The concept of eddy diffusivity is reviewed, and theoretical comparison study is performed to predict heat transfer coefficient using various proposed models for eddy diffusivity at wide range of Prandtl (7-800) and Reynolds numbers (5000- 100 000) in pipe flow. The modified Reynolds analogy equation is employed to start the analysis for predicting the heat transfer coefficient. The influence of Re, Pr and the distance from the wall (y(+)) on the eddy diffusivity and consequently on the heat transfer coefficient and temperature profile is studied and discussed. The results are compared with experimental data. A new expression of thermal eddy diffusivity is been developed by comparing modified form of Reynolds analogy correlation with experimental heat transfer data. Using this new expression more accurate results can be obtained. For future research work, It is interesting to include links to other models and to examine the behaviour of this empirical model in complex flow configurations.