Numerical results f or air undergoing laminar forced-convective heat transf er in the entrance region of a fl at rectangular duct with uniform wall temperature are obtained fo r uniform inlet velocity and temperature profiles . The coupled governing partial differential equations are solved in discretized form with proper ty variations being updated through physical property relations . This enables the physical property and thermofluid solutions to converge simultaneously, resulting in a realistic solution to the governing equations . I • Constant-property results are also obtained , and Nusselt numbers of both the constantand variable-property models are compared with those of other numerical computat ions . t he results of the variable-property model are also compared with available experimental data. The variable-property results exhibit excellent correlation with the available experimetual data. A sensitivity analysis is performed to determ ine the effects of individual kroperty variations on local Nusselt numbers .