Experimental study on flow patterns under natural circulation in a narrow rectangular channel

The change characteristics of flow patterns under natural circulation in a narrow rectangular channel is investigated by the building of an experimental facility, which can be enabled to measure the flow changes and its happening and causes. Experiments have found that, with the increase of heat flux, the flow states are a single phase flow, dispersed bubble flow, slug flow and churn flow. With experimental observation, it is concluded that the churn flow follows the slug flow, the length of the boiling section gets shorter when churn flow happens, and then gets longer with a variation of flow rate. With natural circulation in a narrow rectangular channel is easy to have a more violent churn flow leading to flow instability, thus having an important influence for the heat transfer character. The study of churn flow has an important value to achieve the fluid flow and heat transfer mechanism of natural circulation in a narrow rectangular channel. © 2012 WIT Press.