Title: Non-invasive sensor technology based on guided acoustic waves for the traceable measurement of the flow rate of liquid hydrogen and other cryogenic liquids and energy carriers (Acronym: HydrAmess)

Topic:

Hydrogen is considered a silver bullet in the fight against climate change and is gaining tremendous prominence as an alternative energy source amid the current energy crisis. Whether as a fuel and energy carrier for industry, transportation, or the building sector, hydrogen is expected to increasingly replace fossil fuels, thereby contributing to greenhouse gas neutrality and the preservation of our natural resources.

In Germany, we will continue to have to meet a large portion of our hydrogen demand through imports from abroad. This makes the development of a suitable transport and distribution infrastructure all the more important. Hydrogen can be stored or transported and used as an energy carrier in both gaseous and liquid states. In the case of gaseous hydrogen, storage and transport occur under high pressure. In comparison, the liquid form offers decisive advantages as an energy carrier for many applications due to its higher energy density per volume and lower pressure. Liquid hydrogen can be refueled like a liquid when stored at low temperatures. It is suitable for alternative propulsion systems in shipping and aviation, as well as for electric mobility in trucks. Liquid hydrogen can also be transported over long distances by ship without any problems.

As the hydrogen infrastructure expands, so does the need for suitable measurement and sensor solutions to monitor the volume being transported. To use this new energy source economically, it is essential to be able to measure with high precision how much flows through the pipeline or is dispensed: a calibration-capable and industrial-grade measurement method is required. However, liquid hydrogen poses real challenges for conventional measurement methods. It has a very low temperature of -253°C, must be transported or stored in special vacuum-insulated pipes or tanks, and tends to form gas bubbles when exposed to temperature changes. To date, there is therefore no suitable, industrial-grade, and calibratable measurement method for measuring the flow rate and the volume of liquid hydrogen transported. The Institute for Sensor and Actuator Technology (ISAT) at Coburg University aims to change this and develop a novel acoustic measurement method for flow measurement in liquid hydrogen and other liquid energy carriers. For these research activities, ISAT will receive approximately €1 million in funding from the Federal Ministry of Education and Research under the “FH-Kooperativ” program for the years 2023–2027. The goal of the project is to develop specialized ultrasonic sensor technology based on so-called guided acoustic waves (GAW). The sensor technology is designed to precisely measure the flow of liquids even at the lowest “cryogenic” temperatures. ISAT has been conducting research on GAW sensors since its founding in 2007 and is recognized as a leading expert in this field, with a wide range of projects and publications to its credit. GAW technology is particularly well-suited for measuring liquid hydrogen, as all sensor components required to measure the volume of liquid being transported can be mounted on the outer wall of the pipe. Neither the sensors nor the electronics need to come into contact with the liquid and can therefore be easily thermally insulated. Complicated modifications to existing pipeline systems are not required, as the pipe wall itself becomes the sensor through GAW excitation. Another advantage is the minimal installation space required by the GAW sensors. Sensor integration therefore causes virtually no pressure loss, thereby reducing the likelihood of phase transitions and disruptive gas bubbles forming.

The measurement principle used to measure the volume of liquid hydrogen being transported can be described in simplified terms as follows: The acoustic wave excited on the wall of the pipe is refracted into the liquid due to the difference in the speed of sound between the liquid and the wall material. The refraction of the sound wave occurs similarly to optical refraction at a defined angle, which is why the sound wave is emitted obliquely into the liquid. To determine the flow velocity of a liquid and thus the volume transported, the transit time of the wave is measured both with and against the direction of flow. You can imagine this like paddling a boat in a river, once with the current and once against it. Paddling against the current is slower and takes longer; with the current, you need significantly less time for the same distance. The same applies to the sound wave in and against a flow. Calculating the difference in sound transit times then allows the flow rate to be determined.

Through its partnership with Endress+Hauser Flow Deutschland AG, ISAT has an experienced developer of acoustic sensor technology serving as a mentor for the “HydrAmess” project. Endress+Hauser Flow Deutschland AG was founded in 2008 as SensAction AG, a spin-off from Coburg University, and was integrated into the Swiss measurement technology company Endress+Hauser in 2021. The company will advise ISAT on issues related to measurement signal processing, industrial-grade sensor manufacturing, standardization, and calibration, thereby helping to ensure that the technology being researched in the project is developed in line with market needs.

Area of expertise:    Sensors and analytics

Project leaders:        Prof. Dr. Klaus Stefan Drese and Prof. Dr. Thorsten Uphues

Project period:         February 1, 2023 – February 31, 2027

Funding agency:      Federal Ministry of Education and Research, University of Applied Sciences Cooperative