• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.137-147
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• 2002

Maturity models involving curing temperature and curing ages have been widely used to predict concrete strength, which can accurately estimate concrete strength. However, they may not consider physical quantities such as the characteristics of hydrates and the capillary porosity of microstructures associated with strength development. In order to find out the effects of both factors on a strength increment, the hydration model and the estimation method of the amount of capillary porosity were established, and the compressive strength test of concrete nth various water/cement ratios was carried out considering two test parameters, curing temperature and curing age. In this study, by analyzing the experimental results, a strength estimation model for early-age concrete that can consider the microstructural characteristics such as hydrates and capillary porosity was proposed. Measured compressive strengths were compared with estimated strengths and good agreements were obtained. Consequently, the proposed strength model can estimate compressive strength of concrete with curing age and curing temperature within an acceptable error.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.97-103
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• 2005

In this paper, effects on the heat transport limitation of heat pipe by the wick structural factors were theoretically analyzed for the sintered-copper wick heat pipe. Uniformity of particle size and sintering process were acted as dominant factors on the pore distribution and wick porosity, and small deviations of the wick thickness and the pore size greatly affected the heat transport limitations of the heat pipe. Especially, slight variations of the wick thickness, mean particle radius and capillary radius along the vapor temperatures and inclination angles remarkably changed the capillary limitation of the heat pipe.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.1
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• pp.25-32
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• 2021

For developing the durable eco-concrete, water-repellent and hydrophobic emulsion were prepared by stirring and mixing polymethyl hydrosiloxane and polyvinyl alcohol. After adding the PMHS emulsion cement paste, the hydration reaction characteristics and the change in chemical composition were analyzed through BSE and EDS analysis, and the micropores were evaluated by MIP test. Cement mixed with PMHS emulsion was analyzed to increase the hydration reactivity and to decrease the capillary porosity, but it was found that the capillary porosity varies depending on the degree of dispersion of the emulsion in the cement paste. In the case of the emulsion containing metakaolin, there was little difference in hydration degree and porosity from the case of using only the PMHS emulsion. However, when the cement surface was coated with PMHS emulsion, the contact angle was found to increase significantly compared to OPC, and it was analyzed that especially when PVA fiber was used together, it changed to a hypohydrophobic surface.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.1710-1716
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• 2008

The Loop Heat Pipe (LHP) operates to pump the working fluid by means of the capillary force in a wick structure. Particularly, it is difficult to design and manufacture the evaporator consisted of a grooved container and a compensation chamber as well as the wick structure. This study is related to design and manufacture the grooved container coupled with wick structure, the properties of the wick structure such as the permeability, the porosity, and the maximum capillary pressure were measured to apply the cooling technology for Insulated Gate Bipolar Transistor (IGBT). The container of the LHP was manufactured by the electrical discharge process and the wick structure was sintered with the nickel particle by an axial-press apparatus with the pulse electronic discharge. As results, the properties of the wick were experimentally obtained about 60% of the porosity, 35kPa of the maximum capillary force and $1.53{\times}10-13m2$ of the permeability.

• International Journal of Concrete Structures and Materials
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• v.4 no.1
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• pp.37-43
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• 2010

Theoretical models based on modern interpretations of the morphology and interactions of cement hydration products are developed for prediction of the mechanical properties of hydrated cement paste (hcp). The models are based on the emerging nanostructural vision of calcium silicate hydrate (C-S-H) morphology, and account for the intermolecular interactions between nano-scale calcium C-S-H particles. The models also incorporate the effects of capillary porosity and microcracking within hydrated cement paste. The intrinsic modulus of elasticity and tensile strength of hydrated cement paste are determined based on intermolecular interactions between C-S-H nano-particles. Modeling of fracture toughness indicates that frictional pull-out of the micro-scale calcium hydroxide (CH) platelets makes major contributions to the fracture energy of hcp. A tensile strength model was developed for hcp based on the linear elastic fracture mechanics theories. The predicted theoretical models are in reasonable agreements with empirical models developed based on the experimental performance of hcp.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1225-1230
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• 2004

In this paper, the pressure drops were investigated according to the sintered porous wick structure in loop heat pipe(LHP) by theoretical analysis. LHP has the wick only in evaporator for the circulation of working fluid, so utilizes porous wick structure which pore diameter is very small for large capillary force. This paper investigates the effects of different parameters on the pressure drops of the LHP such as particle diameter of sintered porous wick, wick porosity, vapor line diameter, thickness of wick and heating capacity. Working fluid is water and the material of sintered porous wick is copper. According to the these different parameters, capillary pressure, pressure drop in wick were analized by theoretical design method of LHP.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.16 no.12
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• pp.1107-1116
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• 2004

In this paper, the effects of diverse parameters on the operation of loop heat pipe (LHP), such as particle diameter of sintered porous wick, wick porosity, vapor line diameter, thickness of wick and heating capacity were investigated by a theoretical analysis. A LHP has a wick only in its evaporator for the circulation of working fluid, and utilizes a porous wick structure of which pore size is very small to obtain a large capillary force. The working fluid is water and the material of sintered porous wick is copper. For these different parameters, capillary pressure, pressure drop in wick, pressure drops and temperature distribution were analyzed by a theoretical design method of LHP.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.185-194
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• 1998

Flow-induced voids during resin impregnation and poor fiber wetting give serious effects on the mechanical properties of composites in resin transfer molding process. In order to better understand the characteristics of resin flow and to investigate the mechanism of void formation, flow visualization experiment for the resin impregnation was carried out on plain weaving glass fiber mats using silicon oils with various viscosity values. The permeability and the capillary pressure for the fiber mats of different porosities were obtained by measuring the penetration length of the resin with time and with various injection pressure. At low porosity and low operating pressure, the capillary pressure played a significant role in impregnation process. Video-assisted microscopy was used in taking the magnified photograph of the flow front of the resin to investigate the effect of the capillary pressure on the void formation. The results showed that the voids were formed easily when the capillary pressure was relatively high. No voids were detected above the critical capillary number of 2.75$\times$$10^{-3}, and below the critical number the void content increased exponentially with decrease of the capillary number. The content of void formed was independent of the viscosity of the resin. For a given capillary number, the void content reduced with the lower porosity of the fiber mat.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.11
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• pp.880-889
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• 2002

The purpose of the present study is to examine the factors affecting the heat transfer limitations of screen mesh heat pipe for electronic cooling by theoretical analysis. Diameter of pipe was 6 mm, and mesh numbers are 50, 100, 150, 200 and 250 and water was selected as a working fluid. According to the change of mesh number, wick layer, inclination and saturation temperature, capillary pressure, pumping pressure, liquid friction coefficient in wick, vapor friction coefficient, capillary limitation, entrainment limitation, sonic limitation and boiling limitation we analyzed by theoretical design method of a heat pipe. As some results, the capillary limitation in small diameter of heat pipe is largely affected by mesh number and wick layer.

• Journal of the Korean Wood Science and Technology
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• v.47 no.1
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• pp.8-20
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• 2019

This study was conducted to analyze the pore structure of Yellow poplar. Cross-sectional surfaces of heartwood and sapwood of Yellow poplar (Liriodendron tulipifera) were observed by SEM, and the true density of the heartwood, intermediate wood and sapwood were measured by gas pycnometery, while gas permeability and pore size of heartwood, intermediate wood and sapwood were measured by capillary flow porometery. The pores were classified as through pore, blind pore and closed pore. It was determined that the permeability was increased due to the content and size of through pore being increased although the total porosity of specimen showed slight difference from pith to bark. The content of through pore porosity was 33.754 % of heartwood and 47.810 % of sapwood, showed an increasing trend from pith to bark, however, those for the blind pore porosity and closed pore porosity were 27.890 % and 19.492 % for heartwood and 19.447 % and 4.660 % for sapwood, showed a decreasing trend from pith to bark. The max pore size of specimens was increased by about 5 times from $5.927{\mu}m$ to $31.334{\mu}m$, and mean flow pore size was increased by about 315 times from $0.397{\mu}m$ to $12.437{\mu}m$ from pith to bark.