Flow, level & control
Thermal-mass measuremenT
principle The best choice for hydrogen-ready gas meters
By Sensirion’s Michele Monitaro, key account manager (Industrial Market) and Konrad Domanski, product manager (Gas Metering Solutions)
a)
sector contributes significantly to Europe’s CO2 emissions. A promising strategy in this respect is
T b) c)
Figure 1: MEMS (micro-electromechanical system)- based calorimetric sensor element: no gas flowing (a), no gas flowing with heating element activated (b), gas flowing with heating element activated (c).
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gradually replacing natural gas with renewable gases, such as sustainably produced hydrogen or biogas. The use of hydrogen in particular is likely to be a favourable course of action, and preparations are already underway to switch the entire gas infrastructure in line with this planned transition (e.g. starting in 2025, all new gas boilers sold in the UK have to be compatible with pure hydrogen). Gas meters are an essential part of gas infrastructure, and are indispensable in reliably and fairly billing gas consumption. In this article, the experts at Sensirion examine the metrological behaviour of thermal- mass gas meters operating with natural gas mixtures containing significant amounts of hydrogen and pure hydrogen. The article will present measurement data, discuss measurement accuracy and operational safety, and explain why it will still be possible to maintain thermal-mass gas meters’ compact size regardless of the hydrogen content, which is the key advantage that hydrogen-ready solutions have over the other metering technologies.
he European Green Deal is the strategic plan to make the European Union carbon neutral by 2050. Decarbonising the energy sector will be vital to achieving this goal, as this
An IntroDuctIon to the therMAl-MASS MeASureMent prIncIple A calorimetric sensor element based on MEMS (micro-electromechanical system), as shown in Figure 1a), is the core element of any thermal- mass flow sensor, such as those used in gas meters. The sensor element can be found on a membrane on a silicon chip and consists of a micro-heating element and temperature sensors that are integrated upstream and downstream. When an electric current flows through the micro-heating element, it generates a temperature profile on the membrane. If no gas is flowing, the temperature is identical at both the upstream and the downstream temperature sensors (see Figure 1b)). If gas flows across the membrane, it generates a heat flow – in other words, it causes the temperature profile on the membrane to change – resulting in a temperature change between the upstream and downstream temperature sensors (see Figure 1c)). The resulting difference in temperature between the two sensors creates a precisely measurable sensor signal that is a function of the flow velocity: the greater the difference in temperature, the greater the gas’ flow velocity over the sensor element. The thermal-mass flow measurement principle
January 2022 Instrumentation Monthly
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