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The problem of vapor/liquid interaction and entrainment in falling film evaporators is analyzed. Attention is focused primarily on horizontal tube falling film evaporators where liquid falls from one tube to the next in either a droplet or column mode. A criterion is presented for the onset of column formation, and equations are derived for the deflection of droplets and columns due to vapor crossflow. Based on an experimental study of drop detachment and breakup, a correlation is established for the resulting droplet sizes. For high vapor crossflow velocities, a criterion is presented for the inception of liquid entrainment by a process known as stripping. Based on the foregoing models, conditions are defined under which vapor/liquid interaction and entrainment are important for falling film evaporators.

A unified model relating surface variables to the nucleate pool boiling characteristics was developed. A simple vapor trapping mechanism was postulated and a geometrical model constructed for idealized conical cavities relating the effective radius for nucleation to cavity radius, cone angle and contact angle. This model for individual cavities was extended to the entire surface providing an expression for the cumulative site density in terms of geometrical parameters. A gas diffusion technique was developed to measure the effective radius for natural cavities and was used successfully to verify the nucleation criteria AT = 2T sv /h p. A transient heat conduction model was experimentally verified for watf an organics at atmospheric pressure and was incorporated into a unified expression showing explicitly the role of surface geometry and contact angle. This equation shows that hb = (a/A) bAT n/A.

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The kilities a£ Argcmae Sakirand Laboratory a r e oumed by ltfie UaOtedl State$ G m mmeat, Undsr Eke terms of a eontsaet (W-32-109-Znf;-3%) batwee$ &e U. 5. Department of hergy, Argeane Universttier Aesoela%an and The Uaivaraity of (=%doago, ; t h Waiversitp eril@sya the staff rrnd operates the Laboratory Sn aecrrrdance w i f p~licieiir and program fosa~ulatad, ape proved and reviewed by the Aaeoeiation.