• Nuclear Engineering and Technology
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• 제52권5호
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• pp.918-924
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• 2020

Film boiling is of great importance in nuclear safety as it directly influences the integrity of nuclear fuel in case of accidents involving loss of coolant. Recently, nuclear power plant safety under earthquake conditions has received much attention. However, to the best of our knowledge, there are no existing studies reporting film boiling in an oscillating system. Most previous studies for film boiling were performed on stationary systems. In this study, numerical simulations were performed for saturated film boiling of water on a horizontal surface under low frequencies to investigate the effect of system oscillation on film boiling heat transfer. A coupled level-set and volume-of-fluid method was used to track the interface between the vapor and liquid phases. With a fixed oscillation amplitude, overall, heat transfer decreases with oscillation frequency. However, there is a frequency region in which heat transfer remains nearly constant. This lock-on phenomenon occurs when the oscillation frequency is near the natural bubble release frequency. With a fixed oscillation frequency, heat transfer decreases with oscillation amplitude. With a fixed maximum amplitude of the additional gravity, heat transfer is affected little by the combination of oscillation amplitude and frequency.

• 대한기계학회논문집B
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• 제21권2호
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• pp.294-302
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• 1997

Falling-film evaporation experiments for aqueous solution of lithium bromide (LiBr) were performed on a horizontal smooth 19.05-mm-dia copper tube. Average heat transfer coefficients were obtained with varied film Reynolds numbers, system pressures, LiBr concentrations and degrees of wall superheat. Heat transfer coefficients increase with increasing system pressure and decreasing concentration. For degrees of wall superheat, the heat transfer coefficient did not't show the distinct trend. For this experimental ranges, heat transfer coefficients showed maximum values at an optimal film Reynolds number. The results of this work were compared with pool boiling data reported previously, and it was shown that the heat transfer performance is superior to the pool boiling.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2291-2296
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• 2007

Thermal transport from vertical heated surface to falling liquid film in a channel has been investigated experimentally. Air-flow is introduced into channel to make a counter flow against falling liquid film. This problem is of particular interest in the design of direct contact heat exchange system, such as cooling tower, evaporative cooling system, absorption cooling system, and distillation system. The effects of channel width and air flow rate on the heat transfer to falling liquid film are studied in detail. The results obtained indicate that heat transfer rate is gradually decreased with an increase in the channel width without air flow as well as with air flow in a channel. It is also found that heat transfer rate of air-flow is increased while heat transfer rate of falling liquid film is decreased with an increase in the air flow rate at a given channel width. However, total heat transfer rate form the heated surface is increased as the air flow rate is increased.

• 대한기계학회논문집B
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• 제32권5호
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• pp.335-341
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• 2008

Thermal transport from vertical heated surface to falling liquid film in a channel has been investigated experimentally. Air-flow is introduced into channel to make a counter flow against falling liquid film. This problem is of particular interest in the design of direct contact heat exchange system, such as cooling tower, evaporative cooling system, absorption cooling system, and distillation system. The effects of channel width and air flow rate on the heat transfer to falling liquid film are studied in detail. The results obtained indicate that heat transfer rate is gradually decreased with an increase in the channel width without air flow as well as with air flow in a channel. It is also found that heat transfer rate of air-flow is increased while heat transfer rate of falling liquid film is decreased with an increase in the air flow rate at a given channel width. However, total heat transfer rate from the heated surface is increased as the air flow rate is increased.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.327-331
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• 1997

This paper presents the non-linear modeling and design of a robust sliding mode controller for film transfer systems. The tension of a film is sensitive to the speed difference between a winder and an unwinder. The change of the roll-radius as well as the moment of inertia result in the film transfer system begin variable and non-linear. In designing the robust controller. Two major aims are considered. The first aim is hat the web transferring speed tracks at any given reference speed; the second one is that the tension of the film tracks at any given reference tension. To verify the control algorithm, a Simulink model was built and compared with a conventional PID controller. In a computer simulation study, the suggested robust sliding mode controller shows better performance than the PID controller a various control inputs.

• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.69-79
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• 2000

Falling film rectification involves simultaneous heat and mass transfer between vapor and solution film. In the present work, the adiabatic rectification process of ammonia-water vapor by the falling solution film on the vertical plate was investigated. The continuity momentum, energy and diffusion equations for the solution film and the vapor mixture were formulated in integral forms and solved numerically, The model could predict the film thickness, the pressure gradient, and the mass transfer rate. The effects of Reynolds number and ammonia concentration of solution and vapor mixture, rectifier length, and the enhancement of mass transfer coefficient in each phases were investigated. The stripping of water in vapor mixture occurred near the entrance of ammonia solution, which imposed the proper size of an adiabatic rectifier. Rectifier efficiency increased as film Reynolds number increased and as vapor mixture Reynolds number decreased. The improvement of rectifier efficiency was significant with the enhancement of mass transfer coefficient in falling film.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.226-234
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• 2002

A systematic study of the role of transfer films on friction properties was performed with various temperatures in the brake system. An NAO friction material specimens containing 9 ingredients were tested using a pad-on-disk type friction tester A new method of measuring the transfer film thickness was developed by considering the electrical resistance of the transfer film using a 4-point probe technique. The properties of transfer film such as surface morphology and film distribution vaied according to the relative amount of graphite and magnesium oxide. By using SEM, it was possible to obtain information about the chemical composition of the transfer film. Results showed that there detected a threshold value of the relative amount of a two active materials to maintain a certiain thickness of a transfer film. Results also showed that formation of friction layer generated on the friction surface was strongly affected by chemical action of two ingredients during sliding due to chemical reaction of solid lubricants at different interface temperature. The results suggested that no apparent relationship between transfer film thickness and the average friction coefficient was founded and friction characteristics were affected more by the property of the solid lubricant and abrasive in the material.

• 설비공학논문집
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• 제11권3호
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• pp.414-421
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• 1999

Falling film rectification involves simultaneous heat and mass transfer between vapor and liquid interface. In the present work, the adiabatic rectification process of ammonia-water vapor on the vertical plate was investigated. The continuity, momentum, energy and diffusion equations for the solution film and vapor mixture were formulated in integral forms and solved numerically. The model could predict the film thickness, the pressure gradient, and the mass transfer rate. The effects of Reynolds number and ammonia concentration of solution and vapor mixture, rectifier length, and the enhancement of mass transfer in each phases were investigated. The stripping of water in vapor mixture occurred new the entrance of ammonia solution, which imposed the proper size of an adiabatic rectifier. Rectifier efficiency increased as film Reynolds number increased and as vapor mixture Reynolds number decreased. The improvement of rectifier efficiency was significant with the enhancement of mass transfer in falling film.

• Journal of Korean Dental Science
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• 제4권1호
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• pp.20-25
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• 2011

Purpose: To describe the newly developed Film image transfer system (FITS) for proper positioning of the orthodontic mini-implant in the narrow interdental space and considerations for better application. Materials and Methods: A patient who was planning to have orthodontic mini-implant treatment on the posterior maxilla was recruited to assess the feasibility of FITS. Dental radiographic film and bite record was taken. And then the film image was transferred on the photographic emulsion coated model using transfer light through film projector (enlarger). After exposing the photo emulsion coating on the model, the image was developed with a working solution for a paper developer and fixed. The surgical guide for the mini-implant was fabricated from the transported FITS data. Results: The completed surgical guide was easily placed intraorally, and allowed a simple and rapid placement of the mini-implant. The site of the implant placement was accurate as planned position. Conclusion: In the reported case, The FITS technique represents an effort to minimize risk to the patient and produce consistently good results based upon accurate information about the anatomy of the implant site.

• Journal of Mechanical Science and Technology
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• 제17권4호
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• pp.581-589
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• 2003

Film absorption involves simultaneous heat and mass transfer in the gas-liquid system. While the non-absorbable gas does not participate directly In the absorption process. its pretence does affect the overall heat and mass transfer. An experimental study was performed to investigate the heat and mass transfer characteristics of LiBr-H$_2$O solution flow ing over 6-row horizontal tubes with the water vapor absorption in the pretence of non-absorbable gases. The volumetric concentration of non-absorbable gas, air, was varied from 0.17 to 10.0%. The combined effects of the solution flow rate and its concentration on the heat and mass transfer coefficients were also examined. The presence of 2％ volumetric concentration of air resulted in a 25% reduction in the Nusselt number and 41% reduction in the Sherwood number Optimum film Reynolds number was found to exist at which the heat and mass transfer reach their maximum value independent of air contents. Reduced Nusselt and Sherwood numbers. defined as the ratio of Nusselt and Sherwood numbers at given non-absorbable gas content to that with pure water vapor, were correlated to account for the reduction in the heat and mass transfer due to non-absorbable gases in a falling film absorption process.