• Journal of Mechanical Science and Technology
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• v.15 no.9
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• pp.1328-1338
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• 2001

The objective of this study is to present flow and pressure drop characteristics of R22 in adiabatic capillary tubes of inner diameters of 1.2 to 2.0mm, and tube lengths of 500 to 2000mm. Distributions of temperature and pressure along capillary tubes and the refrigerant flow rates through the tubes were measured for several condensing temperatures and various degrees of subcooling at the capillary tube inlet. Condensing temperatures of R22 were selected as 40, 45, and 50$^{\circ}C$ at the capillary tube inlet, and the degree of subcooling was adjusted to 1 to 18$^{\circ}C$. Experimental results including mass flow rates and pressure drops of R22 in capillary tubes were provided. A new correlation based on Buckingham II theorem to predict the mass flow rate through the capillary tube was presented considering major parameters which affect the flow and pressure drop characteristcis.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1719-1724
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• 2002

A previously designed capillary viscometer with measuring differential pressure was modified to measure the viscosity of non-Newtonian fluids including unadulterated blood continuously over numerous shear rates in a single measurement. Because of unavoidable experimental noise and a limited number of data, the previous capillary viscometer experienced an inaccuracy and could not directly determine a viscosity without an iterative calculation. However, in the present measurement there are numerous data available near the point of interest so that the numeric value of the derivative, d(In Q)/d(In Q$\sub$w/), is no longer sensitive to the method of differentiation. In addition, relatively low and wide shear rate viscosity measurements were possible because of the present precision pressure-scanning method with respect to time. For aqueous polymer solutions, excellent agreement was found between the results from the pressure-scanning capillary viscometer and those from a commercially available rotating viscometer. In addition, the pressure-scanning capillary viscometer measured the viscosity of unadulterated whole blood without adding any anticoagulants.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.6 s.237
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• pp.763-771
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• 2005

This paper is an experimental study on the performance according to a capillary tube diameter and length in a domestic small multi refrigerator[kimchi refrigerator]. Pressure drop in a capillary tube is predicted by theoretical analysis and experimental method as the reduction of capillary tube diameter from 0.74 to 0.6 mm. The differences between experimental results and analytical results are mainly caused by friction factor in a capillary tube. Because there are no adequate equations used to calculate pressure drop of capillary tube diameter under 1.0mm. The empirical equations necessary for interpretation of capillary tube were derived from capillary tube test results data using curve fitting method. This study shows that the optimized designs of system, which is capillary tube length and refrigerant charge amount, are 2000mm, 83g at the capillary tube diameter 0.6mm and 3000mm, 73g at the capillary tube diameter 0.74mm. And capillary design tools and system matching techniques necessary for development of the kimchi refrigerator were also developed through this study.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.1598-1603
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• 2004

This paper is an experimental study on the performance characteristic with a variation of capillary diameter and length. The performance characteristic of a refrigeration system is predicted that it is occurring changes of flow pattern and pressure drop in a capillary tube because of reduction of capillary diameter 0.74 to 0.6 mm. The difference between experimental results and analytical results is mainly caused by values of friction factor for using to calculate pressure drop through a small diameter capillary tube under 0.74mm. The experimental equation is derived from capillary tube test data using curve fitting method.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.1-6
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• 2003

The purpose of the present study is to investigate the capillary heat transportation limitation in heat pipe according to the change of screen mesh wick porosity. Diameter of pipe was 6 mm, and mesh numbers are 100, 150, 200 and 250 and water was selected as a working fluid. According to the change of wick porosity and mesh number, the capillary pressure, pumping pressure, liquid friction coefficient in wick, vapor friction coefficient, and capillary heat transportation limitation are analyzed by theoretical design method of a heat pipe. As some results, the capillary heat transportation limitation in screen mesh wick heat pipe is largely affected by wick porosity and mesh number.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1533-1542
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• 2003

In the present study, the characteristics of pressure oscillation and heat transfer performance in an oscillating capillary tube heat pipe were experimentally investigated with respect to the heat flux, the charging ratio of working fluid, and the inclination angle to the horizontal orientation. The experimental results showed that the frequency of pressure oscillation was between 0.1 Hz and 1.5 Hz at the charging ratio of 40 vol.%. The saturation pressure of working fluid in the oscillating capillary tube heat pipe increased as the heat flux was increased. Also, as the charging ratio of working fluid was increased, the amplitude of pressure oscillation increased. When the pressure waves were symmetric sinusoidal waves at the charging ratios of 40 vol.% and 60 vol.%, the heat transfer performance was improved. At the charging ratios of 20 vol.% and 80 vol.%, the waveforms of pressure oscillation were more complicated, and the heat transfer performance reduced. At the charging ratio of 40. vol.%, the heat transfer performance of the OCHP was at the best when the inclination angle was 90$^{\circ}$ the pressure wave was a sinusoidal waveform, the pressure difference was at the least, the oscillation amplitude was at the least, and the frequency of pressure oscillation was the highest.

• 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.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.2123-2128
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• 2004

In this study, analysis is made for the effects of groove shape on the thermal performance of a axial groove heat pipe. The mathematical models of two-phase flow in grooved heat pipe are presented for the capillary limitation in steady state. Generally, the heat pipe performance depends on the capillary pressure and liquid flow. The friction force of liquid flow through the groove increases with the groove width decreased, and then the capillary pressure is improved in the gas-liquid interface of groove. Therefore, the optimal groove width shaper exists for the maximum thermal performance of heat pipe. In this paper, the optimal groove shape and scale are presented by considering both capillary pressure and liquid flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.6
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• pp.383-389
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• 2016

Based on a surface design with rectangular cavities and channels, we investigated the effects of gravity and capillary pressure on pool-boiling Critical Heat Flux (CHF). The microcavity structures could prevent liquid flow by the capillary pressure effect. In addition, the microchannel structures contributed to induce one-dimensional liquid flow on the boiling surface. The relationship between the CHF and capillary flow was clearly established. The driving potentials for the liquid supply into a boiling surface can be generated by the gravitational head and capillary pressure. Through an analysis of pool boiling and visualization data, we reveal that the liquid supplement to maintain the nucleate boiling condition on a boiling surface is closely related to the gravitational pressure head and capillary pressure effect.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.1777-1782
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• 2003

This paper presents the design, fabrication, and testing of the capillary-induced pressure drop valve, thermocapillary pumping of liquid droplet in hydrophilic channels and the splitting of droplet. The capillaryinduced pressure drop is derived with thermodynamic approach considering three-dimensional meniscus shape which is essential for calculating pressure drop in the diverging shape channel when the aspect ratio is close to one. The micro channel is fabricated via MEMS processes, which consists of the liquid stop valve to retard the liquid droplet, thermocapillary pumping region and the bifurcation region. Also the micro heaters are fabricated to drive the droplet by thermocapillary. The theoretical approaches agree well with the experimental data. The functionality of capillary valve is confirmed to be valid when the aspect ratio is smaller than one. To overcome the difficulty in splitting of the droplet due to the pressure drop in the general Y-shape channel, the protrusion shape is employed for easy splitting in the bifurcation channel.