A numerical study is carried out on natural convection in a twodimensional trapezoidal enclosure with a centered discrete heater.For a fixed area discrete heater

in the range of aspect ratio ε from 1 to 6

rotation angle θ from 0° to 90°

and Rayleigh number from 103 to 106

the changes of isotherms

streamlines and Nuave in the trapezoidal enclosure are studied.The simulation results show that heat transfer mechanism in the trapezoidal enclosure changes from conduction to convection as Ra increases

and Nuave increases simultaneously.The variations of ε and θ also have great effect on the heat transfer in the enclosure

and the increase of ε has a positive effect on the heat transfer.Nuave reaches the maximum or minimum value at different values of Ra and ε.