Journal of Energy Engineering (에너지공학)

The Korean Society for Energy (한국에너지학회)
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The Effects of Top and Bottom Lids on the Natural Convection Heat Transfer inside Vertical Cylinders

수직 원형관 내부에서 발생하는 자연대류 열전달에서 상·하단 마개의 영향

  • Kang, Gyeong-Uk (Department of Nuclear and Energy Engineering, Institute for Nuclear Science and Technology, Jeju National University) ;
  • Chung, Bum-Jin (Department of Nuclear and Energy Engineering, Institute for Nuclear Science and Technology, Jeju National University)
  • Received : 2011.08.18
  • Accepted : 2011.09.15
  • Published : 2011.09.30
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Abstract

The effects of top and bottom lids on the natural convection heat transfer phenomena inside vertical cylinders were investigated experimentally for $Ra_{Lw}$ from $9.26{\times}10^9$ to $7.74{\times}10^{12}$. Using the concept of analogy between heat and mass transfer, a cupric acid-copper sulfate electroplating system was employed as mass transfer experiments replacing heat transfer experiments. The natural convection heat transfer of both-open cylinders in laminar and turbulent flows was in good agreement with the existing heat transfer correlations developed for vertical plates. The effects of top and bottom lids on the heat transfer rates were very similar to the studies of Krysa et al. and Sedahmed et al. and Chung et al. With the copper lids, the bottom-closed cavity showed the highest heat transfer rates and then followed both-closed, top-closed, both-open ones in both laminar and turbulent flows. However with the acryl lids, the similar trends were observed except that the heat transfer rates for both-open were higher than top-closed one. The use of the copper lids increased the heat transfer rates compared to the acryl lids due to the hydrodynamic interaction of the flows developed for the different heated faces. This study extended the ranges of flow conditions of the existing literatures and proposed the empirical correlations.

수직 원형관 내부의 자연대류 열전달 현상이 상 하단 마개 유무 그리고 마개의 가열 및 단열조건에 따라 어떻게 변화하는지 $Ra_{Lw}$ 수 $9.26{\times}10^9\sim7.74{\times}10^{12}$의 범위에 대해 실험적으로 연구하였다. 상사성의 원리를 이용하여 열전달 실험을 대신하여 황산-황산구리 수용액의 전기도금계를 이용한 물질전달 실험을 수행하였다. 실험결과, 수직 원형관의 위와 아래가 열린 경우 자연대류 열전달은 기존의 수직평판에 대한 그것과 일치하였고 상 하단 마개의 영향 따른 열전달의 변화는 Krysa 등, Sedahmed 등과 Chung 등이 실험한 현상과 일치하였다. 구리 마개를 사용한 경우 측정된 열전달은 층류와 난류영역에서 원형관의 아래만 막혔을 때가 가장 높게 측정되었고 다음으로는 위와 아래가 모두 막힌 경우, 위만 막힌 경우 그리고 위와 아래가 모두 열린 경우의 순으로 열전달이 변화하였다. 한편, 아크릴 마개를 사용한 경우에는 그 경향은 비슷했지만 위와 아래가 모두 열린 경우가 위만 막힌 경우보다 열전달이 높았다. 구리 마개를 사용한 경우 아크릴 마개보다 열전달이 높았다. 이는 서로 다른 가열벽면에서 발생된 유동의 상호작용에 기인하였기 때문인 것으로 판단된다. 본 실험을 통하여 기존연구보다 확장한 유동영역과 기하구조에 대하여 열전달의 영향을 관찰하였고, 층류와 난류영역에 대한 자연대류 열전달 상관식을 제시하였다.

Keywords

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