Heat Transfer from a Rotating Sphere

Abstract

Heat transfer from a rotating sphere of relatively large diameter in air flow was measured to estimate heat transfer coefficients between fluid and solid in gas-solid two-phase flow. The effect of air velocity fluctuation generated by simple harmonic vibrations of a sphere was also studied experimentally.
Heat transfer coefficients of the rotating sphere in still air were smaller than in the data obtained by Kreith et al. The following experimental equation was obtained :
Nu=2+0.37 (r·d·ω·ρ_a/μ) ^1/2
In the air flow, heat transfer coefficients were controlled by rotation of the sphere at r·ω/u above 3.0. At r·ω/u below 0.7 the influence of rotation was negligible. The experimental results were affected by vibrations of the sphere in the region of low Reynolds and rotational Reynolds number.