Experimental investigations of laminar mixed convection in a square array of bare rods

The validity of employing the fully-developed flow and isolated-cell assumptions was investigated experimentally. A test section with 16 electrically heated rods (only 4 were loaded) was designed and built. Detailed velocity and temperature profiles along the centerline of the subchannels were measured, for uniform lateral power distributions, at three axial planes utilizing the hydrogen bubble technique and movable thermocouples, respectively. The computational results for the test conditions obtained from the above single-cell, fully-developed flow analysis were then compared to the experimental data. Results of the data comparison showed that the fully-developed flow analysis tends to overestimate the buoyancy effects and provides only a conservative estimation of the buoyancy forces. Flow developing effects should be taken into account to properly reduce the degree of conservatism