Investigation of Mixing and No-Flow Characteristics of Hydrogen-Methane blends in Low and High Reynolds Number Scenarios

Abstract

Hydrogen has been identified as a viable clean energy carrier as part of Energy Transition. The adoption of hydrogen energy will require the design and installation of new infrastructure and thus before a full-scale shift can occur, blends of hydrogen and natural gas will first be integrated into the existing natural gas transmission and distribution infrastructure. This study focuses on the use of methane-hydrogen blends within domestic gas piping systems and explores both mixing and no-flow scenarios for the blends of these two gases. Methane and hydrogen possess distinct physical properties, with methane having a density almost eight times that of hydrogen under standard conditions, and hydrogen containing only one-fifth of the volumetric energy density of methane under similar conditions. Thus, to maintain the same energy supply that just the natural gas provides, larger volumes of methane-hydrogen blends will be required. The physical differences necessitate a comprehensive investigation from both physical and safety point of view. This study examines the mixing and no-flow characteristics of methane-hydrogen blends under laminar and turbulent flow conditions in a specially designed apparatus constructed using ¾” black steel piping. The experimental apparatus includes a 10’ (3 m) long horizontal optical test section with optical windows at either end, vertical risers, a serpentine section, and various pipe fittings like Tees, elbows, unions and valves to simulate a customer-side domestic gas piping system. One end of the optical test section is equipped with a He-Ne laser source, while the other end incorporates a Shack-Hartmann wavefront sensor. The optical measurements quantify the gas activity within the horizontal optical test section. Each component gas has a unique refractive index, and the measurements capture the resulting optical aberrations, which become more evident as the gases separate within the optical test section. An optical variance is computed and used to quantify the gas activity. Physical parameters including temperature and pressure are also monitored during experiments. Two Peristaltic pumps with a combined maximum flow capacity of up to 70 liters per minute (LPM) are used to achieve either a laminar or turbulent flow. The research also explores the time required for the component gases to blend completely from an initial unmixed state, thus providing a Time-to-Mix and consequently, a Distance-to-Mix plot against Reynolds number. The experiments employ both a proxy gas mixture (nitrogen-helium) for the development of experimental procedures and system characterization, as well as various compositions of methane-hydrogen blends. Beyond the study of mixing and no-flow behaviour, the research conducts leak experiments from the horizontal test section, after extended period of no-flow, to evaluate the behavior of stratified blends during leaks and analyze the composition of leaked gases using gas chromatography. Time-to-Mix and Distance-to-Mix plots indicate a significant reduction in gas mixing time at higher Reynolds Numbers. Gas chromatography analysis of the leak experiments show no notable change in the leak sample composition from the original gas composition for various stopped flow durations. The research provides novel insight into previously less explored areas, including the no-flow behavior of methane-hydrogen blends in domestic gas piping systems, the time required for blending, and the composition of gas blend leaked after extended no-flow duration at varying valve settings.