This paper shows the results of a computational study relating to the calculation of heat and mass transfer coefficients in the entry region of a circular duct. Laminar flow with temperature dependent physical properties is used. The results are compared with the classical results obtained for a fluid with constant physical properties. It is seen that a plot of the Nusselt number versus the inverse Graetz number does not yield a unique curve, but rather depends on the channel diameter, wall temperature or flux value, and the inlet fluid velocity. The deviation from the curve obtained with constant physical properties increases as the velocity decreases.