Contributed paper Subcooled critical heat flux: an assessment of the risk to front-end and beamline components of synchrotron light sources B. BRAJUSKOVIC 1 † , D. CAPATINA 1 , J. COLLINS 1 , P. DEN HARTOG 1 AND J. RENEKER 2 1 Argonne National Laboratory, Advanced Photon Source, AES Division, 9700 S. Cass Ave., Argonne. IL 60439-4800, USA 2 Sandia National Laboratories, Pulsed Power Sciences Center, 1515 Eubank Blvd. SE, Albuquerque, NM 87185, USA (Received 14 June 2010; accepted 27 August 2010) X-ray absorbers in the front ends and beamlines of synchrotron light sources are exposed to very high thermal loads. Many facilities, such as the Advanced Photon Source, are investigating upgrades that will further increase the thermal load. The likelihood of exceeding the limit of subcooled critical heat flux (CHF) in these components was examined. The assessment was performed for both cur- rently possible off-normal operational conditions, such as might occur in the event of a failure of multiple safety interlocks, and the anticipated operating con- ditions that may result from future upgrades. The subcooled CHF values were cal- culated using empirical equations frequently cited in the literature and then compared with the computed values of the heat flux at the walls of the component cooling channels in cases where the cooling wall temperature exceeded the water saturation temperature at local hydraulic conditions. Having in mind that the great majority of the available empirical correlations were developed for the con- ditions characteristic for the operation of heat exchangers in the nuclear power industry, the limitations of this approach are discussed and an experimental study of the subcooled CHF values in the conditions similar to those expected in the front-end and beamline components is proposed. 1. Introduction Critical heat flux (CHF) is a phenomenon that manifests in sudden and severe drop in heat transfer efficiency. Once the heat flux reaches its critical level, a small further increase of heat flux leads to very large and instant increase in the temperature of the heat exchanger walls that can cause catastrophic material failure known as burn-out. The CHF phenomenon is caused by the sudden creation of a thin layer of vapour that separates cooling walls of cooling channels from the bulk liquid. Thus, CHF can occur only in those heat exchangers that are † Email address for correspondence: bran@aps.anl.gov Diamond Light Source Proceedings, Vol 1, e8, page 1 of 4 © Diamond Light Source Ltd 2010 MEDSI-6 2010 doi:10.1017/S204482011000016X