Advancements in the development of the isothermal gas calorimeter based on Alexandrov’s principle

Abstract The Isothermal gas calorimeter based on Alexandov's design is a robust and versatile device that can be used for the determination of the heat of combustion of new emerging gas mixtures, such as biogas, biomethane or hydrogen enriched gases. This calorimeter is easily adaptable to these new gas mixtures which, due to the large range of densities and compositions, challenge other more expensive techniques used for this purpose, namely gas chromatography. New technologies (new mass flow controllers and simulations heater) were implemented and the performance under the new circumstances analysed. The analysis showed relevant weaknesses that need to be addressed for an optimal performance for the new gas mixtures, such as heat losses, or the selection of the working fluid. The uncertainty budget performed under the new developments showed that the calorimeter can determine the calorific value of gas mixtures with a relative uncertainty lower than Ur = 0.5 % (k = 2). However, this value will be improved further once the weaknesses discovered in the performed analysis are addressed.