Work Package 3 focuses on SI-traceable temperature measurements for liquefied gases, including LNG and LH₂. The objective is to determine the accuracy of (bio-) LNG in field temperature measurements and to achieve low uncertainty (target is <0.5 K) in industrial conditions while maintaining traceability to the SI unit, the kelvin.

Task 3.1 – Modelling of Temperature Sensors: Two complementary modelling approaches were developed: a 3D finite element model (COMSOL) and a 2D finite-volume model. Validation showed agreement within 2%, confirming reliability.

Figure 1. Modelling sensor behaviour

Key insight: Vapour phase formation near the thermometer significantly impacts measurement accuracy and response time.

Task 3.2 – Calibration and Extrapolation: Calibration of 12 industrial thermometers has been completed between 77 K and 273 K. Work focuses on evaluating extrapolation methods to reach LNG (111 K) and LH₂ (20 K) conditions.

Figure 2. Calibration curves for 12 thermometers with their calibration uncertainties

NPL will calibrate thermometers down to 20 K using cryostats, while TU Ilmenau develops calibration facilities. These activities will support uncertainty evaluation.

Figure 3. NPL cryostat facilities

Task 3.3 – Uncertainty Evaluation: A complete uncertainty budget will be developed, incorporating modelling, calibration, and extrapolation contributions to achieve target uncertainty of 0.5 °C (k=2).

IMPACT: Delivering traceable, cost-effective temperature measurement solutions for LNG and hydrogen industries.