• Journal of Mechanical Science and Technology
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• v.19 no.6
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• pp.1378-1389
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• 2005

This work provides the fundamental knowledge of energy transport characteristics during very short-pulse laser heating of semiconductors from a microscopic viewpoint. Based on the self-consistent hydrodynamic equations, in-situ interactions between carriers, optical phonons, and acoustic phonons are simulated to figure out energy transport mechanism during ultrafast pulse laser heating of a silicon substrate through the detailed information on the time and spatial evolutions of each temperature for carriers, longitudinal optical (LO) phonons, acoustic phonons. It is found that nonequilibrium between LO phonons and acoustic phonons should be considered for ultrafast pulse laser heating problem, two-peak structures become apparently present for the subpicosecond pulses because of the Auger heating. A substantial increase in carrier temperature is observed for lasers with a few picosecond pulse duration, whereas the temperature rise of acoustic and phonon temperatures is relatively small with decreasing laser pulse widths. A slight lagging behavior is observed due to the differences in relaxation times and heat capacities between two different phonons. Moreover, the laser fluence has a significant effect on the decaying rate of the Auger recombination.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.210-211
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• 2018

In this study, the ultrasonic pulse velocity of the concrete cooled to room temperature after heating and the concrete during heating were evaluated. Also, the ultrasonic pulse velocity and mechanical properties of concrete were compared. As a result, the ultrasonic pulse velocity decreased when the concrete degraded during heating, and the ultrasonic pulse velocity of the cooled concrete decreased significantly. Which is consistent with the deterioration of mechanical properties of concrete.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.167-175
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• 2007

A predictive pulse control strategy as a means of improving the energy efficiency of radiant floor heating systems is explored. Experiments at the apartment with floor heating system are conducted to assess and compare the energy performance of the predictive pulse control strategy with an existing conventional control strategy. The Results showed that new suggested PPCM( Predictive Pulse Control Method) was available to decrease the gap of $1{\sim}1.5^{\circ}C$ between maximum and minimum indoor temperature of each rooms. Therefore PPCM method was favor to radiant floor heating system which have a delay time of 10-20 minutes for heat transfer by floor layers.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.1978-1987
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• 2014

Power requirement to the induction heating system varies during the heating process. A closed loop control is required to have a smooth control over the power. In this work, a constant frequency pulse density modulation based power tracking control scheme for domestic induction heating system is developed using the Fuzzy Logic Controller. In the conventional power modulation schemes, the switching losses increase with the change in the load. The proposed pulse density modulation scheme maintains minimum switching losses for the entire load range. This scheme is implemented for the class-D series resonant inverter system. Fuzzy logic controller based power tracking control scheme is developed for domestic induction heating power supply for various power settings. The open loop and closed loop simulation studies are done using the MATLAB/Simulink simulation tool. The control logic is implemented in hardware using the PIC16F877A microcontroller. Fuzzy controller tracks the set power by changing the pulse density of the gate pulses applied to the inverter. The results obtained are used to know the effectiveness of the fuzzy logic controller to achieve the set power.

• International Journal of Air-Conditioning and Refrigeration
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• v.10 no.1
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• pp.1-9
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• 2002

Effects of temperature coefficients fur dielectric constants on transient reflectances and thermal responses have been investigated for a metal(gold) thin-film during ultrashort pulse laser heating. Heating processes are simulated using the conventional conduction model(parabolic one-step, POS), the parabolic tow-step model(PTS), the hyperbolic two-step model(HTS). Results fro the HTS model are very similar to those from the PTS model, since the laser heating time in this study is considerably greater than the electron relaxation time. PTS and HTS models, however, result in completely different temperature profiles from those obtained by the POS model due to slow electron-lattice interactions compared to laser pulse duration. Transient reflectances are directly estimated from the linear relationship between electron temperature and complex dielectric constants, while conventional approaches assume that the change in reflectances is proportional to that in temperatuer. Reflectances at the front surface vary considerably for various dielectric constants, while those at the rear surface remain unchanged relatively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.34 no.2
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• pp.136-141
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• 2021

Heating cables, widely used in office buildings, factories, streets and railways, deteriorate in electrical insulation during operation. The insulation deterioration of heating cables leads to electric discharges that can cause electrical fires. With this background, this paper dealt with a condition monitoring technique for heating cables by the analysis of discharge signals to prevent electrical fires. Insulation deterioration was simulated using an arc generator specified in UL1699 under AC operation, and the characteristic and propagation of discharge signals were analyzed on a 100 meter-long heating cable. Discharge signals produced by insulation deterioration were detected as a voltage pulse because they are as small as a few mV and they are attenuated through propagation path. The frequency spectrum of discharge signals mainly existed in the range from 70 kHz to 110 kHz, and the maximum attenuation of the signal was 84.8% at 100 meters away from the discharge point. Based on the experimental results, a monitoring device, which is composed of a high pass filter with the cut-off frequency of 70 kHz, a comparator, a wave shaper and a microprocessor, was designed and fabricated. Also, an algorithm was designed to discriminate the discharge signal in the presence of noise, compared with the pulse repetition period and the number of pulse counts per 100ms. In the experiment, the result showed that the prototype monitoring device could detect and discriminate the discharge signals produced at every discharge point on a heating cable.

• Applied Microscopy
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• v.48 no.4
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• pp.128-129
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• 2018

Soft ferromagnetic materials are utilized for various electromagnetic devices such as magnetic recording heads and magnetic shielding. In situ observation of magnetic microstructures and domain wall motions are prerequisite for understanding and improving their magnetic properties. In this work, by the Fresnel (out-of-focus) method of Lorentz microscopy, we observe the domain wall motions of polycrystalline Ni/Ti thin film layers triggered by single-shot laser pulse. Random motions of domain walls were visualized at every single pulse.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2482-2487
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• 2007

Numerical simulations are conducted for the analysis of a thermal mass air flow sensor with periodic heating pulses on silicon-nitride ($Si_3N_4$) thin membrane structure. This study aims to find the locations of temperature sensors on the thin membrane and the heating pulse conditions, that the higher sensitivity can be achieved, for the development of a MEMS fabricated mass air flow sensor which is driven in periodic heating pulse. The simulations, thus, focus on the membrane temperature profile according to variation of the flow velocity, heating duration time and imposed power. The flow velocity of the simulations is ranging from 3 m/s to 35 m/s, heating duration time from 1 ms to 3 ms and imposed power from 50 mW to 90 mW. The corresponding Reynolds numbers vary from 1000 to 10000.

• Journal of the Korean Ceramic Society
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• v.43 no.4 s.287
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• pp.259-263
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• 2006

The applicability of UPT (Ultrasound Pulse Thermography) for real-time defect detection of the ceramic heating plate is described. The ceramic heating plate with superior insulation and high radiation is used to control the water temperature in underwater environment. The underwater temperature control system can be damaged owing to the short circuit, which resulted from the defect of the ceramic heating plate. A high power ultrasonic energy with pulse duration of 280 ms was injected into the ceramic heating plate in the vertical direction. The ultrasound excited vibration energy sent into the component propagate inside the sample until they were converted to the heat in the vicinity of the defect. Therefore, an injection of the ultrasound pulse wave which results in heat generation, turns the defect into a local thermal wave transmitter. Its local emission is monitored and recorded via the thermal infrared camera at the surface which is processed by image recording system. Measurements were Performed on 4 kinds of samples, composed of 3 intact plates and the defect plate. The observed thermal image revealed two area of crack in the defective ceramic heating plate.

• The Transactions of the Korean Institute of Power Electronics
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• v.5 no.2
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• pp.192-199
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• 2000

This paper describes a Phase-Shift Pulse Modulation(PSPM) and Frequency Trad이ng Pulse Modulation(FTPM) s series resonant high-frequency inverter using IGBT for the power control of high-frequency induction heating u using Neuro-Fuzzy, which is practically applied for 20kHz~500kHz induction-heating and melting power supply in i indust껴aJ fields. The adaptive frequency tracking based on the PSPM(phase-shifting pulse modulation) r regulation scherne is presented in or$\tau$ler to l11lmmlZe svvitching losses. The trially-produced breadboards using N Neuro Fuzzy controller are successfully demonstrated cUld cliscussed.