• International Journal of Air-Conditioning and Refrigeration
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• 제8권2호
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• pp.1-10
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• 2000

This research is concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different vertical tubes were tested with and without an additive of normal octyl alcohol. The test tubes are a bare tube, a groove tube, a corrugated tube and a spring-inserted tube. The additive concentration is about 0.08 mass%. The heat transfer coefficient is measured as a function of the film Reynolds number in the range of 20~200. Experiments are carried out at higher cooling water temperature of $35^{\circ}C$to simulate an air cooling condition for several kinds of absorber testing tubes. The experimental results with and without surfactant are compared. The enhancement of heat transfer by Marangoni convection effect which is generated by addition of the surfactant is observed in each test tube. Especially, it is clarified that the tube with an spring-inserted has the enhancement effect.

• 한국결정성장학회지
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• 제33권4호
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• pp.145-152
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• 2023

2.31 × 10⁴ ≤ Gr_t ≤ 4.68 × 10⁴의 범위에서 온도 Grashof 수(Gr_t)의 변화에 대하여, 소스와 결정영역에서의 평균 Nusselt수를 나타내고 있다. 결정영역에서의 평균 Nusselt 수가 소스영역에서의 평균 Nusselt 수 보다 2배 이상 큰 것으로 나타나고 있다. 소스영역에서의 평균 Nusselt 수는 온도 Grashof 수(Gr_t)에 대하여, 증가하는 경향을 보여주고 있으며, 반면에 결정영역에서의 평균 Nusselt 수는 온도 Grashof 수(Gr_t)에 대하여, 감소하는 경향을 나타나고 있다. 3.28 × 10⁵ ≤ Gr_s ≤ 4.43 × 10⁵의 범위에서 농도 Grashof 수(Gr_s)의 변화에 대하여, 소스와 결정영역에서의 평균 Sherwood 수를 나타내고 있다. 소스영역과 결정영역에서의 평균 Sherwood 수는 농도 Grashof 수(Gr_s)가 증가함에 따라, 감소하는 경향을 보이고 있다. 결정영역에서의 평균 Sherwood 수는 소스영역에서의 평균 Sherwood 수보다 약 4배 정도 크다.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제20권4호
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• pp.309-332
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• 2016

Finite element method has been applied to solve the fundamental governing equations of natural convective, electrically conducting, incompressible fluid flow past an infinite vertical plate surrounded by porous medium in presence of thermal radiation, viscous dissipation, Soret and Dufour effects. In this research work, the results of coupled partial differential equations are found numerically by applying finite element technique. The sway of significant parameters such as Soret number, Dufour number, Grashof number for heat and mass transfer, Magnetic field parameter, Thermal radiation parameter, Permeability parameter on velocity, temperature and concentration evaluations in the boundary layer region are examined in detail and the results are shown in graphically. Furthermore, the effect of these parameters on local skin friction coefficient, local Nusselt number and Sherwood numbers is also investigated. A very good agreement is noticed between the present results and previous published works in some limiting cases.

• 한국기계가공학회지
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• 제17권2호
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• pp.68-76
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• 2018

A vortex tube is a simple energy separating device that splits a compressed air stream into a cold and hot stream without any external energy supply or chemical reactions. The efforts of many researchers and designers have been focused on improvement of vortex tube efficiency by changing the parameters affecting vortex tube operation. The effective parameters are nozzle specifications and inflow pressure conditions. Effects of different nozzle cross-sectional area and number of nozzles are evaluated by computational fluid dynamics (CFD) analysis. In this study, CFD analysis of 3-D steady state and turbulent flow through a vortex tube was performed. We investigated the cold air mass flow rate, the cold air temperature, and the cold air heat transfer rate behavior of a vortex tube by utilizing seven straight nozzles and four inflow pressure conditions.

• Korea-Australia Rheology Journal
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• 제20권1호
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• pp.1-6
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• 2008

Absorption rate of carbon dioxide was measured in the aqueous xanthan gum (XG) solution in the range of 0-0.15 wt% containing 2-amino-2-methyl-1-propanol (AMP) of $0-2\;kmol/m^3$ in a flat-stirred vessel with an impeller of 0.05m and agitation speed of 50rpm at $25^{\circ}C$ and 0.101 MPa. The volumetric liquid-side mass transfer coefficient ($k_La$) of $CO_2$, which was correlated with the viscosity and the elastic behavior of XG solution containing Deborah number as an empirical formula, was used to estimate the chemical absorption rate of $CO_2\;(R_A)$. $R_A$, which was estimated by mass transfer mechanism based on the film theory using the physicochemical properties and the kinetics of reaction between $CO_2$ and AMP, was compared with the measured rate. The aqueous XG solution with elastic property of non-Newtonian liquid made $R_A$ increased compared with Newtonian liquid based on the same viscosity of the solution.

• 한국해양공학회지
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• 제2권2호
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• pp.130-137
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• 1988

This thesis introduced that character of a treatment technique for a mading synthetic resin Hifiow-Ring. The material system of packings make an experiment air$NH_{3}$/air$H_{2}SO_{4}$, $SO_{2}$-air/NaOH, $NH_{3}$-air/$/H_{2}SO_{4}$ under general conditions. Lattices packing compared with conventional packings was proved low pressure loss and high separation efficiency for high loading per trans unit. And an inflow materal tested for absorption and rectification, it made an experiment under a range regular temperature, low energy and small amount of money. That made possible in simple equation, volume material tranfer coefficient$\beta_{L}$ . a by absorption or $\beta_{V}$ .a calculated in all range loading. The peculiarity pressure loss $\Delta\;P/NUT_{ov}$ for Hiflow-ring contributed to a fall cost of energy, a grade number of a vacuum rectification and absorption calculation.

• 천문학회보
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• 제44권1호
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• pp.46.3-46.3
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• 2019

We present our observational and theoretical investigation of Raman-scattered features in symbiotic stars (SySts). SySts are long interacting binaries, consisting of a hot compact star and an evolved giant, whose interaction via accretion process is at the origin of a tangled network of gas and dust nebulae. These systems are ideal objects to study a variety of important astrophysical problems, and have also been proposed as possible progenitors of type Ia supernova. In this talk, we emphasize that Raman-scattered features are exclusive spectroscopic tools to probe the stellar wind accretion processes in SySts. We studied mass transfer and mass loss processes in SySts using high resolution spectra obtained with 1.8m telescope at Mt. Bohyun and the 6.5m Magellan-Clay telescope combining with the theoretical modeling of radiative transfer of Raman-scattered features. We also note that there are a much smaller number of SySts known in our Galaxy, implying the necessity of systematic search programs. In view of the fact that Raman O VI features at $6830{\AA}$ are found in only bona fide SySts, we will carry out a photometric search of objects with Raman O VI features using a narrow band filter centered at $6830{\AA}$ in Local group galaxies.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.149-154
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• 1997

Based on the full Navier-Stokes solutions, the thermohydrodynamic performance of a long journal bearing is investigated. A numerical method based on Galerkin's procedure and B-spline test functions has been presented for solving two-dimensional problems involving fluid flow and heat transfer. For numerical stability the artificial compressibility is employed to the conservation of mass. The discretized algebraic equations are solved by Newton's method. Effects of varying the speed of an inner cylinder to load carrying capacity are investigated. The results indicated that the increase of the speed of an inner cylinder has a significant effect on the temperature profile and ultimately on the performance.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제12권1호
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• pp.25-32
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• 2008

A pin fin is optimized based on the increasing rate of heat loss by using a two-dimensional analytic method. The optimum heat loss, corresponding optimum thermal resistance and fin length are presented as a function of the fin base thickness, convection characteristic numbers ratio, fin outer radius and ambient convection characteristic number. One of the results shows that both the optimum heat loss and fin length decrease linearly whereas the optimum thermal resistance increases very slightly with increase of the fin base thickness.

• 대한기계학회논문집B
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• 제22권6호
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• pp.888-898
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• 1998

The present study investigated the effects of the experimental parameters on the cooling characteristics of the multichip module cooled by the indirect liquid cooling method using water and paraffin slurry. The experimental parameters are mass fraction of 2.5 ~ 7.5% for paraffin slurry, heat flux of 10 ~ 40 W/cm$^{2}$ for the simulated VLSI chips and Reynolds numbers of 5,300 ~ 15,900. The apparatus consisted of test section, paraffin slurry maker, pump, constant temperature baths, flowmeter, etc. The test section made of in-line, four-row array of 12 heat sources for simulating 4 * 3 multichip module which was flush mounted on the top wall of a horizontal rectangular channel with the aspect ratio of 0.2. The inlet temperature was 20 deg. C for all experiments. The size of paraffin slurry was constant as 10 ~ 40 .mu.m befor and after the experiment. The chip surface temperatures for paraffin slurry with the mass fraction of 7.5% showed lower by 16 deg. C than those for water when the heat flux is 40 W/cm$^{2}$. The local heat transfer coefficients for the paraffin slurry with the mass fraction of 7.5% were larger by 17 ~ 25% than those for water at the first and the fourth row. The local heat transfer coefficients reached to a row-number-independent, thermally fully developed value approximately after the third row. The local Nusselt numbers at the fourth row for paraffin slurry with the mass fraction of 7.5% were larger by 23 ~ 29% than those for water.