• Journal of the Korean Ceramic Society
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• v.29 no.12
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• pp.919-925
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• 1992

Continuous synthesis process for monodispersed zirconia powders with ultrasonic wave mixing was developed. Reactant solutions were flowed through a T-tube with small diameter and then mixed in a microscale with ultrasonification. Reaction and aging were followed during the mixed solution of reactants is in plug flowing through a narrow long teflon tubing. Zr(n-OC4H9)4 in ethanol and H2O in ethanol were used as reactants. From this process monodispersed, spherical, non-agglomerated, singlet hydrated zirconia powders with 0.6 $\mu\textrm{m}$ average size were obtained. Geometrical standard deviation of the particle size distribution was less than 1.2 with ultrasonic mixing, and the geometrical standard deviation was not affected by the flow rate of the reactants.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.946-952
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• 2005

The $CO_{2}$ refrigeration cycle is expected to reduce the compressor work and increase the COP by applying two-phase ejector as a device for the recovery of dissipated expansion energy. In this study, the performance of the cycle was simulated and effects of the ejector shapes on the performance of the $CO_{2}$ refrigeration cycle were investigated. The following results were obtained through the cycle simulation. The COP of the $CO_{2}$ refrigeration cycle with two-phase ejector flow which expansion is occured in the isentropic manner is increased by a maximum of 24 $\%$ than the basic cycle with expansion valve If the velocity nonequilibrium in the mixing process is assumed the COP of the cycle is increased with the increase of the length and the decrease of the section area of the mixing tube. The best cycle performance is obtained when the divergent angle of diffuser is 7.

• Korean Journal of Hydrosciences
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• v.8
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• pp.1-17
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• 1997

Prandtl's mixing length theory was modified to obtain a power velocity distribution in which the coefficient and the exponent are variable over a range from : $$ A simple suspended-sediment concentration distribution was developed from the modified velocity distribytion : $ With nominal values of $\beta$=1.0, $\kappa$=0.4 and visual accumulation tube values of the fall velocity, the comparison between the theory and field measurements by the USGS on the Rio Grande is fair. Doubling the value of the exponent results in a good comparison. Further researches are needed for choosing the values of $\beta$, $\kappa$, and fall velocity values, and consideration on the effects of large-scale turbulence and secondary flows are necessary for them. In a pragmatic sense, on any gaging sites the close analysis of very detailed measurements can establish its specific coefficient and exponent.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.04a
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• pp.170-171
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• 2022

In recent years, due to the occurrence of traffic accidents caused by black ice in winter, the number of personal injuries is increasing rapidly. Black ice is a phenomenon that occurs like a thin layer of ice on the road surface. Accordingly, many developments of heat-generating concrete are being developed to remove ice by increasing the temperature by supplying constant electricity to places where black ice is likely to occur. These heating elements are being developed by mixing a conductive material represented by carbon nanotubes with concrete. However, research up to now has been focused on efficient temperature rise and derivation of the optimum mixing ratio, and the evaluation of maintaining heat generation performance during continuous repetition is insufficient. Therefore, in this study, a heating test specimen was manufactured and 50V power was repeatedly supplied to evaluate the heating characteristics.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2303-2308
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• 2007

Experiments were performed to determine the thermal (or turbulent) diffusion coefficient (TDC) and to investigate the critical heat flux (CHF) performance in the 5${\times}$5 rod bundle with 5 unheated rods which are supported by Hybrid Mixing Vane. In this study, HFC-134a fluid was used as working fluid and the fluid temperature were measured in the important subchannels. To determine the TDC value, the measured fluid temperatures were compared with the predicted values obtained from the MATRA code. The best optimized value of ${\beta}$ was found to be 0.02 by considering prediction statistics, i.e., average and standard deviations of the differences between the experimental results and code calculations. Using the best optimized value of ${\beta}$ as 0.02, the MATRA code predicts the test results of the fluid temperature within ${\pm}$1.0 % of error. According to the experimental results on CHF of 5 non-heating guide tubes, the case with non-heating guide tube showed a little good performance in terms of CHF.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1900-1905
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• 2007

A micro cyclone combustor was developed to be used as a heat source of thermoelectric power generator (TPG). The cyclone combustor was designed so that fuel and air were supplied to the combustion chamber separately. The mixing and flow characteristics in the combustor were investigated numerically. The global equivalence ratio (${\Phi}$), defined using the fuel and air flow rates, was introduced to examine the flow features of the combustor. The mixing of fuel and air inside the combustor could be well understood using the fuel concentration distribution. It was found that the weak recirculating zone was formed upper the fuel-supplying tube in case of ${\Phi}$ < 1.0. In addition, it was found that small regions that have a negative axial velocity exist near the fuel injection ports. It is assumed that these negative axial velocity regions can stabilize a flame inside the micro cyclone combustor.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.13-18
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• 2003

Heat pipes with binary mixture fabricated and tested for applications where condenser temperature is in a range of $10^{\circ}C$ to $130^{\circ}C$. The pipe materials 8.0 mm O.D. cupper tube and the working fluids are ethanol-water mixtures. The total length of test of the heat pipe was 1710mm in which evaporator section was 1570mm, adiabatic section was 50mm and condenser section was 90mm. Mixing ratios of ethanol and water could be variable in mole fraction. Temperature of condenser section was $10^{\circ}C$, $80^{\circ}C$ and $130^{\circ}C$. Heat pipe performance experimental study was accomplished with change of mixing ratio in these temperatures. The fill charge ratio was 20% of the heat pipe volume. Wick structure was woven-wire and method of experimental work was that thermal load was increased 20W step until the heat pipe wall temperature reached at $150^{\circ}C$. Results were following: At coolant $10^{\circ}C$ and $130^{\circ}C$, mixing ratio that have beat thermal performance was 0.8M+ and at coolant $80^{\circ}C$, was 0.3 ${\sim}$ 0.5 M+.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.12
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• pp.1042-1047
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• 2007

A micro cyclone combustor was developed to be used as a heat source of thermoelectric power generator (TPG). The cyclone combustor was designed so that fuel and air were supplied to the combustion chamber separately. The mixing and flow characteristics in the combustor were investigated numerically. The global equivalence ratio ($\Phi$), defined using the fuel and air flow rates, was introduced to examine the flow features of the combustor. The mixing of fuel and air inside the combustor could be well understood using the fuel concentration distribution. It was found that the weak recirculating zone was formed upper the fuel-supplying tube in case of ${\Phi}$<1.0. In addition, it was found that small regions that have a negative axial velocity exist near the fuel injection ports. It is assumed that these negative axial velocity regions can stabilize a flame inside the micro cyclone combustor.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.62-69
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• 1998

Spiral tube heat exchangers can find numerous applications in many engineering field. Flow in spital tubes is interest to engineers due to occurrence of secondary flow which enhances the cross-sectional mixing and the heat transfer rate. In the present study, an incompressible viscous 3-D flow in spiral tubes with rectangular cross-section of various torsion rate and Reynolds number is studied by using a finite volume method. It is shown that the axial velocity profile is affected by the secondary flow motion. Because there is some difference from correlation proposed by Hur et al., a lot of analysis and arrangement of experimental results are needed. This study showed the results of variation of hydrodynamic entry length for torsion and Re numbers.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.811-813
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• 2008

To see the effect of magnesium on adhesion to natural zeolites, a series of batch tests were performed in this research. Mixed bacteria were sampled from the digestion tank at a local sewage treatment plant in Seoul. Magnesium-zeolites were synthesized by mixing natural zeolites with 0.096 M, 0.24 M, and 0.48 M of MgCl2 solution. For comparison, manganese and trivalent ferric zeolites were also prepared. Two grams of 0.2 mm $\sim$ 0.3 mm sized zeolites(non-treated, Mg, Mn and Fe(III) treated zeolites) and 20 mL of water were mixed in a Corex 25 mL tube. Five milliliters of culture solution including bacteria was added to the tube. The tubes were equilibrated in a shaking incubator at mesophilic temperature $(30{\pm}2^{\circ}C)$. The bacterial concentrations were measured with a Microluminometer (New Horizons 3550i) and total organic carbon (TOC) spectrophotometer (Multi NC-3100).