Influences of side wall angle on heat transfer of power-law fluids in trapezoidal enclosures

In recent years, there is an important increase in technological applications of non-Newtonian fluids (NNF). NNFs are preferred over Newtonian fluids (NF) because of their superior hydrodynamic and thermal properties. NNFs are particularly used as damping fluid in shock absorbers, raw material for making of armors in defense industry and insulator in thermal systems. The use of NNF has become widespread in thermal systems in order to prevent over-heating problem which affects the efficiency. This study presents a numerical analysis for the natural convection in a two dimensional trapezoidal (isosceles trapezoid) enclosure filled with power-law NNF. The effects of various parameters are investigated on heat transfer on the bottom wall by developing a two dimensional model of such a cell. The bottom edge of the trapezoidal enclosure is considered as hot, top edge as cold while the side walls are considered as adiabatic. The considered parameters are power-law index (n) and Rayleigh number (Ra) and also the trapezoid side wall angle altering in the range of 0≤≤20. The power-law index has been varied in the range of 0.6≤≤1.8 and Rayleigh number in the range of 103≤≤105 while Prandtl number has been kept constant as 1000. The results reveal that the mean Nusselt number (̅̅̅̅ ) on bottom wall of trapezoid increases by increasing trapezoid angle and decreasing power-law index. According to evidences of the study, it may be suggested that the use of power-law NNFs may contribute to increase efficiency by averting the over-heating problems in trapezoidal thermal systems which are regarded as a significant application field in green and renewable energy systems.papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016