• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.4
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• pp.184-191
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• 2004

In order to improve the performance of a 2 room heat pump with a constant speed compressor, the optimum refrigeration circuit of the heat pump with different cooling and heating capacities is developed by applying capillary tubes. The refrigeration circuit is composed of four parts; a heating circuit, a cooling circuit, a by-pass circuit and a balance circuit. The performance of the 2 room heat pump are investigated from a rating experiment and a reliability experiment, using the calorimeter. Results of the rating experiment show that the capacity of heat pump is about $93\%$ of the design value. In particular, the capacity of the cooling single operation is about $13\%$ higher than the design value, and the capacity of the heating multi operation is about $5\%$ higher than the design value. From the reliability experi-ment, it is found that the lowest driving voltage of the compressor is about $75\%$ of the rating voltage. Also the compressor is reoperated normally under the flood back and the over load.

• Journal of Mechanical Science and Technology
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• v.20 no.1
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• pp.51-58
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• 2006

To compensate for the motion errors in hydrostatic tables, a method to actively control the clearance of a bearing corresponding to the amount of error using actively controlled capillaries is introduced in this paper. The design method for an actively controlled capillary that considers the output rate of a piezo actuator and the amount of error that must be corrected is described. The basic characteristics of such a system were tested, such as the maximum controllable range of the error, micro-step response, and available dynamic bandwidth when the capillary was installed in a hydrostatic table. The tests demonstrated that the maximum controllable range was $2.4\;{\mu}m$, the resolution was 27 nm, and the frequency bandwidth was 5.5 Hz. Simultaneous compensation of the linear and angular motion errors using two actively controlled capillaries was also performed for a hydrostatic table driven by a ballscrew and a DC servomotor. An iterative compensation method was applied to improve the compensation characteristics. Experimental results showed that the linear and angular motion errors were improved to $0.12{\mu}m$ and 0.20 arcsec, which were about $1/15^{th}$ and $1/6^{th}$ of the initial motion errors, respectively. These results confirmed that the proposed compensation method improves the motion accuracy of hydrostatic tables very effectively.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.295-300
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• 2002

The construction of the T-shaped post-column flow cell has been changed to enhance the practicability as a UV-visible absorbance detector for capillary electrophoresis. In this new design, a rectangular cube-shaped inner structure is employed, which completely fits the outer rectangular tubing. This arrangement has greatly facilitated the fabrication of the T-cells. In addition, the volume for the auxiliary flow has been dramatically reduced down to 300 ${\mu}L$, and its volume flow rate is optimized at 4.2 ${\mu}L$/min. The short optical path length in the sheath flows (500 ${\mu}m$ on each side) minimizes background absorption, and thus enhances its performance in low-UV wavelengths. We have optimized the auxiliary flow rate at 50 ${\mu}m$/s, so that migration times are insensitive to the flow rate. This optimization has improved repeatabilities in migration times and peak heights. A double-beam detection scheme using a pair of photodiodes is employed to increase the signal-to-noise ratio.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.317-322
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• 2005

This study is aimed to analyze the effects of heat pipe shape on the heat transfer in solar collector with a axial grooved heat pipe. In the design of a heat pipe. two of the most important criteria to be met are the operating temperature range and the maximum heat transport capacity, When the operating temperature range is known and the working fluid has been selected, the maximum heat transport capacity depends strongly on capillary pressure and liquid flow. The heat transport capacity of the heat pipe will depend on the geometry of the heat pipe, the wick structure. the vapor channel shape. groove number. cooling temperature. condenser length and pipe diameter. So various shapes are used for mathematical models of two-phase flow in grooved heat pipe. From the results. the adequate groove shape and scale are presented by considering the heat transport and capillary limitation.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.1
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• pp.1-9
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• 2003

The examinations of the operating mechanism of an oscillating capillary tube heat pipe (OCHP) using the visualization method revealed that the working fluid in the OCHP oscillated to the axial direction by the contraction and expansion of vapor plugs. The contraction and expansion were due to the formation and extinction of bubbles in the evaporating and condensing part, respectively The actual physical mechanism, whereby the heat which was transferred in such an OCHP was complex and not well understood. In this study, a theoretical model of the OCHP was developed to model the oscillating motion of working fluid in the OCHP. The differential equations of two-phase flow were applied and simultaneous non-linear partial differential equations were solved. From the analysis of the numerical results, it was found that the oscillating motion Of working fluid in the OCHP was affected by the operation and design conditions such as the heat flux, the charging ratio of working fluid and the hydraulic diameter of flow channel. The simulation results showed that the proposed model and solution could be used for estimating the operating mechanism in the OCHP.

• Journal of the Korean Society of Visualization
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• v.21 no.1
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• pp.110-118
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• 2023

Characterizing the extensional rheological properties of non-Newtonian fluids is crucial in many industrial processes, such as inkjet printing, injection molding, and fiber engineering. However, educational institutions and research laboratories with budget constraints have limited access to an expensive commercial extensional rheometer. In this study, we developed a custom-made extensional rheometer using a CO₂ laser cutting machine and 3D printer. Furthermore, we utilized a smartphone with a low-cost microscopic lens for achieving a high spatial resolution of images. The aqueous polyethylene-oxide (PEO) solutions and a Boger fluid were prepared to characterize their extensional properties. A transition from a visco-capillary to an elasto-capillary regime was observed clearly through the developed rheometer. The extensional relaxation time and viscosity of the aqueous PEO solutions with a zero-shear viscosity of over 300 mPa·s could be quantified in the elasto-capillary regime. The extensional properties of the solutions with relatively small zero shear viscosity could be calculated using a smartphone's slow-motion feature with increasing temporal resolution of the images.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1507-1519
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• 2003

The two-phase flow patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the flow pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R -142b was achieved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.953-960
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• 2012

An AMTEC (alkali metal thermal electric converter) is a device that is used for the direct conversion of heat to electricity. Sodium is used as the working fluid, and its circulation is driven by a capillary wick. The wicks used for circulation include an evaporator wick, artery wick, and condenser wick, and each wick has a pressure drop because of the circulation of liquid and vapor. For the circulation of sodium, the capillary pressure of the evaporator wick must be greater than the total pressure drop in the wicks. In this study, the pressure drop in the evaporator wick, artery wick, and condenser wick and the heat loss from the evaporator to the condenser through the artery wick were analyzed for the design of a 100 W AMTEC prototype. It was found that a particle diameter of 10 ${\mu}m$ is suitable for the evaporator wick to maintain a capillary pressure greater than total pressure drop in the circulation loop.

• Journal of the Korean Society of Visualization
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• v.19 no.3
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• pp.15-21
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• 2021

In this study, we investigated the dynamics of a droplet impacting rough hydrophobic surfaces through high-speed imaging. Micrometer-sized structures with grooves and pillars were fabricated on smooth Polydimethylsiloxane (PDMS) surfaces by laser ablation. We used Newtonian and non-Newtonian liquid droplets to study the drop impact dynamics. De-ionized water and aqueous glycerin solutions were used for the Newtonian liquid droplet. The solutions of xanthan gum in water were prepared to provide elastic property to the Newtonian droplet. We found that the orientation of the surface structures affected the maximal spreading diameter of the droplet due to the degree of slippage. During the droplet retraction, the dynamic receding contact angles were measured to be around 90° or less. It resulted in the formation of the micro-capillary bridges between the receding droplet and the surface structures. Then, the rupture of the capillary bridge led to the formation of micrometer-sized droplets on top of the surface structures. The size of the microdroplets was found to increase with increasing the impacting velocity and viscosity of the Newtonian liquid droplets. However, the size of the isolated microdroplets decreased with enhancing the elasticity of the droplets, and the size of the non-Newtonian microdroplets was not affected by the impacting velocity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.04a
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• pp.67-68
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• 2011