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Boiling of natural sea water in falling film evaporators

Authors
Journal
Desalination
0011-9164
Publisher
Elsevier
Publication Date
Volume
18
Issue
1
Identifiers
DOI: 10.1016/s0011-9164(00)84075-8

Abstract

Abstract Under conditions normally encountered in falling film evaporators for sea water, the boiling mechanism is one of evaporation at the continuous liquid-vapor interface with little nucleation involved. In smooth tubes, the heat transfer coefficient for the inlet-section is considerably higher than for the rest of the tube, and thereby contributes significantly to the average overall heat transfer coefficient, especially in short tubes. In the case of natural sea water, evaporation at the liquid-vapor interface causes large interfacial instabilities. Inlet devices, such as vortex level control and flow distribution, induce instabilities at the inlet of the tubes, thereby causing increased waviness further down. Although these disturbances enhance heat transfer, they increase entrainment and the tendency for scale formation in fluted tubes. Spirally corrugated tubes have significantly better heat transfer characteristics than smooth tubes. Heat transfer improvement caused by surfactant addition in smooth tubes depends strongly on the temperature difference.

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