Performance comparison of rectangular and toroidal natural circulation loops under steady and transient conditions

The last few decades have witnessed an intense research on single-phase natural circulation loops (NCLs). Nevertheless, a meticulous literature survey suggests incorporation of different modelling approaches and various types of characterizing parameters. As a result it becomes difficult to compare the performance of NCLs with different geometrical configurations. The present study focuses upon the development of a unified model for the analysis of single-phase NCLs, with constant heat flux heating and convective cooling. Characterizing parameters have been defined such that they are applicable to any geometrical configuration. The developed model has been validated against available experimental results and then employed to compare steady and dynamic performance of rectangular and toroidal loops with identical dimensions. Rectangular loop exhibits larger flow rates under the same operating conditions. However, toroidal loop is inherently more stable which can be attributed to the prevalent weaker buoyancy force. Stability maps for both the loops have also been developed and toroidal loops expectedly exhibit wider stable zone of operation. (C) 2012 Elsevier Masson SAS. All rights reserved.