One-dimensional modelling of the nozzle cooling with cryogenic oxygen flowing through helical channels in a hybrid rocket

A one-dimensional model of the cooling process occurring in a hybrid-rocket nozzle working with cryogenic oxygen flowing through helical channels is addressed in this work. Although the regenerative cooling system in rocket engines involves further complexity, it is here investigated as an option for the suppression of graphite-nozzle erosion in hybrid rockets. The model is based on the solution of the conservation equations of mass, momentum, and energy of the coolant. The Modified Benedict-Webb-Rubin equation of state was used for its accuracy in both the fluid phases of oxygen. The conservation equations for the coolant flow are coupled with a one-dimensional heat transfer model for the evaluation of the nozzle wall temperature at both the cold and hot sides, which has allowed assessing the developed model prediction capabilities by means of the data collected from three engine hot firings. Thus, parametric analyses were carried out to show the effect of the number of helical channels and evaluate the performance improvement obtained in supercritical conditions.