Ho-Young KWAK

Prof. Dr.  Ho-Young Kwak (Emeritus Professor, Chung-Ang University – South Korea)

Ho-Young Kwak received B.S. from Seoul National University in 1971 and M.A. in plasma physics and Ph. D. in mechanical engineering from the University of Texas at Austin, USA in 1978 and 1981, respectively. He joined ME faculty, Chung-Ang University, Korea in 1981 and served 35 years and is currently emeritus professor there. His research interests are in bubble nucleation and dynamics, sonoluminescence phenomena, and exergy and thermoeconomic analysis for thermal systems. He is a permanent member of Korean Academy of Science and Technology.


TOPIC: Characteristics and Applications of Sonoluminescence Phenomena

Sonoluminescence (SL) is the light emission associated with the catastrophic bubble collapse of micro bubble (5~8 μm in radius) oscillating under ultrasound of frequency, 5 kHz ~ 40 kHz. The light emission from a single bubble (SBSL) in water is characterized by picosecond flashes of continuous spectrum with no major peaks and the bubble wall acceleration exceeds 1011 g at the moment of the collapse. The temperature and pressure at the collapse exceed 10000 K and 10000 atm, respectively. However, the exact mechanism of the light emission characterized by picosecond flashes of continuous spectrum has not been identified, whether it is of thermal blackbody and/or bremsstrahlung radiation origin. SL characteristics from a single bubble such as pulse shape, spectrum radiance from micro and submicron bubbles in water and a new paradigm of SL, which displays alternating pattern of on/off luminescence pulse in sulfuric acid solutions will be discussed with our hydrodynamic model. Our hydrodynamic model is just solving the conservation equations such as mass, momentum and energy equations for the gas inside the bubble and for the liquid outside the bubble wall analytically.