Vapor compression vertical tube foam evaporation

Abstract

Vertical tube foam evaporation* (VTFE) has been shown to provide a 4- to 6-fold increase in the evaporation-side heat transfer coefficient, and evaporator performance enhancements ranging from 50 to 200 percent for downflow and upflow vertical tube evaporators using double-fluted aluminum-brass distillation tubes. This process relies upon the addition of 1–20 parts per million of a selected surfactant to the feed, and imposition of foamy two-phase vapor-liquid flow over the heat transfer surfaces. Recent data obtained with a new 5000 US gpd VTFE pilot plant operated by the vapor compression (VC) technique is reported, showing the promise of applying this technology to seawater conversion and water reuse, in comparison with a conventional VC-VTE operation. Test data includes overall heat transfer coefficients obtained on several typical saline waters, showing that substantial capital cost and energy reductions are obtainable with VTFE. Capital costs are reduced as a consequence of the lower heat transfer surface area required by VTFE, and energy cost reductions follow from a reduction in the ΔT and VC compression ratio provided by VTFE.