• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.2
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• pp.478-483
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• 2017

This paper investigated experimentally the performance of cooling systems using thermoelectric and piezoelectric modules for local heating and temperature control, such as a handheld electronic devices. The temperature distribution of the cooling region using thermoelectric modules was measured when the piezoelectric module was and was not with a frequency of 80Hz and 110Hz. The coefficients of performance were also calculated by the temperature results, and the thermo-flow phenomena in the cold region was visualized under the same conditions. The results of the temperature distribution measurements and the coefficient of performance showed that the cooling performance of the cooling system using thermoelectric modules can be improved by operating the piezoelectric module. In addition, when the piezoelectric module was operated based on the result of visualization in the cold region, which was formed by thermoelectric modules, the performance thermoelectric cooling was improved by the thermo-flow formed in the entire cold region as the forced convection of vibration was generated on the local cold region by the piezoelectric module.

• Journal of Convergence for Information Technology
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• v.11 no.2
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• pp.90-97
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• 2021

In this study, a Bi2Te3 thermoelectric generator (TEG) was fabricated to convert unused thermal energy into useful electrical energy. For the performance test, a dedicated experiment device consisting of a heating block operating with cartridge heaters and a cooling block through which a refrigerant flows was constructed. A 3×3 array of thermocouples was mounted on the heating block and the cooling block, respectively, to derive the temperature fields and heat transfer rate onto both sides of the TEG. Experiments were conducted for a total of 9 temperature differences, obtaining V-I and P-R curves. The results of 7 variables including Seebeck coefficients that have a major effect on performance were presented as a function of the temperature difference. The feasibility of the energy recovery performance of the developed TEG was verified from the maximum power output of 7.5W and conversion efficiency of 11.3%.

• Journal of Bio-Environment Control
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• v.27 no.4
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• pp.294-301
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• 2018

In winter, thermal screens are widely used to reduce heat loss from greenhouse to save energy. Unfortunately, not much data are available to the farmer to compare thermal screens while selecting the one that meets their specific requirements. Thus, there is a need to investigate the thermal performance of thermal screens. To address this issue, the Building Energy Simulation (BES) model of a hot box was used to calculate the overall heat transfer coefficient (U-value) of the thermal screens. To validate the model, computed and experimental U-values of single-and double-layered polyethylene (PE) material were compared. This validated model was used to predict the U-values of the selected thermal screens under defined weather conditions. We quantified the U-values of each selected material and significant changes in their U-values were noted in response to different weather conditions. Notably, the thermal properties of the tested screens were taken from the previous literature to calculate U-values using the BES model. The U-values of the thermal screens can help researchers and farmers evaluate their screens and make pre-design decisions that suit their investment capabilities.

• Journal of Energy Engineering
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• v.24 no.1
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• pp.42-50
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• 2015

To evaluate the heat removal capability of a condenser tube in the PCCS of an advanced nuclear power plant, a steam condensation experiment in the presence of noncondensable gas on a vertical tube is performed. The average heat transfer coefficient is measured on a vertical tube of 40 mm in O.D. and 1.0 m in length. The experiments covers the pressures of 2-4 bar, and the mass fraction of air ranges from 0.1 up to 0.7. From the experimental results, the effects of the total pressure and the concentration of air on the condensation heat transfer coefficient are investigated. The measured data are compared with the predictions by Uchida's and Tagami's correlations, and it is revealed that these models underestimate the condensation heat transfer coefficient of the steam-air mixture.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.934-939
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• 2012

In this study, the performance validation of a PAO-AIR heat exchanger developed for the ECS(Environmental Control System) of a UAV(Unmanned Aerial Vehicle) has been carried out. The performance goals of a PAO-AIR heat exchanger were established by the system schematic analysis. And a heat exchanger to be met the ECS performance was developed by a detailed design and a precision manufacture. Using the developed heat exchanger, the experiment about pressure loss and effectiveness, overall heat transfer coefficient to prove the developed PAO-AIR heat exchanger performance in various conditions as well as a design point of heat exchanger was performed and the experimental results were analyzed. As the experimental results, the performance and characteristic of a PAO-AIR heat exchanger developed for the ECS of a UAV were analyzed and the development suitability was proved.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.8
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• pp.961-966
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• 2013

A coupled governing equation of thermoelectric materials can be converted into an uncoupled form to predict the effective Seebeck coefficient of thermoelectric composites, where modified Eshelby model is adopted. The predicted results by the present approach for serial- and parallel-connected composites and composite with spherical inclusions are compared with theoretical and experimental results from literatures to be justified. It is shown that the predictions by the theoretical approaches coincide exactly and show in good agreement with the experiments.

• Journal of Energy Engineering
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• v.15 no.1 s.45
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• pp.28-34
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• 2006

The convective heat transfer on the outer surface of tube arrays perpendicular to the flow direction was experimentally investigated. The test sections which include the aligned and staggered arrangements were made and the local heat transfer coefficients on the outer surface of the tube were measured after the Hour has been fully developed. The results showed that the local heat transfer coefficients of the staggered arrangement, which has transverse pitch of 0.075 m and longitudinal pitch of 0.08 m, were about 15% greater than that of the aligned arrangement. Also, the overall mom Nusselt number of the former was greater thu that of the latter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.5
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• pp.713-723
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• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• Journal of Energy Engineering
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• v.9 no.3
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• pp.202-211
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• 2000

본 연구는 다양한 각도를 가지는 와이어코일을 사용하여 관내 단상 열전달 촉진 및 압력강하 특성 실험을 수행하였다. 작동유체는 순수 물과 에틸렌글리콜을 체적비율로 50% 혼합하여 사용하였으며, 시험부 관지름은 11mm와 13.88mm이고, 시험부 길이는 760mm를 사용하였다. 평활관과 와이어코일을 삽입한 열전달촉진관에 대한 관내 열전달계수와 마찰계수는 실험에서 측정한 온도, 유량, 압력강하 값을 기초로 구하였다. 와이어코일에 대한 거친표면해석을 수행하였으며, 그 결과를 거칠기 래이놀즈수에 대한 운동량전송 거칠기함수와 열전달 거칠기함수로 표현하였으며 이에 대한 상관식을 제시하였다. 이 상관식들은 거칠기 레이놀즈수, 코일 각도, 프란틀수의 함수로 표현하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.253-253
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• 2015

최근 세계적으로 대체 에너지는 중요한 이슈가 되고 있으며 특히 열전 재료는 유망한 에너지 기술로서 주목 받고 있다. 특히 고 직접화 전자 소자의 발열 문제를 해결하기 위해, 소형화와 정밀 온도 제어가 가능한 박막형 열전 소자에 대한 관심이 크다. 박막형 열전소자 중 산화물 반도체계에 대한 연구가 활발히 진행되고 있으며, 이러한 산화물 반도체계 중 In2O3는 BiTe, PbTe 등의 기존의 재료에 비해 독성이 낮을 뿐만 아니라 고온에서 열적 안정성이 우수하여 고온에서 적용 불가능한 금속계 열전 재료의 한계를 극복할 수 있다는 장점을 가진다. 좋은 성능의 열전 재료는 높은 전기 전도도 및 제백 계수 그리고 낮은 열전도도 특성을 가져야 한다. 비정질 구조를 가지는 박막 열전 재료는 격자에 의한 열 전도도가 낮기 때문에 결정질 구조와 비교하여 전체 열 전도도 값이 낮을 것으로 기대된다. 이러한 특성을 바탕으로 본 연구에서는 비정질 구조를 갖는 ZnO와 SnO2를 동시에 첨가한 In2O3 박막의 전기적 특성과 열전 특성에 관한 연구를 하였다.