Experimental investigation on the steady, external laminar mixed convection heat transfer characteristics around a large diameter horizontal rotating cylinder

In order to investigate steady, external laminar mixed convection, mainly the correlations about the heat transfer and the critical Reynolds number around a horizontal rotating isothermal cylinder, a particularly manufactured micro-thermocouple is employed to measure the temperature distribution in the thermal boundary layer around the cylinder surface at different rotational speeds, n. The results indicate that there exists a critical Reynolds number Rer,cri as the mean Nusselt number Nu¯ varies with the rotational Reynolds number Rer. The rotation of the cylinder can lead to a nonuniform distribution of local Nussel number Nuφ, and the phenomenon becomes more obvious as Rer exceeds Rer,cri. Nu¯ changes according to a certain rule with Rer. As Rer < Rer,cri, the rotation has little impact on Nu¯, and the free convection heat transfer plays a dominant role, but as Rer ≥ Rer,cri, Nu¯ increases with increasing Rer, and the heat transfer characteristics are influenced by both the natural and the forced rotational convections simultaneously. Based on the experimental data, the correlations about the heat transfer can be expressed as Nu¯=0.530.0018Rer2.66+Gr⋅Pr0.25, and the critical Reynolds number Rer,cri can be determined by Rer,cri = 3.05(Gr ⋅ Pr)0.456.