Anastasios Badarlis

Measurement of Gas Thermal Properties Using the Parametric Reduced-Order Modeling Approach

This paper deals with a thermal gas property micro-sensor. The proposed modeling approach of the sensor was based on reduced order modeling, in contrast to the traditional analytical modelling approach, which is the standard for this kind of sensors. This sensor was deployed for the measurement of the thermal conductivity (k) and the volumetric heat capacity (ρcp) of gases and works according to the temperature oscillation technique. A proper model is crucial for the measurement accuracy. The scope of this paper was to investigate the applicability of a sensor model based on a reduced-order modeling approach, intending to improve the performance of this sensor, as the behavior of the sensor can be modeled much more accurately than using an analytical model. For this reason, a parametric model-order reduction technique using proper orthogonal decomposition was applied. The main advantage of the reduced-order model is the high accuracy in the modeling of the conductive heat transfer problem, while it requires low computation effort. The approach was tested experimentally, where the model was calibrated in two pure gases and evaluated in 21 gases and gas mixtures. The sensor achieved an accuracy in the thermal conductivity of 6.5% and in the volumetric heat capacity of 3.2%.

Measurement and Evaluation of the Gas Density and Viscosity of Pure Gases and Mixtures Using a Micro-Cantilever Beam

Measurement of gas density and viscosity was conducted using a micro-cantilever beam. In parallel, the validity of the proposed modeling approach was evaluated. This study also aimed to widen the database of the gases on which the model development of the micro-cantilever beams is based. The density and viscosity of gases are orders of magnitude lower than liquids. For this reason, the use of a very sensitive sensor is essential. In this study, a micro-cantilever beam from the field of atomic force microscopy was used. Although the current cantilever was designed to work with thermal activation, in the current investigation, it was activated with an electromagnetic force. The deflection of the cantilever beam was detected by an integrated piezo-resistive sensor. Six pure gases and sixteen mixtures of them in ambient conditions were investigated. The outcome of the investigation showed that the current cantilever beam had a sensitivity of 240 Hz/(kg/m3), while the accuracy of the determined gas density and viscosity in ambient conditions reached ±1.5% and ±2.0%, respectively.