• Title/Summary/Keyword: Heat flow resistance

Search Result 300, Processing Time 0.023 seconds

A Study on the Two-Dimensional Phase Change Problem in a Rectangular Mold with Air-Gap Resistance to Heat Flow (공기층 저항을 고려한 사각형 주형내에서의 2차원 상변화문제에 관한 연구)

  • 여문수;손병진;김우승
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.16 no.6
    • /
    • pp.1205-1215
    • /
    • 1992
  • The solidification rate is of special importance in determining the casting structures and properties. The heat transfer characteristics at the interface between the mold and the casting is one of the major factors that control the solidification rate. The thermal resistance exists due to the air-gap formation at the mold/casting interface during the freezing process. In this study two-dimensional Stefan problem with air-gap resistance in the rectangular mold is considered and the heat transfer characteristics is numerically examined by using the enthalpy method. The effects of the major parameters, such as mold geometry, thermal conductivity, heat transfer coefficient, and initial temperature of casting, on the thermal characteristics are investigated.

Modelling Heat Transfer Through CRUD Deposited on Cladding Tube in UNIST-DISNY Facility (UNIST-DISNY 설비 피복관에 침적된 크러드의 열전달 모델링)

  • Seon Oh YU;Ji Yong Kim;In Cheol Bang
    • Transactions of the Korean Society of Pressure Vessels and Piping
    • /
    • v.19 no.2
    • /
    • pp.109-116
    • /
    • 2023
  • This study presents a CRUD modelling to simulate the thermal resistance behavior of CRUD, deposited on the surface of a cladding tube of a fuel assembly. When heat produced from fuels transfers to a coolant through a cladding tube, the CRUD acting as an additional thermal resistance is expressed as two layers, i.e., a solid oxide layer and an imaginary fluid layer, which are added to the experimental tube's heat structure of the MARS-KS input data. The validation calculation for the experiments performed in UNIST-DISNY facility showed that the center and surface temperatures of the cladding tube increased as the porosity and the steam amount inside pores of the CRUD got higher. In addition, the temperature gradient in the imaginary fluid layer was calculated to be larger than that in the solid oxide part, indicating that the steam amount inside the layer acted more largely as thermal resistance. It was also evaluated through sensitivity calculations that the cladding tube temperature was more sensitive to the CRUD porosity and the steam amount in pores than to the inlet flow rate of the coolant.

An Experimental Study on the Effects of Porous Layer Treatment on Evaporative Cooling of an Inclined Surface (다공물질 표면처리가 경사판의 증발냉각에 미치는 영향에 관한 실험적 연구)

  • Lee Dae Young;Lee Jae Wan;Kang Byung Ha
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.17 no.1
    • /
    • pp.25-32
    • /
    • 2005
  • Falling film heat transfer has been widely used in many applications in which heat and mass transfer occur simultaneously, such as evaporative coolers, cooling towers, absorption chillers, etc. In such cases, it is desirable that the falling film spreads widely on the surface forming thin liquid film to enlarge contact surface and to reduce the thermal resistance across the film and/or the flow resistance to the vapor stream over the film. In this work, the surface is treated to have thin porous layer on the surface. With this treatment, the liquid can be spread widely on the surface by the capillary force resulting from the porous structure. In addition to this, the liquid can be held within the porous structure to improve surface wettedness regardless of the surface inclination. The experiment on the evaporative cooling of an inclined surface has been conducted to verify the effectiveness of the surface treatment. It is measured that the evaporative heat transfer increases about $50\%$ by the porous layer treatment as compared with that from orignal bare surfaces.

Characteristics of Indium-Tin-Oxide Electrode for Continuous-flow PCR Chip (연속흐름 중합효소연쇄반응칩 제작을 위한 인듐 산화막 전극의 특성분석)

  • Joung, Seung-Ryong;Kim, Jun-Hyeok;Yi, In-Je;Kang, C.J.;Kim, Yong-Sang
    • The Transactions of The Korean Institute of Electrical Engineers
    • /
    • v.56 no.3
    • /
    • pp.561-565
    • /
    • 2007
  • We propose glass and PDMS (polydimethylsiloxane) chips for DNA amplification with continuous-flow PCR (polymerase chain reaction). The PDMS microchannel was fabricated using a negative molding method for sample injection. Three heaters and sensors of ITO (indium-tin-oxide) thin films were fabricated on glass chip. ITO heaters and sensors were calibrated accurately for the temperature control of the liquid flow. ITO heater generated stable heat versus applied power. ITO sensor resistance was changed linearly versus temperature increase as a RTD (resistance temperature detector) sensor. As a result, we enable precision temperature control of continuous-flow PCR chip. Using the continuous-flow PCR chip DNA plasmid pKS-GFP 720 bp was successfully amplified.

Theoretical Analysis of Heat Transport Limitation in a Screen Mesh Wick Heat Pipe

  • Lee, Ki-Woo;Park, Ki-Ho;Lee, Wook-Hyun;Rhi, Seok-Ho
    • International Journal of Air-Conditioning and Refrigeration
    • /
    • v.12 no.1
    • /
    • pp.1-9
    • /
    • 2004
  • The purpose of the present study is to examine the heat transport limitations in a screen mesh heat pipe for electronic cooling by theoretical analysis. Diameter of pipe was 6mm, and mesh numbers were 50, 100, 150, 200 and 250, and water was investigated as working fluid. According to the change of mesh number, wick layer, inclination and saturation temperature, the maximum heat transport limitations by capillary, entraintment, sonic and boiling were analyzed by a theoretical design method of heat pipe, including capillary pressure, pumping pressure, liquid friction coefficient in wick, vapor friction coefficient, etc. Based on the results, the capillary limitation in a small diameter of heat pipe is largely affected by mesh number and wick layer. Mesh number of 250 is desirable not to be used in pipe diameter of 6 mm, because capillary heat transport limitation decreases by the abrupt increase of liquid friction pressure due to the small liquid flow area. For the heat transport of 15 watt in 6mm diameter pipe, mesh number of 100 and one layer is an optimum wick condition, which thermal resistance is the smallest.

Dialysis in parallel-flow rectangular membrane modules with external reflux for improved performance

  • Yeh, Ho-Ming;Cheng, Tung-Wen;Chen, Kuan-Hung
    • Membrane and Water Treatment
    • /
    • v.1 no.2
    • /
    • pp.159-169
    • /
    • 2010
  • The effect of external recycle on the performance of dialysis in countercurrent-flow rectangular membrane modules was investigated both theoretically and experimentally. Theoretical analysis of mass transfer in parallel-flow device with and without recycle is analogous to heat transfer in parallel-flow heat exchangers. Experiments were carried out with the use of a microporous membrane to dialyze urea aqueous solution by pure water. In contrast to a device with recycle, improvement in mass transfer is achievable if parallel-flow dialysis is operated in a device of same size with recycle which provides the increase of fluid velocity, resulting in reduction of mass-transfer resistance, especially for rather low feed volume rate.

Heat Transfer Analysis of a Heat Exchanger for an Air-Compressor of a Railway Vehicle Based on Cooling Air Flow Measurement (냉각공기 유속 측정에 기반한 철도차량용 공기압축기 열교환기의 열전달 특성 분석)

  • Ahn, Joon;Kim, Moo Sun;Jang, Seongil
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.29 no.9
    • /
    • pp.447-454
    • /
    • 2017
  • In this study, local velocity distribution of cooling air in a heat exchanger used in an air compressor for a railway car was measured and heat transfer characteristics of the heat exchanger were analyzed. First, heat transfer coefficient and fin performance of the cooling air side were predicted and was checked if the fin of the heat exchanger was effectively used. Distribution of air flow rate at high temperature side was predicted through pipe network analysis and heat resistance at high temperature and low temperature side were predicted and compared. Spatial distribution of temperature in the interior and surface of the square channel constituting high-temperature side was predicted and appropriateness of the size of the heat exchanger was examined. As a result of the analysis, the present size of the heat exchanger could be reduced and it could be effective to promote heat transfer inside the heat exchanger rather than outside to improve performance of the heat exchanger.

Numerical Study of Laminar Flow and Heat Transfer in Curved Pipe Flow (곡관에서의 층류 유동 및 열전달에 관한 수치해석 연구)

  • Kang, Changwoo;Yang, Kyung-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.37 no.10
    • /
    • pp.941-951
    • /
    • 2013
  • A three dimensional numerical simulation of laminar flow and heat transfer in fully developed curved pipe flow has been performed to study the effects of Dean number and pipe curvature on the flow and temperature fields under the thermal boundary condition of axially uniform wall heat flux. The Reynolds number under consideration ranges from 100 to 4000, and the Prandtl number is 0.71. The curvature ratios are 0.01, 0.025, 0.05 and 0.1. The axial velocity and temperature profiles and the local Nusselt number obtained from the present study are in good agreement with the previous numerical and experimental results currently available. To show the effects of pipe curvature on the flow and heat transfer, the resistance coefficients and heat transfer coefficients are computed and compared with the results of the previous theoretical and experimental studies. The averaged Nusselt number is correlated with Dean and Prandtl numbers. Furthermore, the critical Reynolds number for transition to turbulent flow is observed to depend upon the curvature ratio.

Pressure Drop and Heat Transfer Characteristics of Multi-Layer Screen (적층 스크린의 압력강하 및 열전달 특성)

  • Song, Tae-Ho;Ahn, Cheol-Woo;Kim, Chang-Kee;Ko, Hyun-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.24 no.3
    • /
    • pp.419-425
    • /
    • 2000
  • Multiple layer of wire screen is widely used in many compact devices to filter particulates and to heat or cool fluids. However, data of flow resistance and heat transfer through such layers are rare to find and thus they are experimentally investigated in this study. Compressed air is made to flow through it to find the Ergun constants over a wide range of the Reynolds number. Also, unsteady heating of the wire screen is performed to find the equivalent heat transfer coefficient between the screen and the air by fitting the unsteady air temperature. The obtained coefficients are expressed in terms of the Reynolds number and the Prandtl number.

An Experimental Study on the Frost Prevention using Micro Liquid Film of an Antifreeze Solution

  • Chang Young-Soo;Yun Won-Nam
    • International Journal of Air-Conditioning and Refrigeration
    • /
    • v.14 no.2
    • /
    • pp.66-75
    • /
    • 2006
  • The effect of antifreeze solution liquid film on the frost prevention is experimentally investigated. It is desirable that the antifreeze solution spreads widely on the heat exchanger surface forming thin liquid film to prevent frost nucleation while having small thermal resistance across the film. A porous layer coating technique is adopted to improve the wettability of the antifreeze solution on a parallel plate heat exchanger. The antifreeze solution spreads widely on the heat exchanger surface with $100{\mu}m$ thickness by the capillary force resulted from the porous structure. It is observed that the antifreeze solution liquid film prevents a parallel plate heat exchanger from frosting. The reductions of heat and mass transfer rate caused by the thin liquid film are only $1{\sim}2%$ compared with those for non-liquid film surface.