• Title, Summary, Keyword: Thermal resistance

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A Study on the Insulation of Thermal Clothing Under Dynamic Air Condition (풍속 존재 시 쾌적보온성 의복의 온열특성에 관한 연구)

  • Song, Min-Kyu;Kwon, Myoung-Sook
    • Journal of the Korean Society of Costume
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    • v.58 no.9
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    • pp.29-37
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    • 2008
  • The purpose of this study was to investigate insulation of thermal clothing under still and dynamic air conditions(with 2.1m/sec air velocity) and decrease of insulation in both conditions, to analyze correlations among them, and to estimate insulation and decrease of insulation using factors, such as fabric insulation, fabric weight, clothing weight, air permeability, and water vapor resistance. A total of 25 kinds of clothing were tested(9 types for suits, 6 types of jacket, 5 types for shirts, and 5 types for trousers). The results of this study were as follows; Thermal resistance of clothing under the dynamic air condition decreased comparing to that of clothing under still air condition in all types of clothing. Decrease in shirts was the biggest(47.5%), followed by suits(39.51%), trousers(37.48%), and jackets(34.49%) in sequence. Thermal resistance of clothing under dynamic air condition showed very high correlation(0.98, p<0.01) with that of clothing under still air condition, followed by thermal resistance of fabric(0.86, p<0.01). Decrease in thermal resistance of clothing showed the highest correlation with air permeability. It didn't show correlation with other factors. Regression analysis showed that fabric thickness would be useful factor for estimating thermal resistance of clothing and air permeability also would be useful factor for estimating decrease in thermal resistance of clothing.

Characterization of Thermal Contact Resistance Doped with Thermal Interface Material (접촉열전도재를 도포한 접촉열저항 특성연구)

  • Bajracharya, Iswor;Ito, Yoshimi;Nakayama, Wataru;Moon, Byeong-Jun;Lee, Sun-Kyu
    • Journal of the Korean Society for Precision Engineering
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    • v.30 no.9
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    • pp.943-950
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    • 2013
  • This paper describes the thermal contact resistance and its effect on the performance of thermal interface material. An ASTM D 5470 based apparatus is used to measure the thermal interface resistance. Bulk thermal conductivity of different interface material is measured and compared with manufacturers' data. Also, the effect of grease void in the contact surface is investigated using the same apparatus. The flat type thermal interface tester is proposed and compared with conventional one to consider the effect of lateral heat flow. The results show that bulk thermal conductivity alone is not the basis to select the interface material because high bulk thermal conductivity interface material can have high thermal contact resistance, and that the center voiding affects the thermal interface resistance seriously. On the aspect of heat flow direction, thermal impedance of the lateral heat flow shows higher than that of the longitudinal heat flow by sixteen percent.

Effects of some factors on the thermal-dissipation characteristics of high-power LED packages

  • Ji, Peng Fei;Moon, Cheol-Hee
    • Journal of Information Display
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    • v.13 no.1
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    • pp.1-6
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    • 2012
  • Decreasing the thermal resistance is the critical issue for high-brightness light-emitting diodes. In this paper, the effects of some design factors, such as chip size (24 and 35 mil), substrate material (AlN and high-temperature co-fired ceramic), and die-attach material (Ag epoxy and PbSn solder), on the thermal-dissipation characteristics were investigated. Using the thermal transient method, the temperature sensitivity parameter, $R_{th}$ (thermal resistance), and junction temperature were estimated. The 35-mil chip showed better thermal dissipation, leading to lower thermal resistance and lower junction temperature, owing to its smaller heat source density compared with that of the 24-mil chip. By adopting an AlN substrate and a PbSn solder, which have higher thermal conductivity, the thermal resistance of the 24-mil chip can be decreased and can be made the same as that of the 35-mil chip.

The Effects of Parka on Subject Wear Sensation as to Thermal Resistance (파카의 보온성에 따른 착용감에 관한 연구)

  • Lee Yoon-Jung;Lee Soon-Won
    • Journal of the Korean Society of Clothing and Textiles
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    • v.13 no.3
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    • pp.295-303
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    • 1989
  • This study is to measure the thermal resistance of 7 types of Parka of different materials with thermal manikin and to compare their effects on physiological responses & subjective wear sensations. Following are the results obtained from the experiments 1) From the thermal manikin experiment, i) As an outer layer, although not significant, water proof fabric was warmer than water proof-vapor permeable fabric. ii) In case of insulating material, down was better for thermal resistance than polyester wadding of the same thickness. Moreover, as the down was thicker, it had more efficiency in thermal resistance. However, the marginal efficiency of thickness was found to be decreasing. 2) From the male-subject experiments, i) Chest temperature, mean skin temperature & microclimate temperature showed the same results on thermal resistance as those of the thermal manikin experiment. ii) Only during rest periods, there was a significant difference among 5 insulating materials in the sense of microclimate humidity. The almost same conclusion was obtained from the above experiments. Even the outer layer did not significantly affect thermal resistance & subjective wear sensation, insulating materials had a significant influence upon them. But in case of 3.5 cm down, it gave less comfortable than that of the thinner. Therefore the optional one for the best comfort & thermal resistance among 7 combinatins is the outer layer of water proff-vapor permeable & insulating material of 2.1 cm down.

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Thermal characteristics of defective carbon nanotube-polymer nanocomposites

  • Unnikrishnan, V.U.;Reddy, J.N.;Banerjee, D.;Rostam-Abadi, F.
    • Interaction and multiscale mechanics
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    • v.1 no.4
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    • pp.397-409
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    • 2008
  • The interfacial thermal resistance of pristine and defective carbon nanotubes (CNTs) embedded in low-density polyethylene matrix is studied in this paper. Interface thermal resistance in nanosystems is one of the most important factors that lead to the large variation in thermal conductivities in literature and the novelty of this paper lies in the estimation of the interfacial thermal resistance for defective nanotubes-systems. Thermal properties of CNT nanostructures are estimated using molecular dynamics (MD) simulations and the simulations were carried out for various temperatures by rescaling the velocities of carbon atoms in the nanotube. This paper also deals with the mesoscale thermal conductivities of composite systems, using effective medium theories by considering the size effect in the form of interfacial thermal resistance and also using the conventional micromechanical methods like Hashin-Shtrikman bounds and Wakashima-Tsukamoto estimates.

The effects of Clothing Materials and Multi-layered Textiles on Thermal Resistance Value (보온력에 미치는 피복재료와 겹침의 영향)

  • 손원교;차옥선
    • Journal of the Korean Home Economics Association
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    • v.37 no.11
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    • pp.157-165
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    • 1999
  • This study was carried out to examine the effect of clothing materials and multi-layered textiles on thermal resistance value. Cotton, polyester, wool, silk, rayon and acetate were selected for the specimens. Thermal resistance value was tested with 2 kinds of methods(thermo labo II and BK type tester). The results were as follows; 1. The effects of clothing materials for thermal resistance value were decreased by adding layers. 2. When the fabrics are measured with multiple layers, the fabric of the lowest thermal resistance value at single layer was showed the highest increasing tendency for all test methods.

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Evaluation of Ground Effective Thermal Properties and Effect of Borehole Thermal Resistance on Performance of Ground Heat Exchanger (지중 유효 열물성 산정 및 지중열교환기 성능에 대한 보어홀 열저항의 영향)

  • Sohn, Byonghu
    • Transactions of the Korea Society of Geothermal Energy Engineers
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    • v.8 no.4
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    • pp.32-40
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    • 2012
  • Geothermal heat pump(GHP) systems use vertical borehole heat exchangers to transfer heat to and from the surrounding ground via a heat carrier fluid that circulates between the borehole and the heat pump. An Important feature associated with design parameters and system performance is the local thermal resistances between the heat carrier flow channels in the borehole and the surrounding ground. This paper deals with the in-situ experimental determination of the effective thermal properties of the ground. The recorded thermal responses together with the line-source theory are used to determine the thermal conductivity and thermal diffusivity, and the steady-state borehole thermal resistance. In addition, this paper compares the experimental borehole resistance with the results from the different empirical and theoretical relations to evaluate this resistance. Further, the performance simulation of a GHP system with vertical borehole heat exchangers was conducted to analyze the effect of the borehole thermal resistance on the system performance.

A Study on Assessment Method of Crack Resistance and Thermal Shock Resistance in Hardfacing for Hot Forging Die (열간단조 금형 육성용접부 내균열성 및 내열충격성 평가방법에 관한 연구)

  • Cho, Sang-Myung;Kim, Sung-Ho;Jung, Yun-Ho;Baek, Seung-Hui;Jang, Jong-Hun;Park, Chul-Gyu;Woo, Hee-Chul;Jung, Byong-Ho
    • Journal of Welding and Joining
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    • v.28 no.3
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    • pp.79-85
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    • 2010
  • Hardfacing is one of the frequently applying method to increase surface hardness in hot forging die. Recently, hardfacing receives great attention due to it's repair availability and low cost. In hot forging die, crack resistance and thermal shock resistance have been considered as major properties, However there are few studies for the assessment of these properties. So, it is necessary to establish the assessment method for crack resistance and thermal shock resistance in hardfacing for hot forging die. In this study, flux cored arc welding was applied to make hardfacing welds. Three point bending test was carried out to assess hardfacing weld's crack resistance, and high temperature bending test using salt bath was developed for thermal shock resistance. Consequently, it was possible to assess crack resistance and thermal shock resistance of hardfacing welds for hot forging die quantitatively.

Thermal Characteristics of Men's Suit Ensembles (남성용 정장의 온열특성 연구)

  • Song, Min-Kyu;Jeon, Byung-Ik
    • Fashion & Textile Research Journal
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    • v.1 no.3
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    • pp.264-274
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    • 1999
  • The thermal resistance of 60 men's suits for summer and winter was measured to determine their thermal characteristics and physical properties, including air permeability, weight, and thickness of the jackets and trousers consisted of the ensembles were measured to predict the thermal resistance of garments and ensembles. In this study, general physical properties of the men' suit ensembles were determined. In general, thickness and weight of winter ensembles were greater than those of summer ensembles. A factor which could distinguish the difference between summer and winter ensembles was the air permeability. The air permeability of summer ensembles was 3~6 times greater than those of winter ensembles. For the thermal characteristics, the thermal resistance of winter ensembles were higher than those of summer ensembles. When the wind was involved, the thermal resistance of both ensembles decreased up to 30%. In addition, the equations were developed to predict the thermal resistance of the garments and ensembles when there was no air velocity and the thermal resistance of the ensembles with air velocity of 1.2 m/sec. Looking at the equations, thickness, weight, and size of the garments were the definite factors that affect the thermal resistance of the samples.

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Thermal Shock Resistance Property of TaC Added Ti(C,N)-Ni Cermets (TaC 첨가 Ti(C,N)-Ni 서멧의 내열충격 특성)

  • Shin, Soon-Gi
    • Korean Journal of Materials Research
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    • v.24 no.10
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    • pp.526-531
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    • 2014
  • Thermal shock resistance property has recently been considered to be one of the most important basic properties, in the same way that the transverse-rupture property is important for sintered hard materials such as ceramics, cemented carbides, and cermets. Attempts were made to evaluate the thermal shock resistance property of 10 vol% TaC added Ti(C,N)-Ni cermets using the infrared radiation heating method. The method uses a thin circular disk that is heated by infrared rays in the central area with a constant heat flux. The technique makes it possible to evaluate the thermal shock strength (Tss) and thermal shock fracture toughness (Tsf) directly from the electric powder charge and the time of fracture, despite the fact that Tss and Tsf consist of the thermal properties of the material tested. Tsf can be measured for a specimen with an edge notch, while Tss cannot be measured for specimens without such a notch. It was thought, however, that Tsf might depend on the radius of curvature of the edge notch. Using the Tsf data, Tss was calculated using a consideration of the stress concentration. The thermal shock resistance property of 10 vol% TaC added Ti(C,N)-Ni cermet increased with increases in the content of nitrogen and Ni. As a result, it was considered that Tss could be applied to an evaluation of the thermal shock resistance of cermets.