Session: 06-03: Hydrogen Injection and Mixing

Paper Number: 140954

140954 - Mixing and Warming Characterisation of Cryogenic Hydrogen Jets Through Proper Orthogonal Decomposition 

Abstract: 

Hydrogen is being increasingly used as an alternative fuel for vehicles and aircraft propulsion. For long-distance and/or large-scale transportation and storage, liquid hydrogen or cryo-compressed hydrogen with typical densities of 70 g/L, are more promising than warm compressed hydrogen. The use of cryogenic compressed hydrogen introduces new challenges for existing safety standards. In the event of potential leaks, the resulting jets are characterised by intense heat and mass transfer. Furthermore, given the storage pressure and leak diameters, these jets can acquire extremely high velocities, which in combination with the ultra-low temperature prevailing introduce considerable challenges to characterize the physics of complex cryogenic hydrogen jets.

In this study, using a novel CFD framework specifically tailored to ultra cold dynamics, we analyse the warming and diffusion of a hydrogen cryogenic gas jet into atmospheric air. The simulated conditions are based on an experimental vertical jet, Stagnation conditions are characteristic of unintended leaks from pipe systems that connect cryogenic hydrogen storage tanks and could be encountered at a fuel cell refuelling station. Jets with pressure up to 5 bar and temperatures just above the saturation liquid temperature were examined.

Comparisons are made to the centerline mass fraction and temperature decay rates, the radial profiles of mass fraction and the contours of volume fraction. Satisfactory agreement with the measurements was found in terms of centerline mass fraction and temperature. 

To characterize the mixing and warming mechanisms of such cold jets, a principle component analysis (PCA) method, namely the proper orthogonal decomposition (POD) technique, is also performed on the simulated data sampled at a fixed domain but at different instants in time. The combined role of the mass and heat flux on heating the cold hydrogen jet is observed. The POD shows the role of turbulent fluctuations in warming the core of the jet. The heat flux observed in the outer plume instead is not captured by the low-order temporal fluctuations, which means that thermal diffusion is responsible for the warming in this region.

Presenting Author: Giovanni Tretola University of Oxford

Presenting Author Biography: After graduating from the University of Sannio (Benevento, IT) with a degree in Energy Engineering, Dr Tretola pursued his career in energy research, completing a Ph.D. in Mechanical Engineering at the Imperial College London. His doctoral research, titled "Large Eddy Simulation of atomisation process using the Eulerian Stochastic Fields method", focused on numerical simulations of turbulent sprays through probabilistic approaches.

Following his Ph.D., he conducted postdoctoral research at the University of Brighton, where he worked on th enumerical modelling of multiphase flow at cryogenic conditions. He then moved to Kings’ College London, where he worked on the development of advanced computational techniques to study the liquid/solid interaction.

Dr Tretola currently works as a Research Assistant at University of Oxford, working on Hydrogen Safety through computational fluid dynamic and machine learning methods.

Authors:

Giovanni Tretola University of Oxford
Li Shen University of Oxford
Felix Leach University of Oxford
Konstantina Vogiatzaki University of Oxford