Natural convection of power-law fluid in a horizontal annulus between outer cylinder and inner flat tube

Authors: Benhizia Oussama, Bouzit Mohamed

Volume 10, Issue 4, Paper No. 100402


Natural convection in two-dimensional space created by putting horizontal flat tube concentrically in cooled horizontal cylinder is studied numerically. The model solved using the ANSYS CFX package. The numerical simulations covered a range of power-law index 0.6≤n≤1.4, Prandtl number 10≤Pr≤103 and Rayleigh number 103≤Ra≤105. The effects of the previous parameters on the flow pattern, the average Nusselt number and the dimensionless temperature and velocity profiles have been investigated.

The results showed that the average Nusselt number increases with increasing Rayleigh number and decreases with increasing the power-law index. The best case among the range of parameters considered here is the heat transfer rate of pseudo-plastic fluids (n=0.6), then the Newtonian fluids (n=1) and finally, the dilatant fluids (n=1.4). It is shown that the sharpness cooling effect of pseudo-plastic fluids and the sharpness insulating effect of dilatant fluids hugely affected by the increasing of Rayleigh number. The Prandtl number has almost no effects on the heat transfer rate in the range considered here. The results for the average Nusselt number and the dimensionless temperature have been compared versus some previous works and showed good agreement.

Keywords: Natural convection,Non-Newtonian fluid, Power-law model, Horizontal flat tube, Nusselt number

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