Gyeonghwan Lee

Study on the Thermal and Flow Characteristics on the Periodically Arranged Semi-Circular Ribs in a Rectangular Channel

The article investigates turbulent flow characteristics and heat transfer enhancement on periodically arranged semicircular ribs fitted in a rectangular channel. The channel was fabricated as the aspect ratio of AR 5, rib height to hydraulic diameter ratio was 0.07, and rib height to channel height ratio was set as e/H 0.117 for various rib pitch to rib height ratios between 8 and 14. In order to predict realistic phenomena of heat transfer and flow characteristics near the wall, shear stress transport k-ω turbulence and v2-f turbulence models were chosen. The results of numerical analysis show turbulent flow characteristics, heat transfer enhancement, and the effect of friction as observed experimentally. The results shows that turbulent kinetic energy (k) is closely related to diffusion of recirculation flow, and results from v2-f turbulence model simulation are in agreement with experimental values.

A Study on Gas Pressure Fluctuation Characteristics inside the Snubber and Pipe of Hydrogen

Hydrogen fuel cell is a developing technology that allows great amount of electrical power to be obtained using a source of hydrogen gas. It is a proven environment-friendly potential future fuel. During compression of hydrogen gas in reciprocating compressor, pressure fluctuation is built up. The pressure fluctuation and its reduction by the snubber are studied in this experiment. For different motor frequencies, the input and output pressure amplitude varies from 0.228 kPa–2.081 kPa and 0.095 kPa–0.898 kPa. The pressure magnitudes are 101.451–105.172 kPa and 101.388–102.565 kPa for input and output of the snubber, respectively. The acryl snubber reduces0.796 kPa (57.31%) pressure amplitude on average with restoring its high pressure. Detail information about the pressure including the critical pressure zone inside the tube like snubber part and the whole system can be obtained by CFD.