In this paper a mathematical model for the convection section of industrial furnaces (energy recovery) is presented. In the paper, method of heat transfer on the outside and inside of smooth and finned tubes in the convection section has been investigated. After review of the various models of heat transfer, an appropriate model was selected, and the software for calculating the amount of heat which is transferred to the tubes in each row and the distribution of gas and fluid temperature according to rows of tubes were prepared. At the end, the numericaldata obtained from the simulation program are compared with the measured data collected from primary reformer of Razi petrochemical plant and convection section of fired process heater.
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