Jeong-Hwan Heo

Visualization of Natural Convection Heat Transfer on Horizontal Cylinder Using the Copper Electroplating System

Natural convection heat transfer phenomena on a horizontal cylinder have been studied experimentally in order to investigate the applicability of analogy experimental methodology using a copper electroplating system and to visualize the local heat transfer rates depending on the angular position and the diameter of the horizontal cylinder. In the copper electroplating system, the copper ion produced at the anode moves by convection and diffusion to the cathode and reduces at the cathode, representing the heat transfer. By using aluminum cathode with a distinguishable color, the amount of copper plated could visualize the amount of heat transferred depending on the angular position of the cylinder. The diameter of the cylinder is varied from 0.01m to 0.15m, which correspond to Rayleigh numbers in the range of 1.73×10 7

Natural Convection Heat Transfer on Inclined Plates

Natural convection heat transfers on inclined flat plates were measured for Grashof numbers of 8.06×10 7 and 3.45×10 9 by using a copper sulfate electroplating system. The inclinations of the plates were varied from upward-facing horizontal to downward-facing horizontal. Test results for the downward-facing plate agree well with the existing theory that the Nusselt number can be calculated by replacing gravitational acceleration, g with g cosθ in the heat transfer correlation for the vertical plate. The natural convection flows for the upward-facing plate follow two distinct flow regimes: boundary layer regime and flow separation regime. The copper plating pattern for the upward-facing plates clearly reveals the flow separation points.

A Calculation of the Cosmic Radiation Dose of a Semiconductor in a Geostationary Orbit Satellite Depending on the Shield Thickness

Cosmic ray is composed of nuclear particles moving at a light speed. The cosmic ray affects the performance and the reliability of semiconductor devices by ionizing the semiconductor material. In this study, the radiation effects of protons, electrons, and photons, which compose the cosmic ray, on the GOS(Geostationary Orbit Satellite) were evaluated using the Monte-Carlo N-Particle code. The GOS was chosen due to the comparatively long exposure to the cosmic ray as it stays in the geostationary orbit more than 10 years. As the absorbed dose of semiconductor from electrons is much larger than those of protons, photons, and the secondary radiation, most of the radiation exposure of the semiconductors in the GOS results from that of electrons. When we compare the calculated absorbed dose with the radio-resistance of semiconductor, the Intel 486 of the Intel company is not suitable for the GOS applications due to its low radio-resistance. However RH3000-20 of MIPS and Motorola 602/603e can be applied to the Satellite when the aluminium shield is thicker than 3 mm.

Effect of Horizontal Pitch-to-Diameter Ratio on the Natural-Convection Heat Transfer of Two Staggered Cylinders

This study measured the natural-convection heat transfer of two vertically staggered cylinders with varying vertical pitch-to-diameter (/D) and horizontal pitch-to-diameter (/D) ratios. The measured heat-transfer rates for the lower cylinder agreed well with the existing heat-transfer correlations for a single cylinder. At the smallest /D, the rising plume from the lower cylinder provides the upper cylinder with a preheated flow, and the heat-transfer rates of the upper cylinder decrease, but increase very sensitively with /D. However, at the largest /D, the velocity effect dominates, and the heat-transfer rates of the upper cylinder are larger than that of a single cylinder, and decrease less sensitively with /D. Even if /D is increased, the heat-transfer rate of the upper cylinder is higher than that of the lower cylinder because of the chimney and side flow effects. This work expanded the flow ranges to turbulent flows. The cupric acid-copper sulfate () electroplating system was adopted for the measurements of the mass-transfer rates instead of the heat-transfer experiments based on the analogy concept. The measurements were made by varying /D (1.02-5) and /D (0-2) in both laminar and turbulent flows. The Rayleigh number ranged from to , and the Prandtl number was 2,014.

Effect of Adiabatic Sidewalls on Natural Convection in a Rectangular Cavity

In this study, we investigated the effects of adiabatic walls on natural convection in various rectangular cavities experimentally and numerically. Heat transfer rates were measured for cavities with and without adiabatic sidewalls by varying Grashof number from 1.53 × 10 7 to 1.01 × 10 10 . Some typical test results were successfully simulated using FLUENT. In the case of very narrow cavities, where the adiabatic walls were very close to each other, it was difficult to perform experiments; therefore, FLUENT simulations were performed. The existing heat transfer correlations for rectangular cavities were well predicted by the experimental and numerical results. As expected, the effects of adiabatic walls were restricted to the very narrow region near the walls. This study was carried out during the development of an analogy experimental method in which heat-transfer systems are replaced with mass-transfer systems using copper sulfate electroplating systems. The results of this study provide theoretical background of handling adiabatic walls during the design of test facilities.