The Effect of Turbulence-Suspended Light Particles on Dryout for Pool Boiling From a Horizontal Surface

Experimental measurements are reported which indicate the relationship between particle loading and dryout heat flux for pool boiling from a horizontal surface covered with a mixture of water and light particles. This study specifically examines the dryout conditions for particles which have low settling velocities and are easily suspended by the bubble-generated turbulence in the liquid pool above the surface. Dryout data are presented for pool boiling of mixtures of saturated water and glass beads with diameters ranging from 0.105 mm to 0.475 mm. Data are also presented for methanol and glass beads. At high particle loadings, a portion of the load is suspended, while the remainder forms a layer on the surface. The dryout mechanism apparently is similar to the Helmholtz instability mechanism previously identified as the cause of dryout in shallow beds of heavy particles. However, the suspension of particles in the liquid pool produces very unusual trends in the dryout data. In particular, conditions have been observed in which a decrease in the heat flux can cause dryout to occur. An approximate theoretical model of the particle suspension mechanism is proposed and used to predict the dryout conditions for very light particles. This model explains the trends in the data and predicts dryout conditions which compare favorably with the experimental results for very light particles.