Speaker
Description
Two phase CO₂ cooling is increasingly adopted in low temperature and high heat flux applications across detector and tracking system infrastructures, where its favourable thermophysical properties offer significant potential for compact, low mass thermal management solutions. However, the onset of dry-out remains a critical design concern: while partial boiling enhances heat transfer, transitioning to a vapour dominated regime risks thermal runaway and structural damage. As a result, current engineering approaches often rely on overly conservative operating margins, limiting the achievable thermal efficiency. Understanding and predicting dry-out behaviour in milli-scale channels in therefore remains essential for advanced detector cooling system design.
This work presents a new theoretical model developed at the University of Bath and validated at the LUCASZ facility to predict the onset of dry-out in 1 mm diameter stainless steel milli-channels under controlled two phase CO₂ flow conditions. Unlike established correlations, the proposed model is independent of saturation temperature and heat flux, enabling its generalisation across a wide range of operating conditions and test configurations. Experimental validation employed a 180 mm test section instrumented with highspeed T type thermocouples at 12 axial locations, supported by preconditioning of the inlet flow through an electric heater, pressure control, and a uniform flow orifice arrangement. The test section was housed within a vacuum chamber to ensure thermal isolation.
Analysis of the experimental data demonstrates that dry-out onset can be expressed through an exponential correlation with pipe diameter, providing a robust and transferable predictor of vapour quality thresholds. The results further identify liquid–vapour interface stability as the dominant physical mechanism governing dry-out in milli scale geometries. By enabling accurate prediction of this transition without restrictive assumptions on temperature or heat flux, the model offers a pathway to more optimised CO₂ based cooling architectures, supporting next generation detector mechanics and thermal management strategies.