Abstract
Cryogenic liquid propellants are used in liquid rocket engines to obtain high specific impulse. The flow rates are controlled by turbopumps that deliver liquid propellant to the engine at high pressure levels. Due to the very low saturation temperature of the cryogenic propellant, in the first phases of the transient operation, in which the engine is at ambient temperature, its surfaces are subject to boiling conditions. The effect of boiling on the heat transfer between the solid and the fluid needs to be well characterized in order to correctly predict the cryopump metal temperature temporal evolution and the necessary amount of propellant. With the aim of benchmarking numerical tools against experimental data, a representative test case was chosen. This consists of a stator-rotor-stator spinning disc reactor studied under single-phase and two-phase heat transfer conditions. The numerical approaches used are represented by a 1D network solver, where the pressure drop and heat transfer are calculated by correlations, and Computational Fluid Dynamics (CFD) simulations, carried out with ANSYS Fluent. Both the numerical tools returned a reasonable agreement in single-phase conditions, also thanks to the use of adequate correlations in the flow network solver and typical conditions for the CFD simulations. Two-phase conditions on the contrary are more challenging, with underpredictions up to 20% and 80%, respectively. The issues are ascribable to the use of correlations that are inadequate to capture the two-phase phenomena occurring in the srs reactor and numerical limitations in the actual implementation of the boiling model in the CFD solver.
Highlights
The stator-rotor-stator spinning disk reactor proved to be a challenging test case for the numerical tools employed in the context of this activity
The Computational Fluid Dynamics (CFD) simulations were characterized by a slight overprediction of the heat transfer effectiveness
This effect might be ascribed to the ideal conditions considered in the CFD simulations, which might contribute to reducing the temperature difference between the fluids and to enhance the heat transfer rate
Summary
Flow network solvers are the most appropriate tools to preliminary design and analyse components and systems of the two-phase heat transfer phenomena This approach relies on 1D modelling, complex 3D problems must be simplified and typically represented by a series of interconnected elements linked by nodes, composing the equivalent flow network. Three dimensional (3D) CFD allow us to account for realistic geometrical features, variable boundary conditions in space and time as well as complex flow fields This represents a considerable advantage compared to empirical approaches based on 1D flow networks or simplified scenarios such as straight channels, pool or thin film boiling. The test case offers experimental data on different fluids (water and dichloromethane) and different heat transfer scenarios (single-phase and two-phase), as well as both stationary and rotating conditions It considers a low-pressure level and mini annular channels between circular disks. The benchmark of the tools will be valuable for their subsequent exploitation for design and analysis purposes
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