• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.170-173
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• 2007

Cooling characteristics of a liner were investigated by a film cooling method using a gas nitrogen in a rocket engine. High temperature gas of this test was made by mixing liquid nitrogen with combustion gas of a liquid rocket. A supply system of gas nitrogen was additionally constructed to the existing test facility of liquid rocket engine, and a new test section consisted of a liner and a gas injection ring was manufactured. A 10 second firing test for finding cooling characteristics of the liner was successfully conducted and liner surface temperatures and hot gas temperature was obtained.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.2
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• pp.99-106
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• 2005

Falling film heat transfer has been widely used in many applications in which heat and mass transfer occur simultaneously, such as evaporative coolers, cooling towers, absorption chillers, etc. In such cases, it is desirable that the falling film spreads widely on the surface to form a thin liquid film to enlarge contact surface and to reduce the thermal resistance across the film and/or the flow resistance to the vapor stream over the film. In this respect, hydrophilic treatment of the surface has been tried to improve the surface wettability by decreasing the contact angle between the liquid and the surface. However, the hydrophilic treatment was found not very effective to increase the surface wettedness of inclined surfaces, since the liquid flow forms rivulet patterns instead of a thin film as it flows down the inclined surface and accelerates gradually by the gravity. In this work, a novel method is suggested to improve the surface wettedness enormously. In this work, the surface is treated to have a thin hydrophilic porous layer on the surface. With this treatment, the liquid can spread widely on the surface by the capillary force resulting from the porous structure. In addition to this, the liquid can be held within the porous structure to improve surface wettedness regardless of the surface inclination. The experiment on the evaporative cooling of inclined surfaces has been conducted to verify the effectiveness of the surface treatment. It is measured that the latent heat transfer increases almost by $80\%$ at the hydrophilic porous layer coated surface as compared with the untreated surface.

• The KSFM Journal of Fluid Machinery
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• v.15 no.2
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• pp.41-44
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• 2012

In order to cool the turbine blade under high temperature operating conditions, the film-cooling method is generally applied. In this study, $CO_2$ was used as working fluid and it helped the operating system to prevent the loss of compressed air. The trapezoidal diffuser shape was adopted at the cross section of hole and the characteristics of heat flow with various working fluids were numerically studied. In particular, the different mixture ratios of $CO_2$, such as various density ratios of 0.2, 0.8, and 1.0, respectively, were considered. Numerical results are graphically depicted with various conditions.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.5
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• pp.905-909
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• 2007

Crystalline and micro-structural characteristics of ZnO thin films which were deposited on p-Si(100) with cooling naturally down of pre-heated substrate during RF magnetron sputter deposition, were investigated by XRD and SEM in this paper. The film which was prepared on the substrate which was pre-heated to $400^{\circ}C$ before deposition and then cooled naturally down during deposition, showed the most outstanding c-axis preferred orientation. The ZnO thin film having the best crystalline result were applied to SMR type FBAR device and resonance properties of the device were investigated by network analyzer. It showed that resonance frequency was 2.05 GHz, return loss was -30.64 dB, quality factor was 3169 and electromechanical coupling factor was 0.4 %. This deposition method would be very useful for application of surface acoustic wave filter or film bulk acoustic wave resonator.

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.71-78
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• 2002

All modem, aerospace gas turbines must operate with hot stage gas temperature several hundreds of degrees hotter than the melting temperatures of the materials used in their construction. Complicated cooling schemes need to be employed in the combustor walls and In the high pressure turbine stages. Internal passages are cast or machined into the hot sections of aero-gas turbine engines and air from the compressor is used for cooling. In many cases, the cooling system is engineered to utilize jets of high velocity air, which impinge on the internal surfaces of the components. They are divided by Impinging cooling method and Vortex cooling method. Specially, Research of new cooling system(Vortex cooling method) that overcome inefficiency of film cooling and limitation of space. The focus of new cooling system that improve greatly cooling efficiency using quantity's cooling air which is less is set in surface heat transfer elevation. Therefore, In this study, the numerical analysis have been performed for characteristic of flow and thermal in the swirl chamber and compared with the flow field measurement by LDV. especially, for understanding of high heat transfer efficiency in vicinity of wall. we considered flow structure and mechanism of vortex and heat transfer characteristic in variation of Reynolds number.

• Nuclear Engineering and Technology
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• v.54 no.11
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• pp.4329-4337
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• 2022

Jet impinging device is designed for decay heat removal on horizontal fuel rods in a low temperature heating reactor. An experimental system with a fuel rod simulator is established and experiments are performed to evaluate water film covering capacity, within 0.0287-0.0444 kg/ms mass flow rate, 0-164.1 kW/m² heating flux and 13.8-91.4℃ feeding water temperature. An effective method to obtain the film coverage rate by infrared equipment is proposed. Water film flowing patterns are recoded and the film coverage rates at different circumference angles are measured. It is found the film coverage rate decreases with heating flux during single-phase convection, while increases after onset of nucleate boiling. Besides, film coverage rate is found affected by Marangoni effect and film accelerating effect, and surface wetting is significantly facilitated by bubble behavior. Based on the observed phenomenon and physical mechanism, dry-out depth and initial dry-out rate are proposed to evaluate film covering potential on a heating surface. A model to predict film coverage rate is proposed based on the data. The findings would have reliable guide and important implications for further evaluation and design of decay heat removal system of new reactors, and could be helpful for passive containment cooling research.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.4
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• pp.453-462
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• 1994

An unsteady quasi one-dimensional model of momentum, heat and mass transfer in a falling film of a vertical plate absorber which is cooled by air was developed using the integral method. Energy conservation of the absorber wall is considered in the model. The model can predict absorption rate, film thickness and mean velocity as well as concentration and temperature profiles. Predictions of steady state temperature and concentration profiles for LiBr/water system for constant wall temperature condition are in good agreement with the two-dimensional finite difference method solutions. Effects of operating conditions, such as convective heat transfer coefficient between the cooling air and the absorber wall, cooling air temperature and film thickness at inlet, on absorption rate of water vapor into LiBr/water solution were shown.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.456-466
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• 2004

An experimental study has been conducted to investigate the flow and heat/mass transfer characteristics within a rectangular film cooling hole of normal injection angle for various blowing ratios and Reynolds numbers. The results are compared with those for the square hole. The experiments have been performed using a naphthalene sublimation method and the flow field has been analyzed by numerical calculation using a commercial code (FLUENT). The heat/mass transfer around the hole entrance region is enhanced considerably due to the reattachment of separated flow and the vortices generated within the hole. At the hole exit region, the heat/mass transfer increases because the main flow induces a secondary vortex. It is observed that the overall heat/mass transfer characteristics are similar to those for the square hole. However, the different heat/mass transfer patterns come out due to increased aspect ratio. Unlike the square hole, the heat/mass transfer on the trailing edge side of hole entrance region has two peak regions due to split flow reattachment, and heat/mass transfer on the hole exit region is less sensitive to the blowing ratios than the square hole.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.867-868
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• 2011

Transient Analysis on heat transfer of rocket engine combustion chamber and wall temperature variation was carried out, especially, calculations of LOx/kerosene rocket engine with/without fuel film-cooling were conducted. Convective and radiative heat flux inside combustion chamber wall were calculated by the empirical equations for rocket engine combustion, and conduction of wall interior was calculated by numerical method with 2D axisymmetric grid. In this calculations the transient variations of wall temperature, the location changes of peak temperature and so on affected by film-cooling were analyzed.

• Korea-Australia Rheology Journal
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• v.12 no.2
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• pp.119-124
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• 2000

Employing the Phan-Thien tanner (PTT) fluids model, dynamic behavior of the non-isothermal melt spinning has been investigated. Subjects such as draw resonance instability, the effects of spinline cooling and of the fluid viscoelasticity on the spinning dynamics have been studied using the governing equations of the system. In particular, the draw resonance criterion based on the traveling times of various kinematic waves in the spinline has been confirmed, the reason why the spinline cooling is stabilizing is analyzed, and the effect of fluid viscoelasticity on the spinline stability is summarized. It is believed that the same method as in this study can be applied with equal ease to other extension deformation processes like film casting and film blowing.