- The transient response of three types of fins (longitudinal, spine and annular), each with three possible shapes (rectangular, triangular and parabolic) is analyzed using numerical solutions. Four initial conditions involving step changes are examined. Two initial conditions concern the heating up of fins by exposing the base to constant temperature or constant heat flux. Two other initial conditions concern the cooling down of operating fins by dissipating heat to the surroundings exclusively, or together with heat dissipation to the base. Characteristics and detailed results from which the temperature distribution at any time can be predicted are presented graphically.