As can be seen from Figure 2.4, when the pressure is fixed and does not reach the supercritical state, the specific heat capacity of carbon dioxide decreases with the increase of temperature. When the state just enters the supercritical state, the specific heat capacity will change greatly. From the figure, it can be seen that the specific heat capacity reaches the extreme value at 7.37Mpa and 30.95℃, while under the condition of high specific heat capacity, it is necessary to absorb more heat to change the phase state of the substance, so carbon dioxide needs to absorb more heat in this state.