Mixed convection heat transfer in a 5 × 5 rod bundles

- Experiment on turbulent mixed convection heat transfer in a 5 × 5 was performed.
- Heat transfer impairment have been observed in current experiment.
- Buoyancy effect on heat transfer in rod bundles should not be neglect.
- New correlations have been established for mixed convection in rod bundles.

In order to investigate the buoyancy effect on heat transfer in rod bundles, experiments were performed at low flow rate with Reynolds number ranging from 1 × 103 to 3 × 104 in a 5 × 5 squarely arrayed rod bundles. The diameter of the rods are 10 mm with a pitch of 13.3 mm, and the length of the test section is about 3 m. The rods are heated uniformly by a DC power, and cooled by pressurized water. The experimental data indicates that Weisman's correlation predicts well within a deviation less than 10% in forced turbulent convection, but overestimates the Nusselt number in mixed convection conditions. It's been found that mixed convection heat transfer in rod bundles is similar to that in simple channels, with increasing of free convection component, the heat transfer tends to be impairs firstly, and then followed by enhancement. The experimental data also indicates that buoyancy effect on heat transfer should not be neglected even when Reynolds number is about 15,000 under some certain heating conditions. New empirical correlations have been proposed for the prediction of forced turbulent convection heat transfer and mixed convection heat transfer in rod bundles respectively.