• Solar Energy
• /
• v.10 no.1
• /
• pp.5-13
• /
• 1990

In the present investigation, experiments and numerical analysis during melting process of a phase change material were performed to research heat transfer phenomena generated by means of conduction and natural convection in the vertical tube at inward melting. The phase change material used in the experiments is 99 percent pure n-Docosane paraffin($C_{22}H_{46}$). In the results, it is found that the velocity of phase change interface at the top of tube is faster than at the bottom of tube because of the effect of natural convection, and the distribution of velocity at the liquid region is little affected by the initial temperature of phase change material. The velocity of phase change interface is slower as the initial temperature of phase change material is lower, and the effect of natural convection is larger as the aspect ratio of tube is larger. In tendency of heat transfer phenomena, the experimental results were well corresponded with numerical results. But there were a little disagrements between the results of experiment and numerical analysis because of the assumption of the constant volumetric expansion coefficient in numerical analysis.

• Journal of radiological science and technology
• /
• v.10 no.1
• /
• pp.75-83
• /
• 1987

The insulating oil used for X-ray tube housing were degraded by X-ray irrdiation, high temperature and high anode voltage for normal operation. This study was measured the conduction current-X-ray dose, heating degradation, time, temperature and electric field characteristics and the dependense of electrode materials and gap length in the X-ray irradiatied insulating oil under of D.C voltage. The obtained results can be summarized as following. 1. The conduction current of X-ray irradiated insulating oil is more about $2.5{\sim}3$ times as large as than that of non x-ray irradiated, and is become saturation phenomena after some degree. 2. The conduction current of many times heating x-ray irradiated insulating oil is more than that of a few times heating. 3. The higher temperature x-ray irradiated insulating oil is increased, the more conduction current, and that is increased about ten times as large as when it's temperatures is increased to $80^{\circ}C\;at\;30^{\circ}C$, twenty five times at $100^{\circ}C$. 4. The dependence of electrode materials is appeared at the low electric field, and the small gap length with Fe > Cu > Al. 5. The low electric field than 3000 v/cm is appeared Ohm's law region, and the high is become saturation region at the I-E characteristics. 6. The larger gap length is become, the more conduction current is increased at the same electric field.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.5 no.4
• /
• pp.35-42
• /
• 1991

Recently, HID lamps have been considered as important in regard to the trend of energy saving, and increasingly and diversely used in various ways. This paper will show the simulating models concerning high-pressure arc discharge system directly applicable for its design and manufacture, and analyze its various characteristics. For warm-up characteristics, the evaporating process of inner atoms is described in terms of second-order differential equation: for the thermal conduction from are axis to discharge wall and outer bulb, its transfer process is introduced according to five first-order differential equations. Under the steady state satisfying LTE, the time-variant characteristics are suggested by means of time-dependent energy balance equation derived from fluid equations, approximation of radiation energy and material functions in the discharge tube. The simulating models concerning these equations are then applied for high-pressure mercury lamp.

• The Transactions of the Korean Institute of Electrical Engineers C
• /
• v.54 no.5
• /
• pp.190-197
• /
• 2005

A reliable and compact pulse power supply using a thyratron and a magnetic pulse compression (MPC) circuit was developed for a metal vapor laser. The life time of the pulse power supply is expected to be much longer than that of a conventional thyratron-discharge type pulse power supply. A thyratron generated a long pulse of its conduction pulse width 500 ns and then it was compressed to less than 80 ns of its output voltage rise time by a three stage MPC circuit. This pulse power supply was applied to a laser plasma tube of 30 mm inner diameter and 1.5 m discharge length. It was operated several hundreds hours without any troubles.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.14 no.6
• /
• pp.1621-1628
• /
• 1990

Numerical solutions are presented for the heat transfer from radiating and convecting fins. Consideration is given to thin, annular fins attached to a tube surface for which the temperature is constant. Fin to fin, fin to base, and fin to environment radiative interactions are considered. It is assumed that the radiating surface is diffuse-gray, the environment is black, and the surrounding fluid is transparent. The radiation terms are formulated by using Poljak's net-radiation methoad. The mathematical description of the simultaneously heat transport by conduction, convection, and radiation leads to a nonlinear integro-differential equation. This has been solved for a wide range of the pertinent physical parameters by using finite difference method and iteration method based on the Newton-Raphson technique. The temperature distributions, heat transfer rates, fin efficiencies, and fin effectivenesses are presented in dimensionless form. The results definitely indicate that the use of fins leads to a significant increase in heat transfer compared with the unfinned tube.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.5
• /
• pp.1301-1309
• /
• 1994

A study of heat transfer and thermophoretic particle deposition has been carried out for the Modified Chemical Vapor Deposition(MCVD) process. A new concept utilizing two torches is suggested to simulate the heating effects from repeated traversing torches. Calculation results for the wall temperatures and deposition efficiency are in good agreement with experimental data. The effects of variable properties are included and heat flux boundary condition is used to simulate the moving torch heating. A conjugate heat transfer which includes heat conduction through solid layer and heat teansfer in a gas in a tube is analyzed. Of particular interests are the effects of torch speeds and solid layer thicknesses on the deposition efficiency, rate and the tapered entry length.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.17 no.2
• /
• pp.101-109
• /
• 2005

The purpose of this study is to investigate the performance of outdoor heat exchanger for heat pump using carbon dioxide. Two types of fin and tube heat exchangers (2 rows for type A and 3 rows for B) are tested. Both heat exchangers have counter-cross flow and 1-circuit arrangement. Test results such as heat transfer rate, pressure drop characteristics and temperature distribution in the heat exchanger are shown with respect to mass flow rate of refrigerant and frontal air velocity For cooling mode, the minimum temperature difference between air and refrigerant of type B is smaller than that of type A by $1^{circ}C$, but the pressure loss of air side is much higher for type B by $29\%$. It is found that a large temperature gradient of carbon dioxide during gas cooling Process Promotes thermal conduction through tube wall and fins which results in degradation of heat transfer performance. For heating mode operation, type B heat exchanger shows higher heat transfer performance compared to type A. However, because pressure loss of refrigerant side of type B is much greater than that of type A, the refrigerant outlet pressure of type B becomes lower than that of type A.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.23 no.4
• /
• pp.338-342
• /
• 2010

Carbon nanotubes (CNTs) have excellent electrical, chemical stability, mechanical and thermal properties. The MWCNT films were investigated as a transparent electrode for the solar cell, OLED, and field-emission display. MWCNT films were fabricated by air spray method, whose process is quite low-costed, using the multi-walled CNTs solution on glass substrates. Moreover, the most stable film was fabricated when the spraying time was 60 sec. The film that was sprayed with the MWCNT dispersion for 60 sec, has 300nm thick. And its electric resistivity, transmittance rate, mobility and carrier concentration are $6{\times}10^{-2}{\Omega}{\cdot}cm$, 50% at ${\lambda}=550mm$, $4.3{\times}10^{-2}cm^2/V{\cdot}s$ and $2.1{\times}10^{21}cm^{-3}$, respectively. Also, absorption energy of MWCNT films show from 3.9 eV to 4.6 eV. Furthermore, we can use MWCNT films fabricated by the spray method for the transparent electrode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1996.05a
• /
• pp.252-255
• /
• 1996

Superconducting current lead is one of the promising applications of the oxide high-Tc superconductors, because they have the advantage of decreasing heat conduction to low temperature region, comparing with a conventional cooper alloy lead. High critical current density is a key factor for the applications such as current lead. (Bi,Pb)$_2$Sr$_2$Ca$_2$Cu$_3$O$\_$x/ high Tc superconductor haute been investigated in terms of critical current density. Bi-2223 superconducting current lead made by CIP and solid state sintering process. Bi-2223 current lead that heat treated at 836$^{\circ}C$ for 240 h in 1/13 P$\_$O$_2$/ had over 150 A/$\textrm{cm}^2$ of critical current density at 77K. We knew that the superconducting properties of tube type current leads were better than rods type of them. And we investigated the relation of Bi-2223 formation and heat treatment condition by XRD and SEM analysis.

• Transactions of Materials Processing
• /
• v.24 no.1
• /
• pp.13-19
• /
• 2015

For an accurate analysis of hot stamping, a coupled simulation with different aspects of the process(i.e. mechanical, thermal, and phase transformation) is needed. However, coupled simulations are time consuming and costly. Therefore, the current study proposes a simplified method focused on the forming for the hot stamping simulation of a coupled torsion beam axle (CTBA) tubular beam. In this simplified method, non-isothermal conditions were assumed and only conduction was considered, since it represents the majority of the heat transfer during hot stamping. In addition, temperature and strain rate effects were also included. Moreover, an isothermal simulation was conducted and compared with a non-isothermal simulation. Finally, the simulations were verified by experiments. In conclusion, the proposed method is shown to be effective for the development of tube-type parts, and it effectively predicts the deformation of the tubular beam during hot stamping.