Heat Transfer for Hydrogen-based Propulsion

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Heat Transfer for Hydrogen-based PropulsionAim: Develop novel light-weight heat-transfer solutions suitable for liquid hydrogen in aircraft engine applications.Objectives: - Combine steady and transient experiments with CFD to explore the flow and heat transfer processes used to heat and pressurise cryogenic hydrogen.- Measure the extent of heat transfer inhibition caused by density changes and study the effects of transients on flow and heat transfer.- Explore the scope for non-volatile, proxy fluids to represent cryogenic hydrogen to ease experiments in the Oxford Thermofluids Institute's laboratory.- Develop innovative instrumentation to study cryogenic and supercritical liquid hydrogen boundary layer transition in the microchannels used in the heat exchangers.Brief description: This project will explore key enabling technologies for the use of hydrogen in aircraft propulsion as one potential avenue in achieving carbon reduction. Liquid hydrogen requires compression and heating before being introduced into the combustion chamber. The proposed research in two-phase flow heat exchangers would enable conditioning of hydrogen in the fuel system prior to burning in combustor and is therefore critical to the success of hydrogen burning combustion. The influence of tube entry effects, surface roughness, curvature and turbulators on steady and transient heat transfer characteristics will be studied and appropriate models developed to aid heat exchanger design and support numerical modelling validation. Novelty of Research Methodology: We will explore the extent of any heat transfer inhibition caused by density changes as the liquid hydrogen is heated. The extreme absolute temperatures and temperature ratios (surface to fluid) introduce key challenges in instrumentation requirements for high accuracy measurements. To address the development of cryogenic measurement methods for thermal management, we will use liquid nitrogen at the outset. This approach will serve as a risk mitigation before performing liquid hydrogen experiments. Experiments with varying hydraulic diameter, from much less than to much great than capillary length scale will be conducted. We will quantify the impact of flow dynamics when vapour bubbles diameters are comparable to the tube diameter. Such conditions can result in low and high heat transfer coefficients and control the pressure drop and flow distributions within multiphase flows. We will design and build uniform heat flux boundary condition test sections for cryogenic experiments and implement electrical resistive heating in thin-walled stainless steel tubes to provide well-defined boundary conditions. These data will form the core test vehicle for experimental studies of liquid hydrogen flow on both shell and tube side of heat exchanger designs.The project will lead to the production of a holistic model of a turbofan followed by parametric studies which will vary heat exchanger size, thermodynamic cycle and weight to achieve efficiency metrics for overall system level performance.This project falls within the EPSRC 'Building a green future'/ 'Energy and decarbonisation theme'. Companies or Collaborators involved: The Oxford Thermofluids Institute and Rolls-Royce.