• Title, Summary, Keyword: Thermal

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Effects of Noise on Indoor Thermal Sensation and Comfort (소음이 실내 온열감과 온열쾌적감에 미치는 영향)

  • Yang, Wonyoung
    • KIEAE Journal
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    • v.17 no.1
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    • pp.83-89
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    • 2017
  • Purpose: Thermal sensation or thermal comfort was randomly used in many studies which focused on combined effects of thermal and acoustic environments on human perception. However, thermal sensation and thermal comfort are not synonyms. Thermal comfort is more complex human perception on thermal environment than thermal sensation. This study aims to investigate effects of noise on thermal sensation and thermal comfort separately, and also to investigate effects of temperature on acoustic sensation and comfort. Method: Combined thermal and acoustic configurations were simulated in an indoor environmental chamber. Twenty four participants were exposed to two types of noise (fan and babble) with two noise levels (45 dBA and 60 dBA) for an hour in each thermal condition of PMV-1.53, 0.03, 1.53, 1.83, respectively. Temperature sensation, temperature preference, thermal comfort, noisiness, loudness, annoyance, acoustic comfort, indoor environmental comfort were evaluated in each combined environmental condition. Result: Noise did not affected thermal sensation, but thermal comfort significantly. Temperature had an effect on acoustic comfort significantly, but no effect on noisiness and loudness in overall data analysis. More explicit interactions between thermal condition and noise perception showed only with the noise level of 60 dBA. Impacts of both thermal comfort and acoustic comfort on the indoor environmental comfort were analyzed. In adverse thermal environments, thermal comfort had more impact than acoustic comfort on indoor environmental comfort, and in neutral thermal environments, acoustic comfort had more important than thermal comfort.

Effect of Thermal Grease on Thermal Conductivity for Mild Steel and Stainless Steel by ASTM D5470 (ASTM D5470 방법으로 연강과 스테인리스강의 열전도도 측정시 열그리스의 영향)

  • Cho, Young-Wook;Hahn, Byung-Dong;Lee, Ju Ho;Park, Sung Hyuk;Baeg, Ju-Hwan;Cho, Young-Rae
    • Korean Journal of Materials Research
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    • v.29 no.7
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    • pp.443-450
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    • 2019
  • Thermal management is a critical issue for the development of high-performance electronic devices. In this paper, thermal conductivity values of mild steel and stainless steel(STS) are measured by light flash analysis(LFA) and dynamic thermal interface material(DynTIM) Tester. The shapes of samples for thermal property measurement are disc type with a diameter of 12.6 mm. For samples with different thickness, the thermal diffusivity and thermal conductivity are measured by LFA. For identical samples, the thermal resistance($R_{th}$) and thermal conductivity are measured using a DynTIM Tester. The thermal conductivity of samples with different thicknesses, measured by LFA, show similar values in a range of 5 %. However, the thermal conductivity of samples measured by DynTIM Tester show widely scattered values according to the application of thermal grease. When we use the thermal grease to remove air gaps, the thermal conductivity of samples measured by DynTIM Tester is larger than that measured by LFA. But, when we did not use thermal grease, the thermal conductivity of samples measured by DynTIM Tester is smaller than that measured by LFA. For the DynTIM Tester results, we also find that the slope of the graph of thermal resistance vs. thickness is affected by the usage of thermal grease. From this, we are able to conclude that the wide scattering of thermal conductivity for samples measured with the DynTIM Tester is caused by the change of slope in the graph of thermal resistance-thickness.

Thermal Fatigue Life Prediction of Alumina by Finite Difference Model (유한 차분 모델을 이용한 알루미나의 열피로 수명 예측)

  • 이홍림;한봉석
    • Journal of the Korean Ceramic Society
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    • v.30 no.3
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    • pp.229-235
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    • 1993
  • Thermal history and thermal stress of alumina specimen, which occured from thermal shock process, were calculated by finite difference method. Stress intensity factor and crack growth in cyclic thermal fatigue were calculated from single thermal shock temperature history and thermal stress. Cyclic thermal life were estimated by bending strength after cyclic thermal shock under critical thermal shock temperature. Calculated stress intensity factor was compared with real experimental thermal fatigue life of specimen. Fatigue life until critical stress intensity factor and real experimental result were comparable.

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Thermal Analysis of Thermal Printing Head by Numerical Method (수치계산에 의한 열전사 프린팅헤드의 열해석)

  • 조창주;정우남
    • Journal of the Korean Society for Precision Engineering
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    • v.15 no.9
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    • pp.50-55
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    • 1998
  • A thermal printing head is used for heat transcription printing of facsimile or printer. The thermal printing head has multilayered thin films and heaters lined up. Thermal analysis of thermal printing head is important for a design of thermal printing head. Since the heating charateristics of thermal printing head is dependent on the thermal conductivities of multilayerd material, this study made numerical analysis for three dimensional transient heat conduction in mutilayered films by the finite difference method and investigated the effect of various thermal conductivities of thin films. The results of this study will be used to design thermal printing head and select the materials for thermal printing head.

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The thermal impedance spectroscopy on Li-ion batteries using heat-pulse response analysis

  • Barsoukov Evgenij;Jang Jee Hwan;Lee Hosull
    • 한국전기화학회:학술대회논문집
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    • pp.145-161
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    • 2001
  • Novel characterization of thermal properties of a battery has been introduced by defining its frequency-dependent thermal impedance function. Thermal impedance function can be approximated as a thermal impedance spectrum by analyzing experimental temperature transient which is related to the thermal impedance function through Laplace transformation. In order to obtain temperature transient, a process has been devised to generate external heat pulse with heating wire and to measure the response of battery. This process is used to study several commercial Li-ion batteries of cylindrical type. The thermal impedance measurements have been performed using potentionstat/galvanostate controlled digital signal processor, which is more commonly available than flow-meter usually applied for thermal property measurements. Thermal impedance spectra obtained for batteries produced by different manufactures are found to differ considerably. Comparison of spectra at different states of charge indicates independence of thermal impedance on charging state of battery. It is shown that thermal impedance spectrum can be used to obtain simultaneously thermal capacity and thermal conductivity of battery by non-linear complex least-square fit of the spectrum to thermal impedance model. Obtained data is used to simulate a response of the battery to internal heating during discharge. It is found that temperature inside the battery is by one-third larger that on its surface. This observation has to be considered to prevent damage by overheating.

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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.

An Analytical and Experimental Study on the Thermal Shroud Effect to Minimize Thermal Deformation of a High L/D Ratio Cylinder (장축 실린더의 열변형 최소화를 위한 차열관 효과 해석 및 실험 연구)

  • Ahn, Sang-Tae
    • The KSFM Journal of Fluid Machinery
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    • v.10 no.5
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    • pp.54-63
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    • 2007
  • A barrel is a high length-to-diameter ratio cylinder that is influenced by environmental factors such as sunlight, precipitation, wind and clouds. Cross-barrel temperature differences caused by uneven heating or cooling lead to thermal deformation that degrades accuracy. Therefore, a barrel is covered by thermal shrouds to minimize the type of thermal deformation, "fall-of-shot". In this paper, an analytical and experimental study is presented to design the thermal shrouds for a gun barrel and to evaluate the thermal shroud effect. First, an analytical study on the thermal shroud effect to minimize thermal deformation of a gun barrel by sunlight and wind is performed. The coupled analysis of thermal fluid dynamics of the air flow between a barrel and thermal shrouds and thermal stresses of a barrel Is performed to clarify both the thermal shroud effect and the drift in gun muzzle orientation by thermal deformation. Second, experiments are carried out to test and evaluate the thermal shroud effect on the performance of a gun barrel. The drift in gun muzzle orientation against the solar radiation is confirmed by the experiments, and the results well agree with the analytical estimation. Third, three principal design factors that are presumed to have an effect on the performance of the thermal shrouds are also analyzed; sorts of shroud materials, wall-thickness of thermal shrouds, and distance of the gap between a barrel and thermal shrouds.

Investigation of the Thermal Mode-based Thermal Error Prediction for the Multi-heat Sources Model (다중열원모델의 열모드기반 열변위오차 예측)

  • Han, Jun An;Kim, Gyu Ha;Lee, Sun-Kyu
    • Journal of the Korean Society for Precision Engineering
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    • v.30 no.7
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    • pp.754-761
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    • 2013
  • Thermal displacement is an important issue in machine tool systems. During the last several decades, thermal error compensation technology has significantly reduced thermal distortion error; this success has been attributed to the development of a precise, robust thermal error model. A major advantage of using the thermal error model is instant compensation for the control variables during the modeling process. However, successful application of thermal error modeling requires correct determination of the temperature sensor placement. In this paper, a procedure for predicting thermal-mode-based thermal error is introduced. Based on this thermal analysis, temperature sensors were positioned for multiple heat-source models. The performance of the sensors based on thermal-mode error analysis, was compared with conventional methods through simulation and experiments, for the case of a slide table in a transient state. Our results show that for predicting thermal error the proposed thermal model is more accurate than the conventional model.

Thermal Ratchetting of the Conductive Adhesives Joints Subjected to the Thermal Cycles (전도성 접착제의 열경화 응력에 대한 해석)

  • 박주혁;서승호
    • Proceedings of the International Microelectronics And Packaging Society Conference
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    • pp.208-213
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    • 2002
  • When a thermoset conductive adhesive joints are subjected to the thermal cycles, the thermal stresses are developed around the joints. Most of in-plane, hi-axial components of these residual stresses induces large tensile peel stresses and weakens adhesive joints. Also these stresses vary with thermal cycles, and result in thermal fatigue loading and debonding propagation. In this study, the thermal ratchetting effect in conductive adhesive joints are evaluated by the finite element analysis with the viscoelastic material model. In order to Investigate the relationship between thermal ratchetting and glass transition temperature, the mathematical material model has been developed experimentally by dynamic mechanical analysis. These material models are implemented to the finite element analysis with thermal loading cycles. And the stress profiles around the conductive adhesive joints are calculated. It has been observed that the thermal ratchetting occurs when the maximum temperature of thermal cycles is above the glass transition temperature. The peel and shear stress components increase as the thermal loading time increases. This will contributes to thermal fatigue fracture of the joints.

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