A comparative study is presented of literature involving convective heat transfer in annuli. It is shown that more research is needed in the area of convective heat transfer correlations in concentric annuli, as little agreement is found among existing correlations. A correlation predicting Nusselt numbers in annuli with ratios ranging from 1.7 to 3.2 was developed experimentally for water as fluid. The correlation has an accuracy of 3% in terms of experimental values for a Reynolds number range, based on the hydraulic diameter, of 4,000 to 30,000. The correlation was also compared to numerical predictions