Injection rate is the most relevant perturbing effect detected in the ThermoMetric TAM 2277-204 injection calorimeter. In other studies about this subject, several phenomenological expressions can be found. In this work, the connection between sensitivity and heat capacity C = rho c(p)v (rho density, c(p) specific heat and v volume) and injection rate will be proved by physical models, using experimental values of the sensitivity, obtained from Joule effects. Sensitivity decreases when the injection rates and/or the specific heat of the liquids increase.