Characteristics of the heat transfer from a horizontal rotating cylinder surface

•A micro-thermocouple is employed to measure the temperature distribution around the cylinder.•Effects of rotation on ascending-side and descending-side heat transfer differs.•The critical rotational Reynolds number Rer,cri   can be determined by Rer=3.05Gr0.456Rer=3.05Gr0.456.

In order to investigate the characteristics of the convective heat transfer from a large-diameter horizontal rotating isothermal cylinder at higher Gr-numbers (108), a specially designed micro-thermocouple is used to measure the temperature distribution around the cylinder at different rotational speeds n. The results indicate that the effect of rotation on the heat transfer on ascending side is different from that on the descending side. Rotation of the cylinder can lead to a nonuniform distribution of the local Nusselt number Nuφ, especially in the region beyond the critical rotational Reynolds number Rer,cri. There exists a critical Reynolds number Rer,cri when the mean Nusselt number Nu varies with the rotational Reynolds number Rer, and the Rer,cri   can be determined by Rer=3.05Gr0.456Rer=3.05Gr0.456. As Rer < Rer,cri  , rotation has almost no effect on the NuNu and the free convection dominates the heat transfer. As Rer ⩾ Rer,cri, Nu increases with rising Rer, and the heat transfer characteristics are affected by both free and forced convection.