Modelling of the heat transfer coefficient in a nozzle bomb for gun propellant erosivity studies

Nozzle bomb tests are a standard to determine the erosivity of gun propellants. Such tests focus on the mass lost by the nozzle due to the combustion of the explosive. Metallographic examination of the nozzles after testing different ammunitions shows that the heat transfer from the combustion gases to the nozzle is the most important variable that influences the mass loss. Therefore, the determination of the heat transfer coefficient for the different combustion gases is of vital importance to understand nozzle wear in the bomb. Single and double-base explosives, SB and DB respectively, were tested in a nozzle bomb. With the pressure curves obtained in the bomb and the compositions of the combustion gases calculated with the ICT-ThermodynamIC Code ®, the calculation of the heat transfer coefficient for each gas composition is possible. The results show that the calculated temperature in the nozzle for both SB and DB ammunitions is similar but the heat transfer coefficient of the DB ammunition is higher. Thus, the differences between SB and DB erosivities in the nozzle bomb can be explained by the differences between the heat transfer coefficients of the combustion gases. Further investigation on minimizing the heat transfer coefficient of the combustion gases and its applicability on the synthesis of new propellants is needed.