PhD Defence Nando Tolboom | Implications of using gas mixtures in Joule-Thomson coolers driven by sorption-based compressors

Implications of using gas mixtures in Joule-Thomson coolers driven by sorption-based compressors

Nando Tolboom is a PhD student in the department Energy, Materials and Systems. (Co)Promotors are prof.dr.ir. H.J.M. ter Brake from the Faculty of Sciences & Technology, University of Twente.

Sorption driven cryocoolers offer a vibration-free alternative to mechanical systems for sensitive applications like infrared detectors. While using gas mixtures can improve performance, it introduces complexity because of different ad- and desorption characteristics of the individual mixture components, causing the composition of the delivered gas to vary. This thesis investigates these dynamics using a nitrogen and ethane mixture and studies the relevance for future mixture sorption cooler demonstrators.

To address these challenges, first, an in-situ measurement setup was created using dual mass-flow meter: one based on the Coriolis effect and the other on heat capacity. By combining these two physical properties, the system can accurately calculate the gas composition in real time without removing any gas from the closed system. Secondly, a low-thermal-gradient compressor was designed using aluminium discs to ensure uniform temperature during operation. This allows modelling of the adsorption behaviour without the complication of thermal gradients.

Critical aspects studied using this setup were mixture adsorption characteristics and the fitting of the adsorption data. In addition, the charging methodology of the setup was studied for the influence of cycle-to-cycle dynamics. A key takeaway from the study is the significant shift between the initial charging conditions and actual operation. The design of such systems must carefully relate the initial state to the steady state operation, as differences between the charged and resulting composition can be significant. By providing a way to measure and model these dynamic shifts, this work provides the foundation for designing more efficient, multi-component sorption coolers.