Challenge

A high-pressure test system was used to validate production cryoablation needles by measuring ice formation when the product was immersed in an aqueous gel and cooled for a prescribed period. The process involved complex interactions between compressed-gas flow, pressure control, thermodynamics and the Joule–Thomson effect, making test performance sensitive to a number of operating parameters. The objective was to develop a detailed understanding of the underlying process so that an upgraded test system could provide more precise and repeatable product testing.

Engineering Approach

A detailed mathematical model was developed from the governing thermodynamic and fluid-flow relationships to explain the transient behaviour of the complete system. Because multiple products were tested simultaneously, the interacting behaviour of the test system and individual test positions also had to be considered. A bespoke numerical solver was developed in Python to solve the resulting system and investigate its transient response. The model was then used to characterise system behaviour, investigate parameter sensitivity and identify the variables having the greatest influence on test performance.

Outcome

The analysis identified the parameters governing the transient test behaviour and provided an engineering explanation for aspects of the process that had previously been poorly understood. These findings informed the design of a more precise and repeatable test system. A comprehensive Design of Experiments (DOE) programme was subsequently developed to validate the predicted system behaviour and assess the performance of the newly developed test machine. A silencer was also designed to address exhaust noise levels.