First, go expression under setup .. right click --- newwrite the name as T_avin the expression write Average(Temperature, ['heater_wall'], Weight = 'Area) and save the expressionWhen Defining the heat source, click on the arrow on the right and select expression and write IF(T_av < 90 , 18500, 0) and save the expressionNow, Fluent will calculate the average heater_wall temperature and if it is below 90, the heat generation will be 18500. If the temperature goes above 90, the heat generation will be 0https://forum.ansys.com/discussion/comment/112866#Comment_112866

Thank you for your help. nWhen I define the expression, I got that is invalidnn