• Title/Summary/Keyword: thermal losses

Search Result 244, Processing Time 0.033 seconds

Effect of Ondol on Physiological Responses during Sleeping (IV) (온돌환경이 수면시의 생리반응에 미치는 영향 (제4보))

  • Lee, Soon-Won;Kweon, Soo-Ae
    • Korean Journal of Human Ecology
    • /
    • v.7 no.1
    • /
    • pp.183-195
    • /
    • 1998
  • The purpose of this study is to investigate the effect of Ondol on the bedclimate, microclimate and physiological responses of occupants. Four healthy female subjects slept for seven hours in thermal environment of detached house and apartment respectively. Their bedclimate, microclimate, skin temperature, weight loss of body, weight of bedcloth and sleepwear, body movement and subjective sensation were measureed for this study. The results were as follows; The differences of bedclimate, microclimate, skin temperature were significant according to season and residence styles. The occupants of the detached house showed higher temperature and humidity inside quilt and clothes than those of the apartment did on apartment environment. The occupants of the detached house showed higher weight losses of body, heavier weights of quilt than those of the apartment did on apartment environment in the spring, autumn and winter, lower weight losses of mattress in the autumn and winter. The occupants of the detached house moved more than those of the apartment on apartment environment when sleeping. The occupants of the detached house felt higher thermal sensation and lower humidity sensation than those of the apartment did. The occupants of the detached house felt more comfortable than those of the apartment on detached house environment, while the occupants of the apartment felt more comfortable than those of the detached house on apartment environment. The thermal environments of the apartment and the detached house had an effect on the bedclimates, microclimates of occupants and therefore the physiological responses such as skin temperature, rectal temperature, weight loss of body, perspiration and subjective sensation are different during sleeping according to their residential styles on the same environment.

  • PDF

Performance Prediction of Heat Regenerators with using Spheres: Relation between Heat Transfer and Pressure Drop (구형 축열체를 사용한 축열기의 성능예측: 압력손실과 열전달의 관계)

  • 조한창;조길원;이용국
    • Journal of Energy Engineering
    • /
    • v.12 no.1
    • /
    • pp.35-41
    • /
    • 2003
  • Heat regenerator occupied by regenerative materials improves thermal efficiency of regenerative combustion system through the recovery of heat of exhaust gaset. By using one-dimensional two-phase fluid dynamics model, the unsteady thermal flow of heat regenerator with spherical particles, was numerically simulated to evaluate the heat transfer and pressure drop and thereby to suggest the parameter for designing heat regenerator. It takes about 7 hours for the steady state of the flow field in regenerator, in which heat absorption of regenerative particle is concurrent with the same magnitude of heat desorption. The regenerative particle experiences small temperature fluctuation below 10 K during the reversing process. The performance of thermal flow in heat regenerator varies with inlet velocity of exhaust gas and air, configuration of regenerator (cross-sectional area and length) and diameter of regenerative particle. As the gas velocity increases, the heat transfer between gas and particle enhances and with the increase the pressure losses. As particle diameter decreases, the air is preheated higher and the exhaust gases are cooled more with the increase of pressure losses.

EMI Analysis of Soft Switching Inverter on High Power AC Motor Drive (대전력 교류전동기 구동용 소프트 스위칭 인버터의 EMI 해석)

  • 권순걸
    • Journal of the Institute of Convergence Signal Processing
    • /
    • v.3 no.3
    • /
    • pp.76-81
    • /
    • 2002
  • In high power motor drive system, the hard-switching topology produces severs switching losses and EMI noises. Also the inverter switching frequency is thus limited because of excessive loss and thermal handling problem. The primary purpose of the proposed works on the induction motor drive system is to develop an advanced soft-switching inverter topology that is most suitable for high power induction motor drive applications. To make the optimal selection EMI comparison of the switching losses presented. To verify the proposed design procedure, detailed simulation analysis with theoretical and experimental approaches have been done using laboratory prototype.

  • PDF

Optimization of Powder Core Inductors of Buck-Boost Converters for Hybrid Electric Vehicles

  • You, Bong-Gi;Kim, Jong-Soo;Lee, Byoung-Kuk;Choi, Gwang-Bo;Yoo, Dong-Wook
    • Journal of Electrical Engineering and Technology
    • /
    • v.6 no.4
    • /
    • pp.527-534
    • /
    • 2011
  • In the present paper, the characteristics of Mega-Flux$^{(R)}$, JNEX-Core$^{(R)}$, amorphous and ferrite cores are compared to the inductor of buck-boost converters for Hybrid Electric Vehicles. Core losses are analyzed at the condition of 10 kHz sine wave excitations, and permeability fluctuations vs. temperature and magnetizing force will be analyzed and discussed. Under the specifications of the buck-boost converter for 20 kW THS-II, the power inductor will be designed with Mega-Flux$^{(R)}$ and JNEX-Core$^{(R)}$, and informative simulation results will be provided with respect to dc bias characteristics, core and copper losses.

Acceleration in Diffusive-thermal Instability by Heat Losses (열손실에 의한 확산-열 불안정성의 가속화)

  • Park, June-Sung;Park, Jeong;Kim, Jeong-Soo
    • Journal of the Korean Society of Combustion
    • /
    • v.12 no.2
    • /
    • pp.34-41
    • /
    • 2007
  • The dynamic behaviors of counterflow non-premixed flame have been investigated experimentally to study effects of heat losses and Lewis number on edge flame oscillation, which result from the advancing and retreating edge flame motion of outer flame edge at low strain rate flame. For low strain rate flame, lateral conduction heat loss in addition to radiation heat loss could be more remarkable than the others. Oscillatory instabilities appear at fuel Lewis number greater than unity. But excessive lateral conduction heat loss causes edge flame instability even at fuel Lewis number less than unity. The excessive heat loss caused by the smaller burner diameter in which the flame length is an indicator of lateral conduction heat loss extends the region of flame oscillation and accelerates oscillatory instability in comparison to the previous study with the burner diameter of 26mm. Extinction behaviors quite different from the previous study are also addressed.

  • PDF

Acceleration in Diffusive-thermal Instability by Heat Losses (열손실에 의한 확산-열 불안정성의 가속화)

  • Park, June-Sung;Park, Jeong;Lee, Kee-Man;Kim, Jeong-Soo;Kim, Sung-Cho
    • 한국연소학회:학술대회논문집
    • /
    • 2007.05a
    • /
    • pp.145-152
    • /
    • 2007
  • The dynamic behaviors of counterflow non-premixed flame have been investigated experimentally to study effects of heat losses on edge flame oscillation, which result from the advancing and retreating edge flame motion of outer flame edge at low strain rate flame. For low strain rate flame, lateral conduction heat loss in addition to radiation heat loss could be more remarkable than the others. Oscillatory instabilities appear at fuel Lewis number greater than unity. But excessive lateral conduction heat loss causes edge flame instability even at fuel Lewis number less than unity. The dramatic change of burner diameters in which flame length is an indicator of lateral conduction heat loss was applied to examine the onset condition of edge flame oscillation and flame oscillation modes. Especially, extinction behaviors quite different from the previous study were observed.

  • PDF

Review on Magnetic Components: Design & Consideration in VHF Circuit Applications

  • Yahaya, Nor Zaihar;Raethar, Mumtaj Begam Kassim;Awan, Mohammad
    • Journal of Power Electronics
    • /
    • v.9 no.2
    • /
    • pp.180-187
    • /
    • 2009
  • When converters operate in megahertz range, the passive components and magnetic devices generate high losses. However, the eddy current issues and choices of magnetic cores significantly affect on the design stage. Apart from that, the components' reduction, miniaturization technique and frequency scaling are required as well as improvement in thermal capability, integration technique, circuit topologies and PCB layout optimization. In transformer design, the winding and core losses give great attention to the design stage. From simulation work, it is found that E-25066 material manufactured by AVX could be the most suitable core for high frequency transformer design. By employing planar geometry topology, the material can generate significant power loss savings of more than 67% compared to other materials studied in this work. Furthermore, young researchers can use this information to develop new approaches based on concepts, issues and methodology in the design of magnetic components for high frequency applications.

Design and Experimental Investigation of High-Speed Three-Phase Induction Motor for Turbo Blower

  • Kim, Young-Kwan;Lee, Ju
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
    • /
    • v.22 no.3
    • /
    • pp.59-65
    • /
    • 2008
  • High-speed electrical motor has been studied for several applications, i.e. for direct-drive systems of centrifugal compressors and turbo blowers. This paper deals with a design consideration of electromagnetic, mechanical and thermal limits of high-speed induction motor for turbo blower. Basic design concept of high-speed motor was proposed. As the motor is to be operated at high speed, the losses are quite different from conventional low-speed machines. Especially, the increases of rotor eddy current and friction losses could lead to an overheated motor. So, we suggested a special cooling system to reduce temperature rise. And, based upon this design concept, the prototype induction motor(37[kW], 45,000[rpm]) for high-speed turbo blower was designed and 2-D electromagnetic field analysis was implemented. Finally, criteria to evaluate the characteristics of high-speed induction motor have been proposed and tested.

Comparative Analysis of Efficiency and Power Density of Single-Phase and 3-Level Boost Converters for PV System (태양광 시스템용 단상 및 3-레벨 부스트 컨버터의 효율 및 전력밀도 비교 분석)

  • Kim, Chul-Min;Kim, Jong-Soo
    • The Transactions of the Korean Institute of Power Electronics
    • /
    • v.25 no.2
    • /
    • pp.127-132
    • /
    • 2020
  • In this study, single-phase and three-level boost converters applied to the photovoltaic system were compared and analyzed in terms of efficiency and power density according to the input voltage and load conditions. For accurate analysis of efficiency, the losses in each device of the single-phase and three-level boost converters were derived using mathematical equations and simulations by using the PSIM thermal module. Then, the losses were compared with the efficiency confirmed through the actual experiments. Results confirmed that the efficiency and power density can be improved by applying the three-level boost converter to the system according to the selection of the switching frequency.

Influence of Thermal Cycle Test of a 22.9 kV High Temperature Superconducting Cable System (22.9 kV 초전도케이블 시스템의 Thermal Cycle Test 영향)

  • Sohn, S.H.;Lim, J.H.;Yang, H.S.;Ryoo, H.S.;Choi, H.O.;Sung, T.H.;Kim, D.L.;Hwang, S.D.
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
    • /
    • 2007.11a
    • /
    • pp.242-242
    • /
    • 2007
  • To verify the applicability of High Temperature Superconducting (HTS) cable system into the real grid, the HTS cable system with the specification of 22.9 kV, 1250 A, 100 m long was installed in the second quarter of 2006, and the long term field test has been in progress at the KEPCO's Gochang power testing yard. Apart from the conventional power cable, HTS cable system requires sufficient thermo-mechanical strength to endure a large temperature difference. To date, the KEPCO HTS cable system was cooled down and warmed to the room temperature several times to investigate the influence of thermal cycles experimentally. Dielectric properties, critical current dependance and heat losses were evaluated at each step of thermal cycle. The test results showed that thermal cycle did not induce the degradation of dielectric properties, and the critical current decreased to 5 % of the initial value.

  • PDF