Journal of Convergence for Information Technology (융합정보논문지)

Convergence Society for SMB (중소기업융합학회)
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Numerical Study of Mixed Convection Nanofluid in Horizontal Tube

수평원형관내 나노유체의 혼합대류에 관한 수치적 연구

  • Choi, Hoon-Ki (Dept. of Mechanical Engineering, Changwon National University) ;
  • Lim, Yun-Seung (Dept. of Mechanical Engineering, Changwon National University)
  • 최훈기 (창원대학교 기계공학부) ;
  • 임윤승 (창원대학교 기계공학부 대학원)
  • Received : 2019.07.01
  • Accepted : 2019.08.20
  • Published : 2019.08.28
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Abstract

Laminar mixed convection of a nanofluid consists of water and $Al_2O_3$ in a horizontal circular tube has been studied numerically. Two-phase mixture model has been used to investigate hydrodynamic and thermal behaviors of the nanofluid with variables physical properties. Three dimensional Navier-Stokes, energy and volume fraction equations have been discretized using the finite volume method. The Brownian motions of nanoparticles have been considered to determine the thermal conductivity and dynamic viscosity of $Al_2O_3$-Water nanofluid, which depend on temperature. The calculated results show good agreement with the previous numerical data. Results show that in a given Reynolds number (Re), increasing solid nanoparticles volume fraction and Richardson number (Ri) increases the convective heat transfer coefficient and wall shear stress.

수평원형관에서 나노입자인 산화알미늄과 기본유체인 물의 혼합인 나노유체에 대한 층류 혼합대류열전달현상을 유한체적법의 수치적 방법으로 규명하였다. 나노유체에 대하여 2상 혼합모델을 적용하였으며, 나노입자의 물성은 온도와 체적농도의 함수를 사용하였다. 수치해석에 적용한 모든 모델의 타당성 검증을 위하여 Kim등의 실험결과와 비교하였으며 좋은 결과를 얻었다. 벽면을 일정한 열유속으로 가열하므로 나노유체는 벽면부근에서 형성된 부력에 의하여 2차유동이 생성된다. Richardson수와 나노입자의 농도가 증가할수록 강한 2차유동이 형성되어 열전달을 향상시키게 된다. 또한 Richardson수와 나노입자의 농도가 증가하면 대류열전달계수와 전단응력도 증가한다. 이런 연구들은 열교환기의 성능향상을 위하여 나노유체를 적용하는데 기본자료로 활용이 가능하다. 이번 연구를 기반으로 향후 2중관형열교환기등 다양한 열교환기에 적용할 예정이다.

Keywords

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Fig. 1. Definition of numerical domain

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Fig. 2. Grid independence tests

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Fig. 3. Comparison of axial evolution of the convective heat transfer coefficient with the corresponding experimental data [21]

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Fig. 4. Secondary flow for different axial positions at ϕ=0.05 and Ri=1:(a) z*=5, (b)z*=10, (c)z*=20, (d)z*=40, (e)z*=190

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Fig. 5. Secondary flow for different flow conditions at z*=190 :(a) Ri=1, ϕ=0.00, (b) Ri=1, ϕ=0.07, (c) Ri=0.5, ϕ=0.05, (d) Ri=2, ϕ=0.05

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Fig. 6. Axial evolution of the Iso-temperature at ϕ=0.05 and Ri=1:(a)z*=10, (b)z*=20,(c)z*=40, (d)z*=190

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Fig. 7. Axial variation of the center-point temperature for different ϕ at Ri=1.

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Fig. 8. Axial development of the convective heat transfer coefficient for different ϕ at Re=300 and Ri=1.

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Fig. 9. Convective heat transfer coefficient for different Ri and ϕ at Re=300 and z*=190

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Fig. 10. Axial development of the total wall shear stress for different ϕ at Re=300 and Ri=1

Table 1. Properties of Al2O3

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