Critical boiling, vapor block, and prospects for control of miniquenches in channel-cooled magnets

A correlation to ±13% is given for the wide-ranging data of 7 groups who have measured steady-state critical nucleate boiling heat flux, CHF, from a channel wall to helium flowing at known mass flux G. There is no discernible trend in any of the plots of CHF deviation with respect to the six relevant experimental parameters. To achieve quench control in a partially quenched multichanneled magnet, the average mass flux must exceed G, due to vapor block in the quench-affected channels. Equations derived here for are based on both laminar and turbulent flow models. In a proposed method of quench control, isolated miniquenches (involving up to one full turn in separate layers of the conductor) are eliminated by a calculable flow of coolant provided by an immersed circulating pump in parallel with the magnet channels. Prospects for success are enhanced by the fact that in typical forced-flow channel boiling, the first (breakaway) and second (recovery) CHF\´s are reported to be identical, in strong contrast to typical pool boiling. It is also noteworthy that among systems designed to provide (steady-state) CHF, the one considered here is unique in providing a transient heat flux that is greater than the critical steady state flux.