• Title, Summary, Keyword: Heat Transfer Coefficient

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A Study for Evaporation Heat Transfer Characteristic of R22/Rl14 Refrigerant Mixtures in a Horizontal Tube (수평증발관내 R22/R114 혼합냉매의 열전달 특성에 관한 연구)

  • 윤치한;이종인;하옥남
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.12 no.5
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    • pp.502-510
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    • 2000
  • Evaporation heat transfer characteristics were studied in a horizontal tube using R22/R114 non-azotropic refrigerant mixture. the heat transfer coefficient was high in the upper part for pure refrigerants, and heat transfer coefficient was low in the lower part for refrigerant mixtures. In the low quality region where nucleate boiling was dominant, the average heat transfer coefficient was low. In the region where forced convection was dominant, heat transfer coefficient was high. Results show that the heat transfer coefficient for pure refrigerants obtained by experiments were lower than those of Yoshida et al. but agreed well with Jung et al., and Chen et al. data. But the heat transfer coefficients for refrigerant mixtures were lower about 20% than those predicted by the equation for pure refrigerant.

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Effect of Expansion Ratio on Contact Heat Transfer Coefficient in Fin-Tube Heat Exchanger (핀관 열교환기에서 확관율이 접촉열전달계수에 미치는 영향)

  • Lee, Sang-Mu;Park, Byung-Duck
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.24 no.1
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    • pp.45-50
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    • 2012
  • The plate fin and tube type of heat exchanger is widely used in air conditioner, and the heat exchanger is assembled by the mechanical expansion of copper tubes and fastening the aluminum fin. The objective of the present study is to investigate how the mechanical expansion of copper tube affects on the heat transfer performance of a plate fin and tube type heat exchanger. This study has been performed by experimental and numerical methods. The numerical and experimental results show that the tube expansion ratio has a influence on the heat transfer performance. Within the tested expansion ratio, the contact pressure shows the peak value and it decreases as the expansion ratio increases. Air-side heat transfer coefficient increases until the expansion ratio reaches 1.23, and then decreases with the similar pattern to the contact pressure. Also, contact heat transfer coefficient shows the maximum when the contact pressure is highest as well as the air-side heat transfer coefficient.

Measurement of Heat Transfer Coefficient in a Duct with Double Imingement Jets (이중 충돌 제트를 갖는 내부 유로의 열전달 계수 측정)

  • Kwak, Jae-Su
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.14 no.1
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    • pp.9-14
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    • 2006
  • Averaged heat transfer coefficients in the trailing edge model of a turbine blade with double impingements were measured using transient liquid crystals technique and conventional copper plate-thermocouple technique. The detailed distributions of heat transfer coefficients by transient liquid crystals technique were also presented. Results showed that increased heat transfer coefficient due to the inpingements and the averaged heat transfer coefficients increased as Reynolds number increased. Results by transient liquid crystals technique showed that the heat transfer coefficient strongly depended on the main stream temperature used in heat transfer coefficient calculation. The averaged heat transfer coefficients measured by different methods showed similar trend as Reynolds number changed, but the value varied up to 40% depending on the measurement technique.

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Numerical Analysis on the Thermal and Fluid in Air Conditioning Duct for Marine Offshore (해양 구조물용 공조덕트 열유동에 관한 수치해석)

  • Yi, Chung-Seob;Lee, Byung-Ho;Chin, Do-Hun
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.18 no.2
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    • pp.7-13
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    • 2019
  • This study is about distributions of heat transfer in air conditioning duct used for marine and oil drilling ship. As the convective heat transfer coefficient increased, heat transfer was conducted dynamically to inside as it exited to the outlet of duct. So, it was checked that the amount of heat transfer generated at duct increased as the convective heat transfer coefficient increased. In case the convective heat transfer coefficient was low, the temperature of duct showed the relatively high temperature distribution due to the temperature influence of internal fluid as the heat transfer between the outside and inside of the duct. In case of temperature distribution generated the volume of the duct along the change of the convective heat transfer coefficient, it was found out that the temperature descended as heat transfer was promoted and the convective heat transfer coefficient increased.

Determination of the Overall Heat Transfer Coefficient for Non-isothermal Finite Element Analysis (비 등온 유한요소해석을 위한 접면열전달계수의 결정)

  • 강연식;양동열
    • Journal of the Korean Society for Precision Engineering
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    • v.14 no.4
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    • pp.72-77
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    • 1997
  • In the temperature analysis of hot metal forming process, the heat transfer conditions between the work-piece and the tool have improtant influences upon the temperature distribution. The accuracy of thermal analysis depends on the proper description of boundary conditions including heat transfer. At the contact surface of two materials with different temperatures, this requires the knowledge of the overall heat transfer coefficient. In order to determine the overall heat transfer coefficient, a technique is developed. The technique involves temperature measurement by using thermocouples during hot upsetting operations and finite element computation. The overall heat transfer coefficient is determined using a non-linear optimization technique.

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Evaporation heat transfer and Pressure loss in micro-fin tubes and a smooth tube (마이크로핀관과 평활관에서의 증발열전달과 압력손실 특성)

  • 장세환;정시영;홍영기
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.2
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    • pp.215-223
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    • 1999
  • Evaporation heat transfer coefficient and pressure loss were measured for three different micro-fin tubes and a smooth tube. The experiments were carried out with R-22 over a wide range of vapor Quality, mass velocity and heat flux. Heat transfer coefficient of the tube with slightly modified fin shape was found to be higher than that of the commercial reference tube by 60%. The improvement of heat transfer has been achieved without noticeable increase of pressure loss. Heat transfer coefficient was increased with increasing quality, refrigerant mass flux, and heat flux. However, the effect of refrigerant mass flux and heat flux was not great. Heat transfer coefficient at bottom was lower than that at top of the tube in low quality region, which suggested the existence of stratification in the micro-fin tube. Pressure drop was linearly increased with increasing refrigerant quality and was proportional to about square of mass flux.

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Numerical study for the fin efficiency of the heat exchanger having plate fins (판형 휜을 갖는 열교환기의 휜효율에 관한 수치해석적 연구)

  • 강희찬
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.11 no.6
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    • pp.903-911
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    • 1999
  • This study is discussed about the heat transfer coefficient and the fin efficiency of the heat exchanger having plate fins. A new definition for the fin efficiency of the heat exchanger is proposed. More than one hundred cases were tested numerically for the plate fins having uniform and non-uniform heat transfer coefficient. The previous models for the fin efficiency and the pure heat transfer coefficient were applicable to the heat exchanger only when the NTU is very small. It was found that the fin efficiency of the heat exchanger was nearly the same as the normalized fin temperature. The present model could estimate the pure heat transfer coefficient within a few percent in the present test range of 0<NTU<2.5.

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A Study on the Heat Transfer Perfomance of Dimpled Double Pipe Heat Exchanger on a Fuel Cell (연료전지용 딤플형 이중관열교환기의 열전달 성능에 관한 연구)

  • CHO, Dong-Hyun
    • Journal of Fisheries and Marine Sciences Education
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    • v.27 no.6
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    • pp.1727-1733
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    • 2015
  • In the present study, the heat transfer performance of dimpled double-pipe heat exchangers for fuel cells that are utilized as cooling systems of fuel cells was studied. In addition, to comparatively analyze the heat transfer performance of dimpled double-pipe heat exchanger for fuel cells, plain double-pipe heat exchangers were also studied. Experimental results were derived on changes in the Reynolds numbers of the cooling water flowing in dimpled and plain double-pipe heat exchangers and changes in the heat flux of the air. Thereafter, to verify the reliability of the experimental results, the theoretical overall heat transfer coefficients and the experimental overall heat transfer coefficients were comparatively analyzed and the following results were derived. The heat transfer rate lost by the hot air and that of the heat transfer rate obtained by the cooling water were well balanced. The experiments of plain double-pipe heat exchangers and dimpled double-pipe heat exchangers were conducted under normal conditions and the theoretical overall heat transfer coefficient and the experimental overall heat transfer coefficient coincided well with each other. In both plain double-pipe heat exchangers and dimpled double-pipe heat exchangers, heat transfer rates increased as the cooling water flow velocity increased. Under the same experimental conditions, the heat transfer performance of dimpled double-pipe heat exchangers was shown to be higher by 1.2 times than that of plain double-pipe heat exchangers.

Measuring Convective Heat Transfer Coefficient Around a Heated Fine Wire in Cross Flow of Nanofluids (나노유체의 수직유동 속에 놓인 가는 열선주위의 대류열전달계수 측정)

  • Lee, Shin-Pyo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.32 no.2
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    • pp.117-124
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    • 2008
  • Recent researches on nanofluids have mainly focused on the increase of thermal conductivity of nanofluids under static condition. The ultimate goal of using nanofluids, however, is to enhance the heat transfer performance under fluid flow. So it has been highly necessary to devise a simple and accurate measuring apparatus which effectively compares the heat transfer capability between the base and nanofluids. Though the convective heat transfer coefficient is not the complete index for the heat transfer capability, it might be one of useful indications of heat transfer enhancement. In this article, the working principles of experimental system for convective heat transfer coefficient around a heated fine wire in cross flow of nanofluids and its application example to three samples of nano lubrication oils are explained in detail.

Boiling Heat Transfer Characteristics of R-290 in Horizontal Smooth Minichannel (수평미세관내 R-290의 비등열전달 특성)

  • Choi, Kwang-Il;Pamitran, A.S.;Oh, Jong-Taek
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.11
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    • pp.906-914
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    • 2006
  • The present paper dealt with an experimental study of boiling heat transfer characteristics of R-290. Pressure gradient and heat transfer coefficient of the refrigerant flow inside horizontal smooth minichannel were obtained with inner tube diameter of 3.0 mm and length of 2,000 mm. The direct electric heating method was applied for supplying a heat to the refrigerant uniformly. The experiments were conducted with R-290 purity of 99.99%, at saturation temperature of 0 to $10^{\circ}C$, a mass flux range of $50{\sim}250kg/m^2s$, and a heat flux range of $5{\sim}20kW/m^2$. The heat transfer coefficients of R-290 increased with increasing mass flux and saturation temperature, wherein the effect of mass flux was higher than that of the saturation temperature. Heat flux has a low effect on the increasing of heat transfer coefficient. The heat transfer coefficient was compared with six existing heat transfer coefficient correlations. The Zhang et al.'s correlation (2004) gave the best prediction of heat transfer coefficient. A new correlation to predict the two-phase flow heat transfer coefficient was developed based on the Chen correlation. The new correlation predicted the experimental data well with a mean deviation of 11.78% and average deviation of -0.07%.