• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.4
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• pp.1481-1490
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• 1996

This study is intend to improve flow pattern within evaporator, which is low quality and low mass flux, by installing narrow horizontal annular crevice so that enhance heat transfer coefficient. The motive, which made to study heat transfer enhancement by using narrow annular crevice, came from capillary phenomena and pumping force of generating vapor on refrigerant boiling. Tests were run about 5 models of turbulence promoter with CFC-12, in the range of evaporating temperature (15.deg. C), mass flux (50 to 100 kg/m$\^$2/s), heat flux (3.4 to 6.7 kW/m$\^$2/), quality (0.1 to O.5). It is observed that flow pattern within evaporator is changed closely to semi-annular flow or annular flow, of which refrigerant liquid is reached to the upper side of tube by using narrow annular crevice. When the narrow annular crevice is installed in the evaporator tube, local heat transfer coefficient is generally more improved than that of smooth tube. That fact is according to observed result of flow pattern. It is learned that narrow annular crevice has more efficiency at a low mass flux. At the TP-5, enhancement of heat transfer rate is about 170% compare to that of smooth tube on a low mass flux (50 kg/m$\^$2/s), and it is about 134% on a high mass flux (100 kg/M$\^$2/S), so that we know that it is on a very high condition.

• Advances in concrete construction
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• v.7 no.2
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• pp.87-96
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• 2019

Self-compacting concretes (SCC) are highly fluid concrete which can flow without any vibration. Their composition requires a large quantity of fines to limit the risk of bleeding and segregation. The use of crushed sand rich in limestone fines could be an adequate solution for both economic and environmental reasons. This paper investigates the influence of quarry limestone fines from manufactured crushed sand on rheological, mechanical and durability properties of SCC. For this purpose, five mixtures of SCC with different limestone fines content as substitution of crushed sand (0, 5, 10, 15 and 20%) were prepared at constant water-to-cement ratio of 0.40 and $490kg/m^3$ of cement content. Fresh SCC mixtures were tested by slump flow test, V-funnel flow time test, L-box height ratio, segregation resistance and rheological test using a rheometer. Compressive and flexural strengths of SCC mixtures were evaluated at 28 days. Regarding durability properties, total porosity, capillary water absorption and chloride-ion migration were studied at 180 days. For the two test modes in fresh state, the results indicated compatibility between slump flow/yield stress (${\tau}_0$) and V-funnel flow time/plastic viscosity (${\mu}$). Increasing the substitution level of limestone fines in SCC mixtures, contributes to the decrease of the slump flow and the yield stress. All SCC mixtures investigated achieved adequate filling, adequate passing ability and exhibit no segregation. Moreover, the inclusion of limestone fines as crushed sand substitution reduces the capillary water absorption, chloride-ion migration and consequently enhances the durability performance.

• Polymer(Korea)
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• v.26 no.3
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• pp.316-325
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• 2002

The deformation and coalescence behaviors of immiscible LDPE/PS blends (86.5/13.5 vol%) prepared by internal mixer were studied using rheometer and scanning electron microscope. The fine droplets coagulated at initial stage of mixing, and deformed fiber at large strain. The critical capillary number was calculated according to the empirical equation of De Bruijn and it was 0.95, the local capillary number was 3.867. The polymer blends were annealed at $200^{\circ}C$ for various time to investigate morphological change of polymer blends. The maximum size of droplet after annealing at $200^{\circ}C$ was found at ${\gamma}$=1798, and there was destruction of the morphology at 15 minutes of annealing time. The viscosity of matrix was critical to determine a coalescence of droplet.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.8
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• pp.823-829
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• 2014

In the present study, simple models were proposed to predict the capillary-driven flow length in a surfactant-added poly(dimethylsiloxane) (PDMS) rectangular microchannel. Owing to the hydrophobic nature of PDMS, it is difficult to transport water in a conventional PDMS microchannel by means of the capillary force alone. To overcome this problem, microchannels with a hydrophilic surface were fabricated using surfactant-added PDMS. By measuring the contact angle change on the surfactant-added PDMS surface, the behavior was investigated to establish a simple model. In order to predict the filling length induced by the capillary force, the Washburn equation was modified in the present study. From the investigation, it was found that the initial rate-of-change of the contact angle affected the filling length. Simple models were developed for three representative cases, and these can be useful tools in designing microfluidic manufacturing techniques including MIcroMolding In Capillaries (MIMIC).

• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.227-233
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• 2004

Simplified model of slide-fed curtain coating flow has been developed and tested in this study. It rests on the sheet profile equations for curtain thickness in curtain flow and its trajectory derived by the integral momentum balance approach of Higgins and Scriven (1979) and Kistler (1983). It also draws on the film profile equation of film thickness variation in flow down a slide. The equations have been solved in finite difference approximation by Newton iteration with continuation. The results show that how inertia (Rey­nolds number), surface tension (capillary number), inclination angle of the slide, and air pressure difference across the curtain affect sheet trajectory and thickness profile. It has been revealed that approximate models can be useful to easily analyze coating flow dynamics without complex computations, giving qualitative agreement with full theory and with experiment.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.21-27
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• 2003

This paper proposes a new model of the pressure drop for more accurate description of oscillating flow through regenerator under pulsating pressure conditions in contrast to an existing model based on steady flow. For the universal uses of the oscillating flow model, non-dimensional parameters, which consist of Reynolds number, Valensi number gas domain length ratio, oscillating flow friction factor and phase angle of pressure drop, are derived from the capillary tube model of the regenerator. Two correlation equations of the model are obtained from the experiments for the twill square screen regenerators under various operating frequencies and inlet mass flow rates. The oscillating friction factor is a function of only the Reynolds number and the phase angle of pressure drop is a function of the Valensi number and the gas domain length ratio. Experiment is also performed to examine the effects of the shape of screens.

• Korean Membrane Journal
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• v.3 no.1
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• pp.59-68
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• 2001

Unlike existent field flow fractionation, new method, osmotic sink field flow fractionation is introduced and used ultrafiltration hollow fiber membranes as separation channel. This hollow fiber osmotic sink field flow fractionation is called HF-OSFFF. A theory that describes the retention, relaxation, resolution, plate number for the system, has been developed and experimentally verified by separation model of po1ystyrene latex beads. At external field, it is measured that radial flow rates change according to various concentrations of PEG solutions. Concentration of PEG solution vs. radial flow rate is a linear relation. For diameter distribution of unknown polymer sample, HF-OSFFF compared with the commercial capillary hydrodynamic flow fractionation (CHDF).

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.197.2-197.2
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• 2011

Preliminary analysis on the modeling conditions and the simulation results is conducted only to evaluate the correctness of the simulation configuration further to apply for the LASGIT project. Except for the unrealistic modeling conditions for the relations of capillary pressure and relative permeability against water saturation used previously, the simulation results successfully demonstrate Helium propagation typical for two-phase flow. Further elaborated simulation with more realistic parameters should complete the weak points of the preliminary work.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.17-18
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• 2003

Drop deformation in a cylindrical contraction geometry, characterized here by the formation of a thread of drop fluid in the contraction, is predicted using a Volume-of-Fluid numerical technique. The predicted drop shape is found to closely follow the observed deformation. A capillary instability in the developing drop thread in the contraction was predicted, in agreement with experimental observation.

• Water for future
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• v.22 no.3
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• pp.289-298
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• 1989

A review is made of transient phenomena ralation to flow in the vadose zone. Reviewed topics include rapid water table response to rainfall, pulsating flow due to pressure perturbations in the vasoes zone, and the wave-like propagation of increased soil moisture caused by intermittent rainfall. As a basis of interpreting these phenomena, zoning of the vadose zone into a residual water zone, an unsaturated capillaty zone, and a saturated capillary zone are proposed. Possible implications with respect to hydrological processes relating to these phenomena are discussed.