OPTIMIZATION OF HEAT TRANSFER IN WATER-NePCM FILLED CAVITIES THROUGH CYLINDER ROTATION AND SIZE VARIATION

Mixed convection heat transfer within a square cavity filled with nano-encapsulated phase change material (NEPCM), uniformly dispersed in water and containing a rotating heated cylinder centrally located is studied numerically. The combined effect of natural and forced convection on heat transfer released by the heated cylinder and evacuated through the walls of the cavity is investigated. The main control parameters of the problem are the Richardson number (0.1 ≤ Ri ≤ ∞), the dimensionless fusion temperature (0.05 ≤ θ<sub>f</sub> ≤ 0.95), the volume fraction of NEPCM (0% ≤ φ ≤ 5%), the Reynolds number (0 < Re < 401.61), the Stephan number (0.313 ≤ Ste ≤ 1), and the radius of the inner cylinder (0.1 ≤ R ≤ 0.4). The remaining parameters are the Rayleigh number (Ra = 10<sup>5</sup>) and Prandtl number (Pr<sub>f</sub> = 6.2). The results obtained show that mixed convection is dominant within the Ri range from 10 to 10 × 10<sup>2</sup> for R ≤ 0.3; whereas forced convection is the dominant regime for R = 0.4 irrespective of the Ri. The maximum improvement of ~ 14.92% was recorded when the NEPCM suspension volume fraction (φ) was increased from 0% to 5%. Moreover, for Ri = 100 and R = 0.2, the NEPCM fusion temperature of 0.45 yields the best heat transfer performance.