• International Journal of Air-Conditioning and Refrigeration
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• 제9권3호
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• pp.57-62
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• 2001

Falling film heat transfer analyses with aqueous lithium bromide solution were performed to investigate the transfer characteristics of the copper tubes. Finned (knurled) tube and a smooth tube were selected as test specimens. Averaged generation fluxes of water and the heat flux were obtained. As the film flow rate of the solution increased, the generation fluxes of water decreased for both tubes due to the fact that the heat transfer resistance increased with the film thickness. The effect of the enlarged surface area at the knurled tube was supposed to be dominant at a small flow rate. The generation fluxes of water increased with the increasing degree of tube wall superheat. Nucleate boiling is supposed to occur at a wall superheat of 20K for a smooth tube, and at 10K for a knurled tube. The increased performance of the knurled tube was supposed to mainly come from the effect of the increased heating surface area.

• 대한기계학회논문집
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• 제10권1호
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• pp.86-95
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• 1986

본 연구에서는 폭이 일정한 급경사 개수노상(0.15mW*1.6mL)을 상온의 물이 유동할 때 유동율과 수로 급경사에 따른 명입치에서의 유동깊이 변화를 실측을 통하여 밝히고 이념치와 비교하였다.

• Progress in Superconductivity
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• 제9권1호
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• pp.91-95
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• 2007

[ $YBa_2Cu_3O_{7-{\delta}}$ ] films have been prepared on $LaAlO_3$ (100) single-crystal substrates by the metal organic deposition using dichloroacetate precursors (DCA-MOD). DCA precursor solutions with different composition such as; Yttrium-excess(15 at%), barium-poor(25 at%), and a stoichiometric(Y:Ba:Cu=1:2:3) were prepared in order to investigate the effects of precursor composition on the properties of YBCO films prepared by DCA-MOD method. Coated films were calcined at low temperature up to $500^{\circ}C$ in flowing humid oxygen atmosphere. Conversion heat treatment was performed $800^{\circ}C$ for 2 h in flowing Ar gas containing 1000 ppm oxygen with a humidity of 9.45%. For the film prepared using excess yttrium composition, high critical current density ($J_c$) of $>2MA/cm^2$ was obtained whereas, for the films prepared using barium-poor composition, $J_c$ was lower than $1MA/cm^2$.

• 대한기계학회논문집B
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• 제24권8호
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• pp.1085-1096
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• 2000

An experimental study was performed to examine the heat and mass transfer characteristics of $LiBr-H_2O$ solution flowing over a single horizontal tube with the water vapor absorption. Effects of the flow rate and the temperature of the solution at the top of the tube, the absorber pressure and the drainage pattern were considered. The absorption rate depends highly on the absorber pressure at the low flow rate condition while on the solution inlet temperature at the high flow rate condition. Also, when the flow rate is low, the absorption performance with the sheet flow drainage appeared to be higher than that with the dripping/jet drainage. However, at the high flow rate condition, the case became reversed. The liquid film became wavy with the higher absorption rate. The waves were more probable to form with the lower flow rate and temperature of the solution, and with the higher absorber pressure.

• 한국표면공학회지
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• 제31권6호
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• pp.307-316
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• 1998

The effects of surface roughness on chromate conversion coating and the corrosion behavior of galvanized steel sheets were investigated. Surface roughness was differently given to the galvanized steel sheets tested and these were then chromated. Accelerated corrosion test was conducted under the condition of $30^{\circ}C$, 90%RH with flowing 200ppm $SO_2$ gas. The galvanized steels were also exposed to urban environment for 5 weeks. The corrosion rates were measured by weight gain method. The distribution of chromate film and corrosion product on the coating were examined which SEM/EDS. The chromate film formed preferentially at the convex sites rather than at the concave sites on the surface. The corrosion products were found at the concave sites where the chromate film formed rarely. The corrosion product on the coating were found at the concave sites where the chromate film formed rarely. The corrosion rates increased slightly with the surface roughness in accelerated corrosion test but significantly in field test.

• Corrosion Science and Technology
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• 제9권1호
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• pp.8-11
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• 2010

During PEO (plasma-electrolytic-oxidation) treatment of titanium, the relationship between the thickness of oxide film and the measured electrical information was investigated. A simple real time monitoring method based on the electrical information being gathered during PEO treatment is proposed. The proposed method utilizes the current flowing from a high frequency voltage source to calculate the resistance of an oxide film, which is converted into the thickness of an oxide film. This monitoring method can be implemented in PEO system in which an oxide film is grown by constant or pulsed voltage/current sources.

• 한국자기학회지
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• 제5권5호
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• pp.645-649
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• 1995

The depletion of thin liquid films due to the combined effect of centrifugation, surface roughness, and air-shear has recently been studied. While surface roughness of a rotating solid disk can be represented by deterministic cures, it has been argued that spatial random processes provide a more realistic description. Chiefly because of surface roughness, there is an asymptotic limit of retention of a thin film flowing on the rotating disk. The aim of this article is to model the depletion of thin-film flow and analyze the interplay of centrifugation, surface tension, viscosity, air-shear, disjoining pressure, and surface roughness that affect the depletion of the film. Also, the robustness of stochastic description of surface roughness is examined.

• 설비공학논문집
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• 제9권2호
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• pp.144-152
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• 1997

Film absorption involves simultaneous heat and mass transfer in the vapor-liquid system. In the present work, the absorption process of water vapor by an aqueous soluton of LiBr flowing inside of the vertical tube was investigated. The continuity, momentum, energy and diffusion equations for the solution film and vapor were formulated in integral forms and solved numerically. The model could predict the film thickness, the pressure gradient, and the heat and mass transfer rate. Particularly the effects of vapor flow conditions on the absorption process were investigated in terms of the vapor Reynolds number. As the vapor Reynolds number increased, the shear stress at the vapor-solution interface also increased. Consequently solution film became thinner at higher vapor flowrate under the co-currentflow condition. Thinner film was capable of higher heat transfer to the wall and leaded to higher absorption rate of the water vapor into the solution film.

• 한국분무공학회지
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• 제2권4호
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• pp.29-35
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• 1997

Liquid film thickness is measured by $moir\acute{e}$ topography which monitored liquid surface. $Moir\acute{e}$ fringe measurement techniques share the inherent simplicity found in optical interferometric techniques have the advantage of use over a greater range of displacement. $Moir\acute{e}$ fringe are the geometric interference patterns observed when two dense line grating are superposed. Light transmitted through a fixed line grating is deviated by the liquid film surface, producing a distored image of the grating. The $moir\acute{e}$ fringe produced by projection of this optically distored grating onto a second stationary grating permit visualization of the liquid surface and measurement of the liquid film thickness. This study measured the small amplitude of liquid film thickness to the $moir\acute{e}$ fringe pattern produced when spherical metal was dropped glycerin put)1 And the measurement of liquid film thickness flowing down an inclined plate are required to calculate the liquid slope in a position.

• 대한기계학회논문집
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• 제19권6호
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• pp.1501-1509
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• 1995

It is known that the heat and mass transfer characteristics in the absorber are most sensitive of the temperature boost of all the heat exchangers and the development of a more efficient absorber should be highly important. This paper describes absorption experiments made with different inside tube diameters, tube length and tube shapes. The purpose of this study is to acquire basic knowledge about heat and mass transfer in a falling film type absorber with vertical inner tubes. Heat and mass transfer were measured for water vapor absorption into a Lithium Bromide-water solution flowing down an absorber of vertical inner tubes. As a result, insert spring tube compares bare tube and heat transfer improved by order of insert spring tube P2(pitch 20 mm) and P1(pitch 10 mm).