Speakers
Description
Two-phase evaporative CO$_2$ cooling is a leading solution for the thermal management of silicon detectors, enabling high heat removal with limited material budget and nearly isothermal operation in compact geometries. Nevertheless, reliable prediction of flow boiling heat transfer coefficients (HTCs) and the interpretation of the observed trends remain challenging in micro-scale channels, where the strongly temperature-dependent properties of carbon dioxide and confinement effects can alter the dominant mechanisms and challenge the validity of standard correlations.
This work presents an experimental study of boiling CO$_2$ in a single 1 mm inner diameter test section designed for detector-cooling R&D, combining local HTC measurements with high-speed flow visualization through a dedicated transparent section. This allows identification of flow regimes and comparison with existing flow pattern maps.
To extend previous work performed in this experimental setup, inlet conditions are tuned to a wide range of vapour qualities up to dryout inception and, when feasible, beyond. A systematic test matrix is explored in order to quantify the role of saturation temperature ($T_{\mathrm{sat}}$) across detector-relevant conditions, spanning $+15^{\circ}\mathrm{C}$ to $-25^{\circ}\mathrm{C}$, including intermediate points at $+5^{\circ}\mathrm{C}$, $0^{\circ}\mathrm{C}$, $-5^{\circ}\mathrm{C}$ and $-15^{\circ}\mathrm{C}$. For each $T_{\mathrm{sat}}$, three mass fluxes ($G = 530,\ 800,\ 1200\ \mathrm{\frac{kg}{m^{2}s}}$) and six heat fluxes ($q'' = 0,\ 10,\ 20,\ 40,\ 60,\ 70\ \mathrm{\frac{kW}{m^{2}}}$) are investigated.
The present experimental campaign also considers the effect of surface roughness on heat transfer and pressure drop, which was investigated through a selected set of measurements performed in a titanium pipe.
The combined dataset provides temperature-resolved trends of HTC and their dependence on other operating parameters, as well as a visual key for interpreting regime transitions and intermittent behaviours that are difficult to infer from time-averaged signals alone. This study provides further understanding of the physics CO$_2$ flow boiling in a single channel in the millimetre scale, contributing to the development and validation of predictive models for next-generation detector cooling systems.