• 설비공학논문집
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• 제17권5호
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• pp.496-504
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• 2005

Heat recovery ventilators (HRV) are developed in order to satisfy both energy conservation and the improvement of indoor air quality as an alternative for current natural ventilation systems and local mechanical ventilation systems in kitchens and bathrooms. However, the performance of HRV system and the consequent effect on heating and cooling energy saving have not been sufficiently validated quantitatively in case of the application of HRVs in real residences. In this study, field measurement and computer simulation were conducted in both summer and winter period to assess the performance and validate energy conservation effect of HRVs. Under the Korea weather condition, average total heat recovery efficiency was $27\%$ in summer and $46\%$ in winter. According to the field measurement, HRV system can save the energy by $10\%$ in summer and 15$\%$ in winter. Furthermore, according to the simulation assessment, HRV system can save the energy by $17\%$ in summer and $17\%$ in winter.

• International Journal of Aeronautical and Space Sciences
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• 제9권1호
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• pp.31-41
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• 2008

This paper deals with the energy saving problem of the follower aircraft in the loose leader-follower formation geometry in which the lateral separation between formation members is more than a wingspan of the leader aircraft. This formation geometry offers no drag benefit, but has a strategic advantage. In the case of loose formation flight, the follower aircraft usually consumes more energy than the leader aircraft because the follower aircraft should use more thrust to maintain given formation geometry, especially during the turning phase from the outside of the leader"s flight path or join-up phase. A formation control scheme based on the energy maneuverability is proposed in this paper. To design the proposed control law, the velocity command is designed using feedback linearization for the horizontal formation geometry and then coverts it to the altitude command using the energy equation. Numerical simulation is performed to verify the effectiveness of the proposed controller.

• 한국과학교육학회지
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• 제37권5호
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• pp.799-812
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• 2017

에너지는 매우 복합적인 과학개념으로 많은 국가의 과학 교육과정에서 핵심을 이루는 개념이지만, 교수 학습 과정에서 많은 어려움을 야기하는 개념이기도 하다. 본 연구는 한국, 미국, 영국, 싱가포르의 교육과정을 비교분석하여 향후 교육과정 개정 시 고려해야 하는 에너지 교육과정의 쟁점들을 추출하고자 하였다. 이를 위해 한국의 2015 개정교육과정, 미국의 차세대 과학교육표준(NGSS, Next Generation Science Standards), 영국의 과학 교육과정(National curriculum in England: Science programmes of study), 싱가포르의 과학 교육과정(Science syllabus)에서 에너지를 명시적으로 포함하는 성취기준들을 추출하여, 여섯 가지 개념 요소(에너지 형태, 에너지 자원, 에너지 전달, 에너지 전환, 에너지 보존, 에너지 산일)에 따라 분류하고 비교하였다. 에너지 관련 성취기준이 학교 급별, 학문 영역별, 에너지 개념 요소별로 어떻게 분포하는지 빈도 분석을 실시하였고, 에너지 개념 요소별로 내용 분석을 병행하였다. 그 결과 모든 나라의 교육과정 모두에서 에너지 개념의 중요성을 확인할 수 있었지만, 세부적으로는 강조하고 있는 개념 요소와 개념 요소별 내용에 있어서 상당한 차이를 발견하였다. 그 중 다른 나라와 대비되는 한국 교육과정의 가장 큰 특징은 에너지 개념 요소 중 에너지의 형태와 관련된 성취기준의 빈도가 가장 높다는 점, 특정 물리량에 대응하지 않는 체 포괄적인 의미로 사용되는 에너지 형태를 포함하고 있다는 점, 에너지 전달에 비해 좀 더 어려운 개념 요소인 에너지 전환을 강조하고 있는 점, 에너지 보존의 경우 역학적 상황에만 국한하여 성취기준이 제시되고 있는 점, 에너지 개념과 관련하여 '계'를 도입하지 않고 있는 점 등을 들 수 있다. 이러한 차이가 야기하는 교육과정 개편 상의 쟁점들에 대해서 논의하였다.

• 보존과학회지
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• 제28권3호
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• pp.265-276
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• 2012

석조문화재의 보존 복원 작업에 적용할 수 있는 에폭시 수지의 성능을 개선하기 위해 다양한 성분을 조합하여 경화 거동을 제어할 수 있는 접착 시스템을 연구하였다. 사용된 에폭시 수지 주제는 hydrogenated Bisphenol-A (HBA), 경화제로 속경화형 경화제 FH와 저속 경화제 SH를 구성하였으며, 반응성 희석제는 difunctional polyglycidyl epoxide (DPE), 무기 첨가물은 탈크를 사용하였다. 에폭시 수지와 경화제의 혼합 조건에 따라 경화 시 점도, 온도 및 differental scanning calorimetry(DSC)를 이용하여 경화 동력학을 측정하였고, 기계적 특성을 확인하기 위해 무기 첨가물의 함량에 따른 굴곡강도, 인장강도, 압축전단접착강도를 측정하였다. 연구 결과, 다양한 석조문화재의 보존처리 작업에 맞춰 에폭시 수지 구성물의 성분 조합을 통해 경화 특성을 제어하고, 무기 첨가물의 도입을 통해 기계적 특성을 조절하여 성능 개선 및 작업 효율성을 향상 시킨 새로운 접착 시스템을 개발하였다.

• 천문학회보
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• 제35권1호
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• pp.81.1-81.1
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• 2010

We present a detailed description of the blast-wave modeling technique for a very general class of GRB explosions. Providing a simple method of evaluating the blast energy, we demonstrate that a common approximation of pressure balance for the blast wave violates the energy-conservation law significantly for adiabatic blast waves. We show that the energy-violation problem is successfully resolved by the "mechanical model" that we developed. GRB afterglow lightcurves that are produced by the forward and reverse shock waves of the blast wave are presented.

• Journal of Mechanical Science and Technology
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• 제18권5호
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• pp.838-846
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• 2004

Minimum ignition energies of hydrogen/air and methane/air mixtures have been investigated numerically by solving unsteady one-dimensional conservation equations with detailed chemical kinetic mechanisms. Initial kernel size needed for numerical calculation is a sensitive function of initial pressure of a mixture and should be estimated properly to obtain quantitative agreement with experimental results. A simple macroscopic model to determine minimum ignition energy has been proposed, where the initial kernel size is correlated with the quenching distance of a mixture and evaluated from the quenching distance determined from experiment. The simulation predicts minimum ignition energies of two sample mixtures successfully which are in a good agreement with the experimental data for the ranges of pressure and equivalence ratio.

• International Journal of Air-Conditioning and Refrigeration
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• 제13권3호
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• pp.119-127
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• 2005

Liquid pressure amplifiers have been proposed as an energy saving technology for vapor compression refrigeration systems configured with direct-expansion evaporators. The technology utilizes a refrigerant pump in the high pressure liquid line as a means of maintaining a suitable pressure differential across the expansion valve while lowering condensing pressure to achieve the reduction of compressor energy consumption. Applications have been proposed on systems ranging from small unitary air-conditioning to large supermarket and commercial refrigeration systems. This paper clarifies the role of such a device in a vapor compression refrigeration system. Limitations are presented and discussed. Finally, results of detailed analyses are presented to quantify the energy consumption both with and without a liquid pressure amplifier in a unitary air conditioning system. The estimated energy savings associated with the installation of a liquid pressure amplifier are minimal.

• 설비공학논문집
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• 제22권8호
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• pp.530-537
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• 2010

With the advancement of technology, the density of IT equipment, heat load and power consumption continue to increase in high density internal-load dominated buildings as datacenters. To improve the HVAC system's energy performance and efficiency, there is a need to find methods of using outside air. Through cooling tower control that is based on outside wet-bulb temperature, the water-side economizer made it possible to achieve a maximum energy performance improvement of about 16.6% over the basic chilled water system, whereas the air-side economizer, through control based on outdoor air enthalpy, made it possible to achieve about 42.4% improvement.

• Advances in Energy Research
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• 제6권2호
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• pp.145-160
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• 2019

The world population reaches to about 7.7 billion in 2018 from 6.2 billion in 2000. This much growth in population results in increased energy demand and increased food supply. As the conventional energy sources are limited. These may deplete soon if consumed at this rate. So, the world is switching towards the utilization of non-conventional sources of energy. Energy from sun is the best method as it can not only solve the energy issue but also helps in meeting food demand by conserving it. Greenhouses are made for the purpose of food conservation. Various types of solar dryers are developed by researchers till now and still the effort is being putted to make them more efficient. Hybrid greenhouse is also effort toward utilization of solar energy in more efficient way. The paper presents the heat and mass transfer analysis of hybrid greenhouse solar dryer developed by different researchers till now. The review helps the researcher in understanding the heat and mass transfer taking place inside the hybrid greenhouse and how it can be further improved.

• 대한기계학회논문집A
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• 제21권1호
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• pp.12-21
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• 1997

A model for analysis of the crushing mechanism of thin-walled rectangular tube is presented. The crushing modes of rectangular tubes may be characterized as either compact or noncompact and the model presented only considers compact modes. The unloading process in the crushing are categorized into three different stages where the distinction is based on the ratio of outward to inward fold length. Using the kinematic relations and the energy conservation principle, the instantaneous crush load is derived. An approximate equation that considers the rolling behavior is also given so that the crush load history may be established. The equation is experimentally proved.