Dawn Aerospace is start up company that is developing a reusable sub-orbital spaceplane. The MK-II rocket powered spaceplane uses High Test Peroxide for its main engine and reaction control system. Catalyst beds are required to decompose High Test Peroxide (HTP) to steam and Oxygen. To investigate the decomposition of HTP in a pellet catalyst bed a numerical model was developed which is capable of predicting High Test Peroxide flow decomposition in catalyst beds.

The model developed is based on a two-phase flow through the catalyst bed that is chemically reacting by undergoing decomposition. The flow is assumed homogeneous, adiabatic, and continuous resulting in steady state model outputs. Fast equilibrium adsorption and finite rate desorption of Hydrogen Peroxide on to the catalyst surface is assumed in a single step. The decomposition is modelled using the Arrhenius relations. Additionally, the flow pressure losses are computed using an extended Ergun relation for two phase flowthrough packed beds. The model can predict the flow temperature distributions up to 98% reaction advancement. The model was verified by comparing it to existing model results, this showed good agreements in 7 of the 8 cases. The results showed consistently that the model predicted 98% of the decomposition progression is achieved in a shorter catalyst bed length than the catalyst bed lengths in an existing model (4 to 14% shorter). The flow pressure losses of the models showed deviations compared to the existing models ranging from 5.55% to 12.18%. The differences in the flow temperature and flow pressures are discussed and related to the governing theories of the models.

To validate the model, experiments were performed. The test data were used in model validation and a good agreement was found between the test data and the simulated results. The simulated flow temperature and the measured temperature deviated from 0.41% to 1.93% of the adiabatic flow temperature. The overall pressures showed good agreement with the experimental average, with pressure drop deviations less than 1% of the operating pressure. In all experiment cases the flow distribution predicted was within the measured pressure roughness.

Many simulations were performed and compared to investigate the impact of varying design choices and operational conditions. In all cases the flow development along the catalyst bed length was assessed. In comparison to the simulations results it was found that an increase of operational parameters such as pressure promoted gas phase decomposition resulting in shorter bed length requirements. Similarly, the influence of feed High Test Peroxide concentration was evaluated and finding showed increasing concentration to shorten the required bed length. The analysis of the simulated conditions showed that the increase of mass flow inversely impacts the required catalyst bed length. This model serves as tool to identify the operational parameters and their impacts in catalyst beds. The Model outcomes demonstrating the effects of operational parameters and design choices on catalyst bed helps in understanding their interactions and can aid in catalyst bed design and optimisations processes.