was injected into the vessel with electronically controlled common rail injector. Used fuel contains i-octane($C_8H_{18}$), n-dodecane($C_{12}H_{26}$) and n-hexadecane($C_{16}H_{34}$) that were selected as low-, middle- and high-boiling point fuel, respectively. Experimental conditions are 42 MPa, 72 MPa and 112 MPa in injection pressure, $5\;kg/m^3$, $15kg/m^3$ and $30kg/m^3$ in ambient gas density, 300 K, 500 K, 600 K and 700 K in ambient gas temperature, 300 K and 368 K in fuel temperature and different fuel mass fraction. Experimental results indicated that the multi-component fuels made two phase region mixed vapor and liquid so that it would are helpful to improve combustion, for the fuels of high boiling point component could accelerate evaporation very much according as low boiling point fuel was added to high boiling point fuel.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1209-1218
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• 2001

The present paper proposes a new correlation for the flow boiling heat transfer coefficients in the low flow rate condition (Re(sub)LF$\leq$200) within horizontal rectangular channels with small gaps (heights). The gap between the upper and the lower plates of each channel ranges from 0.4 to 2mm while the channel width being fixed to 20mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200kg/㎡s and the channel walls were uniformly heated with the heat flux range of 3-15kW/㎡. The quality range covers from 0.19 to 0.76 and the flow pattern is considered to be annular. The measured heat transfer coefficients increase with the mass flux and the local quality; however the effect of the heat flux appears to be minor. At the low mass flux condition, which is more likely with the smaller gap size, the heat transfer is primarily controlled by the liquid film thickness. The proposed F factor for the heat transfer coefficient in the range of Re(sub)LF$\leq$200 well represents the experimental data within the deviation of $\pm$20%. The Kandlikars flow boiling correlation covers the higher flow-rate range(Re(sub)LF>200) within the deviation of $\pm$20%.

• 설비공학논문집
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• 제21권12호
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• pp.663-670
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• 2009

Two-phase flow boiling heat transfer of R-410A in horizontal small tubes was reported in the present experimental study. The local heat transfer coefficients were obtained over a heat flux range of 5 to 40 kW/$m^2$ a mass flux range of 170 to 600 kg/$m^2s$, a saturation temperature range of 3 to $10^{\circ}C$, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5 and 3.0 mm, and lengths of 330 and 3000 mm, respectively. The test section was heated uniformly by applying a direct electric current to the tubes. The effects on heat transfer of mass flux, heat flux, inner tube diameter, and saturation temperature were presented. The experimental heat transfer coefficients are compared with six existing heat transfer coefficient correlations. A new boiling heat transfer coefficients correlation based on the superposition model for R-410A in small tubes was developed with mean deviation of 10.13%.

• 대한기계학회논문집B
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• 제35권10호
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• pp.1089-1095
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• 2011

열전달 향상을 위한 방법으로 많이 사용되고 있는 마이크로 핀을 포함한 표면 위에서의 핵비등을 액상과 기상에서 질량 및 운동량, 에너지에 대한 지배 방정식을 풀어 수치해석을 수행하였다. 핵비등에서의 기포거동을 계산하기 위해 sharp-interface 레벨셋(level-set) 방법을 상변화 효과와 핀과 캐비티와 같은 잠긴 고체에서의 점착 조건 및 접촉각, 마이크로 액체층에서의 증발 열유속을 포함하도록 수정하였다. 핀과 캐비티를 포함한 표면에서의 기포 생성, 성장, 이탈에 대한 해석을 통하여 핀-캐비티 배열, 핀-핀 간격이 핵비등에서의 기포거동에 중요한 역할을 하는 것을 확인하였다.