박재영 교수

We present a new technique for measuring the temperature profiles of visible LED chips by use of a nematic liquid crystal with IR laser illumination. The LEDs studied have a multi-quantum-well InGaN/GaN/sapphire structure. New features in this technique are the use of a high-power IR laser beam as the sensing light and the insertion of a color filter in the optical path to block the high-intensity LED light. For the LEDs measured, the conversion efficiency decreases by 70% when the junction temp

A numerical study is conducted to grasp the flame structure and NO emissions for a wide range of oxy-fuel combustion (covering from air-blown combustion to pure oxygen combustion) and various mole fractions of recirculated CO2 in a CH4−O2/N2/CO2 counterflow diffusion flame. Special concern is given to the difference of the flame structure and NO emissions between air-blown combustion and oxy-fuel combustion w/o recirculated CO2 and is also focused on chemical effects of recirculated CO2. Air-blo

We present an electrical model for quantum-well light-emitting diodes (LEDs) with a current-spreading layer. The LEDs studied have a multiquantum well (MQW) between p-GaN and the n-GaN grown on sapphire. The model consists of a diode connected with a series resistor resulting from the combined resistance of the p-n junction, contacts, and current spreader. Based upon this model, the I-V curve of the diode itself without the series resistance is extracted from the measured LED I-V curve. The mode

The dilution effect of air stream according to agent type on flame structure and NO emission behaviour is numerically simulated with detailed chemistry in CH4/air counterflow diffusion flame. The volume percentage of diluents (H2O, CO2, and N2) in air stream is systematically changed from 0 to 10. The radiative heat loss term, based on an optically thin model, is included to clearly describe the flame structure and NO emission behaviour especially at low strain rates. The effect of dilution of a

In this letter, we present our thermal study results of GaN-based heterojunction field effect transistors (HFETs). In thermal computation, PAMICE code was used to calculate temperatures in a three-dimension (3-D) model. In the thermal measurement, nematic liquid crystal thermography was employed to determine the peak temperature on the surface of the device chip. The calculated and directly measured temperatures agree well. These methods are valuable in predicting the thermal performance of GaN-

Numerical simulation of CO2 addition effects to fuel and oxidizer streams on flame structure has been conducted with detailed chemistry in H2–O2 diffusion flames of a counterflow configuration. An artificial species, which displaces added CO2 in the fuel- and oxidizer-sides and has the same thermochemical, transport, and radiation properties to that of added CO2, is introduced to extract pure chemical effects in flame structure. Chemical effects due to thermal dissociation of added CO2 causes th