• 한국태양에너지학회:학술대회논문집
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• 2011.11a
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• pp.68-73
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• 2011

This study was performed numerical analysis in order to analyze liquid film flow of heat exchanger tube arrangement and configuration of evaporative multi effect distillation system using medium-temperature. Simulation was accomplished the two-dimensional calculations using commercial analyses program FLUENT based on the FVM(finite volume method). Fresh water generator of this study used Shell & Tubes heat exchanger with Cu_Ni tube, configuration of tube used bare tube and corrugated tube, and arrangement of tube used in-line array and staggered array. Performance of heat exchanger through the formation of liquid film was compared and analyzed. Liquid film flow occurred that falling on heat exchanger tube wall. Result of simulation showed that liquid film thickness of in-line arrangement was found 0.57mm with bare tube and 0.67mm with corrugated tube, respectively. And liquid film thickness of staggered arrangement was found 0.39mm with bare tubes and 0.62mm with corrugated tubes, respectively. Liquid film thickness of corrugated tube showed thicker than bare tube, but heat transfer rates of corrugated tube showed higher than bare tube. The reason was considered that surface area of corrugated tube was wider than bare tube. And liquid film thickness of staggered arrangement showed thinner than in-line arrangement, so thermal performance of staggered arrangement showed higher than in-line arrangement.

• Journal of ILASS-Korea
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• v.11 no.4
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• pp.212-219
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• 2006

The initial film flow development of the high-pressure swirl spray was investigated at different injector operating conditions to analyze film flow development and to provide the input data for the modeling works. This result can be also useful to verify the previously simulated results. The initial flow conditions such as liquid film thickness, flow angle and flow divergence are obtained by visualizing the inside and near the nozzle flow with a microscopic imaging system. The visualized images are quantified using an image processing tool. From the information of liquid film thickness and flow angle, the initial axial and tangential velocity and the swirl number of the swirl spray are successfully determined at various operating conditions. The experimental results showed that the initial liquid film thickness, flow angle and flow divergence are remained constant when the injection pressure is increased. However, initial film conditions are severely changed when the fuel temperature is increased. The swirl number remained constant when the injection pressure is increased while it showed increased value at high fuel temperature condition.

• Nuclear Engineering and Technology
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• v.47 no.4
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• pp.389-397
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• 2015

The effects of mixing vanes (MVs) attached to a grid spacer on the characteristics of air-water annular flows were experimentally investigated. To know the effects, a grid spacer with or without MV was inserted in a vertical circular pipe of 16-mm internal diameter. For three cases (i.e., no spacer, spacer without MV, and spacer with MV), the liquid film thickness, liquid entrainment fraction, and deposition rate were measured by the constant current method, single liquid film extraction method, and double liquid film extraction method, respectively. The MVs significantly promote the re-deposition of liquid droplets in the gas core flow into the liquid film on the channel walls. The deposition mass transfer coefficient is three times higher for the spacer with MV than for the spacer without MV, even for cases 0.3-m downstream from the spacer. The liquid film thickness becomes thicker upstream and downstream for the spacer with MV, compared with the thickness for the spacer without MV and for the case with no spacer.

• Korean Journal of Materials Research
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• v.17 no.10
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• pp.548-554
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• 2007

[ $BaTiO_3$ ] thick film by an interfacial polymerization method was prepared at the liquid/liquid interface between benzyl alcohol saturated solution with the basic catalyst [diethyl amine ($NHEt_2$) or triethylamine ($NEt_3$)], and the water dissolved with $TiO_2$ and $Ba(CH_3COO)_2$. The film thickness increased gradually with an increase in diethyl amine($NHEt_2$) or triethylamine($NEt_3$) volume and the reaction time. The homogeneity of $BaTiO_3$ thick film after sintered at $600^{\circ}C$ was confirmed by EPMA analysis, which showed that both of Ba and Ti element were homogeneously distributed on the surface as well as in the perpendicular direction of the film. The thickness of $BaTiO_3$ film obtained by this process was $8.75\;{\mu}m$.

• Nuclear Engineering and Technology
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• v.53 no.6
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• pp.1821-1833
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• 2021

The gas-liquid counter-current flow limitation (CCFL) is closely related to efficient and safety operation of many equipment in industrial cycle. Air-water countercurrent flow experiments were performed in a tube with diameter of 25 mm to understand the triggering mechanism of CCFL. A parallel electrode probe was utilized to measure film thickness whereby the time domain and frequency domain characteristics of liquid film was obtained. The amplitude of the interface wave is small at low liquid flow rate while it becomes large at high liquid flow rate after being disturbed by the airflow. The spectral characteristic curve shows a peak-shaped distribution. The crest exists between 0 and 10 Hz and the amplitude decreases with the frequency increase. The analysis of visual observation and characteristic of film thickness indicate that two flooding mechanisms were identified at low and high liquid flow rate, respectively. At low liquid flow rate, the interfacial waves upward propagation is responsible for the formation of CCFL onset. While flooding at high liquid flow rate takes place as a direct consequence of the liquid bridging in tube due to the turbulent flow pattern. Moreover, it is believed that there is a transition region between the low and high liquid flow rate.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.75-80
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• 2012

Due to the effect of surface tension, liquid film around a curved edge of solid surface moves from the corner to the flat surface. During this behavior of liquid film, film sagging phenomenon is easily occurred at the solid surface. Behavior of liquid film is determined with the effects of the properties of liquid film and the geometric factors of solid surface. In the present study, 2-D transient CFD simulations were conducted on the behavior of liquid film around a curved edge. The two-phase interfacial flow of liquid film was numerically investigated by using a VOF method in order to predict the film sagging around a curved edge. In the steady state of behavior of liquid film, the liquid film thickness of numerical result showed a good agreement with experimental data. After verifying the numerical results, the characteristics of behavior of liquid film were numerically analyzed with various properties of liquid film such as surface tension coefficient and viscosity. The effects of geometric factors on film sagging were also investigated to reduce the film sagging around a curved edge.

• Tribology and Lubricants
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• v.4 no.1
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• pp.30-35
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• 1988

Liquid crystals have some tribologically favorable lameliar structure. The Performance of ther mottopic liquid crystal was investigated under elastohydrodynamic condition in terms of traction and film thickness. It exhibited low traction and very thin film thickness, which were almost constant over the entire speed range measured. It was also found to have sealing effect like grease. This work has shown that there exists "potential" for using liquid crystals as lubricants.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.1
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• pp.17-26
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• 2005

Both numerical analysis and cold tests for the swirl coaxial type injector were performed to obtain the influence of spray angle, velocity ratio and liquid film thickness for pressure drop and recess. The basic experimental and numerical data obtained in this study can be applicable to the performance design of swirl coaxial type injector. Spray angle was not affected by the applied test pressure drop, but spray angle was affected by tangential velocity ratio and shape factors. Feasibility of numerical analysis for the liquid film thickness and spray angle was confirmed, and the change of liquid film thickness by tangential velocity ratio affected more seriously than pressure drop, and liquid film thickness was decreased with increasing tangential velocity ratio.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.4
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• pp.476-483
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• 2003

A mathematical model is presented to predict the two-phase flow and heat transfer phenomena of the evaporating extended meniscus region in a micro-channel. The pressure difference at the liquid-vapor interface can be obtained by the augmented Laplace-Young equation. The correlative equations for film thickness, pressure, and velocity in the meniscus region are derived by applying the mass, momentum, and energy equations into the control volume. The results show that increasing the heat flux and the liquid inlet velocity cause the length and liquid film thickness of the extended meniscus region to decrease. The variation, however, of the heat flux and liquid inlet velocity has no effect on the profile of film thickness. The majority of heat is transferred through the thin film region that is a very small region in the extended meniscus region. It is also found that the vapor velocity increases gradually in the meniscus region. However, it increases sharply at the junction of the meniscus and thin film regions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.1035-1042
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• 2005

In the present study, the principle of minimum energy is employed to configure the shape of rivulet flowing down an inclined surface. The profile of laminar rivulet is determined by numerical integration. The maximum center thickness, which corresponds to the minimum thickness of falling film, is found to exist regardless of liquid flow rate and is compared with the analytical and experimental data. At small liquid flow rate the center thickness of rivulet and its width increase almost linearly with flow rate. Once the center thickness of rivulet becomes very close to its maximum value, its growth rate retards abruptly. However the width of rivulet increases proportionally to the liquid flow rate and most part of its free surface is as flat as that of stable film. The growth rate of rivulet thickness with respect to liquid flow rate becomes larger at bigger contact angle. The width of rivulet increases rapidly with its flow rate especially at small contact angle, As the liquid-vapor interfacial shear stress increases, the center thickness of rivulet decreases with its flow rate, which is remarkable at small contact angle. However the effect of interfacial shear stress on the width of rivulet is almost negligible.