Peak boiling heat flux on cylinders in a cross flow

Abstract

Analyses of the peak boiling heat flux have traditionally treated either pool boiling or flow boiling situations. Little has been done toward showing how the two processes relate to one another, though observations of burnout on cylindrical heaters have bridged the two situations. This study analyses burnout of horizontal cylinders in a vertical crossflow of increasing velocity, and it reports additional observations in water, methanol and isopropanol. At very low flow rates the structure of escaping jets changes from three to two dimensional. A criterion for the Helmholtz instability of the two-dimensional jets (or vapor sheets) is obtained from a simple mechanical energy balance. The result is a burnout prediction which is accurate at low to moderate velocities. At high velocities the wake appears to narrow and the prediction must be used as a correlation involving a constant which characterizes the sheet width. In both regimes the equations are generally accurate within ±20°. Criteria are also given for the two transitions described above.