A numerical investigation of laminar natural convection heat transfer from small horizontal cylinders at near-critical pressures has been carried out. Carbon dioxide is the test fluid. The parameters varied are: pressure (P), (ii) bulk fluid temperature (Tb), (iii) wall temperature (Tw), and (iv) wire diameter (D). The results of the numerical simulations agree reasonably well with available experimental data. The results obtained are as follows: (i) At both subcritical and supercritical pressures, h is strongly dependent on Tb and Tw. (ii) For Tw < Tsat (for P < Pc) and Tw < Tpc (for P > Pc), the behavior of h as a function of Tw is similar; h increases with increase in Tw. (iii) For P > Pc and large Tw (Tw > Tpc), natural convection heat transfer occurring on the cylinder is similar that observed during film boiling on a cylinder. The heat transfer coefficient decreases as Tw increases. (iv) For subcritical pressures, the dependence of h on D is h ∝ D−0.5 in the range 25.4 ≤ D ≤ 100 μm. For larger values of D (500–5000 μm), h ∝ D−0.24. (v) For supercritical pressures, the dependence of h on D is h ∝ D−0.47 in the range 25.4 ≤ D ≤ 100 μm. For larger values of D (500–5000 μm), h ∝ D−0.27. (vi) For a given P, the maximum heat transfer coefficient is obtained for conditions where Tb < Tpc and Tw ≥ Tpc. Analysis of the temperature and flow field shows that this peak in h occurs when k, Cp, and Pr in the fluid peak close to the heated surface.
Natural Convection From Horizontal Cylinders at Near-Critical Pressures—Part II: Numerical Simulations
Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received September 9, 2011; final manuscript received June 17, 2012; published online December 28, 2012. Assoc. Editor: Ali Ebadian.
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Warrier, G. R., Rousselet, Y., and Dhir, V. K. (December 28, 2012). "Natural Convection From Horizontal Cylinders at Near-Critical Pressures—Part II: Numerical Simulations." ASME. J. Heat Transfer. February 2013; 135(2): 022502. https://doi.org/10.1115/1.4007673
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