• Journal of the Korean Institute of Gas
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• v.16 no.6
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• pp.136-142
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• 2012

Thermodynamic equations for the electric power and temperature in a turbo expander generator (TEG) using pressure energy in a natural gas line are derived. From the equations, it was shown that dominant factor is not the pressure difference but the pressure ratio. The high energy level in the inlet of TEG can be made from nearly no expense of electric energy input, which means TEG can be treated as one of newly available clean energy source. If a post heating method is chosen to heat up expanded natural gas, the usage of cold energy is possible without a refrigeration cycle. The combined TEG and refrigeration system enhances economic benefit much more.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.8
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• pp.1073-1082
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• 1998

When thermal diffusivity is measured by laser flash method, the thermal diffusivity call be calculated front the assumption of the uniformly heated whole surface of the specimen. It has been known that the approximate 5% error is made by the non-uniform energy distribution on the specimen surface of laser pulse heat source. In this study, to obtain the highly-uniformed laser beam, which has both the low non-uniform heating error from non-uniform laser beam and the energy loss, research was carried out on no transmitting loss by optical fiber and high repetitions. In addition, heating error and thermal diffusivity were measured as the measuring positions were varied and compared with the results using the uniform and the non-uniform laser beams. In addition, dole to using the uniformalized laser beam, the whole surface of the specimen was heated uniformly and as a result, it was the thought that this was very effective to reduce the variations of the errors of the thermal diffusivity as the measuring positions were varied. It can be obtained that when the thermal diffusivity of POCO-AXM-5Q1 of SRM in NBS was measured with both the uniform and the non-uniform laser beams, the dispersion error of the former was from 2 to 2.5%, which was more improved than that of the latter.

• Korea-Australia Rheology Journal
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• v.19 no.4
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• pp.201-209
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• 2007

The present paper is concerned with non-isothermal spherical Couette flow of Oldroyd-B fluid in the annular region between two concentric spheres. The inner sphere rotates with a uniform angular velocity while the outer sphere is kept at rest. Moreover, the two spherical boundaries are maintained at fixed temperature values. Hence, the fluid is effect by two heat sources; namely, the viscous heating and the temperature gradient between the two spheres. The viscoelasticity of the fluid is assumed to dominate the inertia such that the latter can be neglected. An approximate analytical solution of the energy and momentum equations is obtained through the expansion of the dynamical fields in power series of Nahme number. The analysis show that, the temperature variation due to the external source appears in the zero order solution and its effect extends to the fluid velocity distribution up to present second order. Viscous heating contributes in the first and second order solutions. In contrast to isothermal case, a first order axial velocity and a second order stream function fields has been appeared. Moreover, at higher orders the temperature distribution depends on the gap width between the two spheres. Finally, there exist a thermal distribution of positive and negative values depend on their positions in the domain region between the two spheres.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.273-275
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• 2005

Active thermography is being used since several years for remote non-destructive testing. It provides thermal images for remote detection and imaging of damages. Also, it is based on propagation and reflection of thermal waves which are launched from the surface into the inspected component by absorption of modulated radiation. For energy deposition, it use external heat sources (e.g., halogen lamp or convective heating) or internal heat generation (e.g., microwaves, eddy current, or elastic wave). Among the external heat sources, the ultrasound is generally used for energy deposition because of defect selective heating up. The heat source generating a thermal wave is provided by the defect itself due to the attenuation of amplitude modulated ultrasound. A defect causes locally enhanced losses and consequently selective heating up. Therefore amplitude modulation of the injected ultrasonic wave turns a defect into a thermal wave transmitter whose signal is detected at the surface by thermal infrared camera. This way ultrasound thermography(UT) allows for selective defect detection which enhances the probability of defect detection in the presence of complicated intact structures. In this paper the applicability of UT for fast defect detection is described. Examples are presented showing the detection of defects in PCB material. Measurements were performed on various kinds of typical defects in PCB materials (both Cu metal and non-metal epoxy). The obtained thermal image reveals area of defect in row of thick epoxy material and PCB.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.3
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• pp.168-172
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• 2013

A preliminary performance test of a 30RT 2-stage screw heat pump was carried out in order to develop a high performance large-scale unutilized energy source heat pump system, which will be used for district heating and cooling. In this study, two issues of the system operating control were investigated. The first issue is the mode switching control from 1-stage to 2-stage. A stable 2-stage heating operation is guaranteed, only if the load-side water inlet temperature is over a certain value, where the 1-stage heating operation should be done first from a cold start. The second issue is oil level control. An oil shortage problem in the low stage compressor, which depends on the degree of suction superheat, was solved by a proper oil level control scheme.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.67 no.2
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• pp.82-89
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• 2018

This paper presents a novel prototype of dual mode control based phase shift ZVS PWM high frequency load resonant inverter with lossless snubber capacitors in addition to a single active auxiliary resonant snubber for electromagnetic induction heating(IH) foam metal based consumer fluid dual packs(DPA) heater. The operating principle in steady state and unique features of this voltage source soft switching high frequency inverter circuit topology are described in this paper. The lossless snubber and auxiliary active resonant snubber assisted constant frequency phase shift ZVS PWM high frequency load resonant inverter employing IGBT power modules actually is capable of achieving zero voltage soft commutation over a widely specified power regulation range from full power to low power. The steady state operating performances of this dual mode phase shift PWM series load resonant high frequency inverter are evaluated and discussed on the basis of simulation and experimental results for induction heated foam metal heater which is designed for compact and high efficient moving fluid heating appliance in the consumer pipeline systems.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.354-354
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• 2011

ZnO 나노와이어는 밴드 갭이 3.37 ev로 큰 밴드 갭을 갖는 물질이며 엑시톤 결합에너지가 60 meV로 GaN(25 meV)같은 다른 반도체보다 매우 크다. 또한 밴드갭 에너지가 큰 GaN, SiC와 같은 반도체에 비해서 화학적, 열적 안정성이 크며 낮은 온도에서 성장이 가능하다는 장점이 있다. 본 연구에서는 pre-heating process를 이용하여 1차원 구조인 ZnO nanowire를 수열합성법으로 합성하였다. 실험방법으로는 E2K glass 기판위에 AZO40 nm를 증착후, 시드층으로 이용하여 ZnO nanowire를 성장하였다. precusor 전구체에는 ZN(NO3)2 ${\cdot}$ 6H2O와 Capping agent으로의 역할을 위해 PEI와 OH-source 공급을 위한 Ammonium chloride를 첨가하여 합성하였고, 그에 따른 ZnO nanowire의 morphology 및 aspect ratio를 조절하고자 하였다. 마지막으로 ZnO 나노와이어의 구조적, 광학적 특성 평가를 하기위해 XRD, FE-SEM, PL 등을 이용하여 측정 하였고, 향후 나노발전기, 태양전지 등 여러 광학기기 등에 전극재료로서 응용 가능성에 대해 알아보고자 하였다.

• Journal of the Korean Society of Industry Convergence
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• v.10 no.1
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• pp.21-26
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• 2007

As DDI or GDI engine discharges very low heat due to its high thermal efficiency, the heat source is not enough for heating the passenger compartment in cold climate condition. To remedy the heating problem, the conventional HFC-134a automotive air-conditioning system has been attempted to run as a heat pump mode. Futhermore, an auxiliary electric heater of new type was equipped to the heat pump air-conditioning loop as a new approach. Hence, a proto-type heat pump air conditioner has been made and tested to investigate the feasibility of the HFC-134a automobile air-conditioning system that could be worked as a heat pump. The experiment results showed that the sufficient heating capacity could be obtained by adding a heat pump with an new electric type auxiliary heater into the conventional heat core in low temperature condition.

• Journal of The Korean Astronomical Society
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• v.29 no.2
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• pp.107-117
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• 1996

We have studied the star forming activities and dust properties of Lynds 1251, a dark cloud located at relatively high galactic latitude. Eleven IRAS point sources identified toward Lynds 1251 are discussed. Estimate of stellar masses, and far-infrared lumnosities of the young stars associated with two prominent IRAS point sources imply that these are T-Tauri stars with masses smaller than $0.3 M_\bigodot$. The low dust temperature of 27 K and low ratio of FIR emission to hydrogen column density are probably due to the lack of internal heating sources. Presumably two low mass young stars do not have enough energy to heat up the dust and gas associated. The dust heating is dominated by the interstellar heating source, and the weaker interstellar radiation field can explain the exceptionally low dust temperatures found in Lynds 1251. The estimated dust mass of Lynds 1251 is just $\~1M_\bigodot$, or about 1/1000 of gas mass, which implies that there must be a substantial amount of colder dust. The infrared flux at $100{\mu}m$ is matching well with $^{13}CO$ peak temperature, while the $^{12}CO$ integrated intensity is matching with the boundary of dust emission. Overall, the dust properties of Lynds 1251 is similar to those of normal dark clouds even though it does have star forming activities.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.2
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• pp.158-162
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• 2006

Micro gas turbine (MGT) has received attention recently as a small-scale distributed power source. Due to many advantages such as their small size, low maintenance cost and minimal vibrations during operation, they are expected to become widespread in a wide range of applications. The exhaust heat emitted by the MGT is in the form of an exhaust gas that is about $270^{\circ}C$ which is an extremely clean gas. Korea Gas Corporation (KOGAS) has researched performance characteristics of a cogeneration system combining 28kW class MGT and 13 USRT class absorption hot and chilled water generator in the local condition. The present results of this study can be summarized as follows: (1) in heating mode, the total efficiency of cogen. system is about $65\%$ and heating capacity is 33kW at 25kW MGP power (2) in cooling mode, COP is about 0.6 at 22kW MGT power.