On the road to more climate-friendly mobility, hydrogen is becoming more important as a new fuel. However, hydrogen refuelling is more complex than gasoline and diesel. Unlike other gases, hydrogen heats up as it expands, resulting in changes in pressure and temperature during refuelling, which must be monitored accurately. That's why Heinrichs Messtechnik GmbH, a subsidiary of the Kobold Group, has developed the TMU-W 004 mass flow meter that ensures precise dosage despite changes in pressure and temperature. This device is the first of its kind to be certified to the international standard OIML R 139 2018 and therefore approved for hydrogen filling stations. A compact and sturdy case protects sensors and measuring loops that use the Coriolis effect and allow for a very accurate flow measurement. The deported electronics converts sensor signals into a mass flow reading, and also measures the temperature of the fluid. The TMU-W 004, suitable for high-pressure applications of up to 1000 bars, is already used in the filling stations of the publicly traded company Nel Hydrogen.
Hydrogen as a fuel is gaining ground in Europe, thanks in part to the stimulus packages adopted by governments. "For passenger cars, hydrogen refuelling is usually 700 bars. This high pressure is necessary to generate the energy density needed for the right measurement conditions, explains Guido Thometzki, CEO of Heinrichs Messtechnik GmbH. During this process, the temperature should not exceed 85 degrees Celsius, because otherwise the tank coating may be damaged. »
As the tank expands and heats up during filling, the hydrogen is cooled before reaching the tank. This high-pressure environment, as well as the small size of the hydrogen molecule, represents significant constraints to achieve an accurate measurement of hydrogen flow.
Based on this observation, Heinrichs Messtechnik GmbH, a subsidiary of the Kobold Group, has modified its coriolis-effect mass flow meter already proven for high-pressure gas applications, and now offers the TMU-W 004, a version specially designed for hydrogen measurement. This flow meter allows you to accurately measure, when filling, the amount of hydrogen transferred to the vehicle's tank. This allows the precise invoice of the quantity filled, which is a prerequisite for refuelling at public hydrogen filling stations. It covers a range of measurements ranging from 0.133 kg/min H2 to 4 kg/min H2.
During the development phase, the use of sophisticated engineering tools made it possible to make numerous simulations on the flow meter structure as well as on the fluid itself, which led to optimal arrangements and dimensions of all mechanical and electromechanical components. As a result, the device has become the first and only flow meter in the world to be certified under the international standard OIML R 139 2018, which covers hydrogen flow measurement systems for vehicles. Norwegian publicly traded company Nel Hydrogen is already successfully using the TMU-W 004 at its gas stations.
The special layout of the sensors gives precise results
In order for the meter to fit best into hydrogen distribution stations, the TMU W004 flow meter was designed much more compactly than previous models. Inside the compact, deformed-resistant case are two U-shaped parallel measuring tubes. "An arousal system vibrates the measuring tubes at their own frequency. When fluid circulates through these tubes, the Coriolis effect causes a shift between these frequencies," explains Mr. Guido Thometzki. "Sensors optimally placed at the measuring tubes detect this shift and send it as an electrical signal to the electronics for a complete processing of the signal. From these signals, the current mass flow is calculated.
The specific architecture of the device - that is, the shape of the measuring tubes and the ideal positioning of the sensors on the tubes - as well as the further harmonization of other components such as bellows, make it a particularly sensitive and precise flow meter, despite the thick walls of the measuring tubes. This robustness of the measuring tubes is necessary to withstand the high pressure of 1000 bars (the test pressure is actually 1500 bars). The sturdy, fully welded case for greater stiffness largely protects the sensitive measuring equipment in it.
The actual volume is then developed from an electronic pulse output. "The user also gets information about the temperature of the fluid, and possibly the density of the fluid. This data can be used to control the compressor that pumps hydrogen, for example by switching to a higher volume or, conversely, by interrupting pumping,"adds Guido Thometzki. The electronics have a two-line LCD display that directly shows the chosen values. This electronics is easy to set up using the four keys on the front. Among the various functions available, the user can define the physical units, the sizes displayed, the outputs and analyze the defects. The transmitter is available in a process version (round waterproof box) or installed in an electric cabinet in rack version. Both types of casings are pressure resistant and are certified as "intrinsic safety," which prevents fires or explosions in the event of a gas leak.
Simulations and flow tests ensure accurate measurement
For the development, manufacture and calibration of its meters, Heinrichs Messtechnik GmbH has used numerous simulation and optimization methods to ensure the accuracy and reliability of its devices in every conceivable condition. "Devices for measuring high-pressure gases such as hydrogen, such as the new TMU-W 004 for hydrogen filling stations, can of course be no exception," explains Thometzki. On the contrary, during the development of TMU-W 004 in particular, we used state-of-the-minute simulation methods specially developed for fluid mechanics and structural design, such as FEM (finite element method), CFD (computational fluid dynamics) and FSI (fluid structure interaction). Only in this way was the TMU-W 004 able to meet the seemingly contradictory requirements of the highest accuracy and extreme reliability of measuring high-pressure gas flows. The measurement accuracy was also expected to remain high despite fluctuations in pressure and temperature during filling. "The fact that the TMU-W 004 not only meets the requirements of the OIML R 139 2018 standard, but far exceeds them with its precision class of 1.5 for hydrogen, shows, above all, what the TMU-W 004 development team has accomplished," concludes Dr. Thomas Chatzikonstantinou, technical director of Heinrichs Messtechnik GmbH.
For more than a hundred years, Heinrichs Messtechnik GmbH, founded in 1911 in Dusseldorf, has been developing and selling flow meters. From the beginning, one of its main markets was the chemical or petrochemical industry. Since the 1960s, the company has developed and marketed all-metal float flow meters. In the mid-1980s, Heinrichs was the first European company to build a mass flow meter using the Coriolis effect, and in the years that followed, it constantly expanded its range. Today, the company has customers in many sectors, including chemistry, oil and gas, energy, plant construction and mechanical engineering. In 2008, Heinrichs joined the Kobold Group, which enabled him to have an extensive sales network through the group's international subsidiaries. Heinrichs develops and manufactures all its products in-house at its headquarters in Cologne.
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