Heat transfer in the radiation chamber of a cylindrical tubular heater is analyzed. An energy-conservation model using cylindrical coordinates in the form of integral and differential equations is used for describing the radiative and convective heat transfer in a combustion chamber. The Monte Carlo method and the difference method are used for solving the energy equation. For calculation inside the tubes

crude oil is treated as a mixture of many pseudo-pure components

and the Soave equation is used for the calculation of vapor-liquid equilibrium and the physical and thermo-dynamical properties of the liquid and vapor phases. Heat transfer and pressure drop of the fluid flow inside the pipe are next estimated. Results calculated by using a PDP-11/45 computer are compared with the operating data of the crude heater in a refinery. It is believed that model developed and the calculation program are acceptable.