This work shows the difference between the results obtained in the electrical calibration and those corresponding to the chemical calibration in a TAM2277-204 flow-calorimeter by Thermometric. This difference is due to the fact that the mixture and the electrical dissipation do not occur in the same place. There are other additional aspects inherent to the mixture dissipation: the mixture does not take place instantaneously and extends in space. The physical model that has been calculated in this work explains the characteristics that are proper to a mixture dissipation and the effects of the injection in a qualitative and quantitative way.