• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.8
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• pp.641-647
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• 2002

Objectives of this paper are to investigate the effect of roughness of micro-hatching tubes on the absorption performance and to develop on experimental correlation of Nusselt as a function of the roughness. Three different micro-scale hatched tubes and a bare tube were tested in the present experiment. $H_{2}O/LiBr$ solution is used as working fluid. It was found that absorption performance of micro-scale hatched tubes were improved upto 2 times with an error band of ${\pm}25%$ compared with the bare tube. An experimental correlation of Nusselt was developed as a function of the roughness.

• Journal of Biomedical Engineering Research
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• v.14 no.2
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• pp.147-153
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• 1993

In this paper, we studied about the micro pressure transmission system using fluid. For the investigation of feasibility of microhydraulic system, the hydraulic characteristics were examined by using the capillary tube system and the micro cylinder system that consists of a rod and a micro capillary tube. A new hydraulic micro actuator using magnetic fluid and an external magnetic field was also investigated. The results showed that our microhydraulic system has the possibility of power transmission in arbitrary directions.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2200-2205
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• 2007

In order to investigate the variation on a heat transfer coefficient during evaporation of $CO_2$, basic experiment on the evaporation heat transfer characteristics in a horizontal micro-channel tube was performed. Hydraulic diameters of micro-channels were 0.68 and 1.46 mm. The experiment apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiments were conducted for various mass fluxes of 300 to 800 kg/$m^2s$, heat fluxes of 10 to 40 kW/$m^2$ and saturation temperatures of -5 to 5$^{\circ}C$. With the increase heat flux, the evaporation heat transfer coefficient increased. And the significantly change of the heat transfer coefficient was observed at any heat flux and mass flux. As the saturation temperature increased and the hydraulic diameter decreased, the heat transfer coefficient increased.

• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.69-75
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• 2006

The microbubbles were used in various fields, such as turbulent control, drag reduction, material science and life science. The X-ray PTV using X-ray micro-imaging technique was employed to mea-sure the size and velocity of micro-bubbles moving in an opaque tube simultaneously. Micro-bubbles of $10{\sim}60{\mu}m$ diameter moving upward in an opaque tube (${\phi}$=2.7mm) were tested. Due to the different refractive indices of water and air, phase contrast X-ray images clearly show the exact size and shape of over-lapped microbubbles. In all of the working fluids tested (deionized water, tap water, 0.01 and 0.10M NaCl solutions), the measured terminal velocity of the microbubbles rising through the solution was proportional to the square of the bubble diameter. The rising velocity was increased with increasing mole concentration. The microbubble can be useful as contrast agent or tracer in life science and biology. The X-ray PTV technique should be able to extract useful information on the behavior of various bio/microscale fluid flows that are not amenable to analysis using conventional methods.

• Proceedings of the KWS Conference
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• 2005.06a
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• pp.106-108
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• 2005

The instrumented fuel irradiation test at a research reactor is needed to evaluate the performance of the developed nuclear fuel. The fuel elements can be designed to measure the center line temperature of fuel pellets during the irradiation test by using temperature sensor. The thermal sensor was composed of thermocouple and sensor sheath. Micro-laser welding technology was adopted to seal between seal tube and sensor sheath with thickness of 0.15 mm. The soundness of welding area has to be confirmed to prevent fission gas of the fuel from leaking out of the element during the fuel irradiation test. In this study, fundamental data for micro-laser welding technology was proposed to seal temperature sensor sheath of the instrumented fuel element. And, micro-laser welding for dissimilar metals between sensor sheath and seal tube was characterized by investigating welding conditions. Moreover, the micro-laser welding technology is closely related to advanced industry. It is expected that the laser material processing technology will be adopted to various a pplications in the industry.

• Journal of the Korean Institute of Gas
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• v.11 no.4
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• pp.35-40
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• 2007

In this paper, evaporation heat transfer characteristics of propane and iso-butane in micro-fin tubes were investigated experimentally. Test section has a micro-fin tube with outside diameter of 12.70 mm, and 75 fins with a fin heights of 0.25 mm. The experimental results summarize as the followings: The average evaporation heat transfer coefficients of He's refrigerants is higher than those of HCFC22, and appeared in the order of iso-butane, propane with respect to the approaching of the high mass flux. The evaporation heat transfer coefficient of micro fin tube is about $10{\sim}80%$ higher than those of smooth tube. This results from the study can be used in the case of designing heat transfer exchanger using hydrocarbons as the refrigerant for the air-conditioning systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.176-184
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• 1999

Numerical and experimental studies were performed to examine the characteristics of heat and mass transfer processes for a Micro Heat Pipe(MHP) with a triangular cross-section. Solutions on mass flow rate, pressure variation, and radius of meniscus were obtained using the mathematical model developed by Faghri and Khrustalev. To obtain an increase in capillary limitation, a triangular tube with curved walls was designed and fabricated. The measurement by microscope showed that the radius at corners of the tube was ranging between 0.03-0.05mm. Performance test for MHPs using the triangular tube with curved walls proved a substantial increasement in heat transport limitation, with 4.5W and 2.0W in case of using water and ethanol as a working fluid, respectively. In the previous study by Faghri a limitation of 0.5W was reported for a water MHP with a regular triangular tube.

• Advances in nano research
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• v.13 no.6
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• pp.545-559
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• 2022

This paper studies the buckling response of nonuniform functionally graded micro-sized tubes according to the high-order tube theory (HOTT) and classical beam theory (CBT) in addition to nonlocal strain gradient theory. The microtube is made of axially functionally graded material (AFGM). Both inner and outer tube radiuses are changed along the tube length; the microtube is the truncated conical type of tube. The nonlinear partial differential (PD) the formulations are obtained on the basis of the energy conservation method. Then, the linear and nonlinear results are computed via a powerful numerical approach. Finally, the impact of various parameters on the stability of axially functionally graded (AFG) microtube regarding the buckling analysis is discussed.

• Journal of Mechanical Science and Technology
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• v.20 no.8
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• pp.1284-1291
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• 2006

Single phase pressure drops in micro tubes were investigated through an experimental measurement and a numerical simulation. Experimental Po was obtained in circular micro tubes with 87 and $118{\mu}m$ diameter with distilled water. Experiments were carried out in laminar flow region with varying the Re 15-450 for the $87{\mu}m$ diameter tubes and 60-1300 for the $118{\mu}m$ diameter tube. No early transition from laminar to turbulent flow was detected for the experimental range. The computational estimation of pressure drop in the $87{\mu}m$ diameter tube was performed with the aid of CFD software. Boundary conditions from experiments were used for the numerical simulation. The results of experimental and numerical studies showed a good agreement with the conventional macro theory.

• International Journal of Air-Conditioning and Refrigeration
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• v.13 no.4
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• pp.184-195
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• 2005

This paper describes the recent work on advanced technology concepts applied to air cooled heat exchangers for residential air-conditioning. The concepts include vortex generators for the air-side, micro-fin or flat tubes for the refrigerant-side. Advances in understanding of heat transfer mechanisms, predictive models are discussed.