• Title/Summary/Keyword: Local Heat

Search Result 1,201, Processing Time 0.029 seconds

VARIATION OF LOCAL POOL BOILING HEAT TRANSFER COEFFICIENT ON 3-DEGREE INCLINED TUBE SURFACE

  • Kang, Myeong-Gie
    • Nuclear Engineering and Technology
    • /
    • v.45 no.7
    • /
    • pp.911-920
    • /
    • 2013
  • Experimental studies on both subcooled and saturated pool boiling of water were performed to obtain local heat transfer coefficients on a $3^{\circ}$ inclined tube of 50.8 mm diameter at atmospheric pressure. The local values were determined at every $45^{\circ}$ from the very bottom to the uppermost of the tube periphery. The maximum and minimum local coefficients were observed at the azimuthal angles of $0^{\circ}$ and $180^{\circ}$, respectively, in saturated water. The locations of the maxima and the minima were dependent on the inclination angle of the tube as well as the degree of subcooling. The major heat transfer mechanisms were considered to be liquid agitation generated by the sliding bubbles and the creation of big size bubbles through bubble coalescence. As a way of quantifying the heat transfer coefficients, an empirical correlation was suggested.

A Study on the Infrared Local Heat Treatment of Curved Line for Aluminum Alloy Sheet (알루미늄 판재의 성형성 향상을 위한 적외선 국부 열처리법의 곡선형태 적용에 관한 연구)

  • Lee, E.H.;Yang, D.Y.
    • Transactions of Materials Processing
    • /
    • v.27 no.2
    • /
    • pp.87-92
    • /
    • 2018
  • Auto industries have tried to employ lightweight alloys to improve the fuel efficiency of manufactured vehicles, as the environmental concern becomes an important issue. Even though the aluminum alloy is one of the most appropriate lightweight alloys for auto parts, the low formability of an aluminum alloy has been an obstacle to its application. In order to resolve the low formability problem, a recent study (Lee et al., 2017 [1]) showed that the infrared (IR) local heat treatment can improve the formability with a reduction of heating energy. However, the aforementioned study was limited to only a linear line heating. Since many of the available auto parts as applicable to vehicle manufacturing have a curved line shape, the heating experiments for a curved line should be studied. The possibility of building IR lamps having complex shapes is an advantage of the IR lamp, since it can control the heating shape. This work conducted the IR local heat treatment for the curved line. The experimental results show that the IR local heat treatment can improve the formability of the aluminum alloy for curved line. Additionally, it is shown that the IR local heat treatment also reduces the heating energy when it is compared with the furnace heating which heats a blank as a whole. A numerical simulation with a stress-based forming limit diagram also supports the experimental results.

Measurement Technique for Single Phase Local Heat Transfer Coefficients of Subchannels in a Rod Bundle using a Copper Sensor (봉다발 부수로의 단상 국부열전달 계수 측정기법에 관한 연구)

  • Seo, Jeong-Sik;Choi, Young-Don;Bea, Kyong-Kuen;An, Jeong-Soo
    • Proceedings of the SAREK Conference
    • /
    • 2007.11a
    • /
    • pp.191-196
    • /
    • 2007
  • This paper presents the measuring technique for local heat transfer coefficients using a copper sensor in a rod bundle with mixing vanes. A copper sensor consists of a cartridge heater and four pieces of thermocouple. The Heater is located at the center of the copper sensor and thermocouples measure the surface temperature of the copper sensor. Unheated copper sensor and heated copper sensor are able to measure the local heat transfer coefficient at the position where the heated copper sensor is installed. However the entire region of a rod bundle is actually not heated, the decay of local heat transfer coefficients measured represents overestimated value rather than an actual value. The calibration curve for local heat transfer coefficients is presented using the correction factor calculated by CFD.

  • PDF

Feasibility study of ground source heat pump system according to the local climate condition (지역 기후 특성에 따른 지열시스템의 도입경제성 차이에 관한 연구)

  • Nam, Yujin
    • KIEAE Journal
    • /
    • v.14 no.4
    • /
    • pp.127-131
    • /
    • 2014
  • The ground source heat pump (GSHP) system is a kind of the temperature differential energy system using relatively stable underground temperature as heat source of space heating and cooling. This system can achieve higher performance of system than it of conventional air source heat pump systems. However, its superiority of the system performance is different according to installation location or local climate, because the system performance depends on the underground condition which is decided by annual average air temperature. In this study, in order to estimate the feasibility of the ground source heat pump system according to the local climate, numerical simulation was conducted using the ground heat transfer model and the surface heat balance model. The case study was conducted in the condition of Seoul, Daejeon, and Busan, In the result, the heat exchange rate of Busan was 34.33 W/m as the largest in heating season and it of Seoul was 40.61 W/m as the largest in cooling.

Control of Impinging Jet Heat Transfer with Mesh Screens (Mesh 스크린을 이용한 충돌제트 열전달 제어에 관한 연구)

  • Cho, Joung-Won;Lee, Sang-Joon
    • Proceedings of the KSME Conference
    • /
    • 2000.11b
    • /
    • pp.267-271
    • /
    • 2000
  • The local heat transfer rate of an axisymmetric submerged air jet impinging on normal to a heated flat plate was investigated experimentally with varying solidity of mesh screen. The mean velocity and turbulent Intensity profiles of streamwise velocity component were measured using a hot-wire anemometry. The temperature distribution on the heated flat surface was measured with thermocouples. The screen installed in front of the nozzle exit(behind of 35mm) modify the jet flow structure and local heat transfer characteristics. For higher solidity screen, turbulence intensity at core lesion is high and increases the local heat transfer rate at nozzle-to-plate spacings(L/D<6). For larger nozzle-to-plate spacings(L/D>6), however, the turbulent Intensities of all screens tested in this study approach to an asymptotic curve, but the small mean velocity at the core region reduces the local heat transfer rate for high solidity screens.

  • PDF

The effect of wall heat conduction on local convection heat transfer from a cylinder in cross flow of air (원형 실린더 주위의 공기로 국소 대류 열전달에 대한 열전도의 영향)

  • 이승홍;이억수
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.10 no.4
    • /
    • pp.440-448
    • /
    • 1998
  • This paper considers the influence of circumferential wall heat conduction for the case of forced convection around a circular cylinder in cross flow of air. Keeping uniform heat generation from the inner surface of the cylinder in radial direction, heat is transferred by wall conduction in the circumferential direction due to the asymmetric nature of the temperature distribution of the cylinder and by convection around the perimeter of the cylinder. The wall conduction depends on conductivity of the cylinder and size of the cylinder radius and thickness and affects the local convective heat transfer rate significantly for geometrically similar surfaces and flow conditions. A nondimensional conjugation parameter K. (=k$_t$R/k$_w$b) has been used to characterize the effect of the circumferntial wall heat conduction. The small values of conjugation parameter K are found to be associated with large effect of wall conduction on the local convective heat transfer rate.

  • PDF

Local and Overall Heat Transfer Characteristics of Fin- Flat Tube Heat Exchanger with Vortex Generators

  • Yoo, Seong-Yeon;Chung, Min-Ho;Park, Dong-Seong
    • International Journal of Air-Conditioning and Refrigeration
    • /
    • v.11 no.3
    • /
    • pp.150-157
    • /
    • 2003
  • Local and overall heat transfer characteristics of fin-flat tube heat exchangers with and without vortex generators were investigated. Local heat transfer coefficients were measured with the heat exchanger model using naphthalene sublimation technique. In case of a fin-flat tube heat exchanger without vortex generators, only the horseshoe vortices formed around tubes augment the heat transfer. On the other hand, longitudinal vortices created artificially by vortex generators additionally enhance heat transfer in case of a fin-flat tube heat exchanger with vortex generators. Overall heat transfer coefficients were measured with the prototypes of the fin-flat tube heat exchanger with and without vortex generators in a wind tunnel and results were compared with those of a fin-circular tube heat exchanger with wavy fin. Friction losses for heat exchangers were also measured and compared. The fin-flat tube heat exchanger with vortex generators is found to be more effective than the fin-circular tube heat exchanger with wavy fin.

An Experimental Study on the Local and Overall Heat Transfer Characteristics of a Fin-Flat Tube Heat Exchanger (납작관형 핀-관 열교환기의 국소 및 총합 열전달 특성에 관한 실험적 연구)

  • 유성연;정민호;박동성;이상섭
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.14 no.11
    • /
    • pp.939-947
    • /
    • 2002
  • Local and overall heat transfer characteristics of fin-flat tube heat exchangers with and without vortex generators are investigated. Local heat transfer coefficients are measured with the heat exchanger model using naphthalene sublimation technique. In case of a fin-flat tube heat exchanger without vortex generators, only the horseshoe vortices formed around tubes augment the heat transfer. On the other hand, longitudinal vortices created artificially by vortex generators enhance heat transfer dramatically in case of a fin-flat tube heat exchanger with vortex generators. Overall heat transfer coefficients are measured with the prototype of the fin-flat tube heat exchanger with and without vortex generators in a wind tunnel and results are compared with those of a fin-circular tube heat exchanger with wavy fin. Friction losses for heat exchangers are also measured and compared. The fin-flat tube heat exchanger with vortex generators is found to be more effective than the fin-circular tube heat exchanger with wavy fin.

Endwall Heat (Mass) Transfer in a Turbine Cascade Under Combustor-Level High Free-Stream Turbulence (연소기 출구 난류 상태에서의 터빈 익열 끝벽 열(물질)전달 특성)

  • Jun, Sang-Bae;Lee, Sang-Woo;Park, Byung-Kyu
    • Proceedings of the KSME Conference
    • /
    • 2001.06d
    • /
    • pp.759-764
    • /
    • 2001
  • Heat (mass) transfer characteristics have been investigated on the endwall of a large-scale linear turbine cascade passage under a combustor-level high free-stream turbulence with a large length scale. Local heat (mass) transfer coefficients are measured by using the naphthalene sublimation technique. The result shows that local heat (mass) transfer on the endwall is greatly enhanced in the central region of the turbine passage, but there is no noticeable change in the local heat (mass) transfer in the region suffering severe heat load. Under the high free-stream turbulence, the local heat (mass) transfer coefficient shows more uniform distribution and its average value across the whole endwall region is increased by 26% of that at low turbulence condition. The heat (mass) transfer data on the endwall strongly supports that well-organized vortices near the endwall tends to suffer an suppression by the high free-stream turbulence.

  • PDF

Local Heat Transfer Measurement and Numerical Analysis in the Ventilated Disc Brake with Semi-Cylindrical Grooves (반 실린더형 홈을 가진 벤틸레이티드 디스크 브레이크에서의 국소열전달 측정 및 수치 해석)

  • Lee Dae-Hee;Park Sung-Bong;Lim Chang-Yul;Kim Heung-Seop;Lee Kwan-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.30 no.6 s.249
    • /
    • pp.587-593
    • /
    • 2006
  • A ventilated disc brake having semi-cylindrical grooves has been proposed to improve the thermal judder by way of heat transfer enhancement. The local heat transfer coefficients were measured in the flow passage of disc brake. These measured local heat transfer data were utilized to do the finite element numerical analysis which predicts the maximum temperatures on the disc brake. The results show that the maximum temperatures on the disc surface with semi-cylindrical grooves are approximately 35.2% lower than those without them.