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112 results on '"Rhi, Seok"'

27. Application of the Analogy between Momentum and Heat Flux in Turbulent Flow of a Straight Tube to a Spiral Tube.

Author

Lee, Kye-Bock, Song, Eui-Hyeok, Lee, Ji-Su, and Rhi, Seok-Ho

Subjects
HEAT transfer in turbulent flow, TURBULENT flow, HEAT flux, FLUX flow, TURBULENCE, SUPERCONDUCTING coils
Abstract

A theory-based prediction method was used to estimate the friction factor and heat transfer rate in the turbulent flow of a helically coiled tube. The secondary flow produced by a centrifugal force improves heat and mass transfer; therefore, spiral coil pipes are widely used in a variety of industrial applications. The law of the wall and the Reynolds analogy, which states that momentum transfer in a turbulent flow is equivalent to heat transfer, were used in this theoretical method. The logarithmic law was used to characterize the velocity profile in the turbulence-dominated region, and the local wall shear stress variation throughout the circumference of the helical tube wall was considered. The friction factor and heat transfer in the turbulent flow of the helically coiled tube were accurately predicted by the model. Using the Reynolds analogy, the local Nusselt number in the circumferential direction of the helical tube wall was determined. The effect of decreasing local heat transfer within the tube while increasing heat transfer outside the tube was quantified. The analogy between the momentum flux and the heat flux in the turbulent flow of the straight tube was also proven to be applicable to the spiral tube. [ABSTRACT FROM AUTHOR]

Published
2022
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29. Heat conduction and thermal expansion of copper–graphite composite as a heat sink.

Author

Lee, SeungHyun, Son, Sung‐hun, Kim, JinSun, Yesuraj, Johnbosco, Kim, Kibum, and Rhi, Seok‐Ho

Subjects
HEAT sinks, THERMAL expansion, HEAT conduction, INSULATED gate bipolar transistors, ENTHALPY, GRAPHITE composites, INDIUM gallium zinc oxide, TRANSISTORS
Abstract

Summary: This study presents the evaluation of the heat transfer characteristics and mechanical deformation of new composite material heat sinks using experimental and computational approaches. First, we synthesized a composite material composed of copper (Cu) and graphite (C) with 60 wt% Cu, with higher thermal conductivity and a lower thermal expansion coefficient than pure Cu and aluminum. The composite material was used to fabricate a heat sink integrated with an insulated‐gate bipolar mode transistor (IGBT) module for enhanced heat dissipation from the IGBT. Compared with the pure Cu heat sink, the composite heat sink decreases the average temperature of the IGBT module by approximately 22 K. It also decreases the total deformation of the heat sink caused by thermal expansion of the material by 78% and the equivalent stress by 25.2%. This study introduces a way to use Cu‐C composite materials in many potential applications, such as heat sinks integrated with IGBT inverters. [ABSTRACT FROM AUTHOR]

Published
2022
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44. A cooling system using two-phase closed thermosyphon for telecommunication MCM: Experiment and simulation

Author

Rhi, Seok-Ho.

Subjects
Engineering, Electronics and Electrical
Abstract

The present study is concerned with a cooling system for multichip modules (MCM) in telecommunication systems. Due to the higher device operation speed and higher packaging density, the resulting heat flux is known to be 1 to 2 W/cm$\sp2$, which is one or two orders of magnitude higher than those of conventional systems, and beyond the capacity of high performance air cooling systems. A cooling system which can deal with a high heat flux of up to 4 W/cm$\sp2$ is the one that employs two-phase closed thermosyphons, (i.e., wickless heat pipes) and the present study presents the results of experimental and simulation study on a cooling system using two-phase closed thermosynphons for the cooling of MCM.

Published
2009
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45. An experimental and analytical (simulation) study on two-phase loop thermosyphons: Very small to very large systems

Author

Rhi, Seok-Ho.

Subjects
Engineering, Mechanical
Abstract

An experimental and analytical (numerical) study was carried out on the fluid flow, heat transfer and instabilities for five (5) small, medium and large scale two-phase loop thermosyphons. The five two-phase closed loop thermosyphons (TLTs) specially designed and constructed for the present study are one small scale loop (SSL: 5.4 mm ID & 1.2 m x 0.5 m; 150 W), two medium scale loops (MSL I: 0.095 mm ID & 0.423 m in width; 60 W and MSL II: 0.0202 m ID & 3 m x 2 m; 1,500 W) and two large scale loops (LSL I: 0.0202 m ID & 1.8 m x 2 m; 7,500 W and LSI II: 0.0202 m ID & 2.208 m x 10 m; 100,000 W). Experimentally, various parameters which would affect the operation of a TLT such as the total system temperature difference, saturation temperature of the working fluid in the system, coolant velocity over the condenser section, coolant temperature, the size of the condenser section, the amount of a working fluid in the system, the choice of working fluids, pressure drop, effectiveness and instability were investigated. Two simulation methods based on thermal resistance net work, lumped and sectorial, are presented. In the simplified model called here as the Lumped method, the evaporator section is dealt as one lumped boiling section, i.e., one empirical equation for a forced convective boiling. However, this model could not simulate the TLTs adequately because of its simplistic approach to cover all the heat transfer modes of the different flow regimes involved in the system by one equation. In the Sectorial method, all possible phenomena which would occur in the evaporator section due to the two-phase boiling process are considered in detail. Flow regimes (bubbly, slug, churn, annular and annular mist etc.), the flow transition between flow regimes and other two-phase parameters involved in two-phase flows are carefully analyzed. The results of two different simulation methods are compared with experimental results and the limitation of the computer simulation for such two-phase heat transfer systems as the TTLs studied is critically discussed. To complement the simulation study for five different scale of TTLs, an analysis was also made on the instability of the SSL as a separate study. (Abstract shortened by UMI.)

Published
2009
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