Multiphysics modeling and experimental validation of low temperature accumulator for cryogenic space propulsion systems

Within the framework of Low Thrust Cryogenic Propulsion (LTCP) systems, a low-temperature accumulator acting as thermal energy storage tank is an interesting option for cyclical processes under intermittent firings avoiding the use of turbopumps in the cryogenic stages. Thus, liquid propellant (oxygen, hydrogen or methane) can be gasified under a fast transient evaporation process cooling the accumulator. On the other hand, the same accumulator can be heated by solar collectors, electrical heaters or by means of evaporated propellants recovering heat losses from fuel cells. To obtain a very high thermal energy storage density, the thermal energy stored in the accumulator is performed using a Phase Change Material (PCM) rounding the different fluid flow tubes which heat or cool the storage tank during periodical cycles. The energy management due to the mismatch between intermittent firings, together with optimum design based on minimum weight with maximum heat transfer capacity has led to developing a numerical simulation model. Thermal and fluid dynamic behavior of multi-physics phenomena in the accumulator is based on coupling the two-phase flow inside tubes working under cryogenic conditions with sensible and latent heat transfer through the tank. The numerical model is divided into: 1) a one-dimensional and transient resolution of the governing equations (conservation of mass, momentum, and energy) for the fluid flow inside ducts; 2) a multi-dimensional and transient resolution of the governing equations in the region occupied by the PCM, incorporating a turbulence model to solve the convection phenomena involved; and 3) a multidimensional and transient treatment of the thermal conduction equation for the solid tubes. The numerical results are validated by means of an experimental cylindrical accumulator test facility, instrumented with 25 thermocouples around the vertical tube which goes through the tank and four multilevel thermocouples columns at different distances radially far from the vertical tube located at the center. The comparative analysis shows a good agreement between both numerical results and experimental data for a wide range of different working conditions showing detailed phenomena analysis, together with the possibilities of this model for design optimization purposes. (C) 2018 Elsevier Masson SAS. All rights reserved.