Abstract: A separated model is developed for the recirculating flow and heat transfer in a kettle reboiler tube bundle. Subcooled boiling at the bottom of the bundle and some recirculating liquid entering the bundle from its sides are considered. Compared with previous models, this model has more reasonable agreement with the experimental results by Cornwell et al. The effects of heat flux, liquid level and subcooled boiling length on the recirculating flow rate and heat transfer coefficient are examined. The height of subcooled fraction of the tube bundle decreases with increasing heat flux. Therefore, the effect of subcooled boiling is outstanding at low and middle heat flux. Owing to the existence of side flow,the recirculating flow rate increases for higher tube rows in the subcooled boiling region, and maintains constant in the saturated boiling region.