Dimensional analysis of critical heat flux in subcooled water flow under one-side heating conditions for fusion application

Abstract

Critical heat flux (CHF) experiments have been carried out to design a high performance cooling device with pressurized subcooled water flow under one-side heating conditions for plasma facing components. Swirl, screw and hypervapotron tubes are the most efficient geometries to remove high incident heat fluxes. A dimensional analysis shows that CHF phenomenon can be featured by dimensionless groups that are the critical Boiling, the Eckert and the Reynolds numbers, the mass enthalpic quality and the ratio between liquid and vapor densities. CHF for uniformly heated smooth tubes, the maximum wall heat flux for smooth and for swirl tubes under one-side heating conditions are predicted with a reasonable accuracy by correlating these five dimensionless groups. An enhancement factor featuring the difference between one-side and uniform heating is also introduced. CHF occurrence under one-side heating is characterized by a normalized temperature, ratio between the maximal wall temperature and the onset of nucleate boiling temperature, which only depends on the pressure. According to finite element calculations performed for smooth and swirl tubes, temperature and heat flux are distributed along the inner wall of the cooling channel under one-side heating conditions. These distributions are characterized by two dimensionless numbers for each geometry: a peaking factor, which is the ratio between the maximal heat flux at the inner wall of the cooling channel and the incident heat flux, and a full width angle at half maximum of wall heat flux at the inner wall of the cooling channel. This study draws the dimensionless groups featuring CHF phenomenon not only under uniform heating, but also under one-side heating, which involve additional normalized parameters.