The heat transfer characteristics in a smooth tube are studied. Based on the available experimental data, a new correlation is proposed to predict the heat transfer coefficients inside tubes of different lengths. The predicted results show that for a range of L/D from 26.31 to 58.14, the heat transfer coefficient may be reduced by 20.56% and increased by 13.31% at the beginning and at the end of this range, respectively. The results obtained from the proposed correlation are compared with other analytical and experimental data, and satisfactory agreement is found. [ABSTRACT FROM AUTHOR]