Calculation of heat balance in burning HMX

Temperature dependences are calculated for a number of physicochemical properties of HMX: the heat capacity of the liquid phase, change in the enthalpy due to heating of the condensed phase to a predetermined temperature, heat of evaporation, saturated vapor pressure, and the vapor diffusion coefficient in low-molecular-weight gases. The data obtained are used to calculate the amount of heat needed to heat the condensed phase to the burning surface temperature in the range of 560–900 K at various degrees of decomposition. The heat of decomposition of HMX under combustion conditions is calculated from the known composition of the reaction products at a pressure of 1 bar. The results of experimental determination of the thermal effects of HMX decomposition by differential scanning calorimetry are presented. The results of the calculations and experiments suggest that at a degree of decomposition $\ge$ 0.6, heat release in the condensed phase can provide heating and evaporation of HMX without heat input from the gas phase. It is shown that the calculated saturation vapor pressures of HMX, which are higher than those presented in the literature, are in better agreement with available experimental data on the HMX vapor concentration profile near the burning surface.