Visualization of Natural Convection Heat Transfer in an Inclined Circular Pipe

As the passive cooling system (PCS) of nuclear reactor has received the considerable attention recently, the studies on natural convection heat transfer in an inclined circular pipe are being gradually carried out. However, the analysis of the results is insufficient although the internal flow formed by interaction of boundary layers is complex unlike the external flow of the pipe. Also most of the studies were conducted for a narrow range of 106<RaD<108 and low Pr. The experimental results are compared with the existing studies for the horizontal pipe and agreed well with Sarac and Korkut. The heat transfer reduces as the increase of the inclination (θ). The reason is that when the heated length of circumferential direction increases, the thickness of boundary layer at the top increases. Another reason is that the acceleration of the flow velocity in the axial direction reduces as the number of the detached plumes decreases. According to the increase of the diameter (D) and length (L), the heat transfer reduces. That's why the thickness of the boundary layer becomes thin with the decrease of heated length and the region of leading edge occupying the boundary layer reduces. Based on this, the internal flow rising vertically in the bottom and flowing along the circumferential direction in the other area was confirmed. Also, it was verified that the influence of the flow formed in each direction is changed according to varying of inclination (θ). This study analyzed the influences of the parameters as well as confirmed the detachment of the boundary layer and internal flow through the visualizations. Based on all of the results, sketch of the flow in the inclined pipe presented.