Geometry Effects on Critical Heat Flux for Subcooled Convective Boiling From an Array of Heated Elements

The critical heat flux (CHF) condition was experimentally determined for subcooled flow boiling from an array of simulated microelectronic devices on one wall of a vertical rectangular passage. A test apparatus was used in these experiments that allowed visual observation of the boiling process while simultaneously measuring the heat flux and surface temperature for ten heat-dissipating elements. Using R-113 as the coolant, the CHF condition was determined for flush and slightly protruding heated elements. As expected, the element farthest downstream was found to reach the CHF condition first in all cases. For both the flush and slightly protruding elements, the trends in the CHF data are similar to those previously reported for subcooled flow boiling on an isolated element. At moderate flow velocities, the critical heat flux predicted by a proposed correlation for subcooled flow boiling from a single element was found to agree well with the multiple-flush-element data if the local fluid subcooling at the last element was used in the correlation. At lower velocities, however, the data deviated from the predicted values. The data for slightly protruding elements were also found to deviate from those for the flush elements at higher velocities. The apparent physical reasons for these trends are discussed in detail.