2015 年 81 巻 824 号 p. 14-00400
The effects of design parameters on natural convection heat transfer from a horizontal heated surface with a heated cylindrical pipe were estimated experimentally. The parameters considered were the heat flux of the horizontal heater and the aspect ratio of the heated cylinder. The flow fields around the horizontal heated surface and the heated cylinder were visualized. The results showed that flow characteristics have three distinctive patterns: non flow reversal, flow reversal occurred only in the heated cylinder and reached to the horizontal heater. The necessary conditions to determine the flow fields were discussed. With decreasing the distance of between the heaters and the aspect ratio of the heated cylinder, the ascending flow velocity in the pipe becomes low and flow reversal occurs. In all flow fields, an increasing in the heat flux of the horizontal heater enhances the heat transfer. In the case of no flow reversal and flow reversal occurred only in the heated cylinder, the heat transfer shows the same tendency and increases with increasing the aspect ratio of the heated cylinder. On the other hand, when flow reversal reaches to the horizontal heater, the heat transfer has a little influence on the heated cylinder conditions. Nusselt number is expressed as a function of the modified Rayleigh number of heaters and the nondimensional height.
