Heat Transfer for Hydrogen-based Propulsion

氢基推进的传热目的：开发适用于飞机发动机液氢应用的新型轻质传热解决方案。-将稳态和瞬态实验与CFD相结合，探索用于加热和加压低温氢气的流动和传热过程。-测量由密度变化引起的传热抑制程度，研究瞬态对流动和传热的影响。-探索非挥发性替代流体的范围，以代表低温氢，以简化牛津热流体研究所实验室的实验。-开发创新仪器，研究换热器微通道中低温和超临界液氢边界层的转变。简要描述：该项目将探索在飞机推进中使用氢的关键使能技术，作为实现碳减排的一种潜在途径。液氢在进入燃烧室之前需要压缩和加热。两相流换热器的研究将使燃料系统中的氢在燃烧室燃烧前得到调节，因此对氢燃烧的成功至关重要。将研究管道入口效应、表面粗糙度、曲率和湍流对稳态和瞬态传热特性的影响，并开发适当的模型来帮助换热器设计和支持数值模拟验证。研究方法的新颖性：我们将探索液氢加热时密度变化引起的任何传热抑制的程度。极端的绝对温度和温度比（表面与流体）为高精度测量的仪器要求带来了关键挑战。为了解决热管理的低温测量方法的发展，我们将在一开始使用液氮。这种方法可以在进行液氢实验之前降低风险。试验采用不同的水力直径，从远小于到远大于毛细管长度尺度。当汽泡直径与管径相当时，我们将量化流动动力学的影响。这种条件可以产生高、低换热系数，控制多相流内的压降和流量分布。设计并搭建低温实验均匀热流边界条件试验段，在薄壁不锈钢管中进行电阻加热，以提供明确的边界条件。这些数据将成为换热器壳侧和管侧液氢流动实验研究的核心试验载体。该项目将生产一个涡轮风扇的整体模型，随后进行参数化研究，这些研究将改变热交换器的尺寸、热力学循环和重量，以实现整体系统级性能的效率指标。该项目属于EPSRC“建设绿色未来”/“能源和脱碳主题”。参与公司或合作者：牛津热流体研究所和劳斯莱斯。

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.