• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.31 no.4
• /
• pp.335-340
• /
• 2007

A new correlation between the Nusselt number based on modified heat transfer coefficient and Reynold number based on droplet-flow-rate was developed for the experimental data. The modified heat transfer coefficient was defined as ratio of wall heat flux to droplet subcooling. In the previous reports, the local heat flux of spray cooling in the film boiling region was experimentally investigated for the water spray region of $D_{max} = 0.0007{\sim}0.03m^3/(m^2s)$ . In the region near the stagnation point of spray flow, a new heat transfer correlation is recommended which shows good predictions for the water spray region of $D_x{\le}0.01m^3/(m^2s)$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.2
• /
• pp.741-751
• /
• 1996

The coupled conduction and convection heat transfer from the protruding heat source in a vertical channel is numerically investigated. Conjugate solution of the two-dimensional energy equation is obtained for the incompressible air flow over the rectangular block with local heat source. It was found that several recirculation zones and separation bubble near the block were related to Re and Gr. And the results show that fractions of the heat transfer through each of the block face, maximum temperature of the block and the relative effect of each parameter on the maximum temperature and heat transfer.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.6 no.3
• /
• pp.211-221
• /
• 1982

Numerical analysis has been made on the heat transfer of two dimensional turbulent channel with a slat type blockage. Especially the effects of the height of slat and Reynolds number on the heat transfer characteristics of channel wall have been investigated. The methods of accelerating the convergence of the numerical solution of governing differential equation have been also examined. Line-by-line iterative method shows higher convergence rate than point-by-point iterative method for solution of both momentum equation and energy equation. The results show that the ratio of heat transfer coefficient of the wall near the blockage to that of the fully developed flow increase with increasing the ratio of blockage to channel height and decreasing the Reynolds number. These trends of variation of heat transfer coefficient with respect to the height of slat and Reynolds number agree with those of Sparrow's experiment on the pipe flow with slat type blockage.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.436-441
• /
• 2003

The present study investigates heat/mass transfer characteristics in rotating two-pass ducts of three different aspect ratios with 90-ribbed surfaces. The results show that the flows generated by the 180-turn, rib turbulators, and duct rotation. The curvature of the 180-turn produces Dean vortices causing high heat/mass transfer in the turning region and in the upstream region of the second-pass. The rib turbulators disturb the main flow by producing reattachment and separation near the ribbed surfaces, and increase heat/mass transfer in the region between the ribs. As the rotation number increases, the heat/mass transfer discrepancy between the leading and the trailing surfaces become larger.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.193-198
• /
• 2003

A gas turbine blade has an internal cooling passage equipped with ribs, which can be modeled as a ribbed channel. We have studied a flow inside a ribbed channel using large eddy simulaton (LES) with a dynamic subgrid-scale model. The simulation results are compared with the experimental ones. The turbulence intensity and local heat transfer near the rib have not been well captured by the conventional Reynolds averaged Navier-Stokes simulation (RANS). However, these variables obtained by the present LES agree well with those from experiments. From the instantaneous velocity and temperature fields, we explain the mechanisms responsible for the local peaks in the heat transfer distribution along the channel wall. We have also investigated the effect of rotation on the flow and heat transfer in the ribbed channel.

• 유체기계공업학회:학술대회논문집
• /
• 2005.12a
• /
• pp.173-177
• /
• 2005

The heat/mass transfer characteristics on the plane tip surface of a high-turning first-stage turbine rotor blade has been investigated by employing the naphthalene sublimation technique. The heat/mass transfer coefficient is measured for four tip clearance height-to-chord ratios of h/c = 1.0%, 2.0%, 3.0%, and 4% at the Reynolds number of $2.09{\times}105$. The result shows that at lower h/c, there exists a strong flow separation/re-attachment process, which results in severe thermal load along the pressure-side comer. As h/c increases, the re-attachment is occurred further downstream of the pressure-side comer with lower thermal load. At higher h/c, a pair of vortices on the tip surface near the leading edge are found along the pressure-side and suction-side comers, and the pressure-side tip vortex have significant influence even on the mid-chord local heat transfer.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
• /
• 1996.04a
• /
• pp.121-131
• /
• 1996

Recently, circulating liquid fluidized bed heat exchangers are widely used in a number of places - chemical, process, food concentration, waste water treatment facilities, etc. In a circulating heat exchanger, solid particles circulate with the liquid, thereby increase the heat transfer and reduce the fouling potential of the heat exchanger. In this study, glass beads were circulated through a vertical tube. The pressure loss and the heat transfer coefficient were measured. At low flow velocities, glass beads enhanced the heat transfer considerably. The enhancement increased as the volume fraction of the glass beads increased. It also increased as the particle diameter increased. The pressure loss showed a similar trend. From the observed particle behavior near tube wall, a possible explanation of the trend is provided.

• Journal of Power Electronics
• /
• v.11 no.3
• /
• pp.256-263
• /
• 2011

This paper utilizes free oscillation and energy injection principles to generate and control the high frequency current in the primary track of a contactless power transfer system. Here the primary power inverter maintains natural resonance while ensuring near constant current magnitude in the primary track as required for multiple independent loads. Such energy injection controllers exhibit low switching frequency and achieve ZCS (Zero Current Switching) by detecting the high frequency current, thus the switching stress, power losses and EMI of the inverter are low. An example full bridge topology is investigated for a contactless power transfer system with multiple pickups. Theoretical analysis, simulation and experimental results show that the proposed system has a fast and smooth start-up transient response. The output track current is fully controllable with a sufficiently good waveform for contactless power transfer applications.

• Journal of Photoscience
• /
• v.6 no.3
• /
• pp.117-121
• /
• 1999

Photoinduced electron transfer of C60 has been studied by the laser photolysis measuring the transient absorption bands in near-IR region. The electron transfer aromatic amines via the triplet state of C60 is confirmed by the decay of the transient absorption bands of the triplet state of C60 and the rise of the anion radical of C60 and the cation radicals of amines. The rate and efficiency of electron transfer are strongly affected by the donor ability of amines and polarity of solvents. Back electron-transfer kinetics is also strongly affected by the solvent polarity.

• Journal of Consumption Culture
• /
• v.15 no.2
• /
• pp.213-247
• /
• 2012

The purpose of this study was to analyze the economic structures of low-income households, and to provide the policy suggestions for their economic well-being. The data for this study was from the 2009 year of the Korea Welfare Panel Survey (KOWEPS). The results are as follows: As for income structure, the low-income households had lower amounts in earned income, business and side-work income, and property income, but a higher amount in transfer income. They had a lower amount in private transfer income, but a higher amount in public transfer income. They had the highest rate of transfer income, showing that the rate of public transfer income was higher than that of private transfer income, and the government assistance was the highest rate in public transfer income. The households in extreme poverty had the lowest amounts in earned income, financial income, private transfer income, but the highest amount in public transfer income. The households in poverty had the lowest amount in transfer income. The households in extreme poverty, poverty and near poverty showed the highest rate in transfer income. As for asset structure, the low-income households had a lower amount in every type of assets. They showed the highest rate in total debt, and had a higher rate in housing asset, but lower rates in real-estate asset, financial asset and other asset. The households in extreme poverty had a lower amount in every type of assets than the households in near poverty. Three types of the low-income households showed the highest rate in housing asset, but the households in extreme poverty was the highest among them. As for expenditure structure, the low-income households had lower amounts in all of the expenditure items. They showed the highest rate in food expenditure, the second highest in other consumption expenditure. The households in extreme poverty showed lower amounts in almost all of the expenditure items than the households in near poverty, but the households in extreme poverty showed a higher amount in monthly rent than the households in neat poverty. Three types of the low-income households showed the highest rate in food expenditure. The expenditure rates of food, monthly rent and light·heat·water for households in extreme poverty were higher than those for the households in near poverty.