• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.1 s.232
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• pp.67-73
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• 2005

The paper presents a single-heater microfluid injector, whose ejected droplet volume is adjusted by digital current path control for a single microheater. The previous droplet volume adjustable methods have used the digital current control for multiple heaters or the analog current control for a single heater, while the present method uses the digital current control for a single microheater. Two different microinjectors, having a rectangular heater and a circular hearter, are designed and fabricated in the chip area of $7.64\;mm{\times}5.26\;mm$. The fabricated microinjectors have been tested and characterized for the number, size, shape and lifetime of the generated bubbles as well as for the volume and velocity of the ejected droplets. The input power for the rectangular heater and the circular heater has been varied in the ranges of $8.7{\sim}24.9{\mu}W\;and\;8.1{\sim}43.8{\mu}W$, respectively. The projected area of the generated bubble has been changed in the ranges of $440{\sim}l,3600{\mu}m^2\;and\;800{\sim}3,300{\mu}m^2$ for the rectangular heater and the circular heater, respectively. The microinjector with the rectangular heater ejects three discrete levels of the droplet in the volume range of $9.4{\sim}20.7pl$ with the velocity range of $0.8{\sim}1.7m/s$, while the microinjector with the circular heater achieves five discrete levels of the droplet in the volume range of $7.4{\sim}27.4pl$ with the velocity range of $0.5{\sim}2.8m/s$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.1-14
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• 1997

Natural convection cooling of discrete heaters located in a two-dimensional vertical open top cavity is investigated experimentally. The five discrete heaters with same heat generation are located on the wall of the cavity. The heaters are arranged in two configurations; flush-mounted on a vertical wall and protruding from the wall about 4.5 mm. The materials used for the vertical walls are copper and epoxy-resin, and air is used as the cooling fluid. The temperature and flow fields in the cavity were visualized by means of Mach-Zehnder interferometer and smoke-method. Also, local temperature measurements are made along the vertical wall. Results are obtained for cavity aspect ratios of 4.6, 7.5 and 9.5 and modified Rayleigh numbers ranging from 10$^{3}$ to 10$^{6}$ . Results indicate that the cooling efficiency for the copper wall is superior to that of the epoxy-resin. For the epoxy-resin wall, the protrusion of the heaters plays a role in decreasing the heat transfer performance. The location of maximum temperature is significantly influenced by the wall materials and heater configurations. Correlations relating the Nusselt number to the modified Rayleigh number are proposed.

• Journal of the Korean Society of Combustion
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• v.16 no.2
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• pp.40-46
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• 2011

The diesel pre-heater has being used in cabin heating and coolant heating of engine to reduce the engine warm up time for commercial vehicle. The pre-heaters are classified as diesel spray combustor and it forms diffusion flame. By using swirler, a recirculation flow of hot product gases is established near the fuel nozzle and it helps the maintaining of diffusion flame. The design difference of swirler can affect on reaction characteristics and temperature distribution inside pre-heater. The purpose of this study is the investigation of the effect of swirler configuration on combustion characteristics. To solve spray combustion problem, the Euler-Lagrange approach discrete model is used to track droplet trajectory and evaporation history. The PDF equilibrium model is used for chemical reaction model. These models are implemented into the FLUENT code.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.235-251
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• 1997

A numerical simulation on the combined natural convection and radiation is carried out in a partially open rectangular enclosure with a heater by using the finite volume and the S-8 discrete ordinate methods. The fluid inside the enclosure is considered as an absorbing, emitting and anisotropic scattering media. The heater causes a natural circulation of the fluid (10$^{5}$ $^{9}$ ) which results in significant in-flow of the ambient cold fluid through the partially open wall. Comparing the results of pure convection with those of the combined convection- radiation, the combined heat transfer results with small Planck numbers (P$_{l}$ <1.0) show much stronger circulation than those of the pure convection, and the fluid circulation is more evident for larger Rayleigh numbers. When one of three radiative properties - the medium absorption coefficient, the wall reflectivity, and the scattering albedo - increases, the fluid circulation and the heat transfer in the enclosure are reduced. The location of the heater and the open ratio of the right wall are also shown to affect the fluid circulation and heat transfer significantly. However, the anisotropy of the scattering phase function is shown to be unimportant for the fluid circulation and heat transfer within the enclosure considered in this study.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.1
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• pp.15-23
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• 1997

An experimental investigation of two-dimensional steady natural convection cooling in a vertical open top cavity with conducting side walls of finite thickness is presented. The various heat-generating discrete heaters are located on one vertical wall of the cavity. When each heater dissipates different amount of power, the purpose of the work is to obtain the optimal array condition of the heaters. The four cases of non-uniform heating conditions are considered. The temperature fields in the cavity were visualized by the interferometer and local temperatures of the vertical wall were measured by thermocouples. The heaters were arranged in two configurations: flush-mounted on a vertical wall or protruding from the wall about 4.5 mm. The vertical wall was constructed out of copper or epoxy-resin sheet. Experiments have been conducted for air with constant Prandtl number(Pr=0.7), the aspect ratio of 4.6, 7.5, 9.5, power input in the range of 0.9 W ~ 4.2 W. For the enhancement of the cooling effectiveness, the upper and lower of vertical wall would give the better position for the heaters of higher heat flux.