Inception of evaporative dryout for CO2 in milliscale pipe flows

Giulio Cantini, Desiree Hellenschmidt, Camila Pedano, Paolo Petagna, Carl Sangan, Mauro Carnevale

Research output: Contribution to journalArticlepeer-review

Abstract

Carbon dioxide is a cost-effective, reliable and environmentally-friendly refrigerant with increasing employment in evaporator design. A clear understanding of the underlying flow physics, coupled with robust prediction of phase change through boiling, is necessary to enable widespread uptake of CO 2 as a coolant. In scenarios such as nuclear reactors or thermal management in silicon detectors (e.g., Large Hadron Collider at CERN), employing saturated CO 2 in milliscale pipes introduces further uncertainties in the design process, particularly regarding its behaviour at high vapour quality. During the phase change process, the fluid exhibits an abrupt decrease in the heat transfer coefficient. Such a condition, known as the onset of dryout, can lead to potentially catastrophic overheating. Two opposing behaviours are observed in the available literature concerned with the onset of dryout, coined in this study as the δ and δ + regimes. The δ regime exhibits decreasing dryout vapour quality with mass flux, while the δ + regime, which is more relevant to CO 2 in millichannels, yields an increasing dryout vapour quality with mass flux. A detailed experimental campaign was conducted at CERN providing unprecedented insight into the phenomena resulting in the inception of dryout. A new theoretical model based on small perturbation theory was developed to accurately predict the dryout phase in the δ + regime. This study provides general theory to predict dryout, which is validated with specifically-acquired data and the wider literature; to the authors’ knowledge all comparable theories fail to extend their applicability beyond the proposers own datasets. Our new theory is independent from the saturation temperature and heat flux, enabling future investigations to be conducted at a single value of the aforementioned quantities, while permitting extrapolation of the trends to a general parameter set. This unique versatility provides a new framework for the design of carbon-dioxide evaporators with novel cooling architectures.

Original languageEnglish
Article number127299
JournalInternational Journal of Heat and Mass Transfer
Volume251
Early online date20 Jun 2025
DOIs
Publication statusE-pub ahead of print - 20 Jun 2025

Data Availability Statement

Data will be made available on request.

Funding

We thank the international research grant (Grant number IES R1 221141) of the Royal Society and Andrew Langley for his technical assistance.

FundersFunder number
Royal Society

    Keywords

    • Boiling CO
    • Dryout inception
    • Liquid film
    • Millichannels
    • Perturbation theory
    • Stability
    • Two-phase flow

    ASJC Scopus subject areas

    • Condensed Matter Physics
    • Mechanical Engineering
    • Fluid Flow and Transfer Processes

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