Cryogenic heat exchanger and fracture mechanics.

 

This technology project  was developed according to the requirements of the European Space Agency (ESA) for the Hermes program. The cryogenic heat exchanger function is to ensure, during all possible vehicle mission phases, the warming of the cryogenic oxygen coming from cryogenic tanks, by the mean of the external fluid loop (a freon type fluid) considered as the “hot” side.

The structure is essentially a cylindric body with a central duct where flows the hot fluid and with a peripheral inner cylinder with helical grooves where the cryogenic oxygen circulates, with a temperature of –183°C at the inlet. The structural analysis for static acceleration, thermal loads, proof and burst pressures, sinusoidal and random excitation was performed using ANSYS.

Because this pressure vessel is considered as a potentially fracture critical item (PFCI) a safe life analysis is also required. The fracture mechanics was analyzed with the ESA code Esacrack which includes specific programs for generating load and stress spectra (Esaload) and for evaluating the crack growth stability (Nasfla/Nasgro) and fatigue analysis (Esafatig).