• Journal of the Korean Society of Propulsion Engineers
• /
• v.26 no.2
• /
• pp.1-11
• /
• 2022

The heat transfer coefficient on the wall, which is used as a boundary condition in the thermal analysis of general contract-divergent supersonic nozzles, affects the thermal analysis accuracy of the entire nozzle. Accordingly, many methods of deriving a heat transfer coefficient have been proposed. In this study, the accuracy of each method was compared. For this purpose, the heat transfer coefficients were calculated through theoretical-based analogy methods, semi-empirical equations, and CFD simulations for the previously performed heat transfer experiment with an isothermal wall and compared with the experimental results. The results show that the Prandtl-Taylor analogy methods and the CFD results with the k-ω SST turbulence model were in good agreement with the experimental results. Furthermore, the Modified Bartz empirical formula showed an overall over-prediction tendency.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.10a
• /
• pp.95-98
• /
• 2003

In woven or knitted preforms for composites, the yams are often twisted for avoiding damage due to the contact with the textile machine elements. When the preforms of twisted yams are used in carbon/carbon composites, the thermal conductivity of the composites varies depending upon the degree of the yarn twist. This paper presents a thermal conductivity model of spun yarn composites. The thermal-electrical analogy and the averaging technique have been adopted in this analysis. The model prediction has been correlated with experimental results in order to confirm the model predictability. Parametric study has also been conducted to examine the effect of the yam twist on the thermal conductivity of spun yarn composites.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.05a
• /
• pp.238-243
• /
• 2001

This paper predicted the thermal conductivity of spatially reinforced composites(SRC) by applying the volume averaging method and the thermal resistance method. The former method employs existing micro-mechanical theories and conventional transformation rules to constitute relations for the unit cells of the composites and the latter one uses the analogy between the diffusion of heat and electrical charge. To verify the theoretical prediction, the thermal conductivity of 4-D(dimensional) SRC was examined experimentally. The comparison of the numerical results with those measured by the experiment showed good agreement.

• Composites Research
• /
• v.30 no.1
• /
• pp.26-34
• /
• 2017

This research presents studies on an improved method to predict the thermal conductivity of woven fabric composites, the effects of geometric structures of woven fabric composites on thermal conductivity, and structural optimization to improve the thermal conductivity using a genetic algorithm. The geometric structures of woven fabric composites were constructed numerically using the information generated on waviness, thickness, and width of fill and warp tows. Thermal conductivities of the composites were obtained using a thermal-electrical analogy. In the genetic algorithm, the chromosome string consisted of thickness and width of the fill and warp tows, and the objective function was the maximum thermal conductivity of woven fabric composites. The results confirmed that an improved method to predict the thermal conductivity was built successfully, and the inter-tow gap effect on the composite's thermal conductivity was analyzed suggesting that thermal conductivity of woven fabric composites was reduced as the gap between tows increased. For structural design, optimized structures for improving the thermal conductivity were analyzed and proposed. Generally, axial thermal conductivity of the fiber tow contributed more to thermal conductivity of woven fabric composites than transverse thermal conductivity of the tows.

• Journal of the Society of Naval Architects of Korea
• /
• v.43 no.2 s.146
• /
• pp.236-245
• /
• 2006

The ventilation performance for the various venting duct arrays has been experimentally compared in the scaled model of the container hold. Most container ships have the ventilation duct system to remove effectively the condensing heat released from container refrigerator. The existing duct system is vertically installed and basically has the number of duct as many as the columns of reefer container stack. In this study, to make up for the weak points having stagnantly hot legions in the centered area of container hold for the present system, the horizontal upward jotting duct system was proposed and proved by temperature rising tests on the scaled model. In this paper, the expected flow regimes and the thermal and hydrodynamic analogies as well as the measured temperature distributions in a hold for various duct types and heat released rates are deeply discussed.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.8 no.1
• /
• pp.28-34
• /
• 1999

According to the development of tool material and the improvement of machinability of cutting material like aluminium alloy, the higher spindle speed is needed. However, the higher speed causes the heat generation of bearings, the deformation of spindle unit parts, and the rotational accuracy of spindle to be worse. Therefore, it is essential to analyze and control the heat generation and the thermal behavior of spindle unit in order to have higher speed and better rotational accuracy. This paper shows the analogy between the analyzation of heat generation and thermal behavior of high speed spindle system by finite element method and the test results of actual temperature rise through running test, and shows the necessity of cooling the spindle and inner ring side of bearings for the thermal balance of high speed spindle system.

• Composites Research
• /
• v.14 no.3
• /
• pp.57-68
• /
• 2001

This paper predicted the thermal conductivity of spatially reinforced composites(SRC) by applying the volume averaging method and the thermal resistance method. The former method employs existing micro-mechanical theories and conventional transformation rules to obtain the constitutive relations for the unit cells of the composites and the latter one uses the analogy between the diffusion of heat and electrical charge. To verify the theoretical predictions, the thermal conductivity of 4-D(dimensional) SRC was examined experimentally. The comparison of the numerical results with those measured by the experiment showed good agreement.

• Journal of Electrical Engineering and Technology
• /
• v.12 no.2
• /
• pp.576-585
• /
• 2017

Dynamic thermal rating (DTR) of overhead transmission lines can provide a significant increase in transmission capacity compared to the static thermal rating. However, the DTR are usually estimated by the traditional thermal model of overhead conductor that is highly dependent on the solar, wind speed and wind direction data. Consequently, the estimated DTR would be unreliable and the safety of transmission lines would be reduced when the solar and wind sensors are out of function. To address this issue, this study proposed a novel thermal model of overhead conductor based on the thermal-electric analogy theory and Markov chain. Using this thermal model, the random variation of conductor temperature can be simulated with any specific current level and ambient temperature, even if the solar and wind sensors are out of function or uninstalled. On this basis, an estimation method was proposed to determine the DTR in the form of probability. The laboratory experiments prove that the proposed method can estimate the DTR reliably without measured solar and wind data.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1995.10a
• /
• pp.377-382
• /
• 1995

An evaluation method of spacer grid thermal mixing performance in rod bundles is suggested based on hydraulic tests in a single phase flow. Heat transfer correlation was derived by the analogy between momentum and heat transfer. Three of major factors, such as blockage ratio of spacer grid, convective flow swirling, and turbulent intensity, were found to be significantly influential to the spacer grid thermal mixing performance. Local heat transfer near spacer grid was predicted for the hydraulic test of 6 ${\times}$ 6 rod bundles with neighboring different spacer grids.

• Journal of Electrical Engineering and Technology
• /
• v.6 no.2
• /
• pp.270-274
• /
• 2011

This paper presents a parameterized simulation program with integrated circuit emphasis (SPICE) model of a two-level microbolometer based on negative-temperature-coefficient thin films, such as vanadium oxide or amorphous silicon. The proposed modeling begins from the electric-thermal analogy and is realized on the SPICE modeling environment. The model consists of parametric components whose parameters are material properties and physical dimensions, and can be used for the fast design study, as well as for the co-design with the readout integrated circuit. The developed model was verified by comparing the obtained results with those from finite element method simulations for three design cases. The thermal conductance and the thermal capacity, key performance parameters of a microbolometer, showed the average difference of only 4.77% and 8.65%, respectively.